From ab853eec2f1d64706f5ef2142c0b4a9c3bc67483 Mon Sep 17 00:00:00 2001
From: Dan Arad <dan.arad@sap.com>
Date: Wed, 20 Jan 2021 12:32:43 +0200
Subject: [PATCH] 6636-custom-editor: support for CustomEditor API

Signed-off-by: Dan Arad <dan.arad@sap.com>
---
 CHANGELOG.md                                  |   6 +-
 NOTICE.md                                     | 164 +---
 examples/api-tests/src/saveable.spec.js       |  56 +-
 .../browser/common-frontend-contribution.ts   |   8 -
 packages/core/src/browser/opener-service.ts   |  26 +-
 .../preferences/preference-contribution.ts    |  47 +-
 packages/core/src/browser/saveable.ts         |   2 +-
 packages/core/src/browser/style/index.css     |   6 +-
 packages/core/src/browser/style/tabs.css      |   1 -
 .../core/src/browser/tree/tree-widget.tsx     |  32 +-
 .../src/common/messaging/proxy-factory.ts     |  20 +-
 .../env-variables/env-variables-server.ts     |   6 +-
 packages/monaco/src/browser/monaco-command.ts |   7 +
 .../src/browser/monaco-editor-service.ts      |  10 +-
 .../src/browser/monaco-editor-zone-widget.ts  |  83 +-
 .../monaco/src/browser/monaco-workspace.ts    |  18 +-
 packages/monaco/src/browser/style/index.css   |   1 -
 .../src/browser/navigator-contribution.ts     |   4 +-
 .../src/common/plugin-api-rpc-model.ts        |  97 ---
 .../plugin-ext/src/common/plugin-api-rpc.ts   | 112 +--
 .../plugin-ext/src/common/plugin-protocol.ts  |  43 +-
 .../src/hosted/browser/hosted-plugin.ts       |  21 +-
 .../src/hosted/node/scanners/scanner-theia.ts |  31 +-
 .../browser/comments/comment-glyph-widget.ts  |  65 --
 .../comments/comment-thread-widget.tsx        | 669 ----------------
 .../comments/comments-context-key-service.ts  |  68 --
 .../browser/comments/comments-contribution.ts | 263 -------
 .../browser/comments/comments-decorator.ts    | 109 ---
 .../main/browser/comments/comments-main.ts    | 450 -----------
 .../main/browser/comments/comments-service.ts | 205 -----
 .../custom-editor-contribution.ts             |  49 ++
 .../custom-editors/custom-editor-opener.tsx   |  94 +++
 .../custom-editors/custom-editor-service.ts   | 108 +++
 .../custom-editor-widget-factory.ts           |  44 ++
 .../custom-editors/custom-editor-widget.ts    | 116 +++
 .../custom-editors/custom-editors-main.ts     | 540 +++++++++++++
 .../src/main/browser/custom-editors/glob.ts   | 742 ++++++++++++++++++
 .../src/main/browser/custom-editors/paths.ts  | 250 ++++++
 .../plugin-custom-editor-registry.ts          | 142 ++++
 .../custom-editors/undo-redo-service.ts       | 120 +++
 .../src/main/browser/main-context.ts          |  10 +-
 .../menus/menus-contribution-handler.ts       |  64 --
 .../browser/plugin-contribution-handler.ts    |  19 +-
 .../main/browser/plugin-ext-deploy-command.ts |   6 +-
 .../browser/plugin-ext-frontend-module.ts     |  27 +-
 .../src/main/browser/style/comments.css       | 339 --------
 .../src/main/browser/webview/pre/main.js      |  72 +-
 .../src/main/browser/webviews-main.ts         |  14 +-
 .../plugin-ext-frontend-electron-module.ts    |   4 +-
 .../electron-webview-widget-factory.ts        |  26 +
 packages/plugin-ext/src/plugin/comments.ts    | 502 ------------
 .../plugin-ext/src/plugin/custom-editors.ts   | 376 +++++++++
 .../plugin-ext/src/plugin/plugin-context.ts   |  26 +-
 .../plugin-ext/src/plugin/plugin-manager.ts   |   3 +-
 packages/plugin-ext/src/plugin/webviews.ts    |  23 +-
 packages/plugin/src/theia-proposed.d.ts       |  24 +
 packages/plugin/src/theia.d.ts                | 289 +++++++
 .../preferences-json-schema-contribution.ts   |  45 +-
 .../src/node/process/process-task-runner.ts   |   5 +
 .../src/browser/terminal-widget-impl.ts       |   2 +-
 .../terminal/src/node/base-terminal-server.ts |   4 +-
 .../src/browser/workspace-commands.ts         |  33 +-
 62 files changed, 3343 insertions(+), 3405 deletions(-)
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comment-glyph-widget.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comment-thread-widget.tsx
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comments-context-key-service.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comments-contribution.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comments-decorator.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comments-main.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/comments/comments-service.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editor-contribution.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editor-opener.tsx
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editor-service.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget-factory.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/custom-editors-main.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/glob.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/paths.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/plugin-custom-editor-registry.ts
 create mode 100644 packages/plugin-ext/src/main/browser/custom-editors/undo-redo-service.ts
 delete mode 100644 packages/plugin-ext/src/main/browser/style/comments.css
 delete mode 100644 packages/plugin-ext/src/plugin/comments.ts
 create mode 100644 packages/plugin-ext/src/plugin/custom-editors.ts

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6e4fcaea00e2c..2e50089923ac2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,5 @@
 # Change Log
 
-## v1.10.0
-
-- [plugin] added `createDeployQuickOpenItem` method to create `DeployQuickOpenItem` in order to make extension deploy command extensible [#8919] (https://github.com/eclipse-theia/theia/pull/8919)
-
 ## v1.9.0 - 16/12/2020
 
 - [cli] updated error reporting for the `download-plugins` script [#8798](https://github.com/eclipse-theia/theia/pull/8798)
@@ -69,7 +65,7 @@
 - [monaco] added ability to compare quick-open entries [#8185](https://github.com/eclipse-theia/theia/pull/8185)
 - [output] improved extensibility of output channel commands [#8733](https://github.com/eclipse-theia/theia/pull/8733)
 - [plugin] added ability to use `viewId` as a progress location [#8700](https://github.com/eclipse-theia/theia/pull/8700)
-- [plugin] added logic to only store webviews when they have a corresponding serializer [#8680](https://github.com/eclipse-theia/theia/pull/8680)
+- [plugin] added logic to only store webviews when they have a corresponding serializer [#8680](https://github.com/eclipse-theia/theia/pull8680)
 - [plugin] added support for `activeColorTheme` and `onDidChangeActiveColorTheme` API [#8710](https://github.com/eclipse-theia/theia/pull/8710)
 - [plugin] added support for semantic highlighting [#8593](https://github.com/eclipse-theia/theia/pull/8593)
 - [plugin] fixed issue where problem matchers specified by task providers are not respected [#8756](https://github.com/eclipse-theia/theia/pull/8756)
diff --git a/NOTICE.md b/NOTICE.md
index 8032856b53e19..6d5da0aea72dc 100644
--- a/NOTICE.md
+++ b/NOTICE.md
@@ -20,27 +20,22 @@ This program and the accompanying materials are made available under the terms
 of the Eclipse Public License v. 2.0 which is available at
 https://www.eclipse.org/legal/epl-2.0. This Source Code may also be made
 available under the following Secondary Licenses when the conditions for such
-availability set forth in the Eclipse Public License v. 2.0 are satisfied:
-(secondary) GPL-2.0 with Classpath-exception-2.0 which is available at GNU
-General Public License v2.0 w/Classpath exception',
-'https://www.gnu.org/software/classpath/license.html.
+availability set forth in the Eclipse Public License v. 2.0 are satisfied: GNU
+General Public License, version 2 with the GNU Classpath Exception which is
+available at https://www.gnu.org/software/classpath/license.html.
 
-SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-with-classpath-exception
+SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 
 ## Source Code
 
 The project maintains the following source code repositories:
 
-* https://github.com/eclipse-theia/theia
 * https://github.com/eclipse/theia-generator-plugin
 * https://github.com/eclipse/theia-yeoman-plugin
 * https://github.com/eclipse/theia-plugin-packager
-* https://github.com/eclipse-theia/theia-cpp-extensions
+* https://github.com/eclipse/theia-cpp-extension
 * https://github.com/eclipse/theia-python-extension
 * https://github.com/eclipse/theia-java-extension
-* https://github.com/eclipse-theia/theia-example
-* https://github.com/eclipse-theia/cryptodetector
-* https://github.com/eclipse-theia/generator-theia-extension
 
 ## Third-party Content
 
@@ -66,78 +61,11 @@ Code copied from project Microsoft/vscode (1.32.3)
 * Project: https://code.visualstudio.com/
 * Source: https://github.com/Microsoft/vscode
 
-Code copied from project Microsoft/vscode (1.32.3)
-
-* License: MIT
-
-code copied from project microsoft/vscode (1.33.1)
-
-* License: MIT
-
 Code copied from project Microsoft/vscode (1.33.1)
 
 * License: MIT
 
-Code copied from project Microsoft/vscode (1.34.0)
-
-* License: MIT
-
-Code copied from project microsoft/vscode (1.41.1)
-
-* License: MIT
-
-code copied from project vscode (1.26.0)
-
-* License: MIT
-
-code copied from project vscode (1.31.0)
-
-* License: MIT
-
-code copied from project vscode (1.33.0)
-
-* License: MIT
-
-code copied from project vscode (1.33.0)
-
-* License: MIT
-
-code copied from project vscode (1.34.0)
-
-* License: MIT
-
-code copied from project vscode (1.36.1)
-
-
-code copied from project vscode (1.36.1)
-
-* License: MIT
-
-code copied from project vscode (1.37.0)
-
-* License: MIT
-
-code copied from project vscode (1.37.0)
-
-* License: MIT
-
-code copied from project vscode-browser-preview (0.4.0)
-
-* License: MIT
-
-Code copied from VS Code (n/a)
-
-* License: MIT
-
-Code copied from VSCode (n/a)
-
-* License: MIT
-
-Code copied from vscode (n/a)
-
-* License: MIT
-
-Code copied from VSCode (n/a)
+code copied from project microsoft/vscode (1.33.1)
 
 * License: MIT
 
@@ -163,14 +91,8 @@ Electron (3.1.7)
    AND (BSD-2-Clause OR MIT OR Apache-2.0) AND ISC AND MIT AND X11 AND
    BSD-2-Clause-FreeBSD AND Public-Domain AND Unlicense AND MPL-2.0 AND
    (BSD-3-Clause OR MPL-2.0) AND CC-BY-3.0 AND (AFL-2.0
-
-Electron (4.2.11)
-
-* License: MIT AND BSD-3-Clause AND LicenseRef-Public-Domain
-
-Electron (9.0.2)
-
-* License: MIT AND BSD-3-Clause AND LicenseRef-Public-Domain
+* Project: https://electronjs.org/
+* Source: https://github.com/electron/electron
 
 electron@2.0.14 (2.0.14)
 
@@ -204,38 +126,10 @@ Icon configure-inverse.svg (n/a)
 * Source:
    https://github.com/Microsoft/vscode/blob/master/src/vs/workbench/contrib/tasks/common/media/configure-inverse.svg#L1
 
-Icons copied from microsoft/vscode-icons version:
-b73945c70f1117c4e65939dd3e10bdd623cb4ef3 (n/a)
-
-* License: CC-BY-4.0
-
-inversify (5.0.1)
-
-* License: MIT
-
-jschardet (1.6.0)
-
-* License: (LGPL-2.1 OR LGPL-2.1+) AND (MIT OR GPL-2.0)
-* Project: https://www.npmjs.com/package/jschardet
-* Source:
-   https://github.com/aadsm/jschardet/tree/28152dd8db5904dc2cf9aa12ef4f8783f713e79a
-
-jschardet (2.1.1)
-
-* License: LGPL-2.1 OR LGPL-2.1+
-
 libffmpeg (FFmpeg) Delivered with Electron (3.1.7)
 
 * License: LGPL-2.1+
 
-libffmpeg (FFmpeg) delivered with Electron (4.2.11)
-
-* License: LGPG-2.1-or-later AND BSD-3-Clause AND MIT AND IJG
-
-libffmpeg (FFmpeg) delivered with Electron (9.0.2)
-
-* License: LGPG-2.1-or-later AND BSD-3-Clause AND MIT AND IJG
-
 long.js (3.2.0)
 
 * License: Apache-2.0
@@ -254,7 +148,7 @@ monaco-typescript (2.3.0)
 
 native-keymap (1.2.5)
 
-* License: BSD-3-Clause AND MIT
+* License: Pending
 * Project: https://github.com/Microsoft/node-native-keymap
 * Source: https://github.com/Microsoft/node-native-keymap
 
@@ -270,21 +164,12 @@ node.js dependencies for Theia (n/a)
    CC0-1.0 AND (BSD-3-Clause OR MPL-2.0) AND Unlicense AND (MIT OR GPL-3.0) AND
    (MIT OR GPL-2.0) AND (Apache-2.0 OR
 
-Preference code copied from vscode (n/a)
-
-
 ps-list (5.0.1)
 
 * License: MIT
 * Project: https://github.com/sindresorhus/ps-list
 * Source: https://github.com/sindresorhus/ps-list
 
-react-perfect-scrollbar:1.5.3 (1.5.3)
-
-* License: MIT
-* Project: https://github.com/goldenyz/react-perfect-scrollbar
-* Source: https://github.com/goldenyz/react-perfect-scrollbar
-
 read-pkg (4.0.1)
 
 * License: MIT
@@ -314,7 +199,7 @@ theia npm node (n/a)
 * License: BSD-2-Clause OR (MIT OR Apache-2.0) AND (AFL-2.1 OR BSD-3-Clause)
    AND Apache-2.0 AND Artistic-2.0 AND BSD-3-Clause AND (BSD-3-Clause OR MIT)
    AND MPL-2.0 AND CC0-1.0 AND CC-BY-3.0 AND CC-BY-4.0 AND CC-BY-SA-2.5 AND
-   GPL-2.0 WITH Autoconf-exception
+   GPL-2.0 WITH Autoconf-ex
 
 theia-cpp-extension npm node (n/a)
 
@@ -343,10 +228,6 @@ VS Code (1.33.0)
 
 * License: MIT
 
-VS Code built-in extensions (1.30.1)
-
-* License: Apache-2.0 AND MIT AND Unicode-DFS-2016 AND CC-BY-4.0 AND W3C 
-
 vscode (1.26.0)
 
 * License: MIT AND LicenseRef-Php_Tmbundle
@@ -363,10 +244,6 @@ vscode-debugadapter-node (n/a)
 
 * License: MIT
 
-vscode-icons (n/a)
-
-* License: CC-BY-4.0 AND MIT
-
 vscode-java (0.36.0)
 
 * License: EPL-1.0
@@ -379,12 +256,6 @@ vscode-java-debug (0.15.0)
 
 * License: MIT
 
-webdriverio (n/a)
-
-* License: MIT
-* Project: http://webdriver.io/
-* Source: https://github.com/webdriverio/webdriverio.git
-
 when (3.7.8)
 
 * License: MIT
@@ -395,24 +266,12 @@ wjordan/browser-path SHA6719d19077b1454bff8b802f9be79cb1b69ebe7e (n/a)
 
 * License: MIT
 
-xterm-addon-fit (0.3.0)
-
-* License: MIT
-
-xterm-addon-search (0.5.0)
-
-* License: MIT
-
 xterm.js (3.9.1)
 
 * License: MIT
 * Project: https://xtermjs.org/
 * Source: https://github.com/xtermjs/xterm.js
 
-xterm.js (4.4)
-
-* License: MIT
-
 yargs (12.0.1)
 
 * License: MIT
@@ -452,6 +311,7 @@ please check the country's laws, regulations and policies concerning the import,
 possession, or use, and re-export of encryption software, to see if this is
 permitted.
 
+
 ## Electron
 
 NOTICE:
@@ -471,3 +331,5 @@ We strongly recommend downstream consumers verify the type of FFmpeg support
 configured and modify as required.  More information on instructions to verify
 can be found here
 https://electronjs.org/docs/development/upgrading-chromium#verify-ffmpeg-support
+
+
diff --git a/examples/api-tests/src/saveable.spec.js b/examples/api-tests/src/saveable.spec.js
index 9bfdd43f16c8e..f8fa31d75fe7c 100644
--- a/examples/api-tests/src/saveable.spec.js
+++ b/examples/api-tests/src/saveable.spec.js
@@ -47,8 +47,6 @@ describe('Saveable', function () {
     const rootUri = workspaceService.tryGetRoots()[0].resource;
     const fileUri = rootUri.resolve('.test/foo.txt');
 
-    const closeOnFileDelete = 'workbench.editor.closeOnFileDelete';
-
     /**
      * @param {FileResource['shouldOverwrite']} shouldOverwrite
      * @returns {Disposable}
@@ -69,7 +67,7 @@ describe('Saveable', function () {
 
     beforeEach(async () => {
         await preferences.set('editor.autoSave', 'off', undefined, rootUri.toString());
-        await preferences.set(closeOnFileDelete, true);
+        await preferences.set('editor.closeOnFileDelete', true);
         await editorManager.closeAll({ save: false });
         await fileService.create(fileUri, 'foo', { fromUserGesture: false, overwrite: true });
         widget =  /** @type {EditorWidget & SaveableWidget} */
@@ -230,6 +228,22 @@ describe('Saveable', function () {
         assert.equal(state.value, 'foo', 'fs should NOT be updated after rejected close');
     });
 
+    it('delete file for saved with editor.CloseOnFileDelete off', async () => {
+        await preferences.set('editor.closeOnFileDelete', false);
+        assert.isFalse(Saveable.isDirty(widget), 'should NOT be dirty before delete');
+        assert.isTrue(editor.document.valid, 'should be valid before delete');
+        const waitForInvalid = new Deferred();
+        const listener = editor.document.onDidChangeValid(() => waitForInvalid.resolve());
+        try {
+            await fileService.delete(fileUri);
+            await waitForInvalid.promise;
+            assert.isFalse(editor.document.valid, 'should be INVALID after delete');
+            assert.isFalse(widget.isDisposed, 'model should NOT be disposed after delete');
+        } finally {
+            listener.dispose();
+        }
+    });
+
     it('accept save on close and reject it', async () => {
         let outOfSync = false;
         toTearDown.push(setShouldOverwrite(async () => {
@@ -449,40 +463,4 @@ describe('Saveable', function () {
         }
     });
 
-    it(`'${closeOnFileDelete}' should keep the editor opened when set to 'false'`, async () => {
-
-        await preferences.set(closeOnFileDelete, false);
-        assert.isFalse(preferences.get(closeOnFileDelete));
-        assert.isFalse(Saveable.isDirty(widget));
-
-        const waitForDidChangeTitle = new Deferred();
-        const listener = () => waitForDidChangeTitle.resolve();
-        widget.title.changed.connect(listener);
-        try {
-            await fileService.delete(fileUri);
-            await waitForDidChangeTitle.promise;
-            assert.isTrue(widget.title.label.endsWith('(deleted)'));
-            assert.isFalse(widget.isDisposed);
-        } finally {
-            widget.title.changed.disconnect(listener);
-        }
-    });
-
-    it(`'${closeOnFileDelete}' should close the editor when set to 'true'`, async () => {
-
-        await preferences.set(closeOnFileDelete, true);
-        assert.isTrue(preferences.get(closeOnFileDelete));
-        assert.isFalse(Saveable.isDirty(widget));
-
-        const waitForDisposed = new Deferred();
-        const listener = editor.onDispose(() => waitForDisposed.resolve());
-        try {
-            await fileService.delete(fileUri);
-            await waitForDisposed.promise;
-            assert.isTrue(widget.isDisposed);
-        } finally {
-            listener.dispose();
-        }
-    });
-
 });
diff --git a/packages/core/src/browser/common-frontend-contribution.ts b/packages/core/src/browser/common-frontend-contribution.ts
index 470e2c2265fbb..d8e9f66869bb5 100644
--- a/packages/core/src/browser/common-frontend-contribution.ts
+++ b/packages/core/src/browser/common-frontend-contribution.ts
@@ -1865,14 +1865,6 @@ export class CommonFrontendContribution implements FrontendApplicationContributi
                     dark: Color.transparent('button.background', 0.5),
                     light: Color.transparent('button.background', 0.5)
                 }, description: 'Background color of secondary buttons.'
-            },
-            {
-                id: 'editorGutter.commentRangeForeground',
-                defaults: {
-                    dark: '#c5c5c5',
-                    light: '#c5c5c5',
-                    hc: '#c5c5c5'
-                }, description: 'Editor gutter decoration color for commenting ranges.'
             }
         );
     }
diff --git a/packages/core/src/browser/opener-service.ts b/packages/core/src/browser/opener-service.ts
index 5739b83870093..08994f11e0ce8 100644
--- a/packages/core/src/browser/opener-service.ts
+++ b/packages/core/src/browser/opener-service.ts
@@ -16,7 +16,7 @@
 
 import { named, injectable, inject } from 'inversify';
 import URI from '../common/uri';
-import { ContributionProvider, Prioritizeable, MaybePromise } from '../common';
+import { ContributionProvider, Prioritizeable, MaybePromise, Emitter, Event, Disposable } from '../common';
 
 export interface OpenerOptions {
 }
@@ -75,6 +75,10 @@ export interface OpenerService {
      * Reject if such does not exist.
      */
     getOpener(uri: URI, options?: OpenerOptions): Promise<OpenHandler>;
+    /**
+     * Event that fires when a new opener is added or remove
+     */
+    onOpenersStateChanged?: Event<void>;
 }
 
 export async function open(openerService: OpenerService, uri: URI, options?: OpenerOptions): Promise<object | undefined> {
@@ -85,11 +89,26 @@ export async function open(openerService: OpenerService, uri: URI, options?: Ope
 @injectable()
 export class DefaultOpenerService implements OpenerService {
 
+    protected readonly additionalHandlers: OpenHandler[] = [];
+
+    protected readonly onOpenersStateChangedEmitter = new Emitter<void>();
+    readonly onOpenersStateChanged = this.onOpenersStateChangedEmitter.event;
+
     constructor(
         @inject(ContributionProvider) @named(OpenHandler)
         protected readonly handlersProvider: ContributionProvider<OpenHandler>
     ) { }
 
+    public addHandler(openHandler: OpenHandler): Disposable {
+        this.additionalHandlers.push(openHandler);
+        this.onOpenersStateChangedEmitter.fire();
+
+        return Disposable.create(() => {
+            this.additionalHandlers.splice(this.additionalHandlers.indexOf(openHandler), 1);
+            this.onOpenersStateChangedEmitter.fire();
+        });
+    }
+
     async getOpener(uri: URI, options?: OpenerOptions): Promise<OpenHandler> {
         const handlers = await this.prioritize(uri, options);
         if (handlers.length >= 1) {
@@ -114,7 +133,10 @@ export class DefaultOpenerService implements OpenerService {
     }
 
     protected getHandlers(): OpenHandler[] {
-        return this.handlersProvider.getContributions();
+        return [
+            ...this.handlersProvider.getContributions(),
+            ...this.additionalHandlers
+        ];
     }
 
 }
diff --git a/packages/core/src/browser/preferences/preference-contribution.ts b/packages/core/src/browser/preferences/preference-contribution.ts
index 566247a0a320c..019a7a64a7817 100644
--- a/packages/core/src/browser/preferences/preference-contribution.ts
+++ b/packages/core/src/browser/preferences/preference-contribution.ts
@@ -106,8 +106,6 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
 
     protected readonly preferences: { [name: string]: any } = {};
     protected readonly combinedSchema: PreferenceDataSchema = { properties: {}, patternProperties: {} };
-    protected readonly workspaceSchema: PreferenceDataSchema = { properties: {}, patternProperties: {} };
-    protected readonly folderSchema: PreferenceDataSchema = { properties: {}, patternProperties: {} };
 
     @inject(ContributionProvider) @named(PreferenceContribution)
     protected readonly preferenceContributions: ContributionProvider<PreferenceContribution>;
@@ -189,9 +187,9 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
             const overridden = this.overriddenPreferenceName(preferenceName);
             if (overridden) {
                 delete this.overridePatternProperties.properties[`[${overridden.overrideIdentifier}]`];
-                this.removePropFromSchemas(`[${overridden.overrideIdentifier}]`);
+                delete this.combinedSchema.properties[`[${overridden.overrideIdentifier}]`];
             } else {
-                this.removePropFromSchemas(preferenceName);
+                delete this.combinedSchema.properties[preferenceName];
             }
             const newValue = change.oldValue;
             const oldValue = change.newValue;
@@ -231,7 +229,7 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
                 if (schemaProps.overridable) {
                     this.overridePatternProperties.properties[preferenceName] = schemaProps;
                 }
-                this.updateSchemaProps(preferenceName, schemaProps);
+                this.combinedSchema.properties[preferenceName] = schemaProps;
 
                 const value = schemaProps.defaultValue = this.getDefaultValue(schemaProps, preferenceName);
                 if (this.testOverrideValue(preferenceName, value)) {
@@ -293,18 +291,6 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
         return this.combinedSchema;
     }
 
-    getSchema(scope: PreferenceScope): PreferenceDataSchema {
-        switch (scope) {
-            case PreferenceScope.Default:
-            case PreferenceScope.User:
-                return this.combinedSchema;
-            case PreferenceScope.Workspace:
-                return this.workspaceSchema;
-            case PreferenceScope.Folder:
-                return this.folderSchema;
-        }
-    }
-
     setSchema(schema: PreferenceSchema): Disposable {
         const changes = this.doSetSchema(schema);
         if (!changes.length) {
@@ -389,31 +375,4 @@ export class PreferenceSchemaProvider extends PreferenceProvider {
     testOverrideValue(name: string, value: any): value is PreferenceSchemaProperties {
         return PreferenceSchemaProperties.is(value) && OVERRIDE_PROPERTY_PATTERN.test(name);
     }
-
-    private updateSchemaProps(key: string, property: PreferenceDataProperty): void {
-        this.combinedSchema.properties[key] = property;
-
-        switch (property.scope) {
-            case PreferenceScope.Workspace:
-                this.workspaceSchema.properties[key] = property;
-                break;
-            case PreferenceScope.Folder:
-                this.folderSchema.properties[key] = property;
-                break;
-        }
-    }
-
-    private removePropFromSchemas(key: string): void {
-        const scope = this.combinedSchema.properties[key].scope;
-
-        delete this.combinedSchema.properties[key];
-        switch (scope) {
-            case PreferenceScope.Workspace:
-                delete this.workspaceSchema.properties[key];
-                break;
-            case PreferenceScope.Folder:
-                delete this.folderSchema.properties[key];
-                break;
-        }
-    }
 }
diff --git a/packages/core/src/browser/saveable.ts b/packages/core/src/browser/saveable.ts
index 959cabc9ebe1b..ad4ca17f276f9 100644
--- a/packages/core/src/browser/saveable.ts
+++ b/packages/core/src/browser/saveable.ts
@@ -58,7 +58,7 @@ export namespace Saveable {
     }
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     export function isSource(arg: any): arg is SaveableSource {
-        return !!arg && ('saveable' in arg);
+        return !!arg && ('saveable' in arg) && is(arg.saveable);
     }
     // eslint-disable-next-line @typescript-eslint/no-explicit-any
     export function is(arg: any): arg is Saveable {
diff --git a/packages/core/src/browser/style/index.css b/packages/core/src/browser/style/index.css
index 1b23814de8c0f..8ad1cfafc9da1 100644
--- a/packages/core/src/browser/style/index.css
+++ b/packages/core/src/browser/style/index.css
@@ -114,8 +114,8 @@ blockquote {
   margin-left: 8px;
 }
 
-.theia-mod-disabled, .theia-mod-disabled:focus {
-  opacity: var(--theia-mod-disabled-opacity) !important;
+.theia-mod-disabled {
+  opacity: var(--theia-mod-disabled-opacity);
 }
 
 .theia-header {
@@ -161,7 +161,7 @@ blockquote {
 
 button.theia-button, .theia-button {
     border: none;
-    color: var(--theia-button-foreground) !important;
+    color: var(--theia-button-foreground);
     background-color: var(--theia-button-background);
     min-width: 65px;
     outline: none;
diff --git a/packages/core/src/browser/style/tabs.css b/packages/core/src/browser/style/tabs.css
index 699e8efb3be8c..2d94ce03e271e 100644
--- a/packages/core/src/browser/style/tabs.css
+++ b/packages/core/src/browser/style/tabs.css
@@ -335,7 +335,6 @@ body.theia-editor-highlightModifiedTabs
 .p-TabBar-content-container {
   display: flex;
   flex: 1;
-  position: relative; /* This is necessary for perfect-scrollbar */
 }
 
 .p-TabBar-toolbar .item {
diff --git a/packages/core/src/browser/tree/tree-widget.tsx b/packages/core/src/browser/tree/tree-widget.tsx
index 4408fab712f57..50bd01b616a6f 100644
--- a/packages/core/src/browser/tree/tree-widget.tsx
+++ b/packages/core/src/browser/tree/tree-widget.tsx
@@ -658,28 +658,40 @@ export class TreeWidget extends ReactWidget implements StatefulWidget {
         if (fontData === undefined) {
             return original;
         }
-        const modified = { ...original }; // make a copy to mutate
+        let modified = original;
         const { color, style } = fontData;
         if (color) {
-            modified.color = color;
+            modified = {
+                ...modified,
+                color
+            };
         }
         if (style) {
             (Array.isArray(style) ? style : [style]).forEach(s => {
-                switch (s) {
+                switch (style) {
                     case 'bold':
-                        modified.fontWeight = s;
+                        modified = {
+                            ...modified,
+                            fontWeight: style
+                        };
                         break;
-                    case 'normal':
-                    case 'oblique':
+                    case 'normal': // Fall through.
+                    case 'oblique': // Fall through.
                     case 'italic':
-                        modified.fontStyle = s;
+                        modified = {
+                            ...modified,
+                            fontStyle: style
+                        };
                         break;
-                    case 'underline':
+                    case 'underline': // Fall through.
                     case 'line-through':
-                        modified.textDecoration = s;
+                        modified = {
+                            ...modified,
+                            textDecoration: style
+                        };
                         break;
                     default:
-                        throw new Error(`Unexpected font style: "${s}".`);
+                        throw new Error(`Unexpected font style: ${style}.`);
                 }
             });
         }
diff --git a/packages/core/src/common/messaging/proxy-factory.ts b/packages/core/src/common/messaging/proxy-factory.ts
index c8cc24f70a38c..815bde49b952c 100644
--- a/packages/core/src/common/messaging/proxy-factory.ts
+++ b/packages/core/src/common/messaging/proxy-factory.ts
@@ -132,8 +132,14 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
      * response.
      */
     listen(connection: MessageConnection): void {
-        connection.onRequest((prop, ...args) => this.onRequest(prop, ...args));
-        connection.onNotification((prop, ...args) => this.onNotification(prop, ...args));
+        if (this.target) {
+            for (const prop in this.target) {
+                if (typeof this.target[prop] === 'function') {
+                    connection.onRequest(prop, (...args) => this.onRequest(prop, ...args));
+                    connection.onNotification(prop, (...args) => this.onNotification(prop, ...args));
+                }
+            }
+        }
         connection.onDispose(() => this.waitForConnection());
         connection.listen();
         this.connectionPromiseResolve(connection);
@@ -153,11 +159,7 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
      */
     protected async onRequest(method: string, ...args: any[]): Promise<any> {
         try {
-            if (this.target) {
-                return await this.target[method](...args);
-            } else {
-                throw new Error(`no target was set to handle ${method}`);
-            }
+            return await this.target[method](...args);
         } catch (error) {
             const e = this.serializeError(error);
             if (e instanceof ResponseError) {
@@ -177,9 +179,7 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
      * methods calls.
      */
     protected onNotification(method: string, ...args: any[]): void {
-        if (this.target) {
-            this.target[method](...args);
-        }
+        this.target[method](...args);
     }
 
     /**
diff --git a/packages/core/src/node/env-variables/env-variables-server.ts b/packages/core/src/node/env-variables/env-variables-server.ts
index d0e687b701847..92644e0a53625 100644
--- a/packages/core/src/node/env-variables/env-variables-server.ts
+++ b/packages/core/src/node/env-variables/env-variables-server.ts
@@ -73,9 +73,9 @@ export class EnvVariablesServerImpl implements EnvVariablesServer {
         const uris: string[] = [];
         const drives = await drivelist.list();
         for (const drive of drives) {
-            for (const mountpoint of drive.mountpoints) {
-                if (this.filterHiddenPartitions(mountpoint.path)) {
-                    uris.push(FileUri.create(mountpoint.path).toString());
+            for (const mounpoint of drive.mountpoints) {
+                if (this.filterHiddenPartitions(mounpoint.path)) {
+                    uris.push(FileUri.create(mounpoint.path).toString());
                 }
             }
         }
diff --git a/packages/monaco/src/browser/monaco-command.ts b/packages/monaco/src/browser/monaco-command.ts
index 9c7499f1857d0..cb9b15c40e7e4 100644
--- a/packages/monaco/src/browser/monaco-command.ts
+++ b/packages/monaco/src/browser/monaco-command.ts
@@ -160,7 +160,14 @@ export class MonacoEditorCommandHandlers implements CommandContribution {
                     );
                 },
                 isEnabled: () => {
+                    /*
+                     * We check monaco focused code editor first since they can contain inline like the debug console and embedded editors like in the peek reference.
+                     * If there is not such then we check last focused editor tracked by us.
+                     */
                     const editor = codeEditorService.getFocusedCodeEditor() || codeEditorService.getActiveCodeEditor();
+                    if (!editor) {
+                        return false;
+                    }
                     if (editorActions.has(id)) {
                         const action = editor && editor.getAction(id);
                         return !!action && action.isSupported();
diff --git a/packages/monaco/src/browser/monaco-editor-service.ts b/packages/monaco/src/browser/monaco-editor-service.ts
index 634b5afab4a42..c55705a3f9543 100644
--- a/packages/monaco/src/browser/monaco-editor-service.ts
+++ b/packages/monaco/src/browser/monaco-editor-service.ts
@@ -24,6 +24,8 @@ import { MonacoToProtocolConverter } from './monaco-to-protocol-converter';
 import ICodeEditor = monaco.editor.ICodeEditor;
 import CommonCodeEditor = monaco.editor.CommonCodeEditor;
 import IResourceInput = monaco.editor.IResourceInput;
+import { CustomEditorWidget } from './monaco-workspace';
+import { MonacoEditorModel } from './monaco-editor-model';
 
 decorate(injectable(), monaco.services.CodeEditorServiceImpl);
 
@@ -55,7 +57,13 @@ export class MonacoEditorService extends monaco.services.CodeEditorServiceImpl {
      * Monaco active editor is either focused or last focused editor.
      */
     getActiveCodeEditor(): monaco.editor.IStandaloneCodeEditor | undefined {
-        const editor = MonacoEditor.getCurrent(this.editors);
+        let editor = MonacoEditor.getCurrent(this.editors);
+        if (!editor && CustomEditorWidget.is(this.shell.activeWidget)) {
+            const model = this.shell.activeWidget.modelRef.object;
+            if (model.editorTextModel instanceof MonacoEditorModel) {
+                editor = MonacoEditor.findByDocument(this.editors, model.editorTextModel)[0];
+            }
+        }
         return editor && editor.getControl();
     }
 
diff --git a/packages/monaco/src/browser/monaco-editor-zone-widget.ts b/packages/monaco/src/browser/monaco-editor-zone-widget.ts
index 6e5768e5cb5e9..ead035eb44427 100644
--- a/packages/monaco/src/browser/monaco-editor-zone-widget.ts
+++ b/packages/monaco/src/browser/monaco-editor-zone-widget.ts
@@ -19,7 +19,6 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { Disposable, DisposableCollection, Event, Emitter } from '@theia/core';
-import { TrackedRangeStickiness } from '@theia/editor/lib/browser';
 
 export interface MonacoEditorViewZone extends monaco.editor.IViewZone {
     id: string;
@@ -27,8 +26,6 @@ export interface MonacoEditorViewZone extends monaco.editor.IViewZone {
 
 export class MonacoEditorZoneWidget implements Disposable {
 
-    private arrow: Arrow | undefined;
-
     readonly zoneNode = document.createElement('div');
     readonly containerNode = document.createElement('div');
 
@@ -45,7 +42,7 @@ export class MonacoEditorZoneWidget implements Disposable {
     );
 
     constructor(
-        readonly editor: monaco.editor.IStandaloneCodeEditor, readonly showArrow: boolean = true
+        readonly editor: monaco.editor.IStandaloneCodeEditor
     ) {
         this.zoneNode.classList.add('zone-widget');
         this.containerNode.classList.add('zone-widget-container');
@@ -56,7 +53,6 @@ export class MonacoEditorZoneWidget implements Disposable {
 
     dispose(): void {
         this.toDispose.dispose();
-        this.hide();
     }
 
     protected _options: MonacoEditorZoneWidget.Options | undefined;
@@ -71,10 +67,10 @@ export class MonacoEditorZoneWidget implements Disposable {
     show(options: MonacoEditorZoneWidget.Options): void {
         let { afterLineNumber, afterColumn, heightInLines } = this._options = { showFrame: true, ...options };
         const lineHeight = this.editor.getOption(monaco.editor.EditorOption.lineHeight);
-        // adjust heightInLines to viewport
-        const maxHeightInLines = Math.max(12, (this.editor.getLayoutInfo().height / lineHeight) * 0.8);
-        heightInLines = Math.min(heightInLines, maxHeightInLines);
-        let arrowHeight = 0;
+        const maxHeightInLines = (this.editor.getLayoutInfo().height / lineHeight) * .8;
+        if (heightInLines >= maxHeightInLines) {
+            heightInLines = maxHeightInLines;
+        }
         this.toHide.dispose();
         this.editor.changeViewZones(accessor => {
             this.zoneNode.style.top = '-1000px';
@@ -96,14 +92,6 @@ export class MonacoEditorZoneWidget implements Disposable {
                 this.editor.changeViewZones(a => a.removeZone(id));
                 this.viewZone = undefined;
             }));
-            if (this.showArrow) {
-                this.arrow = new Arrow(this.editor);
-                arrowHeight = Math.round(lineHeight / 3);
-                this.arrow.height = arrowHeight;
-                this.arrow.show({ lineNumber: options.afterLineNumber, column: 0 });
-
-                this.toHide.push(this.arrow);
-            }
             const widget: monaco.editor.IOverlayWidget = {
                 getId: () => 'editor-zone-widget-' + id,
                 getDomNode: () => this.zoneNode,
@@ -114,6 +102,7 @@ export class MonacoEditorZoneWidget implements Disposable {
             this.toHide.push(Disposable.create(() => this.editor.removeOverlayWidget(widget)));
         });
 
+        this.containerNode.style.top = 0 + 'px';
         this.containerNode.style.overflow = 'hidden';
         this.updateContainerHeight(heightInLines * lineHeight);
 
@@ -133,7 +122,7 @@ export class MonacoEditorZoneWidget implements Disposable {
     }
 
     protected updateTop(top: number): void {
-        this.zoneNode.style.top = top + (this.showArrow ? 6 : 0)  + 'px';
+        this.zoneNode.style.top = top + 'px';
     }
     protected updateHeight(zoneHeight: number): void {
         this.zoneNode.style.height = zoneHeight + 'px';
@@ -177,64 +166,6 @@ export class MonacoEditorZoneWidget implements Disposable {
     }
 
 }
-
-class IdGenerator {
-    private lastId: number;
-    constructor(private prefix: string) {
-        this.lastId = 0;
-    }
-
-    nextId(): string {
-        return this.prefix + (++this.lastId);
-    }
-}
-
-class Arrow implements Disposable {
-
-    private readonly idGenerator = new IdGenerator('.arrow-decoration-');
-
-    private readonly ruleName = this.idGenerator.nextId();
-    private decorations: string[] = [];
-    private _height: number = -1;
-
-    constructor(
-        private readonly _editor: monaco.editor.ICodeEditor
-    ) {}
-
-    dispose(): void {
-        this.hide();
-    }
-
-    set height(value: number) {
-        if (this._height !== value) {
-            this._height = value;
-            this._updateStyle();
-        }
-    }
-
-    private _updateStyle(): void {
-        const style = document.createElement('style');
-        style.type = 'text/css';
-        style.media = 'screen';
-        document.getElementsByTagName('head')[0].appendChild(style);
-        const selector = `.monaco-editor ${this.ruleName}`;
-        const cssText = `border-style: solid; border-color: transparent transparent var(--theia-peekView-border); border-width:
-            ${this._height}px; bottom: -${this._height}px; margin-left: -${this._height}px; `;
-        (<CSSStyleSheet>style.sheet).insertRule(selector + '{' + cssText + '}', 0);
-    }
-
-    show(where: monaco.IPosition): void {
-        this.decorations = this._editor.deltaDecorations(
-            this.decorations,
-            [{ range: monaco.Range.fromPositions(where), options: { className: this.ruleName, stickiness: TrackedRangeStickiness.NeverGrowsWhenTypingAtEdges } }]
-        );
-    }
-
-    hide(): void {
-        this._editor.deltaDecorations(this.decorations, []);
-    }
-}
-
 export namespace MonacoEditorZoneWidget {
     export interface Options {
         afterLineNumber: number,
diff --git a/packages/monaco/src/browser/monaco-workspace.ts b/packages/monaco/src/browser/monaco-workspace.ts
index 909148bfd5049..5d69d7ba6e9e5 100644
--- a/packages/monaco/src/browser/monaco-workspace.ts
+++ b/packages/monaco/src/browser/monaco-workspace.ts
@@ -29,6 +29,8 @@ import { ProblemManager } from '@theia/markers/lib/browser';
 import { MaybePromise } from '@theia/core/lib/common/types';
 import { FileService } from '@theia/filesystem/lib/browser/file-service';
 import { FileSystemProviderCapabilities } from '@theia/filesystem/lib/common/files';
+import { ApplicationShell, Widget } from '@theia/core/lib/browser';
+import { Reference } from '@theia/core/lib/common';
 
 export namespace WorkspaceFileEdit {
     export function is(arg: Edit): arg is monaco.languages.WorkspaceFileEdit {
@@ -48,6 +50,17 @@ export namespace WorkspaceTextEdit {
     }
 }
 
+export namespace CustomEditorWidget {
+    export function is(arg: Widget | undefined): arg is CustomEditorWidget {
+        return !!arg && 'modelRef' in arg;
+    }
+}
+
+export interface CustomEditorWidget extends Widget {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    readonly modelRef: Reference<any>;
+}
+
 export type Edit = monaco.languages.WorkspaceFileEdit | monaco.languages.WorkspaceTextEdit;
 
 export interface WorkspaceFoldersChangeEvent {
@@ -99,6 +112,9 @@ export class MonacoWorkspace {
     @inject(ProblemManager)
     protected readonly problems: ProblemManager;
 
+    @inject(ApplicationShell)
+    protected readonly shell: ApplicationShell;
+
     @postConstruct()
     protected init(): void {
         this.resolveReady();
@@ -162,7 +178,7 @@ export class MonacoWorkspace {
         if (this.suppressedOpenIfDirty.indexOf(model) !== -1) {
             return;
         }
-        if (model.dirty && MonacoEditor.findByDocument(this.editorManager, model).length === 0) {
+        if (model.dirty && MonacoEditor.findByDocument(this.editorManager, model).length === 0 && !CustomEditorWidget.is(this.shell.activeWidget)) {
             // create a new reference to make sure the model is not disposed before it is
             // acquired by the editor, thus losing the changes that made it dirty.
             this.textModelService.createModelReference(model.textEditorModel.uri).then(ref => {
diff --git a/packages/monaco/src/browser/style/index.css b/packages/monaco/src/browser/style/index.css
index 9d95d8e526a77..8cb239480ca3e 100644
--- a/packages/monaco/src/browser/style/index.css
+++ b/packages/monaco/src/browser/style/index.css
@@ -40,7 +40,6 @@
 .monaco-editor .zone-widget {
 	position: absolute;
 	z-index: 10;
-    background-color: var(--theia-editorWidget-background);
 }
 
 .monaco-editor .zone-widget .zone-widget-container {
diff --git a/packages/navigator/src/browser/navigator-contribution.ts b/packages/navigator/src/browser/navigator-contribution.ts
index e75d1838989be..b747e08db5be5 100644
--- a/packages/navigator/src/browser/navigator-contribution.ts
+++ b/packages/navigator/src/browser/navigator-contribution.ts
@@ -457,11 +457,11 @@ export class FileNavigatorContribution extends AbstractViewContribution<FileNavi
 
         registry.registerMenuAction(NavigatorContextMenu.COMPARE, {
             commandId: NavigatorDiffCommands.COMPARE_FIRST.id,
-            order: 'za'
+            order: 'z'
         });
         registry.registerMenuAction(NavigatorContextMenu.COMPARE, {
             commandId: NavigatorDiffCommands.COMPARE_SECOND.id,
-            order: 'zb'
+            order: 'z'
         });
     }
 
diff --git a/packages/plugin-ext/src/common/plugin-api-rpc-model.ts b/packages/plugin-ext/src/common/plugin-api-rpc-model.ts
index 46d8042257693..64aa35a6c38f5 100644
--- a/packages/plugin-ext/src/common/plugin-api-rpc-model.ts
+++ b/packages/plugin-ext/src/common/plugin-api-rpc-model.ts
@@ -17,8 +17,6 @@
 import * as theia from '@theia/plugin';
 import { UriComponents } from './uri-components';
 import { CompletionItemTag } from '../plugin/types-impl';
-import { Event as TheiaEvent } from '@theia/core/lib/common/event';
-import { URI } from 'vscode-uri';
 
 // Should contains internal Plugin API types
 
@@ -564,98 +562,3 @@ export interface AuthenticationProviderInformation {
     id: string;
     label: string;
 }
-
-export interface CommentOptions {
-    /**
-     * An optional string to show on the comment input box when it's collapsed.
-     */
-    prompt?: string;
-
-    /**
-     * An optional string to show as placeholder in the comment input box when it's focused.
-     */
-    placeHolder?: string;
-}
-
-export enum CommentMode {
-    Editing = 0,
-    Preview = 1
-}
-
-export interface Comment {
-    readonly uniqueIdInThread: number;
-    readonly body: MarkdownString;
-    readonly userName: string;
-    readonly userIconPath?: string;
-    readonly contextValue?: string;
-    readonly label?: string;
-    readonly mode?: CommentMode;
-}
-
-export enum CommentThreadCollapsibleState {
-    /**
-     * Determines an item is collapsed
-     */
-    Collapsed = 0,
-    /**
-     * Determines an item is expanded
-     */
-    Expanded = 1
-}
-
-export interface CommentInput {
-    value: string;
-    uri: URI;
-}
-
-export interface CommentThread {
-    commentThreadHandle: number;
-    controllerHandle: number;
-    extensionId?: string;
-    threadId: string;
-    resource: string | null;
-    range: Range;
-    label: string | undefined;
-    contextValue: string | undefined;
-    comments: Comment[] | undefined;
-    onDidChangeComments: TheiaEvent<Comment[] | undefined>;
-    collapsibleState?: CommentThreadCollapsibleState;
-    input?: CommentInput;
-    onDidChangeInput: TheiaEvent<CommentInput | undefined>;
-    onDidChangeRange: TheiaEvent<Range>;
-    onDidChangeLabel: TheiaEvent<string | undefined>;
-    onDidChangeCollapsibleState: TheiaEvent<CommentThreadCollapsibleState | undefined>;
-    isDisposed: boolean;
-}
-
-export interface CommentThreadChangedEventMain extends CommentThreadChangedEvent {
-    owner: string;
-}
-
-export interface CommentThreadChangedEvent {
-    /**
-     * Added comment threads.
-     */
-    readonly added: CommentThread[];
-
-    /**
-     * Removed comment threads.
-     */
-    readonly removed: CommentThread[];
-
-    /**
-     * Changed comment threads.
-     */
-    readonly changed: CommentThread[];
-}
-
-export interface CommentingRanges {
-    readonly resource: URI;
-    ranges: Range[];
-}
-
-export interface CommentInfo {
-    extensionId?: string;
-    threads: CommentThread[];
-    commentingRanges: CommentingRanges;
-}
diff --git a/packages/plugin-ext/src/common/plugin-api-rpc.ts b/packages/plugin-ext/src/common/plugin-api-rpc.ts
index dec1f306ef768..1f98fc730c1d4 100644
--- a/packages/plugin-ext/src/common/plugin-api-rpc.ts
+++ b/packages/plugin-ext/src/common/plugin-api-rpc.ts
@@ -67,12 +67,7 @@ import {
     SearchInWorkspaceResult,
     AuthenticationSession,
     AuthenticationSessionsChangeEvent,
-    AuthenticationProviderInformation,
-    Comment,
-    CommentOptions,
-    CommentThreadCollapsibleState,
-    CommentThread,
-    CommentThreadChangedEvent,
+    AuthenticationProviderInformation
 } from './plugin-api-rpc-model';
 import { ExtPluginApi } from './plugin-ext-api-contribution';
 import { KeysToAnyValues, KeysToKeysToAnyValue } from './types';
@@ -95,6 +90,7 @@ import type {
 import { SerializableEnvironmentVariableCollection } from '@theia/terminal/lib/common/base-terminal-protocol';
 import { ThemeType } from '@theia/core/lib/browser/theming';
 import { Disposable } from '@theia/core/lib/common/disposable';
+import { URI } from 'vscode-uri';
 
 export interface PreferenceData {
     [scope: number]: any;
@@ -705,40 +701,6 @@ export interface TimelineCommandArg {
     uri: string;
 }
 
-export namespace CommentsCommandArg {
-    export function is(arg: Object | undefined): arg is CommentsCommandArg {
-        return !!arg && typeof arg === 'object' && 'commentControlHandle' in arg && 'commentThreadHandle' in arg && 'text' in arg && !('commentUniqueId' in arg);
-    }
-}
-export interface CommentsCommandArg {
-    commentControlHandle: number;
-    commentThreadHandle: number;
-    text: string
-}
-
-export namespace CommentsContextCommandArg {
-    export function is(arg: Object | undefined): arg is CommentsContextCommandArg {
-        return !!arg && typeof arg === 'object' && 'commentControlHandle' in arg && 'commentThreadHandle' in arg && 'commentUniqueId' in arg && !('text' in arg);
-    }
-}
-export interface CommentsContextCommandArg {
-    commentControlHandle: number;
-    commentThreadHandle: number;
-    commentUniqueId: number
-}
-
-export namespace CommentsEditCommandArg {
-    export function is(arg: Object | undefined): arg is CommentsEditCommandArg {
-        return !!arg && typeof arg === 'object' && 'commentControlHandle' in arg && 'commentThreadHandle' in arg && 'commentUniqueId' in arg && 'text' in arg;
-    }
-}
-export interface CommentsEditCommandArg {
-    commentControlHandle: number;
-    commentThreadHandle: number;
-    commentUniqueId: number
-    text: string
-}
-
 export interface DecorationsExt {
     registerDecorationProvider(provider: theia.DecorationProvider): theia.Disposable
     $provideDecoration(id: number, uri: string): Promise<DecorationData | undefined>
@@ -1424,6 +1386,38 @@ export interface WebviewsMain {
     $unregisterSerializer(viewType: string): void;
 }
 
+export interface CustomEditorsExt {
+    $resolveCustomEditorWebview(
+        handle: string,
+        viewType: string,
+        resource: URI,
+        title: string,
+        options: theia.WebviewPanelOptions,
+        cancellation: CancellationToken): Promise<void>;
+    $createCustomDocument(resource: UriComponents, viewType: string, backupId: string | undefined, cancellation: CancellationToken): Promise<{ editable: boolean }>;
+    $disposeCustomDocument(resource: UriComponents, viewType: string): Promise<void>;
+    $undo(resource: UriComponents, viewType: string, editId: number, isDirty: boolean): Promise<void>;
+    $redo(resource: UriComponents, viewType: string, editId: number, isDirty: boolean): Promise<void>;
+    $revert(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;
+    $disposeEdits(resourceComponents: UriComponents, viewType: string, editIds: number[]): void;
+    $onSave(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void>;
+    $onSaveAs(resource: UriComponents, viewType: string, targetResource: UriComponents, cancellation: CancellationToken): Promise<void>;
+    $onMoveCustomEditor(handle: string, newResource: UriComponents, viewType: string): Promise<void>;
+}
+
+export interface CustomTextEditorCapabilities {
+    readonly supportsMove?: boolean;
+}
+
+export interface CustomEditorsMain {
+    $registerTextEditorProvider(viewType: string, options: theia.WebviewPanelOptions, capabilities: CustomTextEditorCapabilities): void;
+    $registerCustomEditorProvider(viewType: string, options: theia.WebviewPanelOptions, supportsMultipleEditorsPerDocument: boolean): void;
+    $unregisterEditorProvider(viewType: string): void;
+    $createCustomEditorPanel(handle: string, title: string, options: theia.WebviewPanelOptions & theia.WebviewOptions): Promise<void>;
+    $onDidEdit(resource: UriComponents, viewType: string, editId: number, label: string | undefined): void;
+    $onContentChange(resource: UriComponents, viewType: string): void;
+}
+
 export interface StorageMain {
     $set(key: string, value: KeysToAnyValues, isGlobal: boolean): Promise<boolean>;
     $get(key: string, isGlobal: boolean): Promise<KeysToAnyValues>;
@@ -1514,35 +1508,6 @@ export interface ClipboardMain {
     $writeText(value: string): Promise<void>;
 }
 
-export interface CommentsExt {
-    $createCommentThreadTemplate(commentControllerHandle: number, uriComponents: UriComponents, range: Range): void;
-    $updateCommentThreadTemplate(commentControllerHandle: number, threadHandle: number, range: Range): Promise<void>;
-    $deleteCommentThread(commentControllerHandle: number, commentThreadHandle: number): Promise<void>;
-    $provideCommentingRanges(commentControllerHandle: number, uriComponents: UriComponents, token: CancellationToken): Promise<Range[] | undefined>;
-}
-
-export interface CommentProviderFeatures {
-    options?: CommentOptions;
-}
-
-export type CommentThreadChanges = Partial<{
-    range: Range,
-    label: string,
-    contextValue: string,
-    comments: Comment[],
-    collapseState: CommentThreadCollapsibleState;
-}>;
-
-export interface CommentsMain {
-    $registerCommentController(handle: number, id: string, label: string): void;
-    $unregisterCommentController(handle: number): void;
-    $updateCommentControllerFeatures(handle: number, features: CommentProviderFeatures): void;
-    $createCommentThread(handle: number, commentThreadHandle: number, threadId: string, resource: UriComponents, range: Range, extensionId: string): CommentThread | undefined;
-    $updateCommentThread(handle: number, commentThreadHandle: number, threadId: string, resource: UriComponents, changes: CommentThreadChanges): void;
-    $deleteCommentThread(handle: number, commentThreadHandle: number): void;
-    $onDidCommentThreadsChange(handle: number, event: CommentThreadChangedEvent): void;
-}
-
 export const PLUGIN_RPC_CONTEXT = {
     AUTHENTICATION_MAIN: <ProxyIdentifier<AuthenticationMain>>createProxyIdentifier<AuthenticationMain>('AuthenticationMain'),
     COMMAND_REGISTRY_MAIN: <ProxyIdentifier<CommandRegistryMain>>createProxyIdentifier<CommandRegistryMain>('CommandRegistryMain'),
@@ -1562,6 +1527,7 @@ export const PLUGIN_RPC_CONTEXT = {
     LANGUAGES_MAIN: createProxyIdentifier<LanguagesMain>('LanguagesMain'),
     CONNECTION_MAIN: createProxyIdentifier<ConnectionMain>('ConnectionMain'),
     WEBVIEWS_MAIN: createProxyIdentifier<WebviewsMain>('WebviewsMain'),
+    CUSTOM_EDITORS_MAIN: createProxyIdentifier<CustomEditorsMain>('CustomEditorsMain'),
     STORAGE_MAIN: createProxyIdentifier<StorageMain>('StorageMain'),
     TASKS_MAIN: createProxyIdentifier<TasksMain>('TasksMain'),
     DEBUG_MAIN: createProxyIdentifier<DebugMain>('DebugMain'),
@@ -1572,8 +1538,7 @@ export const PLUGIN_RPC_CONTEXT = {
     CLIPBOARD_MAIN: <ProxyIdentifier<ClipboardMain>>createProxyIdentifier<ClipboardMain>('ClipboardMain'),
     LABEL_SERVICE_MAIN: <ProxyIdentifier<LabelServiceMain>>createProxyIdentifier<LabelServiceMain>('LabelServiceMain'),
     TIMELINE_MAIN: <ProxyIdentifier<TimelineMain>>createProxyIdentifier<TimelineMain>('TimelineMain'),
-    THEMING_MAIN: <ProxyIdentifier<ThemingMain>>createProxyIdentifier<ThemingMain>('ThemingMain'),
-    COMMENTS_MAIN: <ProxyIdentifier<CommentsMain>>createProxyIdentifier<CommentsMain>('CommentsMain')
+    THEMING_MAIN: <ProxyIdentifier<ThemingMain>>createProxyIdentifier<ThemingMain>('ThemingMain')
 };
 
 export const MAIN_RPC_CONTEXT = {
@@ -1594,6 +1559,7 @@ export const MAIN_RPC_CONTEXT = {
     LANGUAGES_EXT: createProxyIdentifier<LanguagesExt>('LanguagesExt'),
     CONNECTION_EXT: createProxyIdentifier<ConnectionExt>('ConnectionExt'),
     WEBVIEWS_EXT: createProxyIdentifier<WebviewsExt>('WebviewsExt'),
+    CUSTOM_EDITORS_EXT: createProxyIdentifier<CustomEditorsExt>('CustomEditorsExt'),
     STORAGE_EXT: createProxyIdentifier<StorageExt>('StorageExt'),
     TASKS_EXT: createProxyIdentifier<TasksExt>('TasksExt'),
     DEBUG_EXT: createProxyIdentifier<DebugExt>('DebugExt'),
@@ -1603,8 +1569,8 @@ export const MAIN_RPC_CONTEXT = {
     DECORATIONS_EXT: createProxyIdentifier<DecorationsExt>('DecorationsExt'),
     LABEL_SERVICE_EXT: createProxyIdentifier<LabelServiceExt>('LabelServiceExt'),
     TIMELINE_EXT: createProxyIdentifier<TimelineExt>('TimeLineExt'),
-    THEMING_EXT: createProxyIdentifier<ThemingExt>('ThemingExt'),
-    COMMENTS_EXT: createProxyIdentifier<CommentsExt>('CommentsExt')};
+    THEMING_EXT: createProxyIdentifier<ThemingExt>('ThemingExt')
+};
 
 export interface TasksExt {
     $provideTasks(handle: number, token?: CancellationToken): Promise<TaskDto[] | undefined>;
diff --git a/packages/plugin-ext/src/common/plugin-protocol.ts b/packages/plugin-ext/src/common/plugin-protocol.ts
index 7acbb69a25710..bcf4a36b96a1c 100644
--- a/packages/plugin-ext/src/common/plugin-protocol.ts
+++ b/packages/plugin-ext/src/common/plugin-protocol.ts
@@ -71,6 +71,7 @@ export interface PluginPackageContribution {
     configurationDefaults?: RecursivePartial<PreferenceSchemaProperties>;
     languages?: PluginPackageLanguageContribution[];
     grammars?: PluginPackageGrammarsContribution[];
+    customEditors?: PluginPackageCustomEditor[];
     viewsContainers?: { [location: string]: PluginPackageViewContainer[] };
     views?: { [location: string]: PluginPackageView[] };
     viewsWelcome?: PluginPackageViewWelcome[];
@@ -89,6 +90,23 @@ export interface PluginPackageContribution {
     resourceLabelFormatters?: ResourceLabelFormatter[];
 }
 
+export interface PluginPackageCustomEditor {
+    viewType: string;
+    displayName: string;
+    selector?: CustomEditorSelector[];
+    priority?: CustomEditorPriority;
+}
+
+export interface CustomEditorSelector {
+    readonly filenamePattern?: string;
+}
+
+export enum CustomEditorPriority {
+    default = 'default',
+    builtin = 'builtin',
+    option = 'option',
+}
+
 export interface PluginPackageViewContainer {
     id: string;
     title: string;
@@ -112,7 +130,6 @@ export interface PluginPackageCommand {
     title: string;
     category?: string;
     icon?: string | { light: string; dark: string; };
-    enablement?: string;
 }
 
 export interface PluginPackageMenu {
@@ -482,6 +499,7 @@ export interface PluginContribution {
     configurationDefaults?: PreferenceSchemaProperties;
     languages?: LanguageContribution[];
     grammars?: GrammarsContribution[];
+    customEditors?: CustomEditor[];
     viewsContainers?: { [location: string]: ViewContainer[] };
     views?: { [location: string]: View[] };
     viewsWelcome?: ViewWelcome[];
@@ -604,6 +622,16 @@ export interface FoldingRules {
     markers?: FoldingMarkers;
 }
 
+/**
+ * Custom Editors contribution
+ */
+export interface CustomEditor {
+    viewType: string;
+    displayName: string;
+    selector: CustomEditorSelector[];
+    priority: CustomEditorPriority;
+}
+
 /**
  * Views Containers contribution
  */
@@ -638,7 +666,6 @@ export interface PluginCommand {
     category?: string;
     iconUrl?: IconUrl;
     themeIcon?: string;
-    enablement?: string;
 }
 
 export type IconUrl = string | { light: string; dark: string; };
@@ -665,18 +692,6 @@ export interface Keybinding {
     win?: string;
 }
 
-/**
- * Keybinding contribution
- */
-export interface Keybinding {
-    keybinding?: string;
-    command: string;
-    when?: string;
-    mac?: string;
-    linux?: string;
-    win?: string;
-}
-
 /**
  * This interface describes a plugin lifecycle object.
  */
diff --git a/packages/plugin-ext/src/hosted/browser/hosted-plugin.ts b/packages/plugin-ext/src/hosted/browser/hosted-plugin.ts
index 20153fb49aa1f..6967c830c74cc 100644
--- a/packages/plugin-ext/src/hosted/browser/hosted-plugin.ts
+++ b/packages/plugin-ext/src/hosted/browser/hosted-plugin.ts
@@ -62,6 +62,8 @@ import { FrontendApplicationConfigProvider } from '@theia/core/lib/browser/front
 import { environment } from '@theia/application-package/lib/environment';
 import { JsonSchemaStore } from '@theia/core/lib/browser/json-schema-store';
 import { FileService, FileSystemProviderActivationEvent } from '@theia/filesystem/lib/browser/file-service';
+import { PluginCustomEditorRegistry } from '../../main/browser/custom-editors/plugin-custom-editor-registry';
+import { CustomEditorWidget } from '../../main/browser/custom-editors/custom-editor-widget';
 
 export type PluginHost = 'frontend' | string;
 export type DebugActivationEvent = 'onDebugResolve' | 'onDebugInitialConfigurations' | 'onDebugAdapterProtocolTracker';
@@ -151,6 +153,9 @@ export class HostedPluginSupport {
     @inject(JsonSchemaStore)
     protected readonly jsonSchemaStore: JsonSchemaStore;
 
+    @inject(PluginCustomEditorRegistry)
+    protected readonly customEditorRegistry: PluginCustomEditorRegistry;
+
     private theiaReadyPromise: Promise<any>;
 
     protected readonly managers = new Map<string, PluginManagerExt>();
@@ -197,9 +202,10 @@ export class HostedPluginSupport {
         this.taskProviderRegistry.onWillProvideTaskProvider(event => this.ensureTaskActivation(event));
         this.taskResolverRegistry.onWillProvideTaskResolver(event => this.ensureTaskActivation(event));
         this.fileService.onWillActivateFileSystemProvider(event => this.ensureFileSystemActivation(event));
+        this.customEditorRegistry.onPendingOpenCustomEditor(event => this.activateByCustomEditor(event));
 
         this.widgets.onDidCreateWidget(({ factoryId, widget }) => {
-            if (factoryId === WebviewWidget.FACTORY_ID && widget instanceof WebviewWidget) {
+            if ((factoryId === WebviewWidget.FACTORY_ID || factoryId === CustomEditorWidget.FACTORY_ID) && widget instanceof WebviewWidget) {
                 const storeState = widget.storeState.bind(widget);
                 const restoreState = widget.restoreState.bind(widget);
 
@@ -556,6 +562,10 @@ export class HostedPluginSupport {
         await this.activateByEvent(`onCommand:${commandId}`);
     }
 
+    async activateByCustomEditor(viewType: string): Promise<void> {
+        await this.activateByEvent(`onCustomEditor:${viewType}`);
+    }
+
     activateByFileSystem(event: FileSystemProviderActivationEvent): Promise<void> {
         return this.activateByEvent(`onFileSystem:${event.scheme}`);
     }
@@ -713,10 +723,17 @@ export class HostedPluginSupport {
         this.webviewRevivers.delete(viewType);
     }
 
-    protected preserveWebviews(): void {
+    protected async preserveWebviews(): Promise<void> {
         for (const webview of this.widgets.getWidgets(WebviewWidget.FACTORY_ID)) {
             this.preserveWebview(webview as WebviewWidget);
         }
+        for (const webview of this.widgets.getWidgets(CustomEditorWidget.FACTORY_ID)) {
+            (webview as CustomEditorWidget).modelRef.dispose();
+            if ((webview as any)['closeWithoutSaving']) {
+                delete (webview as any)['closeWithoutSaving'];
+            }
+            this.customEditorRegistry.resolveWidget(webview as CustomEditorWidget);
+        }
     }
 
     protected preserveWebview(webview: WebviewWidget): void {
diff --git a/packages/plugin-ext/src/hosted/node/scanners/scanner-theia.ts b/packages/plugin-ext/src/hosted/node/scanners/scanner-theia.ts
index d450055d97fbd..cf1071dba459f 100644
--- a/packages/plugin-ext/src/hosted/node/scanners/scanner-theia.ts
+++ b/packages/plugin-ext/src/hosted/node/scanners/scanner-theia.ts
@@ -47,7 +47,10 @@ import {
     PluginCommand,
     IconUrl,
     ThemeContribution,
-    IconThemeContribution
+    IconThemeContribution,
+    PluginPackageCustomEditor,
+    CustomEditor,
+    CustomEditorPriority
 } from '../../../common/plugin-protocol';
 import * as fs from 'fs';
 import * as path from 'path';
@@ -177,6 +180,15 @@ export class TheiaPluginScanner implements PluginScanner {
             console.error(`Could not read '${rawPlugin.name}' contribution 'grammars'.`, rawPlugin.contributes!.grammars, err);
         }
 
+        try {
+            if (rawPlugin.contributes!.customEditors) {
+                const customEditors = this.readCustomEditors(rawPlugin.contributes.customEditors!);
+                contributions.customEditors = customEditors;
+            }
+        } catch (err) {
+            console.error(`Could not read '${rawPlugin.name}' contribution 'customEditors'.`, rawPlugin.contributes!.customEditors, err);
+        }
+
         try {
             if (rawPlugin.contributes && rawPlugin.contributes.viewsContainers) {
                 const viewsContainers = rawPlugin.contributes.viewsContainers;
@@ -317,7 +329,7 @@ export class TheiaPluginScanner implements PluginScanner {
         return contributions;
     }
 
-    protected readCommand({ command, title, category, icon, enablement }: PluginPackageCommand, pck: PluginPackage): PluginCommand {
+    protected readCommand({ command, title, category, icon }: PluginPackageCommand, pck: PluginPackage): PluginCommand {
         let themeIcon: string | undefined;
         let iconUrl: IconUrl | undefined;
         if (icon) {
@@ -334,7 +346,7 @@ export class TheiaPluginScanner implements PluginScanner {
                 };
             }
         }
-        return { command, title, category, iconUrl, themeIcon, enablement };
+        return { command, title, category, iconUrl, themeIcon };
     }
 
     protected toPluginUrl(pck: PluginPackage, relativePath: string): string {
@@ -467,6 +479,19 @@ export class TheiaPluginScanner implements PluginScanner {
         };
     }
 
+    private readCustomEditors(rawCustomEditors: PluginPackageCustomEditor[]): CustomEditor[] {
+        return rawCustomEditors.map(rawCustomEditor => this.readCustomEditor(rawCustomEditor));
+    }
+
+    private readCustomEditor(rawCustomEditor: PluginPackageCustomEditor): CustomEditor {
+        return {
+            viewType: rawCustomEditor.viewType,
+            displayName: rawCustomEditor.displayName,
+            selector: rawCustomEditor.selector || [],
+            priority: rawCustomEditor.priority || CustomEditorPriority.default
+        };
+    }
+
     private readViewsContainers(rawViewsContainers: PluginPackageViewContainer[], pck: PluginPackage): ViewContainer[] {
         return rawViewsContainers.map(rawViewContainer => this.readViewContainer(rawViewContainer, pck));
     }
diff --git a/packages/plugin-ext/src/main/browser/comments/comment-glyph-widget.ts b/packages/plugin-ext/src/main/browser/comments/comment-glyph-widget.ts
deleted file mode 100644
index 746a39c618e03..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comment-glyph-widget.ts
+++ /dev/null
@@ -1,65 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-import { Disposable } from '@theia/core/lib/common';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/contrib/comments/browser/commentGlyphWidget.ts
-
-export class CommentGlyphWidget implements Disposable {
-
-    private lineNumber!: number;
-    private editor: monaco.editor.ICodeEditor;
-    private commentsDecorations: string[] = [];
-    readonly commentsOptions: monaco.editor.IModelDecorationOptions;
-    constructor(editor: monaco.editor.ICodeEditor) {
-        this.commentsOptions = {
-            isWholeLine: true,
-            linesDecorationsClassName: 'comment-range-glyph comment-thread'
-        };
-        this.editor = editor;
-    }
-
-    getPosition(): number {
-        const model = this.editor.getModel();
-        const range = model && this.commentsDecorations && this.commentsDecorations.length
-            ? model.getDecorationRange(this.commentsDecorations[0])
-            : null;
-
-        return range ? range.startLineNumber : this.lineNumber;
-    }
-
-    setLineNumber(lineNumber: number): void {
-        this.lineNumber = lineNumber;
-        const commentsDecorations = [{
-            range: {
-                startLineNumber: lineNumber, startColumn: 1,
-                endLineNumber: lineNumber, endColumn: 1
-            },
-            options: this.commentsOptions
-        }];
-
-        this.commentsDecorations = this.editor.deltaDecorations(this.commentsDecorations, commentsDecorations);
-    }
-
-    dispose(): void {
-        if (this.commentsDecorations) {
-            this.editor.deltaDecorations(this.commentsDecorations, []);
-        }
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comment-thread-widget.tsx b/packages/plugin-ext/src/main/browser/comments/comment-thread-widget.tsx
deleted file mode 100644
index e95ffb1e162b5..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comment-thread-widget.tsx
+++ /dev/null
@@ -1,669 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-import { MonacoEditorZoneWidget } from '@theia/monaco/lib/browser/monaco-editor-zone-widget';
-import {
-    Comment,
-    CommentMode,
-    CommentThread,
-    CommentThreadCollapsibleState
-} from '../../../common/plugin-api-rpc-model';
-import { CommentGlyphWidget } from './comment-glyph-widget';
-import { BaseWidget, DISABLED_CLASS } from '@theia/core/lib/browser';
-import * as ReactDOM from 'react-dom';
-import * as React from 'react';
-import { MouseTargetType } from '@theia/editor/lib/browser';
-import { CommentsService } from './comments-service';
-import {
-    ActionMenuNode,
-    CommandRegistry,
-    CompositeMenuNode,
-    MenuModelRegistry,
-    MenuPath
-} from '@theia/core/lib/common';
-import { CommentsContextKeyService } from './comments-context-key-service';
-import { RefObject } from 'react';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/contrib/comments/browser/commentThreadWidget.ts
-
-export const COMMENT_THREAD_CONTEXT: MenuPath = ['comment_thread-context-menu'];
-export const COMMENT_CONTEXT: MenuPath = ['comment-context-menu'];
-export const COMMENT_TITLE: MenuPath = ['comment-title-menu'];
-
-export class CommentThreadWidget extends BaseWidget {
-
-    protected readonly zoneWidget: MonacoEditorZoneWidget;
-    protected readonly commentGlyphWidget: CommentGlyphWidget;
-    protected readonly contextMenu: CompositeMenuNode;
-    protected readonly commentFormRef: RefObject<CommentForm> = React.createRef<CommentForm>();
-
-    protected isExpanded?: boolean;
-
-    constructor(
-        editor: monaco.editor.IStandaloneCodeEditor,
-        private _owner: string,
-        private _commentThread: CommentThread,
-        private commentService: CommentsService,
-        protected readonly menus: MenuModelRegistry,
-        protected readonly contextKeyService: CommentsContextKeyService,
-        protected readonly commands: CommandRegistry
-    ) {
-        super();
-        this.toDispose.push(this.zoneWidget = new MonacoEditorZoneWidget(editor));
-        this.toDispose.push(this.commentGlyphWidget = new CommentGlyphWidget(editor));
-        this.toDispose.push(this._commentThread.onDidChangeCollapsibleState(state => {
-            if (state === CommentThreadCollapsibleState.Expanded && !this.isExpanded) {
-                const lineNumber = this._commentThread.range.startLineNumber;
-
-                this.display({ afterLineNumber: lineNumber, afterColumn: 1, heightInLines: 2});
-                return;
-            }
-
-            if (state === CommentThreadCollapsibleState.Collapsed && this.isExpanded) {
-                this.hide();
-                return;
-            }
-        }));
-        this.contextKeyService.commentIsEmpty.set(true);
-        this.toDispose.push(this.zoneWidget.editor.onMouseDown(e => this.onEditorMouseDown(e)));
-        this.toDispose.push(this.contextKeyService.onDidChange(() => {
-            const commentForm = this.commentFormRef.current;
-            if (commentForm) {
-                commentForm.update();
-            }
-        }));
-        this.contextMenu = this.menus.getMenu(COMMENT_THREAD_CONTEXT);
-        this.contextMenu.children.map(node => node instanceof ActionMenuNode && node.action.when).forEach(exp => {
-            if (typeof exp === 'string') {
-                this.contextKeyService.setExpression(exp);
-            }
-        });
-    }
-
-    public getGlyphPosition(): number {
-        return this.commentGlyphWidget.getPosition();
-    }
-
-    public collapse(): void {
-        this._commentThread.collapsibleState = CommentThreadCollapsibleState.Collapsed;
-        if (this._commentThread.comments && this._commentThread.comments.length === 0) {
-            this.deleteCommentThread();
-        }
-
-        this.hide();
-    }
-
-    private deleteCommentThread(): void {
-        this.dispose();
-        this.commentService.disposeCommentThread(this.owner, this._commentThread.threadId);
-    }
-
-    dispose(): void {
-        super.dispose();
-        if (this.commentGlyphWidget) {
-            this.commentGlyphWidget.dispose();
-        }
-    }
-
-    toggleExpand(lineNumber: number): void {
-        if (this.isExpanded) {
-            this._commentThread.collapsibleState = CommentThreadCollapsibleState.Collapsed;
-            this.hide();
-            if (!this._commentThread.comments || !this._commentThread.comments.length) {
-                this.deleteCommentThread();
-            }
-        } else {
-            this._commentThread.collapsibleState = CommentThreadCollapsibleState.Expanded;
-            this.display({ afterLineNumber: lineNumber, afterColumn: 1, heightInLines: 2 });
-        }
-    }
-
-    hide(): void {
-        this.zoneWidget.hide();
-        this.isExpanded = false;
-        super.hide();
-    }
-
-    display(options: MonacoEditorZoneWidget.Options): void {
-        this.isExpanded = true;
-        if (this._commentThread.collapsibleState && this._commentThread.collapsibleState !== CommentThreadCollapsibleState.Expanded) {
-            return;
-        }
-        this.commentGlyphWidget.setLineNumber(options.afterLineNumber);
-        this._commentThread.collapsibleState = CommentThreadCollapsibleState.Expanded;
-        this.zoneWidget.show(options);
-        this.update();
-    }
-
-    private onEditorMouseDown(e: monaco.editor.IEditorMouseEvent): void {
-        const range = e.target.range;
-
-        if (!range) {
-            return;
-        }
-
-        if (!e.event.leftButton) {
-            return;
-        }
-
-        if (e.target.type !== MouseTargetType.GUTTER_LINE_DECORATIONS) {
-            return;
-        }
-
-        const data = e.target.detail;
-        const gutterOffsetX = data.offsetX - data.glyphMarginWidth - data.lineNumbersWidth - data.glyphMarginLeft;
-
-        // don't collide with folding and git decorations
-        if (gutterOffsetX > 14) {
-            return;
-        }
-
-        const mouseDownInfo = { lineNumber: range.startLineNumber };
-
-        const { lineNumber } = mouseDownInfo;
-
-        if (!range || range.startLineNumber !== lineNumber) {
-            return;
-        }
-
-        if (e.target.type !== MouseTargetType.GUTTER_LINE_DECORATIONS) {
-            return;
-        }
-
-        if (!e.target.element) {
-            return;
-        }
-
-        if (this.commentGlyphWidget && this.commentGlyphWidget.getPosition() !== lineNumber) {
-            return;
-        }
-
-        if (e.target.element.className.indexOf('comment-thread') >= 0) {
-            this.toggleExpand(lineNumber);
-            return;
-        }
-
-        if (this._commentThread.collapsibleState === CommentThreadCollapsibleState.Collapsed) {
-            this.display({ afterLineNumber: mouseDownInfo.lineNumber, heightInLines: 2 });
-        } else {
-            this.hide();
-        }
-    }
-
-    public get owner(): string {
-        return this._owner;
-    }
-
-    public get commentThread(): CommentThread {
-        return this._commentThread;
-    }
-
-    private getThreadLabel(): string {
-        let label: string | undefined;
-        label = this._commentThread.label;
-
-        if (label === undefined) {
-            if (this._commentThread.comments && this._commentThread.comments.length) {
-                const onlyUnique = (value: Comment, index: number, self: Comment[]) => self.indexOf(value) === index;
-                const participantsList = this._commentThread.comments.filter(onlyUnique).map(comment => `@${comment.userName}`).join(', ');
-                label = `Participants: ${participantsList}`;
-            } else {
-                label = 'Start discussion';
-            }
-        }
-
-        return label;
-    }
-
-    update(): void {
-        if (!this.isExpanded) {
-            return;
-        }
-        this.render();
-        const headHeight = Math.ceil(this.zoneWidget.editor.getOption(monaco.editor.EditorOption.lineHeight) * 1.2);
-        const lineHeight = this.zoneWidget.editor.getOption(monaco.editor.EditorOption.lineHeight);
-        const arrowHeight = Math.round(lineHeight / 3);
-        const frameThickness = Math.round(lineHeight / 9) * 2;
-        const body = this.zoneWidget.containerNode.getElementsByClassName('body')[0];
-
-        const computedLinesNumber = Math.ceil((headHeight + body.clientHeight + arrowHeight + frameThickness + 8 /** margin bottom to avoid margin collapse */) / lineHeight);
-        this.zoneWidget.show({ afterLineNumber: this._commentThread.range.startLineNumber, heightInLines: computedLinesNumber });
-    }
-
-    protected render(): void {
-        const headHeight = Math.ceil(this.zoneWidget.editor.getOption(monaco.editor.EditorOption.lineHeight) * 1.2);
-        ReactDOM.render(<div className={'review-widget'}>
-            <div className={'head'} style={{ height: headHeight, lineHeight: `${headHeight}px`}}>
-                <div className={'review-title'}>
-                    <span className={'filename'}>{this.getThreadLabel()}</span>
-                </div>
-                <div className={'review-actions'}>
-                    <div className={'monaco-action-bar animated'}>
-                        <ul className={'actions-container'} role={'toolbar'}>
-                            <li className={'action-item'} role={'presentation'}>
-                                <a className={'action-label codicon expand-review-action codicon-chevron-up'}
-                                   role={'button'}
-                                   tabIndex={0}
-                                   title={'Collapse'}
-                                   onClick={() => this.collapse()}
-                                />
-                            </li>
-                        </ul>
-                    </div>
-                </div>
-            </div>
-            <div className={'body'}>
-                <div className={'comments-container'} role={'presentation'} tabIndex={0}>
-                    {this._commentThread.comments?.map((comment, index) => <ReviewComment
-                        key={index}
-                        contextKeyService={this.contextKeyService}
-                        menus={this.menus}
-                        comment={comment}
-                        commentForm={this.commentFormRef}
-                        commands={this.commands}
-                        commentThread={this._commentThread}
-                    />)}
-                </div>
-                <CommentForm contextKeyService={this.contextKeyService}
-                             commands={this.commands}
-                             commentThread={this._commentThread}
-                             menus={this.menus}
-                             widget={this}
-                             ref={this.commentFormRef}
-                />
-            </div>
-        </div>, this.zoneWidget.containerNode);
-    }
-}
-
-namespace CommentForm {
-    export interface Props  {
-        menus: MenuModelRegistry,
-        commentThread: CommentThread;
-        commands: CommandRegistry;
-        contextKeyService: CommentsContextKeyService;
-        widget: CommentThreadWidget;
-    }
-
-    export interface State {
-        expanded: boolean
-    }
-}
-
-export class CommentForm<P extends CommentForm.Props = CommentForm.Props> extends React.Component<P, CommentForm.State> {
-    private readonly menu: CompositeMenuNode;
-    private inputRef: RefObject<HTMLTextAreaElement> = React.createRef<HTMLTextAreaElement>();
-    private inputValue: string = '';
-    private readonly getInput = () => this.inputValue;
-    private readonly clearInput: () => void = () => {
-        const input = this.inputRef.current;
-        if (input) {
-            this.inputValue = '';
-            input.value = this.inputValue;
-            this.props.contextKeyService.commentIsEmpty.set(true);
-        }
-    };
-
-    update(): void {
-        this.setState(this.state);
-    }
-
-    protected expand = () => {
-        this.setState({ expanded: true });
-        // Wait for the widget to be rendered.
-        setTimeout(() => {
-            // Update the widget's height.
-            this.props.widget.update();
-            this.inputRef.current?.focus();
-        }, 100);
-    };
-    protected collapse = () => {
-        this.setState({ expanded: false });
-        // Wait for the widget to be rendered.
-        setTimeout(() => {
-            // Update the widget's height.
-            this.props.widget.update();
-        }, 100);
-    };
-
-    componentDidMount(): void {
-        // Wait for the widget to be rendered.
-        setTimeout(() => {
-            this.inputRef.current?.focus();
-        }, 100);
-    }
-
-    private readonly onInput: (event: React.FormEvent) => void = (event: React.FormEvent) => {
-        // eslint-disable-next-line @typescript-eslint/no-explicit-any
-        const value = (event.target as any).value;
-        if (this.inputValue.length === 0 || value.length === 0) {
-            this.props.contextKeyService.commentIsEmpty.set(value.length === 0);
-        }
-        this.inputValue = value;
-    };
-
-    constructor(props: P) {
-        super(props);
-        this.state = {
-            expanded: false
-        };
-
-        const setState = this.setState.bind(this);
-        this.setState = newState => {
-            setState(newState);
-        };
-
-        this.menu = this.props.menus.getMenu(COMMENT_THREAD_CONTEXT);
-        this.menu.children.map(node => node instanceof ActionMenuNode && node.action.when).forEach(exp => {
-            if (typeof exp === 'string') {
-                this.props.contextKeyService.setExpression(exp);
-            }
-        });
-    }
-
-    render(): React.ReactNode {
-        const { commands, commentThread, contextKeyService } = this.props;
-        const hasExistingComments = commentThread.comments && commentThread.comments.length > 0;
-        return <div className={'comment-form' + (this.state.expanded || commentThread.comments && commentThread.comments.length === 0 ? ' expand' : '')}>
-            <div className={'theia-comments-input-message-container'}>
-                        <textarea className={'theia-comments-input-message theia-input'}
-                                  placeholder={hasExistingComments ? 'Reply...' : 'Type a new comment'}
-                                  onInput={this.onInput}
-                                  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-                                  onBlur={(event: any) => {
-                                      if (event.target.value.length > 0) {
-                                          return;
-                                      }
-                                      if (event.relatedTarget && event.relatedTarget.className === 'comments-button comments-text-button theia-button') {
-                                          this.state = { expanded: false };
-                                          return;
-                                      }
-                                      this.collapse();
-                                  }}
-                                  ref={this.inputRef}>
-                        </textarea>
-            </div>
-            <CommentActions menu={this.menu}
-                            contextKeyService={contextKeyService}
-                            commands={commands}
-                            commentThread={commentThread}
-                            getInput={this.getInput}
-                            clearInput={this.clearInput}
-            />
-            <button className={'review-thread-reply-button'} title={'Reply...'} onClick={this.expand}>Reply...</button>
-        </div>;
-    }
-}
-
-namespace ReviewComment {
-    export interface Props  {
-        menus: MenuModelRegistry,
-        comment: Comment;
-        commentThread: CommentThread;
-        contextKeyService: CommentsContextKeyService;
-        commands: CommandRegistry;
-        commentForm: RefObject<CommentForm>;
-    }
-
-    export interface State {
-        hover: boolean
-    }
-}
-
-export class ReviewComment<P extends ReviewComment.Props = ReviewComment.Props> extends React.Component<P, ReviewComment.State> {
-
-    constructor(props: P) {
-        super(props);
-        this.state = {
-            hover: false
-        };
-
-        const setState = this.setState.bind(this);
-        this.setState = newState => {
-            setState(newState);
-        };
-    }
-
-    protected detectHover = (element: HTMLElement | null) => {
-        if (element) {
-            window.requestAnimationFrame(() => {
-                const hover = element.matches(':hover');
-                this.setState({ hover });
-            });
-        }
-    };
-
-    protected showHover = () => this.setState({ hover: true });
-    protected hideHover = () => this.setState({ hover: false });
-
-    render(): React.ReactNode {
-        const { comment, commentForm, contextKeyService, menus, commands, commentThread } = this.props;
-        const commentUniqueId = comment.uniqueIdInThread;
-        const { hover } = this.state;
-        contextKeyService.comment.set(comment.contextValue);
-        return <div className={'review-comment'}
-                    tabIndex={-1}
-                    aria-label={`${comment.userName}, ${comment.body.value}`}
-                    ref={this.detectHover}
-                    onMouseEnter={this.showHover}
-                    onMouseLeave={this.hideHover}>
-            <div className={'avatar-container'}>
-                <img className={'avatar'} src={comment.userIconPath}/>
-            </div>
-            <div className={'review-comment-contents'}>
-                <div className={'comment-title monaco-mouse-cursor-text'}>
-                    <strong className={'author'}>{comment.userName}</strong>
-                    <span className={'isPending'}>{comment.label}</span>
-                    <div className={'theia-comments-inline-actions-container'}>
-                        <div className={'theia-comments-inline-actions'} role={'toolbar'}>
-                            {hover && menus.getMenu(COMMENT_TITLE).children.map((node, index) => node instanceof ActionMenuNode &&
-                                <CommentsInlineAction key={index} {...{ node, commands, commentThread, commentUniqueId, contextKeyService }} />)}
-                        </div>
-                    </div>
-                </div>
-                <CommentBody value={comment.body.value}
-                             isVisible={comment.mode === undefined || comment.mode === CommentMode.Preview}/>
-                <CommentEditContainer contextKeyService={contextKeyService}
-                                      menus={menus}
-                                      comment={comment}
-                                      commentThread={commentThread}
-                                      commentForm={commentForm}
-                                      commands={commands}/>
-            </div>
-        </div>;
-    }
-}
-
-namespace CommentBody {
-    export interface Props  {
-        value: string
-        isVisible: boolean
-    }
-}
-
-export class CommentBody extends React.Component<CommentBody.Props> {
-    render(): React.ReactNode {
-        const { value, isVisible } = this.props;
-        if (!isVisible) {
-            return false;
-        }
-        return <div className={'comment-body monaco-mouse-cursor-text'}>
-            <div>
-                <p>{value}</p>
-            </div>
-        </div>;
-    }
-}
-
-namespace CommentEditContainer {
-    export interface Props  {
-        contextKeyService: CommentsContextKeyService
-        menus: MenuModelRegistry,
-        comment: Comment;
-        commentThread: CommentThread;
-        commentForm: RefObject<CommentForm>;
-        commands: CommandRegistry;
-    }
-}
-
-export class CommentEditContainer extends React.Component<CommentEditContainer.Props> {
-    private readonly inputRef: RefObject<HTMLTextAreaElement> = React.createRef<HTMLTextAreaElement>();
-    private dirtyCommentMode: CommentMode | undefined;
-    private dirtyCommentFormState: boolean | undefined;
-
-    componentDidUpdate(prevProps: Readonly<CommentEditContainer.Props>, prevState: Readonly<{}>): void {
-        const commentFormState = this.props.commentForm.current?.state;
-        const mode = this.props.comment.mode;
-        if (this.dirtyCommentMode !== mode || (this.dirtyCommentFormState !== commentFormState?.expanded && !commentFormState?.expanded)) {
-            const currentInput = this.inputRef.current;
-            if (currentInput) {
-                // Wait for the widget to be rendered.
-                setTimeout(() => {
-                    currentInput.focus();
-                    currentInput.setSelectionRange(currentInput.value.length, currentInput.value.length);
-                }, 50);
-            }
-        }
-        this.dirtyCommentMode = mode;
-        this.dirtyCommentFormState = commentFormState?.expanded;
-    }
-
-    render(): React.ReactNode {
-        const { menus, comment, commands, commentThread, contextKeyService } = this.props;
-        if (!(comment.mode === CommentMode.Editing)) {
-            return false;
-        }
-        return <div className={'edit-container'}>
-            <div className={'edit-textarea'}>
-                <div className={'theia-comments-input-message-container'}>
-                    <textarea className={'theia-comments-input-message theia-input'}
-                              defaultValue={comment.body.value}
-                              ref={this.inputRef}/>
-                </div>
-            </div>
-            <div className={'form-actions'}>
-                {menus.getMenu(COMMENT_CONTEXT).children.map((node, index) => {
-                        const onClick = () => {
-                            commands.executeCommand(node.id, {
-                                thread: commentThread,
-                                commentUniqueId: comment.uniqueIdInThread,
-                                text: this.inputRef.current ? this.inputRef.current.value : ''
-                            });
-                        };
-                        return node instanceof ActionMenuNode &&
-                            <CommentAction key={index} {...{ node, commands, onClick, contextKeyService }} />;
-                    }
-                )}
-            </div>
-        </div>;
-    }
-}
-
-namespace CommentsInlineAction {
-    export interface Props  {
-        node: ActionMenuNode;
-        commentThread: CommentThread;
-        commentUniqueId: number;
-        commands: CommandRegistry;
-        contextKeyService: CommentsContextKeyService;
-    }
-}
-
-export class CommentsInlineAction extends React.Component<CommentsInlineAction.Props> {
-    render(): React.ReactNode {
-        const { node, commands, contextKeyService, commentThread, commentUniqueId } = this.props;
-        if (node.action.when && !contextKeyService.match(node.action.when)) {
-            return false;
-        }
-        return <div className='theia-comments-inline-action'>
-            <a className={node.icon}
-               title={node.label}
-               onClick={() => {
-                   commands.executeCommand(node.id, {
-                       thread: commentThread,
-                       commentUniqueId
-                   });
-               }} />
-        </div>;
-    }
-}
-
-namespace CommentActions {
-    export interface Props  {
-        contextKeyService: CommentsContextKeyService;
-        commands: CommandRegistry;
-        menu: CompositeMenuNode;
-        commentThread: CommentThread;
-        getInput: () => string;
-        clearInput: () => void;
-    }
-}
-
-export class CommentActions extends React.Component<CommentActions.Props> {
-    render(): React.ReactNode {
-        const {contextKeyService, commands, menu, commentThread, getInput, clearInput } = this.props;
-        return <div className={'form-actions'}>
-            {menu.children.map((node, index) => node instanceof ActionMenuNode &&
-                <CommentAction key={index}
-                               commands={commands}
-                               node={node}
-                               onClick={() => {
-                                   commands.executeCommand(node.id, {
-                                       thread: commentThread,
-                                       text: getInput()
-                                   });
-                                   clearInput();
-                               }}
-                               contextKeyService={contextKeyService}
-                />)}
-        </div>;
-    }
-}
-namespace CommentAction {
-    export interface Props  {
-        contextKeyService: CommentsContextKeyService;
-        commands: CommandRegistry;
-        node: ActionMenuNode;
-        onClick: () => void;
-    }
-}
-
-export class CommentAction extends React.Component<CommentAction.Props> {
-    render(): React.ReactNode {
-        const classNames = ['comments-button', 'comments-text-button', 'theia-button'];
-        const { node, commands, contextKeyService, onClick } = this.props;
-        if (node.action.when && !contextKeyService.match(node.action.when)) {
-            return false;
-        }
-        const isEnabled = commands.isEnabled(node.action.commandId);
-        if (!isEnabled) {
-            classNames.push(DISABLED_CLASS);
-        }
-        return <a
-            className={classNames.join(' ')}
-            tabIndex={0}
-            role={'button'}
-            onClick={() => {
-                if (isEnabled) {
-                    onClick();
-                }
-            }}>{node.label}
-        </a>;
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comments-context-key-service.ts b/packages/plugin-ext/src/main/browser/comments/comments-context-key-service.ts
deleted file mode 100644
index 075623bfb0015..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comments-context-key-service.ts
+++ /dev/null
@@ -1,68 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import { injectable, inject, postConstruct } from 'inversify';
-import { ContextKeyService, ContextKey } from '@theia/core/lib/browser/context-key-service';
-import { Emitter } from '@theia/core/lib/common';
-
-@injectable()
-export class CommentsContextKeyService {
-
-    @inject(ContextKeyService)
-    protected readonly contextKeyService: ContextKeyService;
-    protected readonly contextKeys: Set<string> = new Set();
-    protected readonly onDidChangeEmitter = new Emitter<void>();
-    readonly onDidChange = this.onDidChangeEmitter.event;
-    protected _commentIsEmpty: ContextKey<boolean>;
-    protected _commentController: ContextKey<string | undefined>;
-    protected _comment: ContextKey<string | undefined>;
-
-    get commentController(): ContextKey<string | undefined> {
-        return this._commentController;
-    }
-
-    get comment(): ContextKey<string | undefined> {
-        return this._comment;
-    }
-
-    get commentIsEmpty(): ContextKey<boolean> {
-        return this._commentIsEmpty;
-    }
-
-    @postConstruct()
-    protected init(): void {
-        this.contextKeys.add('commentIsEmpty');
-        this._commentController = this.contextKeyService.createKey<string | undefined>('commentController', undefined);
-        this._comment = this.contextKeyService.createKey<string | undefined>('comment', undefined);
-        this._commentIsEmpty = this.contextKeyService.createKey<boolean>('commentIsEmpty', true);
-        this.contextKeyService.onDidChange(event => {
-            if (event.affects(this.contextKeys)) {
-                this.onDidChangeEmitter.fire();
-            }
-        });
-    }
-
-    setExpression(expression: string): void {
-        this.contextKeyService.parseKeys(expression).forEach(key => {
-            this.contextKeys.add(key);
-        });
-    }
-
-    match(expression: string | undefined): boolean {
-        return !expression || this.contextKeyService.match(expression);
-    }
-
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comments-contribution.ts b/packages/plugin-ext/src/main/browser/comments/comments-contribution.ts
deleted file mode 100644
index 11342199ba440..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comments-contribution.ts
+++ /dev/null
@@ -1,263 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import { inject, injectable } from 'inversify';
-import { CommentingRangeDecorator } from './comments-decorator';
-import { EditorManager, EditorMouseEvent, EditorWidget } from '@theia/editor/lib/browser';
-import { MonacoDiffEditor } from '@theia/monaco/lib/browser/monaco-diff-editor';
-import { CommentThreadWidget } from './comment-thread-widget';
-import { CommentsService, CommentInfoMain } from './comments-service';
-import { CommentThread } from '../../../common/plugin-api-rpc-model';
-import { CommandRegistry, DisposableCollection, MenuModelRegistry } from '@theia/core/lib/common';
-import { URI } from 'vscode-uri';
-import { CommentsContextKeyService } from './comments-context-key-service';
-import { ContextKeyService } from '@theia/core/lib/browser/context-key-service';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/contrib/comments/browser/comments.contribution.ts
-
-@injectable()
-export class CommentsContribution {
-
-    private addInProgress!: boolean;
-    private commentWidgets: CommentThreadWidget[];
-    private commentInfos: CommentInfoMain[];
-    private emptyThreadsToAddQueue: [number, EditorMouseEvent | undefined][] = [];
-
-    @inject(MenuModelRegistry) protected readonly menus: MenuModelRegistry;
-    @inject(CommentsContextKeyService) protected readonly commentsContextKeyService: CommentsContextKeyService;
-    @inject(ContextKeyService) protected readonly contextKeyService: ContextKeyService;
-    @inject(CommandRegistry) protected readonly commands: CommandRegistry;
-
-    constructor(@inject(CommentingRangeDecorator) protected readonly rangeDecorator: CommentingRangeDecorator,
-                @inject(CommentsService) protected readonly commentService: CommentsService,
-                @inject(EditorManager) protected readonly editorManager: EditorManager) {
-        this.commentWidgets = [];
-        this.commentInfos = [];
-        this.commentService.onDidSetResourceCommentInfos(e => {
-            const editor = this.getCurrentEditor();
-            const editorURI = editor && editor.editor instanceof MonacoDiffEditor && editor.editor.diffEditor.getModifiedEditor().getModel();
-            if (editorURI && editorURI.toString() === e.resource.toString()) {
-                this.setComments(e.commentInfos.filter(commentInfo => commentInfo !== null));
-            }
-        });
-        this.editorManager.onCreated(async widget => {
-            const disposables = new DisposableCollection();
-            const editor = widget.editor;
-            if (editor instanceof MonacoDiffEditor) {
-                const originalEditorModel = editor.diffEditor.getOriginalEditor().getModel();
-                if (originalEditorModel) {
-                    const originalComments = await this.commentService.getComments(originalEditorModel.uri);
-                    if (originalComments) {
-                        this.rangeDecorator.update(editor.diffEditor.getOriginalEditor(), <CommentInfoMain[]>originalComments.filter(c => !!c));
-                    }
-                }
-                const modifiedEditorModel = editor.diffEditor.getModifiedEditor().getModel();
-                if (modifiedEditorModel) {
-                    const modifiedComments = await this.commentService.getComments(modifiedEditorModel.uri);
-                    if (modifiedComments) {
-                        this.rangeDecorator.update(editor.diffEditor.getModifiedEditor(), <CommentInfoMain[]>modifiedComments.filter(c => !!c));
-                    }
-                }
-                disposables.push(editor.onMouseDown(e => this.onEditorMouseDown(e)));
-                disposables.push(this.commentService.onDidUpdateCommentThreads(async e => {
-                        const editorURI = editor.document.uri;
-                        const commentInfo = this.commentInfos.filter(info => info.owner === e.owner);
-                        if (!commentInfo || !commentInfo.length) {
-                            return;
-                        }
-
-                        const added = e.added.filter(thread => thread.resource && thread.resource.toString() === editorURI.toString());
-                        const removed = e.removed.filter(thread => thread.resource && thread.resource.toString() === editorURI.toString());
-                        const changed = e.changed.filter(thread => thread.resource && thread.resource.toString() === editorURI.toString());
-
-                        removed.forEach(thread => {
-                            const matchedZones = this.commentWidgets.filter(zoneWidget => zoneWidget.owner === e.owner
-                                && zoneWidget.commentThread.threadId === thread.threadId && zoneWidget.commentThread.threadId !== '');
-                            if (matchedZones.length) {
-                                const matchedZone = matchedZones[0];
-                                const index = this.commentWidgets.indexOf(matchedZone);
-                                this.commentWidgets.splice(index, 1);
-                                matchedZone.dispose();
-                            }
-                        });
-
-                        changed.forEach(thread => {
-                            const matchedZones = this.commentWidgets.filter(zoneWidget => zoneWidget.owner === e.owner
-                                && zoneWidget.commentThread.threadId === thread.threadId);
-                            if (matchedZones.length) {
-                                const matchedZone = matchedZones[0];
-                                matchedZone.update();
-                            }
-                        });
-                        added.forEach(thread => {
-                            this.displayCommentThread(e.owner, thread);
-                            this.commentInfos.filter(info => info.owner === e.owner)[0].threads.push(thread);
-                        });
-                    })
-                );
-                editor.onDispose(() => {
-                    disposables.dispose();
-                });
-                this.beginCompute();
-            }
-        });
-    }
-
-    private onEditorMouseDown(e: EditorMouseEvent): void {
-        let mouseDownInfo = null;
-
-        const range = e.target.range;
-
-        if (!range) {
-            return;
-        }
-
-        if (e.target.type !== monaco.editor.MouseTargetType.GUTTER_LINE_DECORATIONS) {
-            return;
-        }
-
-        const data = e.target.detail;
-        const gutterOffsetX = data.offsetX - data.glyphMarginWidth - data.lineNumbersWidth - data.glyphMarginLeft;
-
-        // don't collide with folding and git decorations
-        if (gutterOffsetX > 14) {
-            return;
-        }
-
-        mouseDownInfo = { lineNumber: range.start };
-
-        const { lineNumber } = mouseDownInfo;
-        mouseDownInfo = null;
-
-        if (!range || range.start !== lineNumber) {
-            return;
-        }
-
-        if (!e.target.element) {
-            return;
-        }
-
-        if (e.target.element.className.indexOf('comment-diff-added') >= 0) {
-            this.addOrToggleCommentAtLine(e.target.position!.line + 1, e);
-        }
-    }
-
-    private async beginCompute(): Promise<void> {
-        const editorModel = this.editor && this.editor.getModel();
-        const editorURI = this.editor && editorModel && editorModel.uri;
-        if (editorURI) {
-            const comments = await this.commentService.getComments(editorURI);
-            this.setComments(<CommentInfoMain[]>comments.filter(c => !!c));
-        }
-    }
-
-    private setComments(commentInfos: CommentInfoMain[]): void {
-        if (!this.editor) {
-            return;
-        }
-
-        this.commentInfos = commentInfos;
-    }
-
-    get editor(): monaco.editor.IStandaloneCodeEditor | undefined {
-        const editor = this.getCurrentEditor();
-        if (editor && editor.editor instanceof MonacoDiffEditor) {
-            return  editor.editor.diffEditor.getModifiedEditor();
-        }
-    }
-
-    private displayCommentThread(owner: string, thread: CommentThread): void {
-        const editor = this.editor;
-        if (editor) {
-            const provider = this.commentService.getCommentController(owner);
-            if (provider) {
-                this.commentsContextKeyService.commentController.set(provider.id);
-            }
-            const zoneWidget = new CommentThreadWidget(editor, owner, thread, this.commentService, this.menus, this.commentsContextKeyService, this.commands);
-            zoneWidget.display({ afterLineNumber: thread.range.startLineNumber, heightInLines: 5 });
-            const currentEditor = this.getCurrentEditor();
-            if (currentEditor) {
-                currentEditor.onDispose(() => zoneWidget.dispose());
-            }
-            this.commentWidgets.push(zoneWidget);
-        }
-    }
-
-    public async addOrToggleCommentAtLine(lineNumber: number, e: EditorMouseEvent | undefined): Promise<void> {
-        // If an add is already in progress, queue the next add and process it after the current one finishes to
-        // prevent empty comment threads from being added to the same line.
-        if (!this.addInProgress) {
-            this.addInProgress = true;
-            // The widget's position is undefined until the widget has been displayed, so rely on the glyph position instead
-            const existingCommentsAtLine = this.commentWidgets.filter(widget => widget.getGlyphPosition() === lineNumber);
-            if (existingCommentsAtLine.length) {
-                existingCommentsAtLine.forEach(widget => widget.toggleExpand(lineNumber));
-                this.processNextThreadToAdd();
-                return;
-            } else {
-                this.addCommentAtLine(lineNumber, e);
-            }
-        } else {
-            this.emptyThreadsToAddQueue.push([lineNumber, e]);
-        }
-    }
-
-    private processNextThreadToAdd(): void {
-        this.addInProgress = false;
-        const info = this.emptyThreadsToAddQueue.shift();
-        if (info) {
-            this.addOrToggleCommentAtLine(info[0], info[1]);
-        }
-    }
-
-    private getCurrentEditor(): EditorWidget | undefined {
-        return  this.editorManager.currentEditor;
-    }
-
-    public addCommentAtLine(lineNumber: number, e: EditorMouseEvent | undefined): Promise<void> {
-        const newCommentInfos = this.rangeDecorator.getMatchedCommentAction(lineNumber);
-        const editor = this.getCurrentEditor();
-        if (!editor) {
-            return Promise.resolve();
-        }
-        if (!newCommentInfos.length) {
-            return Promise.resolve();
-        }
-
-        const { ownerId } = newCommentInfos[0]!;
-        this.addCommentAtLine2(lineNumber, ownerId);
-
-        return Promise.resolve();
-    }
-
-    public addCommentAtLine2(lineNumber: number, ownerId: string): void {
-        const editorModel = this.editor && this.editor.getModel();
-        const editorURI = this.editor && editorModel && editorModel.uri;
-        if (editorURI) {
-            this.commentService.createCommentThreadTemplate(ownerId, URI.parse(editorURI.toString()), {
-                startLineNumber: lineNumber,
-                endLineNumber: lineNumber,
-                startColumn: 1,
-                endColumn: 1
-            });
-            this.processNextThreadToAdd();
-        }
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comments-decorator.ts b/packages/plugin-ext/src/main/browser/comments/comments-decorator.ts
deleted file mode 100644
index c20682e7b0b3d..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comments-decorator.ts
+++ /dev/null
@@ -1,109 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import { injectable } from 'inversify';
-import { CommentInfoMain } from './comments-service';
-import { CommentingRanges, Range } from '../../../common/plugin-api-rpc-model';
-
-@injectable()
-export class CommentingRangeDecorator {
-
-    private decorationOptions: monaco.editor.IModelDecorationOptions;
-    private commentingRangeDecorations: CommentingRangeDecoration[] = [];
-
-    constructor() {
-        this.decorationOptions = {
-            isWholeLine: true,
-            linesDecorationsClassName: 'comment-range-glyph comment-diff-added'
-        };
-    }
-
-    public update(editor: monaco.editor.ICodeEditor, commentInfos: CommentInfoMain[]): void {
-        const model = editor.getModel();
-        if (!model) {
-            return;
-        }
-
-        const commentingRangeDecorations: CommentingRangeDecoration[] = [];
-        for (const info of commentInfos) {
-            info.commentingRanges.ranges.forEach(range => {
-                commentingRangeDecorations.push(new CommentingRangeDecoration(editor, info.owner, info.extensionId, info.label,
-                    range, this.decorationOptions, info.commentingRanges));
-            });
-        }
-
-        const oldDecorations = this.commentingRangeDecorations.map(decoration => decoration.id);
-        editor.deltaDecorations(oldDecorations, []);
-
-        this.commentingRangeDecorations = commentingRangeDecorations;
-    }
-
-    public getMatchedCommentAction(line: number): { ownerId: string, extensionId: string | undefined, label: string | undefined, commentingRangesInfo: CommentingRanges }[] {
-        const result = [];
-        for (const decoration of this.commentingRangeDecorations) {
-            const range = decoration.getActiveRange();
-            if (range && range.startLineNumber <= line && line <= range.endLineNumber) {
-                result.push(decoration.getCommentAction());
-            }
-        }
-
-        return result;
-    }
-}
-
-class CommentingRangeDecoration {
-    private decorationId: string;
-
-    public get id(): string {
-        return this.decorationId;
-    }
-
-    constructor(private _editor: monaco.editor.ICodeEditor, private _ownerId: string, private _extensionId: string | undefined,
-                private _label: string | undefined, private _range: Range, commentingOptions: monaco.editor.IModelDecorationOptions,
-                private commentingRangesInfo: CommentingRanges) {
-        const startLineNumber = _range.startLineNumber;
-        const endLineNumber = _range.endLineNumber;
-        const commentingRangeDecorations = [{
-            range: {
-                startLineNumber: startLineNumber, startColumn: 1,
-                endLineNumber: endLineNumber, endColumn: 1
-            },
-            options: commentingOptions
-        }];
-
-        this.decorationId = this._editor.deltaDecorations([], commentingRangeDecorations)[0];
-    }
-
-    public getCommentAction(): { ownerId: string, extensionId: string | undefined, label: string | undefined, commentingRangesInfo: CommentingRanges } {
-        return {
-            extensionId: this._extensionId,
-            label: this._label,
-            ownerId: this._ownerId,
-            commentingRangesInfo: this.commentingRangesInfo
-        };
-    }
-
-    public getOriginalRange(): Range {
-        return this._range;
-    }
-
-    public getActiveRange(): Range | undefined {
-        const range = this._editor.getModel()!.getDecorationRange(this.decorationId);
-        if (range) {
-            return range;
-        }
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comments-main.ts b/packages/plugin-ext/src/main/browser/comments/comments-main.ts
deleted file mode 100644
index 3944940fc1b78..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comments-main.ts
+++ /dev/null
@@ -1,450 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import {
-    Range,
-    Comment,
-    CommentInput,
-    CommentOptions,
-    CommentThread,
-    CommentThreadChangedEvent
-} from '../../../common/plugin-api-rpc-model';
-import { Event, Emitter } from '@theia/core/lib/common/event';
-import { CommentThreadCollapsibleState } from '../../../plugin/types-impl';
-import {
-    CommentProviderFeatures,
-    CommentsExt,
-    CommentsMain,
-    CommentThreadChanges,
-    MAIN_RPC_CONTEXT
-} from '../../../common/plugin-api-rpc';
-import { Disposable } from '@theia/core/lib/common/disposable';
-import { CommentsService, CommentInfoMain } from './comments-service';
-import { UriComponents } from '../../../common/uri-components';
-import { URI } from 'vscode-uri';
-import { CancellationToken } from '@theia/core/lib/common';
-import { RPCProtocol } from '../../../common/rpc-protocol';
-import { interfaces } from 'inversify';
-import { v4 as uuidv4 } from 'uuid';
-import { CommentsContribution } from './comments-contribution';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/api/browser/mainThreadComments.ts
-
-export class CommentThreadImpl implements CommentThread, Disposable {
-    private _input?: CommentInput;
-    get input(): CommentInput | undefined {
-        return this._input;
-    }
-
-    set input(value: CommentInput | undefined) {
-        this._input = value;
-        this.onDidChangeInputEmitter.fire(value);
-    }
-
-    private readonly onDidChangeInputEmitter = new Emitter<CommentInput | undefined>();
-    get onDidChangeInput(): Event<CommentInput | undefined> { return this.onDidChangeInputEmitter.event; }
-
-    private _label: string | undefined;
-
-    get label(): string | undefined {
-        return this._label;
-    }
-
-    set label(label: string | undefined) {
-        this._label = label;
-        this.onDidChangeLabelEmitter.fire(this._label);
-    }
-
-    private readonly onDidChangeLabelEmitter = new Emitter<string | undefined>();
-    readonly onDidChangeLabel: Event<string | undefined> = this.onDidChangeLabelEmitter.event;
-
-    private _contextValue: string | undefined;
-
-    get contextValue(): string | undefined {
-        return this._contextValue;
-    }
-
-    set contextValue(context: string | undefined) {
-        this._contextValue = context;
-    }
-
-    private _comments: Comment[] | undefined;
-
-    public get comments(): Comment[] | undefined {
-        return this._comments;
-    }
-
-    public set comments(newComments: Comment[] | undefined) {
-        this._comments = newComments;
-        this.onDidChangeCommentsEmitter.fire(this._comments);
-    }
-
-    private readonly onDidChangeCommentsEmitter = new Emitter<Comment[] | undefined>();
-    get onDidChangeComments(): Event<Comment[] | undefined> { return this.onDidChangeCommentsEmitter.event; }
-
-    set range(range: Range) {
-        this._range = range;
-        this.onDidChangeRangeEmitter.fire(this._range);
-    }
-
-    get range(): Range {
-        return this._range;
-    }
-
-    private readonly onDidChangeRangeEmitter = new Emitter<Range>();
-    public onDidChangeRange = this.onDidChangeRangeEmitter.event;
-
-    private _collapsibleState: CommentThreadCollapsibleState | undefined;
-    get collapsibleState(): CommentThreadCollapsibleState | undefined {
-        return this._collapsibleState;
-    }
-
-    set collapsibleState(newState: CommentThreadCollapsibleState | undefined) {
-        this._collapsibleState = newState;
-        this.onDidChangeCollapsibleStateEmitter.fire(this._collapsibleState);
-    }
-
-    private readonly onDidChangeCollapsibleStateEmitter = new Emitter<CommentThreadCollapsibleState | undefined>();
-    readonly onDidChangeCollapsibleState = this.onDidChangeCollapsibleStateEmitter.event;
-
-    private _isDisposed: boolean;
-
-    get isDisposed(): boolean {
-        return this._isDisposed;
-    }
-
-    constructor(
-        public commentThreadHandle: number,
-        public controllerHandle: number,
-        public extensionId: string,
-        public threadId: string,
-        public resource: string,
-        private _range: Range
-    ) {
-        this._isDisposed = false;
-    }
-
-    batchUpdate(changes: CommentThreadChanges): void {
-        const modified = (value: keyof CommentThreadChanges): boolean =>
-            Object.prototype.hasOwnProperty.call(changes, value);
-
-        if (modified('range')) { this._range = changes.range!; }
-        if (modified('label')) { this._label = changes.label; }
-        if (modified('contextValue')) { this._contextValue = changes.contextValue; }
-        if (modified('comments')) { this._comments = changes.comments; }
-        if (modified('collapseState')) { this._collapsibleState = changes.collapseState; }
-    }
-
-    dispose(): void {
-        this._isDisposed = true;
-        this.onDidChangeCollapsibleStateEmitter.dispose();
-        this.onDidChangeCommentsEmitter.dispose();
-        this.onDidChangeInputEmitter.dispose();
-        this.onDidChangeLabelEmitter.dispose();
-        this.onDidChangeRangeEmitter.dispose();
-    }
-}
-
-export class CommentController {
-    get handle(): number {
-        return this._handle;
-    }
-
-    get id(): string {
-        return this._id;
-    }
-
-    get contextValue(): string {
-        return this._id;
-    }
-
-    get proxy(): CommentsExt {
-        return this._proxy;
-    }
-
-    get label(): string {
-        return this._label;
-    }
-
-    get options(): CommentOptions | undefined {
-        return this._features.options;
-    }
-
-    private readonly threads: Map<number, CommentThreadImpl> = new Map<number, CommentThreadImpl>();
-    public activeCommentThread?: CommentThread;
-
-    get features(): CommentProviderFeatures {
-        return this._features;
-    }
-
-    constructor(
-        private readonly _proxy: CommentsExt,
-        private readonly _commentService: CommentsService,
-        private readonly _handle: number,
-        private readonly _uniqueId: string,
-        private readonly _id: string,
-        private readonly _label: string,
-        private _features: CommentProviderFeatures
-    ) { }
-
-    updateFeatures(features: CommentProviderFeatures): void {
-        this._features = features;
-    }
-
-    createCommentThread(extensionId: string,
-                        commentThreadHandle: number,
-                        threadId: string,
-                        resource: UriComponents,
-                        range: Range,
-    ): CommentThread {
-        const thread = new CommentThreadImpl(
-            commentThreadHandle,
-            this.handle,
-            extensionId,
-            threadId,
-            URI.revive(resource).toString(),
-            range
-        );
-
-        this.threads.set(commentThreadHandle, thread);
-
-        this._commentService.updateComments(this._uniqueId, {
-            added: [thread],
-            removed: [],
-            changed: []
-        });
-
-        return thread;
-    }
-
-    updateCommentThread(commentThreadHandle: number,
-                        threadId: string,
-                        resource: UriComponents,
-                        changes: CommentThreadChanges): void {
-        const thread = this.getKnownThread(commentThreadHandle);
-        thread.batchUpdate(changes);
-
-        this._commentService.updateComments(this._uniqueId, {
-            added: [],
-            removed: [],
-            changed: [thread]
-        });
-    }
-
-    deleteCommentThread(commentThreadHandle: number): void {
-        const thread = this.getKnownThread(commentThreadHandle);
-        this.threads.delete(commentThreadHandle);
-
-        this._commentService.updateComments(this._uniqueId, {
-            added: [],
-            removed: [thread],
-            changed: []
-        });
-
-        thread.dispose();
-    }
-
-    deleteCommentThreadMain(commentThreadId: string): void {
-        this.threads.forEach(thread => {
-            if (thread.threadId === commentThreadId) {
-                this._proxy.$deleteCommentThread(this._handle, thread.commentThreadHandle);
-            }
-        });
-    }
-
-    updateInput(input: string): void {
-        const thread = this.activeCommentThread;
-
-        if (thread && thread.input) {
-            const commentInput = thread.input;
-            commentInput.value = input;
-            thread.input = commentInput;
-        }
-    }
-
-    private getKnownThread(commentThreadHandle: number): CommentThreadImpl {
-        const thread = this.threads.get(commentThreadHandle);
-        if (!thread) {
-            throw new Error('unknown thread');
-        }
-        return thread;
-    }
-
-    async getDocumentComments(resource: URI, token: CancellationToken): Promise<CommentInfoMain> {
-        const ret: CommentThread[] = [];
-        for (const thread of [...this.threads.keys()]) {
-            const commentThread = this.threads.get(thread)!;
-            if (commentThread.resource === resource.toString()) {
-                ret.push(commentThread);
-            }
-        }
-
-        const commentingRanges = await this._proxy.$provideCommentingRanges(this.handle, resource, token);
-
-        return <CommentInfoMain>{
-            owner: this._uniqueId,
-            label: this.label,
-            threads: ret,
-            commentingRanges: {
-                resource: resource,
-                ranges: commentingRanges || []
-            }
-        };
-    }
-
-    async getCommentingRanges(resource: URI, token: CancellationToken): Promise<Range[]> {
-        const commentingRanges = await this._proxy.$provideCommentingRanges(this.handle, resource, token);
-        return commentingRanges || [];
-    }
-
-    getAllComments(): CommentThread[] {
-        const ret: CommentThread[] = [];
-        for (const thread of [...this.threads.keys()]) {
-            ret.push(this.threads.get(thread)!);
-        }
-
-        return ret;
-    }
-
-    createCommentThreadTemplate(resource: UriComponents, range: Range): void {
-        this._proxy.$createCommentThreadTemplate(this.handle, resource, range);
-    }
-
-    async updateCommentThreadTemplate(threadHandle: number, range: Range): Promise<void> {
-        await this._proxy.$updateCommentThreadTemplate(this.handle, threadHandle, range);
-    }
-}
-
-export class CommentsMainImp implements CommentsMain {
-    private readonly proxy: CommentsExt;
-    private documentProviders = new Map<number, Disposable>();
-    private workspaceProviders = new Map<number, Disposable>();
-    private handlers = new Map<number, string>();
-    private commentControllers = new Map<number, CommentController>();
-
-    private activeCommentThread?: CommentThread;
-    private readonly commentService: CommentsService;
-
-    constructor(rpc: RPCProtocol, container: interfaces.Container) {
-        this.proxy = rpc.getProxy(MAIN_RPC_CONTEXT.COMMENTS_EXT);
-        container.get(CommentsContribution);
-        this.commentService = container.get(CommentsService);
-        this.commentService.onDidChangeActiveCommentThread(async thread => {
-            const handle = (thread as CommentThread).controllerHandle;
-            const controller = this.commentControllers.get(handle);
-
-            if (!controller) {
-                return;
-            }
-
-            this.activeCommentThread = thread as CommentThread;
-            controller.activeCommentThread = this.activeCommentThread;
-        });
-    }
-
-    $registerCommentController(handle: number, id: string, label: string): void {
-        const providerId = uuidv4();
-        this.handlers.set(handle, providerId);
-
-        const provider = new CommentController(this.proxy, this.commentService, handle, providerId, id, label, {});
-        this.commentService.registerCommentController(providerId, provider);
-        this.commentControllers.set(handle, provider);
-        this.commentService.setWorkspaceComments(String(handle), []);
-    }
-
-    $unregisterCommentController(handle: number): void {
-        const providerId = this.handlers.get(handle);
-        if (typeof providerId !== 'string') {
-            throw new Error('unknown handler');
-        }
-        this.commentService.unregisterCommentController(providerId);
-        this.handlers.delete(handle);
-        this.commentControllers.delete(handle);
-    }
-
-    $updateCommentControllerFeatures(handle: number, features: CommentProviderFeatures): void {
-        const provider = this.commentControllers.get(handle);
-
-        if (!provider) {
-            return undefined;
-        }
-
-        provider.updateFeatures(features);
-    }
-
-    $createCommentThread(handle: number,
-                         commentThreadHandle: number,
-                         threadId: string,
-                         resource: UriComponents,
-                         range: Range,
-                         extensionId: string
-    ): CommentThread | undefined {
-        const provider = this.commentControllers.get(handle);
-
-        if (!provider) {
-            return undefined;
-        }
-
-        return provider.createCommentThread(extensionId, commentThreadHandle, threadId, resource, range);
-    }
-
-    $updateCommentThread(handle: number,
-                         commentThreadHandle: number,
-                         threadId: string,
-                         resource: UriComponents,
-                         changes: CommentThreadChanges): void {
-        const provider = this.commentControllers.get(handle);
-
-        if (!provider) {
-            return undefined;
-        }
-
-        return provider.updateCommentThread(commentThreadHandle, threadId, resource, changes);
-    }
-
-    $deleteCommentThread(handle: number, commentThreadHandle: number): void {
-        const provider = this.commentControllers.get(handle);
-
-        if (!provider) {
-            return;
-        }
-
-        return provider.deleteCommentThread(commentThreadHandle);
-    }
-
-    private getHandler(handle: number): string {
-        if (!this.handlers.has(handle)) {
-            throw new Error('Unknown handler');
-        }
-        return this.handlers.get(handle)!;
-    }
-
-    $onDidCommentThreadsChange(handle: number, event: CommentThreadChangedEvent): void {
-        const providerId = this.getHandler(handle);
-        this.commentService.updateComments(providerId, event);
-    }
-
-    dispose(): void {
-        this.workspaceProviders.forEach(value => value.dispose());
-        this.workspaceProviders.clear();
-        this.documentProviders.forEach(value => value.dispose());
-        this.documentProviders.clear();
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/comments/comments-service.ts b/packages/plugin-ext/src/main/browser/comments/comments-service.ts
deleted file mode 100644
index d51940efd1cf1..0000000000000
--- a/packages/plugin-ext/src/main/browser/comments/comments-service.ts
+++ /dev/null
@@ -1,205 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import { injectable } from 'inversify';
-import { URI } from 'vscode-uri';
-import { Event, Emitter } from '@theia/core/lib/common/event';
-import {
-    Range,
-    CommentInfo,
-    CommentingRanges,
-    CommentThread,
-    CommentThreadChangedEvent,
-    CommentThreadChangedEventMain
-} from '../../../common/plugin-api-rpc-model';
-import { CommentController } from './comments-main';
-import { CancellationToken } from '@theia/core/lib/common/cancellation';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/contrib/comments/browser/commentService.ts
-
-export interface ResourceCommentThreadEvent {
-    resource: URI;
-    commentInfos: CommentInfoMain[];
-}
-
-export interface CommentInfoMain extends CommentInfo {
-    owner: string;
-    label?: string;
-}
-
-export interface WorkspaceCommentThreadsEventMain {
-    ownerId: string;
-    commentThreads: CommentThread[];
-}
-
-export const CommentsService = Symbol('CommentsService');
-
-export interface CommentsService {
-    readonly onDidSetResourceCommentInfos: Event<ResourceCommentThreadEvent>;
-    readonly onDidSetAllCommentThreads: Event<WorkspaceCommentThreadsEventMain>;
-    readonly onDidUpdateCommentThreads: Event<CommentThreadChangedEventMain>;
-    readonly onDidChangeActiveCommentThread: Event<CommentThread | null>;
-    readonly onDidChangeActiveCommentingRange: Event<{ range: Range, commentingRangesInfo: CommentingRanges }>;
-    readonly onDidSetDataProvider: Event<void>;
-    readonly onDidDeleteDataProvider: Event<string>;
-
-    setDocumentComments(resource: URI, commentInfos: CommentInfoMain[]): void;
-
-    setWorkspaceComments(owner: string, commentsByResource: CommentThread[]): void;
-
-    removeWorkspaceComments(owner: string): void;
-
-    registerCommentController(owner: string, commentControl: CommentController): void;
-
-    unregisterCommentController(owner: string): void;
-
-    getCommentController(owner: string): CommentController | undefined;
-
-    createCommentThreadTemplate(owner: string, resource: URI, range: Range): void;
-
-    updateCommentThreadTemplate(owner: string, threadHandle: number, range: Range): Promise<void>;
-
-    updateComments(ownerId: string, event: CommentThreadChangedEvent): void;
-
-    disposeCommentThread(ownerId: string, threadId: string): void;
-
-    getComments(resource: URI): Promise<(CommentInfoMain | null)[]>;
-
-    getCommentingRanges(resource: URI): Promise<Range[]>;
-
-    setActiveCommentThread(commentThread: CommentThread | null): void;
-}
-
-@injectable()
-export class PluginCommentService implements CommentsService {
-
-    private readonly onDidSetDataProviderEmitter: Emitter<void> = new Emitter<void>();
-    readonly onDidSetDataProvider: Event<void> = this.onDidSetDataProviderEmitter.event;
-
-    private readonly onDidDeleteDataProviderEmitter: Emitter<string> = new Emitter<string>();
-    readonly onDidDeleteDataProvider: Event<string> = this.onDidDeleteDataProviderEmitter.event;
-
-    private readonly onDidSetResourceCommentInfosEmitter: Emitter<ResourceCommentThreadEvent> = new Emitter<ResourceCommentThreadEvent>();
-    readonly onDidSetResourceCommentInfos: Event<ResourceCommentThreadEvent> = this.onDidSetResourceCommentInfosEmitter.event;
-
-    private readonly onDidSetAllCommentThreadsEmitter: Emitter<WorkspaceCommentThreadsEventMain> = new Emitter<WorkspaceCommentThreadsEventMain>();
-    readonly onDidSetAllCommentThreads: Event<WorkspaceCommentThreadsEventMain> = this.onDidSetAllCommentThreadsEmitter.event;
-
-    private readonly onDidUpdateCommentThreadsEmitter: Emitter<CommentThreadChangedEventMain> = new Emitter<CommentThreadChangedEventMain>();
-    readonly onDidUpdateCommentThreads: Event<CommentThreadChangedEventMain> = this.onDidUpdateCommentThreadsEmitter.event;
-
-    private readonly onDidChangeActiveCommentThreadEmitter = new Emitter<CommentThread | null>();
-    readonly onDidChangeActiveCommentThread = this.onDidChangeActiveCommentThreadEmitter.event;
-
-    private readonly onDidChangeActiveCommentingRangeEmitter = new Emitter<{ range: Range, commentingRangesInfo: CommentingRanges }>();
-    readonly onDidChangeActiveCommentingRange: Event<{ range: Range, commentingRangesInfo: CommentingRanges }> = this.onDidChangeActiveCommentingRangeEmitter.event;
-
-    private commentControls = new Map<string, CommentController>();
-
-    setActiveCommentThread(commentThread: CommentThread | null): void {
-        this.onDidChangeActiveCommentThreadEmitter.fire(commentThread);
-    }
-
-    setDocumentComments(resource: URI, commentInfos: CommentInfoMain[]): void {
-        this.onDidSetResourceCommentInfosEmitter.fire({ resource, commentInfos });
-    }
-
-    setWorkspaceComments(owner: string, commentsByResource: CommentThread[]): void {
-        this.onDidSetAllCommentThreadsEmitter.fire({ ownerId: owner, commentThreads: commentsByResource });
-    }
-
-    removeWorkspaceComments(owner: string): void {
-        this.onDidSetAllCommentThreadsEmitter.fire({ ownerId: owner, commentThreads: [] });
-    }
-
-    registerCommentController(owner: string, commentControl: CommentController): void {
-        this.commentControls.set(owner, commentControl);
-        this.onDidSetDataProviderEmitter.fire();
-    }
-
-    unregisterCommentController(owner: string): void {
-        this.commentControls.delete(owner);
-        this.onDidDeleteDataProviderEmitter.fire(owner);
-    }
-
-    getCommentController(owner: string): CommentController | undefined {
-        return this.commentControls.get(owner);
-    }
-
-    createCommentThreadTemplate(owner: string, resource: URI, range: Range): void {
-        const commentController = this.commentControls.get(owner);
-
-        if (!commentController) {
-            return;
-        }
-
-        commentController.createCommentThreadTemplate(resource, range);
-    }
-
-    async updateCommentThreadTemplate(owner: string, threadHandle: number, range: Range): Promise<void> {
-        const commentController = this.commentControls.get(owner);
-
-        if (!commentController) {
-            return;
-        }
-
-        await commentController.updateCommentThreadTemplate(threadHandle, range);
-    }
-
-    disposeCommentThread(owner: string, threadId: string): void {
-        const controller = this.getCommentController(owner);
-        if (controller) {
-            controller.deleteCommentThreadMain(threadId);
-        }
-    }
-
-    updateComments(ownerId: string, event: CommentThreadChangedEvent): void {
-        const evt: CommentThreadChangedEventMain = Object.assign({}, event, { owner: ownerId });
-        this.onDidUpdateCommentThreadsEmitter.fire(evt);
-    }
-
-    async getComments(resource: URI): Promise<(CommentInfoMain | null)[]> {
-        const commentControlResult: Promise<CommentInfoMain | null>[] = [];
-
-        this.commentControls.forEach(control => {
-            commentControlResult.push(control.getDocumentComments(resource, CancellationToken.None)
-                .catch(e => {
-                    console.log(e);
-                    return null;
-                }));
-        });
-
-        return Promise.all(commentControlResult);
-    }
-
-    async getCommentingRanges(resource: URI): Promise<Range[]> {
-        const commentControlResult: Promise<Range[]>[] = [];
-
-        this.commentControls.forEach(control => {
-            commentControlResult.push(control.getCommentingRanges(resource, CancellationToken.None));
-        });
-
-        const ret = await Promise.all(commentControlResult);
-        return ret.reduce((prev, curr) => {
-            prev.push(...curr);
-            return prev;
-        }, []);
-    }
-}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-contribution.ts b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-contribution.ts
new file mode 100644
index 0000000000000..531ef56c47c23
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-contribution.ts
@@ -0,0 +1,49 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+import { injectable, inject } from 'inversify';
+import { CommandRegistry, CommandContribution, SelectionService } from '@theia/core/lib/common';
+import { ApplicationShell, CommonCommands } from '@theia/core/lib/browser';
+import { CustomEditorWidget } from './custom-editor-widget';
+import { FileService } from '@theia/filesystem/lib/browser/file-service';
+import { FileDialogService } from '@theia/filesystem/lib/browser';
+
+@injectable()
+export class CustomEditorContribution implements CommandContribution {
+
+    @inject(ApplicationShell)
+    protected readonly shell: ApplicationShell;
+
+    @inject(FileService)
+    protected readonly fileService: FileService;
+
+    @inject(FileDialogService)
+    protected readonly fileDialogService: FileDialogService;
+
+    @inject(SelectionService)
+    protected readonly selectionService: SelectionService;
+
+    registerCommands(commands: CommandRegistry): void {
+        commands.registerHandler(CommonCommands.UNDO.id, {
+            isEnabled: () => this.shell.activeWidget instanceof CustomEditorWidget,
+            execute: () => (this.shell.activeWidget as CustomEditorWidget).undo()
+        });
+        commands.registerHandler(CommonCommands.REDO.id, {
+            isEnabled: () => this.shell.activeWidget instanceof CustomEditorWidget,
+            execute: () => (this.shell.activeWidget as CustomEditorWidget).redo()
+        });
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-opener.tsx b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-opener.tsx
new file mode 100644
index 0000000000000..34efbb9c8abfc
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-opener.tsx
@@ -0,0 +1,94 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+import { inject } from 'inversify';
+import { PreviewEditorOpenerOptions } from '@theia/editor-preview/lib/browser';
+import URI from '@theia/core/lib/common/uri';
+import { ApplicationShell, OpenerOptions, OpenHandler, Widget, WidgetManager } from '@theia/core/lib/browser';
+import { CustomEditorPriority, CustomEditorSelector } from '../../../common';
+import * as glob from './glob';
+import { CustomEditor } from '../../../common';
+import { CustomEditorWidget } from './custom-editor-widget';
+import { v4 } from 'uuid';
+import { Emitter } from '@theia/core';
+
+export class CustomEditorOpener implements OpenHandler {
+
+    readonly id: string;
+    readonly label: string;
+
+    private readonly onOpenCustomEditorEmitter = new Emitter<CustomEditorWidget>();
+    readonly onOpenCustomEditor = this.onOpenCustomEditorEmitter.event;
+
+    constructor(
+        private readonly editor: CustomEditor,
+        @inject(ApplicationShell) protected readonly shell: ApplicationShell,
+        @inject(WidgetManager) protected readonly widgetManager: WidgetManager
+    ) {
+        this.id = `custom-editor-${this.editor.viewType}`;
+        this.label = this.editor.displayName;
+    }
+
+    canHandle(uri: URI, options?: PreviewEditorOpenerOptions): number {
+        if (this.matches(this.editor.selector, uri)) {
+            return this.getPriority();
+        }
+        return 0;
+    }
+
+    getPriority(): number {
+        switch (this.editor.priority) {
+            case CustomEditorPriority.default: return 500;
+            case CustomEditorPriority.builtin: return 400;
+            case CustomEditorPriority.option: return 300;
+            default: return 200;
+        }
+    }
+
+    async open(uri: URI, options?: OpenerOptions): Promise<Widget | undefined> {
+        let widget: CustomEditorWidget | undefined;
+        const widgets = this.widgetManager.getWidgets(CustomEditorWidget.FACTORY_ID) as CustomEditorWidget[];
+        widget = widgets.find(w => w.viewType === this.editor.viewType && w.resource.toString() === uri.toString());
+
+        if (widget?.isVisible) {
+            return this.shell.revealWidget(widget.id);
+        }
+        if (widget?.isAttached) {
+            return this.shell.activateWidget(widget.id);
+        }
+        if (!widget) {
+            const id = v4();
+            widget = await this.widgetManager.getOrCreateWidget<CustomEditorWidget>(CustomEditorWidget.FACTORY_ID, { id });
+            widget.viewType = this.editor.viewType;
+            widget.resource = uri;
+        }
+
+        this.onOpenCustomEditorEmitter.fire(widget);
+    }
+
+    matches(selectors: CustomEditorSelector[], resource: URI): boolean {
+        return selectors.some(selector => this.selectorMatches(selector, resource));
+    }
+
+    selectorMatches(selector: CustomEditorSelector, resource: URI): boolean {
+        if (selector.filenamePattern) {
+            if (glob.match(selector.filenamePattern.toLowerCase(), resource.path.name.toLowerCase() + resource.path.ext.toLowerCase())) {
+                return true;
+            }
+        }
+        return false;
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-service.ts b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-service.ts
new file mode 100644
index 0000000000000..228118776ccc4
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-service.ts
@@ -0,0 +1,108 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+// copied and modified from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/workbench/contrib/customEditor/browser/customEditors.ts
+
+import { injectable } from 'inversify';
+import URI from '@theia/core/lib/common/uri';
+import { Reference } from '@theia/core/lib/common/reference';
+import { CustomEditorModel } from './custom-editors-main';
+
+@injectable()
+export class CustomEditorService {
+    protected _models = new CustomEditorModelManager();
+    get models(): CustomEditorModelManager { return this._models; }
+}
+
+export class CustomEditorModelManager {
+
+    private readonly references = new Map<string, {
+        readonly viewType: string,
+        readonly model: Promise<CustomEditorModel>,
+        counter: number
+    }>();
+
+    add(resource: URI, viewType: string, model: Promise<CustomEditorModel>): Promise<Reference<CustomEditorModel>> {
+        const key = this.key(resource, viewType);
+        const existing = this.references.get(key);
+        if (existing) {
+            throw new Error('Model already exists');
+        }
+
+        this.references.set(key, { viewType, model, counter: 0 });
+        return this.tryRetain(resource, viewType)!;
+    }
+
+    async get(resource: URI, viewType: string): Promise<CustomEditorModel | undefined> {
+        const key = this.key(resource, viewType);
+        const entry = this.references.get(key);
+        return entry?.model;
+    }
+
+    tryRetain(resource: URI, viewType: string): Promise<Reference<CustomEditorModel>> | undefined {
+        const key = this.key(resource, viewType);
+
+        const entry = this.references.get(key);
+        if (!entry) {
+            return undefined;
+        }
+
+        entry.counter++;
+
+        return entry.model.then(model => ({
+            object: model,
+            dispose: once(() => {
+                if (--entry!.counter <= 0) {
+                    entry.model.then(x => x.dispose());
+                    this.references.delete(key);
+                }
+            }),
+        }));
+    }
+
+    disposeAllModelsForView(viewType: string): void {
+        for (const [key, value] of this.references) {
+            if (value.viewType === viewType) {
+                value.model.then(x => x.dispose());
+                this.references.delete(key);
+            }
+        }
+    }
+
+    private key(resource: URI, viewType: string): string {
+        return `${resource.toString()}@@@${viewType}`;
+    }
+}
+
+export function once<T extends Function>(this: unknown, fn: T): T {
+    const _this = this;
+    let didCall = false;
+    let result: unknown;
+
+    return function (): unknown {
+        if (didCall) {
+            return result;
+        }
+
+        didCall = true;
+        result = fn.apply(_this, arguments);
+
+        return result;
+    } as unknown as T;
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget-factory.ts b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget-factory.ts
new file mode 100644
index 0000000000000..5864dac9240e3
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget-factory.ts
@@ -0,0 +1,44 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+import { CustomEditorWidget } from '../custom-editors/custom-editor-widget';
+import { interfaces } from 'inversify';
+import { WebviewWidgetIdentifier, WebviewWidgetExternalEndpoint } from '../webview/webview';
+import { WebviewEnvironment } from '../webview/webview-environment';
+
+export class CustomEditorWidgetFactory {
+
+    readonly id = CustomEditorWidget.FACTORY_ID;
+
+    protected readonly container: interfaces.Container;
+
+    constructor(container: interfaces.Container) {
+        this.container = container;
+    }
+
+    async createWidget(identifier: WebviewWidgetIdentifier): Promise<CustomEditorWidget> {
+        const externalEndpoint = await this.container.get(WebviewEnvironment).externalEndpoint();
+        let endpoint = externalEndpoint.replace('{{uuid}}', identifier.id);
+        if (endpoint[endpoint.length - 1] === '/') {
+            endpoint = endpoint.slice(0, endpoint.length - 1);
+        }
+        const child = this.container.createChild();
+        child.bind(WebviewWidgetIdentifier).toConstantValue(identifier);
+        child.bind(WebviewWidgetExternalEndpoint).toConstantValue(endpoint);
+        return child.get(CustomEditorWidget);
+    }
+
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget.ts b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget.ts
new file mode 100644
index 0000000000000..3aef36eaa6ed2
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editor-widget.ts
@@ -0,0 +1,116 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+import { injectable, inject, postConstruct } from 'inversify';
+import URI from '@theia/core/lib/common/uri';
+import { CopyFileOptions, FileOperation } from '@theia/filesystem/lib/common/files';
+import { NavigatableWidget, Saveable, SaveableSource } from '@theia/core/lib/browser';
+import { CustomEditorService } from '../custom-editors/custom-editor-service';
+import { Reference } from '@theia/core/lib/common/reference';
+import { WebviewWidget } from '../webview/webview';
+import { UndoRedoService } from './undo-redo-service';
+import { CustomEditorModel } from './custom-editors-main';
+
+@injectable()
+export class CustomEditorWidget extends WebviewWidget implements SaveableSource, NavigatableWidget {
+    id: string;
+    static FACTORY_ID = 'plugin-custom-editor';
+
+    @inject(CustomEditorService)
+    protected readonly customEditorService: CustomEditorService;
+
+    @inject(UndoRedoService)
+    protected readonly undoRedoService: UndoRedoService;
+
+    resource: URI;
+
+    protected _modelRef: Reference<CustomEditorModel>;
+    get modelRef(): Reference<CustomEditorModel> {
+        return this._modelRef;
+    }
+    set modelRef(modelRef: Reference<CustomEditorModel>) {
+        this._modelRef = modelRef;
+        this.doUpdateContent();
+        Saveable.apply(this);
+    }
+    get saveable(): Saveable {
+        return this._modelRef?.object;
+    }
+
+    @postConstruct()
+    protected init(): void {
+        super.init();
+        this.id = CustomEditorWidget.FACTORY_ID + ':' + this.identifier.id;
+        this.toDispose.push(this.fileService.onDidRunOperation(e => {
+            if (e.isOperation(FileOperation.MOVE)) {
+                this.doMove(e.target.resource);
+            }
+        }));
+    }
+
+    undo(): void {
+        this.undoRedoService.undo(this.resource);
+    }
+
+    redo(): void {
+        this.undoRedoService.redo(this.resource);
+    }
+
+    async saveAs(source: URI, target: URI, options?: CopyFileOptions): Promise<void> {
+        const result = await this._modelRef?.object.saveAs(source, target, options);
+        this.doMove(target);
+        return result;
+    }
+
+    getResourceUri(): URI | undefined {
+        return this.resource;
+    }
+
+    createMoveToUri(resourceUri: URI): URI | undefined {
+        return this.resource.withPath(resourceUri.path);
+    }
+
+    storeState(): CustomEditorWidget.State {
+        return {
+            ...super.storeState(),
+            strResource: this.resource.toString(),
+        };
+    }
+
+    restoreState(oldState: CustomEditorWidget.State): void {
+        const { strResource } = oldState;
+        this.resource = new URI(strResource);
+        super.restoreState(oldState);
+    }
+
+    private _moveHandler?: (newResource: URI) => void;
+
+    public onMove(handler: (newResource: URI) => Promise<void>): void {
+        this._moveHandler = handler;
+    }
+
+    private doMove(target: URI): void {
+        if (this._moveHandler) {
+            this._moveHandler(target);
+        }
+    }
+}
+
+export namespace CustomEditorWidget {
+    export interface State extends WebviewWidget.State {
+        strResource: string
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/custom-editors-main.ts b/packages/plugin-ext/src/main/browser/custom-editors/custom-editors-main.ts
new file mode 100644
index 0000000000000..eb8f0617d3399
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/custom-editors-main.ts
@@ -0,0 +1,540 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+// some code copied and modified from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/workbench/api/browser/mainThreadCustomEditors.ts
+
+import { interfaces } from 'inversify';
+import { MAIN_RPC_CONTEXT, CustomEditorsMain, CustomEditorsExt, CustomTextEditorCapabilities } from '../../../common/plugin-api-rpc';
+import { RPCProtocol } from '../../../common/rpc-protocol';
+import { HostedPluginSupport } from '../../../hosted/browser/hosted-plugin';
+import { PluginCustomEditorRegistry } from './plugin-custom-editor-registry';
+import { CustomEditorWidget } from './custom-editor-widget';
+import { Emitter } from '@theia/core';
+import { UriComponents } from '../../../common/uri-components';
+import { URI } from 'vscode-uri';
+import TheiaURI from '@theia/core/lib/common/uri';
+import { Disposable, DisposableCollection } from '@theia/core/lib/common/disposable';
+import { Reference } from '@theia/core/lib/common/reference';
+import { CancellationToken, CancellationTokenSource } from '@theia/core/lib/common/cancellation';
+import { MonacoEditorModel } from '@theia/monaco/lib/browser/monaco-editor-model';
+import { EditorModelService } from '../text-editor-model-service';
+import { CustomEditorService } from './custom-editor-service';
+import { FileService } from '@theia/filesystem/lib/browser/file-service';
+import * as files from '@theia/filesystem/lib/common/files';
+import { UndoRedoService } from './undo-redo-service';
+import { WebviewsMainImpl } from '../webviews-main';
+import { WidgetManager } from '@theia/core/lib/browser/widget-manager';
+import { ApplicationShell, DefaultUriLabelProviderContribution, FormatType, Saveable, SaveOptions } from '@theia/core/lib/browser';
+import { CopyFileOptions } from '@theia/filesystem/lib/common/files';
+import { WebviewOptions, WebviewPanelOptions } from '@theia/plugin';
+import { WebviewWidgetIdentifier } from '../webview/webview';
+import { EditorPreferences } from '@theia/editor/lib/browser';
+
+const enum CustomEditorModelType {
+    Custom,
+    Text,
+}
+
+export class CustomEditorsMainImpl implements CustomEditorsMain, Disposable {
+
+    protected readonly pluginService: HostedPluginSupport;
+    protected readonly shell: ApplicationShell;
+    protected readonly textModelService: EditorModelService;
+    protected readonly fileService: FileService;
+    protected readonly customEditorService: CustomEditorService;
+    protected readonly undoRedoService: UndoRedoService;
+    protected readonly customEditorRegistry: PluginCustomEditorRegistry;
+    protected readonly labelProvider: DefaultUriLabelProviderContribution;
+    protected readonly widgetManager: WidgetManager;
+    protected readonly editorPreferences: EditorPreferences;
+    private readonly proxy: CustomEditorsExt;
+    private readonly editorProviders = new Map<string, Disposable>();
+
+    constructor(rpc: RPCProtocol,
+        container: interfaces.Container,
+        readonly webviewsMain: WebviewsMainImpl,
+    ) {
+        this.pluginService = container.get(HostedPluginSupport);
+        this.shell = container.get(ApplicationShell);
+        this.textModelService = container.get(EditorModelService);
+        this.fileService = container.get(FileService);
+        this.customEditorService = container.get(CustomEditorService);
+        this.undoRedoService = container.get(UndoRedoService);
+        this.customEditorRegistry = container.get(PluginCustomEditorRegistry);
+        this.labelProvider = container.get(DefaultUriLabelProviderContribution);
+        this.editorPreferences = container.get(EditorPreferences);
+        this.widgetManager = container.get(WidgetManager);
+        this.proxy = rpc.getProxy(MAIN_RPC_CONTEXT.CUSTOM_EDITORS_EXT);
+    }
+
+    dispose(): void {
+        for (const disposable of this.editorProviders.values()) {
+            disposable.dispose();
+        }
+        this.editorProviders.clear();
+    }
+
+    $registerTextEditorProvider(
+        viewType: string, options: WebviewPanelOptions, capabilities: CustomTextEditorCapabilities): void {
+        this.registerEditorProvider(CustomEditorModelType.Text, viewType, options, capabilities, true);
+    }
+
+    $registerCustomEditorProvider(viewType: string, options: WebviewPanelOptions, supportsMultipleEditorsPerDocument: boolean): void {
+        this.registerEditorProvider(CustomEditorModelType.Custom, viewType, options, {}, supportsMultipleEditorsPerDocument);
+    }
+
+    protected async registerEditorProvider(
+        modelType: CustomEditorModelType,
+        viewType: string,
+        options: WebviewPanelOptions,
+        capabilities: CustomTextEditorCapabilities,
+        supportsMultipleEditorsPerDocument: boolean,
+    ): Promise<void> {
+        if (this.editorProviders.has(viewType)) {
+            throw new Error(`Provider for ${viewType} already registered`);
+        }
+
+        const disposables = new DisposableCollection();
+
+        disposables.push(
+            this.customEditorRegistry.registerResolver(viewType, async widget => {
+                const { resource, identifier } = widget;
+                widget.options = options;
+
+                const cancellationSource = new CancellationTokenSource();
+                let modelRef = await this.getOrCreateCustomEditorModel(modelType, resource, viewType, cancellationSource.token);
+                widget.modelRef = modelRef;
+
+                widget.onDidDispose(() => {
+                    // If the model is still dirty, make sure we have time to save it
+                    if (modelRef.object.dirty) {
+                        const sub = modelRef.object.onDirtyChanged(() => {
+                            if (!modelRef.object.dirty) {
+                                sub.dispose();
+                                modelRef.dispose();
+                            }
+                        });
+                        return;
+                    }
+
+                    modelRef.dispose();
+                });
+
+                if (capabilities.supportsMove) {
+                    const onMoveCancelTokenSource = new CancellationTokenSource();
+                    widget.onMove(async (newResource: TheiaURI) => {
+                        const oldModel = modelRef;
+                        modelRef = await this.getOrCreateCustomEditorModel(modelType, newResource, viewType, onMoveCancelTokenSource.token);
+                        this.proxy.$onMoveCustomEditor(identifier.id, URI.file(newResource.path.toString()), viewType);
+                        oldModel.dispose();
+                    });
+                }
+
+                const _cancellationSource = new CancellationTokenSource();
+                await this.proxy.$resolveCustomEditorWebview(
+                    identifier.id,
+                    viewType,
+                    URI.file(resource.path.toString()),
+                    this.labelProvider.getName(resource)!,
+                    options,
+                    _cancellationSource.token
+                );
+            })
+        );
+
+        this.editorProviders.set(viewType, disposables);
+    }
+
+    $unregisterEditorProvider(viewType: string): void {
+        const provider = this.editorProviders.get(viewType);
+        if (!provider) {
+            throw new Error(`No provider for ${viewType} registered`);
+        }
+
+        provider.dispose();
+        this.editorProviders.delete(viewType);
+
+        this.customEditorService.models.disposeAllModelsForView(viewType);
+    }
+
+    protected async getOrCreateCustomEditorModel(
+        modelType: CustomEditorModelType,
+        resource: TheiaURI,
+        viewType: string,
+        cancellationToken: CancellationToken,
+    ): Promise<Reference<CustomEditorModel>> {
+        const existingModel = this.customEditorService.models.tryRetain(resource, viewType);
+        if (existingModel) {
+            return existingModel;
+        }
+
+        switch (modelType) {
+            case CustomEditorModelType.Text: {
+                const model = CustomTextEditorModel.create(viewType, resource, this.textModelService, this.fileService);
+                return this.customEditorService.models.add(resource, viewType, model);
+            }
+            case CustomEditorModelType.Custom: {
+                const model = MainCustomEditorModel.create(this.proxy, viewType, resource, this.undoRedoService, this.fileService, this.editorPreferences, cancellationToken);
+                return this.customEditorService.models.add(resource, viewType, model);
+            }
+        }
+    }
+
+    protected async getCustomEditorModel(resourceComponents: UriComponents, viewType: string): Promise<MainCustomEditorModel> {
+        const resource = URI.revive(resourceComponents);
+        const model = await this.customEditorService.models.get(new TheiaURI(resource), viewType);
+        if (!model || !(model instanceof MainCustomEditorModel)) {
+            throw new Error('Could not find model for custom editor');
+        }
+        return model;
+    }
+
+    async $onDidEdit(resourceComponents: UriComponents, viewType: string, editId: number, label: string | undefined): Promise<void> {
+        const model = await this.getCustomEditorModel(resourceComponents, viewType);
+        model.pushEdit(editId, label);
+    }
+
+    async $onContentChange(resourceComponents: UriComponents, viewType: string): Promise<void> {
+        const model = await this.getCustomEditorModel(resourceComponents, viewType);
+        model.changeContent();
+    }
+
+    async $createCustomEditorPanel(
+        panelId: string,
+        title: string,
+        options: WebviewPanelOptions & WebviewOptions
+    ): Promise<void> {
+        const view = await this.widgetManager.getOrCreateWidget<CustomEditorWidget>(CustomEditorWidget.FACTORY_ID, <WebviewWidgetIdentifier>{ id: panelId });
+        this.webviewsMain.hookWebview(view);
+        view.title.label = title;
+        const { enableFindWidget, retainContextWhenHidden, enableScripts, localResourceRoots, ...contentOptions } = options;
+        view.options = { enableFindWidget, retainContextWhenHidden };
+        view.setContentOptions({
+            allowScripts: enableScripts,
+            localResourceRoots: localResourceRoots && localResourceRoots.map(root => root.toString()),
+            ...contentOptions,
+            ...view.contentOptions
+        });
+        if (view.isAttached) {
+            if (view.isVisible) {
+                this.shell.revealWidget(view.id);
+            }
+            return;
+        }
+        this.webviewsMain.addOrReattachWidget(view, { preserveFocus: true });
+    }
+}
+
+export interface CustomEditorModel extends Saveable, Disposable {
+    readonly viewType: string;
+    readonly resource: URI;
+    readonly readonly: boolean;
+    saveAs(resource: TheiaURI, targetResource: TheiaURI, currentOptions?: files.CopyFileOptions): Promise<void>;
+}
+
+export class MainCustomEditorModel implements CustomEditorModel {
+
+    private currentEditIndex: number = -1;
+    private savePoint: number = -1;
+    private readonly edits: Array<number> = [];
+    private isDirtyFromContentChange = false;
+    private ongoingSave?: CancellationTokenSource;
+    autoSave: 'on' | 'off';
+    autoSaveDelay: number;
+    private readonly toDispose = new DisposableCollection();
+
+    private readonly onDirtyChangedEmitter = new Emitter<void>();
+    readonly onDirtyChanged = this.onDirtyChangedEmitter.event;
+
+    static async create(
+        proxy: CustomEditorsExt,
+        viewType: string,
+        resource: TheiaURI,
+        undoRedoService: UndoRedoService,
+        fileService: FileService,
+        editorPreferences: EditorPreferences,
+        cancellation: CancellationToken,
+    ): Promise<MainCustomEditorModel> {
+        const { editable } = await proxy.$createCustomDocument(URI.file(resource.path.toString()), viewType, undefined, cancellation);
+        return new MainCustomEditorModel(proxy, viewType, resource, editable, undoRedoService, fileService, editorPreferences);
+    }
+
+    constructor(
+        private proxy: CustomEditorsExt,
+        readonly viewType: string,
+        private readonly editorResource: TheiaURI,
+        private readonly editable: boolean,
+        private readonly undoRedoService: UndoRedoService,
+        private readonly fileService: FileService,
+        private readonly editorPreferences: EditorPreferences
+    ) {
+        this.autoSave = this.editorPreferences.get('editor.autoSave', undefined, editorResource.toString());
+        this.autoSaveDelay = this.editorPreferences.get('editor.autoSaveDelay', undefined, editorResource.toString());
+
+        this.toDispose.push(
+            this.editorPreferences.onPreferenceChanged(event => {
+                if (event.preferenceName === 'editor.autoSave') {
+                    this.autoSave = this.editorPreferences.get('editor.autoSave', undefined, editorResource.toString());
+                }
+                if (event.preferenceName === 'editor.autoSaveDelay') {
+                    this.autoSaveDelay = this.editorPreferences.get('editor.autoSaveDelay', undefined, editorResource.toString());
+                }
+            })
+        );
+    }
+
+    get resource(): URI {
+        return URI.file(this.editorResource.path.toString());
+    }
+
+    get dirty(): boolean {
+        if (this.isDirtyFromContentChange) {
+            return true;
+        }
+        if (this.edits.length > 0) {
+            return this.savePoint !== this.currentEditIndex;
+        }
+        return false;
+    }
+
+    setProxy(proxy: CustomEditorsExt): void {
+        this.proxy = proxy;
+    }
+
+    dispose(): void {
+        if (this.editable) {
+            this.undoRedoService.removeElements(this.editorResource);
+        }
+        this.proxy.$disposeCustomDocument(this.resource, this.viewType);
+    }
+
+    get readonly(): boolean {
+        return !this.editable;
+    }
+
+    changeContent(): void {
+        this.change(() => {
+            this.isDirtyFromContentChange = true;
+        });
+    }
+
+    pushEdit(editId: number, label: string | undefined): void {
+        if (!this.editable) {
+            throw new Error('Document is not editable');
+        }
+
+        this.change(() => {
+            this.spliceEdits(editId);
+            this.currentEditIndex = this.edits.length - 1;
+        });
+
+        this.undoRedoService.pushElement(
+            this.editorResource,
+            () => this.undo(),
+            () => this.redo(),
+        );
+    }
+
+    private async undo(): Promise<void> {
+        if (!this.editable) {
+            return;
+        }
+
+        if (this.currentEditIndex < 0) {
+            // nothing to undo
+            return;
+        }
+
+        const undoneEdit = this.edits[this.currentEditIndex];
+        this.change(() => {
+            --this.currentEditIndex;
+        });
+        await this.proxy.$undo(this.resource, this.viewType, undoneEdit, this.dirty);
+    }
+
+    private async redo(): Promise<void> {
+        if (!this.editable) {
+            return;
+        }
+
+        if (this.currentEditIndex >= this.edits.length - 1) {
+            // nothing to redo
+            return;
+        }
+
+        const redoneEdit = this.edits[this.currentEditIndex + 1];
+        this.change(() => {
+            ++this.currentEditIndex;
+        });
+        await this.proxy.$redo(this.resource, this.viewType, redoneEdit, this.dirty);
+    }
+
+    private spliceEdits(editToInsert?: number): void {
+        const start = this.currentEditIndex + 1;
+        const toRemove = this.edits.length - this.currentEditIndex;
+
+        const removedEdits = typeof editToInsert === 'number'
+            ? this.edits.splice(start, toRemove, editToInsert)
+            : this.edits.splice(start, toRemove);
+
+        if (removedEdits.length) {
+            this.proxy.$disposeEdits(this.resource, this.viewType, removedEdits);
+        }
+    }
+
+    private change(makeEdit: () => void): void {
+        const wasDirty = this.dirty;
+        makeEdit();
+
+        if (this.dirty !== wasDirty) {
+            this.onDirtyChangedEmitter.fire();
+        }
+
+        if (this.autoSave === 'on') {
+            const handle = window.setTimeout(() => {
+                this.save();
+                window.clearTimeout(handle);
+            }, this.autoSaveDelay);
+        }
+    }
+
+    async revert(options?: Saveable.RevertOptions): Promise<void> {
+        if (!this.editable) {
+            return;
+        }
+
+        if (this.currentEditIndex === this.savePoint && !this.isDirtyFromContentChange) {
+            return;
+        }
+
+        const cancellationSource = new CancellationTokenSource();
+        this.proxy.$revert(this.resource, this.viewType, cancellationSource.token);
+        this.change(() => {
+            this.isDirtyFromContentChange = false;
+            this.currentEditIndex = this.savePoint;
+            this.spliceEdits();
+        });
+    }
+
+    async save(): Promise<void> {
+        if (!this.editable) {
+            return;
+        }
+
+        const cancelable = new CancellationTokenSource();
+        const savePromise = this.proxy.$onSave(this.resource, this.viewType, cancelable.token);
+        this.ongoingSave?.cancel();
+        this.ongoingSave = cancelable;
+
+        try {
+            await savePromise;
+
+            if (this.ongoingSave === cancelable) { // Make sure we are still doing the same save
+                this.change(() => {
+                    this.isDirtyFromContentChange = false;
+                    this.savePoint = this.currentEditIndex;
+                });
+            }
+        } finally {
+            if (this.ongoingSave === cancelable) { // Make sure we are still doing the same save
+                this.ongoingSave = undefined;
+            }
+        }
+    }
+
+    async saveAs(resource: TheiaURI, targetResource: TheiaURI, options?: CopyFileOptions): Promise<void> {
+        if (this.editable) {
+            const source = new CancellationTokenSource();
+            await this.proxy.$onSaveAs(this.resource, this.viewType, URI.file(targetResource.path.toString()), source.token);
+            this.change(() => {
+                this.savePoint = this.currentEditIndex;
+            });
+        } else {
+            // Since the editor is readonly, just copy the file over
+            await this.fileService.copy(resource, targetResource, { overwrite: false });
+        }
+    }
+}
+
+// copied from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/workbench/contrib/customEditor/common/customTextEditorModel.ts
+export class CustomTextEditorModel implements CustomEditorModel {
+
+    private readonly toDispose = new DisposableCollection();
+    readonly autoSave: 'on' | 'off';
+
+    private readonly onDirtyChangedEmitter = new Emitter<void>();
+    readonly onDirtyChanged = this.onDirtyChangedEmitter.event;
+
+    static async create(
+        viewType: string,
+        resource: TheiaURI,
+        editorModelService: EditorModelService,
+        fileService: FileService
+    ): Promise<CustomTextEditorModel> {
+        const model = await editorModelService.createModelReference(resource);
+        return new CustomTextEditorModel(viewType, resource, model, fileService);
+    }
+
+    constructor(
+        readonly viewType: string,
+        readonly editorResource: TheiaURI,
+        private readonly model: Reference<MonacoEditorModel>,
+        private readonly fileService: FileService
+    ) {
+        this.toDispose.push(
+            this.editorTextModel.onDirtyChanged(e => {
+                this.onDirtyChangedEmitter.fire();
+            })
+        );
+    }
+
+    dispose(): void {
+        this.toDispose.dispose();
+        this.model.dispose();
+    }
+
+    get resource(): URI {
+        return URI.file(this.editorResource.path.toString());
+    }
+
+    get dirty(): boolean {
+        return this.editorTextModel.dirty;
+    };
+
+    get readonly(): boolean {
+        return this.editorTextModel.readOnly;
+    }
+
+    get editorTextModel(): MonacoEditorModel {
+        return this.model.object;
+    }
+
+    revert(options?: Saveable.RevertOptions): Promise<void> {
+        return this.editorTextModel.revert(options);
+    }
+
+    save(options?: SaveOptions): Promise<void> {
+        return this.editorTextModel.save(options);
+    }
+
+    async saveAs(resource: TheiaURI, targetResource: TheiaURI, options?: CopyFileOptions): Promise<void> {
+        await this.save({ formatType: FormatType.ON });
+        await this.fileService.copy(resource, targetResource, options);
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/glob.ts b/packages/plugin-ext/src/main/browser/custom-editors/glob.ts
new file mode 100644
index 0000000000000..f492315e6a9b6
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/glob.ts
@@ -0,0 +1,742 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+// copied from https://github.com/Microsoft/vscode/blob/bf7ac9201e7a7d01741d4e6e64b5dc9f3197d97b/src/vs/base/common/glob.ts
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+'use strict';
+
+import * as strings from '@theia/core/lib/common/strings';
+import * as paths from './paths';
+import { CharCode } from '@theia/core/lib/common/char-code';
+
+/* eslint-disable @typescript-eslint/no-shadow, no-null/no-null */
+export interface IExpression {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    [pattern: string]: boolean | SiblingClause | any;
+}
+
+export interface IRelativePattern {
+    base: string;
+    pattern: string;
+    pathToRelative(from: string, to: string): string;
+}
+
+export function getEmptyExpression(): IExpression {
+    return Object.create(null);
+}
+
+export interface SiblingClause {
+    when: string;
+}
+
+const GLOBSTAR = '**';
+const GLOB_SPLIT = '/';
+const PATH_REGEX = '[/\\\\]';        // any slash or backslash
+const NO_PATH_REGEX = '[^/\\\\]';    // any non-slash and non-backslash
+const ALL_FORWARD_SLASHES = /\//g;
+
+function starsToRegExp(starCount: number): string {
+    switch (starCount) {
+        case 0:
+            return '';
+        case 1:
+            return `${NO_PATH_REGEX}*?`; // 1 star matches any number of characters except path separator (/ and \) - non greedy (?)
+        default:
+            // Matches:  (Path Sep OR Path Val followed by Path Sep OR Path Sep followed by Path Val) 0-many times
+            // Group is non capturing because we don't need to capture at all (?:...)
+            // Overall we use non-greedy matching because it could be that we match too much
+            return `(?:${PATH_REGEX}|${NO_PATH_REGEX}+${PATH_REGEX}|${PATH_REGEX}${NO_PATH_REGEX}+)*?`;
+    }
+}
+
+export function splitGlobAware(pattern: string, splitChar: string): string[] {
+    if (!pattern) {
+        return [];
+    }
+
+    const segments: string[] = [];
+
+    let inBraces = false;
+    let inBrackets = false;
+
+    let char: string;
+    let curVal = '';
+    for (let i = 0; i < pattern.length; i++) {
+        char = pattern[i];
+
+        switch (char) {
+            case splitChar:
+                if (!inBraces && !inBrackets) {
+                    segments.push(curVal);
+                    curVal = '';
+
+                    continue;
+                }
+                break;
+            case '{':
+                inBraces = true;
+                break;
+            case '}':
+                inBraces = false;
+                break;
+            case '[':
+                inBrackets = true;
+                break;
+            case ']':
+                inBrackets = false;
+                break;
+        }
+
+        curVal += char;
+    }
+
+    // Tail
+    if (curVal) {
+        segments.push(curVal);
+    }
+
+    return segments;
+}
+
+function parseRegExp(pattern: string): string {
+    if (!pattern) {
+        return '';
+    }
+
+    let regEx = '';
+
+    // Split up into segments for each slash found
+    // eslint-disable-next-line prefer-const
+    let segments = splitGlobAware(pattern, GLOB_SPLIT);
+
+    // Special case where we only have globstars
+    if (segments.every(s => s === GLOBSTAR)) {
+        regEx = '.*';
+    }
+
+    // Build regex over segments
+    // tslint:disable-next-line:one-line
+    else {
+        let previousSegmentWasGlobStar = false;
+        segments.forEach((segment, index) => {
+
+            // Globstar is special
+            if (segment === GLOBSTAR) {
+
+                // if we have more than one globstar after another, just ignore it
+                if (!previousSegmentWasGlobStar) {
+                    regEx += starsToRegExp(2);
+                    previousSegmentWasGlobStar = true;
+                }
+
+                return;
+            }
+
+            // States
+            let inBraces = false;
+            let braceVal = '';
+
+            let inBrackets = false;
+            let bracketVal = '';
+
+            let char: string;
+            for (let i = 0; i < segment.length; i++) {
+                char = segment[i];
+
+                // Support brace expansion
+                if (char !== '}' && inBraces) {
+                    braceVal += char;
+                    continue;
+                }
+
+                // Support brackets
+                if (inBrackets && (char !== ']' || !bracketVal) /* ] is literally only allowed as first character in brackets to match it */) {
+                    let res: string;
+
+                    // range operator
+                    if (char === '-') {
+                        res = char;
+                    }
+
+                    // negation operator (only valid on first index in bracket)
+                    // tslint:disable-next-line:one-line
+                    else if ((char === '^' || char === '!') && !bracketVal) {
+                        res = '^';
+                    }
+
+                    // glob split matching is not allowed within character ranges
+                    // see http://man7.org/linux/man-pages/man7/glob.7.html
+                    // tslint:disable-next-line:one-line
+                    else if (char === GLOB_SPLIT) {
+                        res = '';
+                    }
+
+                    // anything else gets escaped
+                    // tslint:disable-next-line:one-line
+                    else {
+                        res = strings.escapeRegExpCharacters(char);
+                    }
+
+                    bracketVal += res;
+                    continue;
+                }
+
+                switch (char) {
+                    case '{':
+                        inBraces = true;
+                        continue;
+
+                    case '[':
+                        inBrackets = true;
+                        continue;
+
+                    case '}':
+                        // eslint-disable-next-line prefer-const
+                        let choices = splitGlobAware(braceVal, ',');
+
+                        // Converts {foo,bar} => [foo|bar]
+                        // eslint-disable-next-line prefer-const
+                        let braceRegExp = `(?:${choices.map(c => parseRegExp(c)).join('|')})`;
+
+                        regEx += braceRegExp;
+
+                        inBraces = false;
+                        braceVal = '';
+
+                        break;
+
+                    case ']':
+                        regEx += ('[' + bracketVal + ']');
+
+                        inBrackets = false;
+                        bracketVal = '';
+
+                        break;
+
+                    case '?':
+                        regEx += NO_PATH_REGEX; // 1 ? matches any single character except path separator (/ and \)
+                        continue;
+
+                    case '*':
+                        regEx += starsToRegExp(1);
+                        continue;
+
+                    default:
+                        regEx += strings.escapeRegExpCharacters(char);
+                }
+            }
+
+            // Tail: Add the slash we had split on if there is more to come and the remaining pattern is not a globstar
+            // For example if pattern: some/**/*.js we want the "/" after some to be included in the RegEx to prevent
+            // a folder called "something" to match as well.
+            // However, if pattern: some/**, we tolerate that we also match on "something" because our globstar behavior
+            // is to match 0-N segments.
+            if (index < segments.length - 1 && (segments[index + 1] !== GLOBSTAR || index + 2 < segments.length)) {
+                regEx += PATH_REGEX;
+            }
+
+            // reset state
+            previousSegmentWasGlobStar = false;
+        });
+    }
+
+    return regEx;
+}
+
+// regexes to check for trivial glob patterns that just check for String#endsWith
+const T1 = /^\*\*\/\*\.[\w\.-]+$/;                                        // **/*.something
+const T2 = /^\*\*\/([\w\.-]+)\/?$/;                                            // **/something
+const T3 = /^{\*\*\/[\*\.]?[\w\.-]+\/?(,\*\*\/[\*\.]?[\w\.-]+\/?)*}$/;     // {**/*.something,**/*.else} or {**/package.json,**/project.json}
+const T3_2 = /^{\*\*\/[\*\.]?[\w\.-]+(\/(\*\*)?)?(,\*\*\/[\*\.]?[\w\.-]+(\/(\*\*)?)?)*}$/;     // Like T3, with optional trailing /**
+const T4 = /^\*\*((\/[\w\.-]+)+)\/?$/;                                        // **/something/else
+const T5 = /^([\w\.-]+(\/[\w\.-]+)*)\/?$/;                                    // something/else
+
+export type ParsedPattern = (path: string, basename?: string) => boolean;
+
+// The ParsedExpression returns a Promise iff hasSibling returns a Promise.
+// eslint-disable-next-line max-len
+export type ParsedExpression = (path: string, basename?: string, hasSibling?: (name: string) => boolean | Promise<boolean>) => string | Promise<string> /* the matching pattern */;
+
+export interface IGlobOptions {
+    /**
+     * Simplify patterns for use as exclusion filters during tree traversal to skip entire subtrees. Cannot be used outside of a tree traversal.
+     */
+    trimForExclusions?: boolean;
+}
+
+interface ParsedStringPattern {
+    (path: string, basename: string): string | Promise<string> /* the matching pattern */;
+    basenames?: string[];
+    patterns?: string[];
+    allBasenames?: string[];
+    allPaths?: string[];
+}
+interface ParsedExpressionPattern {
+    (path: string, basename: string, name: string, hasSibling: (name: string) => boolean | Promise<boolean>): string | Promise<string> /* the matching pattern */;
+    requiresSiblings?: boolean;
+    allBasenames?: string[];
+    allPaths?: string[];
+}
+
+const CACHE = new Map<string, ParsedStringPattern>();  // new LRUCache<string, ParsedStringPattern>(10000); // bounded to 10000 elements
+
+const FALSE = function (): boolean {
+    return false;
+};
+
+const NULL = function (): string {
+    return null!;
+};
+
+function parsePattern(arg1: string | IRelativePattern, options: IGlobOptions): ParsedStringPattern {
+    if (!arg1) {
+        return NULL;
+    }
+
+    // Handle IRelativePattern
+    let pattern: string;
+    if (typeof arg1 !== 'string') {
+        pattern = arg1.pattern;
+    } else {
+        pattern = arg1;
+    }
+
+    // Whitespace trimming
+    pattern = pattern.trim();
+
+    // Check cache
+    const patternKey = `${pattern}_${!!options.trimForExclusions}`;
+    let parsedPattern = CACHE.get(patternKey);
+    if (parsedPattern) {
+        return wrapRelativePattern(parsedPattern, arg1);
+    }
+
+    // Check for Trivias
+    let match: RegExpExecArray;
+    if (T1.test(pattern)) { // common pattern: **/*.txt just need endsWith check
+        const base = pattern.substr(4); // '**/*'.length === 4
+        parsedPattern = function (path, basename): string {
+            return path && strings.endsWith(path, base) ? pattern : null!;
+        };
+    } else if (match = T2.exec(trimForExclusions(pattern, options))!) { // common pattern: **/some.txt just need basename check
+        parsedPattern = trivia2(match[1], pattern);
+    } else if ((options.trimForExclusions ? T3_2 : T3).test(pattern)) { // repetition of common patterns (see above) {**/*.txt,**/*.png}
+        parsedPattern = trivia3(pattern, options);
+    } else if (match = T4.exec(trimForExclusions(pattern, options))!) { // common pattern: **/something/else just need endsWith check
+        parsedPattern = trivia4and5(match[1].substr(1), pattern, true);
+    } else if (match = T5.exec(trimForExclusions(pattern, options))!) { // common pattern: something/else just need equals check
+        parsedPattern = trivia4and5(match[1], pattern, false);
+    }
+
+    // Otherwise convert to pattern
+    // tslint:disable-next-line:one-line
+    else {
+        parsedPattern = toRegExp(pattern);
+    }
+
+    // Cache
+    CACHE.set(patternKey, parsedPattern);
+
+    return wrapRelativePattern(parsedPattern, arg1);
+}
+
+function wrapRelativePattern(parsedPattern: ParsedStringPattern, arg2: string | IRelativePattern): ParsedStringPattern {
+    if (typeof arg2 === 'string') {
+        return parsedPattern;
+    }
+
+    return function (path, basename): string | Promise<string> {
+        if (!paths.isEqualOrParent(path, arg2.base)) {
+            return null!;
+        }
+
+        return parsedPattern(paths.normalize(arg2.pathToRelative(arg2.base, path)), basename);
+    };
+}
+
+function trimForExclusions(pattern: string, options: IGlobOptions): string {
+    return options.trimForExclusions && strings.endsWith(pattern, '/**') ? pattern.substr(0, pattern.length - 2) : pattern; // dropping **, tailing / is dropped later
+}
+
+// common pattern: **/some.txt just need basename check
+function trivia2(base: string, originalPattern: string): ParsedStringPattern {
+    const slashBase = `/${base}`;
+    const backslashBase = `\\${base}`;
+    const parsedPattern: ParsedStringPattern = function (path, basename): string {
+        if (!path) {
+            return null!;
+        }
+        if (basename) {
+            return basename === base ? originalPattern : null!;
+        }
+        return path === base || strings.endsWith(path, slashBase) || strings.endsWith(path, backslashBase) ? originalPattern : null!;
+    };
+    const basenames = [base];
+    parsedPattern.basenames = basenames;
+    parsedPattern.patterns = [originalPattern];
+    parsedPattern.allBasenames = basenames;
+    return parsedPattern;
+}
+
+// repetition of common patterns (see above) {**/*.txt,**/*.png}
+function trivia3(pattern: string, options: IGlobOptions): ParsedStringPattern {
+    const parsedPatterns = aggregateBasenameMatches(pattern.slice(1, -1).split(',')
+        .map(pattern => parsePattern(pattern, options))
+        .filter(pattern => pattern !== NULL), pattern);
+    const n = parsedPatterns.length;
+    if (!n) {
+        return NULL;
+    }
+    if (n === 1) {
+        return <ParsedStringPattern>parsedPatterns[0];
+    }
+    const parsedPattern: ParsedStringPattern = function (path: string, basename: string): string {
+        for (let i = 0, n = parsedPatterns.length; i < n; i++) {
+            if ((<ParsedStringPattern>parsedPatterns[i])(path, basename)) {
+                return pattern;
+            }
+        }
+        return null!;
+    };
+    const withBasenames = parsedPatterns.find(pattern => !!(<ParsedStringPattern>pattern).allBasenames);
+    // const withBasenames = arrays.first(parsedPatterns, pattern => !!(<ParsedStringPattern>pattern).allBasenames);
+    if (withBasenames) {
+        parsedPattern.allBasenames = (<ParsedStringPattern>withBasenames).allBasenames;
+    }
+    const allPaths = parsedPatterns.reduce((all, current) => current.allPaths ? all.concat(current.allPaths) : all, <string[]>[]);
+    if (allPaths.length) {
+        parsedPattern.allPaths = allPaths;
+    }
+    return parsedPattern;
+}
+
+// common patterns: **/something/else just need endsWith check, something/else just needs and equals check
+function trivia4and5(path: string, pattern: string, matchPathEnds: boolean): ParsedStringPattern {
+    const nativePath = paths.nativeSep !== paths.sep ? path.replace(ALL_FORWARD_SLASHES, paths.nativeSep) : path;
+    const nativePathEnd = paths.nativeSep + nativePath;
+    // eslint-disable-next-line @typescript-eslint/no-shadow
+    const parsedPattern: ParsedStringPattern = matchPathEnds ? function (path, basename): string {
+        return path && (path === nativePath || strings.endsWith(path, nativePathEnd)) ? pattern : null!;
+        // eslint-disable-next-line @typescript-eslint/no-shadow
+    } : function (path, basename): string {
+        return path && path === nativePath ? pattern : null!;
+    };
+    parsedPattern.allPaths = [(matchPathEnds ? '*/' : './') + path];
+    return parsedPattern;
+}
+
+function toRegExp(pattern: string): ParsedStringPattern {
+    try {
+        const regExp = new RegExp(`^${parseRegExp(pattern)}$`);
+        return function (path: string, basename: string): string {
+            regExp.lastIndex = 0; // reset RegExp to its initial state to reuse it!
+            return path && regExp.test(path) ? pattern : null!;
+        };
+    } catch (error) {
+        return NULL;
+    }
+}
+
+/**
+ * Simplified glob matching. Supports a subset of glob patterns:
+ * - * matches anything inside a path segment
+ * - ? matches 1 character inside a path segment
+ * - ** matches anything including an empty path segment
+ * - simple brace expansion ({js,ts} => js or ts)
+ * - character ranges (using [...])
+ */
+export function match(pattern: string | IRelativePattern, path: string): boolean;
+export function match(expression: IExpression, path: string, hasSibling?: (name: string) => boolean): string /* the matching pattern */;
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export function match(arg1: string | IExpression | IRelativePattern, path: string, hasSibling?: (name: string) => boolean): any {
+    if (!arg1 || !path) {
+        return false;
+    }
+
+    return parse(<IExpression>arg1)(path, undefined, hasSibling);
+}
+
+/**
+ * Simplified glob matching. Supports a subset of glob patterns:
+ * - * matches anything inside a path segment
+ * - ? matches 1 character inside a path segment
+ * - ** matches anything including an empty path segment
+ * - simple brace expansion ({js,ts} => js or ts)
+ * - character ranges (using [...])
+ */
+export function parse(pattern: string | IRelativePattern, options?: IGlobOptions): ParsedPattern;
+export function parse(expression: IExpression, options?: IGlobOptions): ParsedExpression;
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export function parse(arg1: string | IExpression | IRelativePattern, options: IGlobOptions = {}): any {
+    if (!arg1) {
+        return FALSE;
+    }
+
+    // Glob with String
+    if (typeof arg1 === 'string' || isRelativePattern(arg1)) {
+        const parsedPattern = parsePattern(arg1 as string | IRelativePattern, options);
+        if (parsedPattern === NULL) {
+            return FALSE;
+        }
+        const resultPattern = function (path: string, basename: string): boolean {
+            return !!parsedPattern(path, basename);
+        };
+        if (parsedPattern.allBasenames) {
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            (<ParsedStringPattern><any>resultPattern).allBasenames = parsedPattern.allBasenames;
+        }
+        if (parsedPattern.allPaths) {
+            // eslint-disable-next-line @typescript-eslint/no-explicit-any
+            (<ParsedStringPattern><any>resultPattern).allPaths = parsedPattern.allPaths;
+        }
+        return resultPattern;
+    }
+
+    // Glob with Expression
+    return parsedExpression(<IExpression>arg1, options);
+}
+
+export function hasSiblingPromiseFn(siblingsFn?: () => Promise<string[]>): ((name: string) => Promise<boolean>) | undefined {
+    if (!siblingsFn) {
+        return undefined;
+    }
+
+    let siblings: Promise<Record<string, true>>;
+    return (name: string) => {
+        if (!siblings) {
+            siblings = (siblingsFn() || Promise.resolve([]))
+                .then(list => list ? listToMap(list) : {});
+        }
+        return siblings.then(map => !!map[name]);
+    };
+}
+
+export function hasSiblingFn(siblingsFn?: () => string[]): ((name: string) => boolean) | undefined {
+    if (!siblingsFn) {
+        return undefined;
+    }
+
+    let siblings: Record<string, true>;
+    return (name: string) => {
+        if (!siblings) {
+            const list = siblingsFn();
+            siblings = list ? listToMap(list) : {};
+        }
+        return !!siblings[name];
+    };
+}
+
+function listToMap(list: string[]): Record<string, true> {
+    const map: Record<string, true> = {};
+    for (const key of list) {
+        map[key] = true;
+    }
+    return map;
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export function isRelativePattern(obj: any): obj is IRelativePattern {
+    const rp = obj as IRelativePattern;
+
+    return rp && typeof rp.base === 'string' && typeof rp.pattern === 'string' && typeof rp.pathToRelative === 'function';
+}
+
+/**
+ * Same as `parse`, but the ParsedExpression is guaranteed to return a Promise
+ */
+export function parseToAsync(expression: IExpression, options?: IGlobOptions): ParsedExpression {
+    // eslint-disable-next-line @typescript-eslint/no-shadow
+    const parsedExpression = parse(expression, options);
+    return (path: string, basename?: string, hasSibling?: (name: string) => boolean | Promise<boolean>): string | Promise<string> => {
+        const result = parsedExpression(path, basename, hasSibling);
+        return result instanceof Promise ? result : Promise.resolve(result);
+    };
+}
+
+export function getBasenameTerms(patternOrExpression: ParsedPattern | ParsedExpression): string[] {
+    return (<ParsedStringPattern>patternOrExpression).allBasenames || [];
+}
+
+export function getPathTerms(patternOrExpression: ParsedPattern | ParsedExpression): string[] {
+    return (<ParsedStringPattern>patternOrExpression).allPaths || [];
+}
+
+function parsedExpression(expression: IExpression, options: IGlobOptions): ParsedExpression {
+    const parsedPatterns = aggregateBasenameMatches(Object.getOwnPropertyNames(expression)
+        .map(pattern => parseExpressionPattern(pattern, expression[pattern], options))
+        .filter(pattern => pattern !== NULL));
+
+    const n = parsedPatterns.length;
+    if (!n) {
+        return NULL;
+    }
+
+    if (!parsedPatterns.some(parsedPattern => (<ParsedExpressionPattern>parsedPattern).requiresSiblings!)) {
+        if (n === 1) {
+            return <ParsedStringPattern>parsedPatterns[0];
+        }
+
+        // eslint-disable-next-line @typescript-eslint/no-shadow
+        const resultExpression: ParsedStringPattern = function (path: string, basename: string): string | Promise<string> {
+            // eslint-disable-next-line @typescript-eslint/no-shadow
+            // tslint:disable-next-line:one-variable-per-declaration
+            for (let i = 0, n = parsedPatterns.length; i < n; i++) {
+                // Pattern matches path
+                const result = (<ParsedStringPattern>parsedPatterns[i])(path, basename);
+                if (result) {
+                    return result;
+                }
+            }
+
+            return null!;
+        };
+
+        // eslint-disable-next-line @typescript-eslint/no-shadow
+        const withBasenames = parsedPatterns.find(pattern => !!(<ParsedStringPattern>pattern).allBasenames);
+        if (withBasenames) {
+            resultExpression.allBasenames = (<ParsedStringPattern>withBasenames).allBasenames;
+        }
+
+        // eslint-disable-next-line @typescript-eslint/no-shadow
+        const allPaths = parsedPatterns.reduce((all, current) => current.allPaths ? all.concat(current.allPaths) : all, <string[]>[]);
+        if (allPaths.length) {
+            resultExpression.allPaths = allPaths;
+        }
+
+        return resultExpression;
+    }
+
+    const resultExpression: ParsedStringPattern = function (path: string, basename: string, hasSibling?: (name: string) => boolean | Promise<boolean>): string | Promise<string> {
+        let name: string = null!;
+
+        // eslint-disable-next-line @typescript-eslint/no-shadow
+        for (let i = 0, n = parsedPatterns.length; i < n; i++) {
+            // Pattern matches path
+            const parsedPattern = (<ParsedExpressionPattern>parsedPatterns[i]);
+            if (parsedPattern.requiresSiblings && hasSibling) {
+                if (!basename) {
+                    basename = paths.basename(path);
+                }
+                if (!name) {
+                    name = basename.substr(0, basename.length - paths.extname(path).length);
+                }
+            }
+            const result = parsedPattern(path, basename, name, hasSibling!);
+            if (result) {
+                return result;
+            }
+        }
+
+        return null!;
+    };
+
+    const withBasenames = parsedPatterns.find(pattern => !!(<ParsedStringPattern>pattern).allBasenames);
+    if (withBasenames) {
+        resultExpression.allBasenames = (<ParsedStringPattern>withBasenames).allBasenames;
+    }
+
+    const allPaths = parsedPatterns.reduce((all, current) => current.allPaths ? all.concat(current.allPaths) : all, <string[]>[]);
+    if (allPaths.length) {
+        resultExpression.allPaths = allPaths;
+    }
+
+    return resultExpression;
+}
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function parseExpressionPattern(pattern: string, value: any, options: IGlobOptions): (ParsedStringPattern | ParsedExpressionPattern) {
+    if (value === false) {
+        return NULL; // pattern is disabled
+    }
+
+    const parsedPattern = parsePattern(pattern, options);
+    if (parsedPattern === NULL) {
+        return NULL;
+    }
+
+    // Expression Pattern is <boolean>
+    if (typeof value === 'boolean') {
+        return parsedPattern;
+    }
+
+    // Expression Pattern is <SiblingClause>
+    if (value) {
+        const when = (<SiblingClause>value).when;
+        if (typeof when === 'string') {
+            const result: ParsedExpressionPattern = (path: string, basename: string, name: string, hasSibling: (name: string) => boolean | Promise<boolean>) => {
+                if (!hasSibling || !parsedPattern(path, basename)) {
+                    return null!;
+                }
+
+                const clausePattern = when.replace('$(basename)', name);
+                const matched = hasSibling(clausePattern);
+                return matched instanceof Promise ?
+                    matched.then(m => m ? pattern : null!) :
+                    matched ? pattern : null!;
+            };
+            result.requiresSiblings = true;
+            return result;
+        }
+    }
+
+    // Expression is Anything
+    return parsedPattern;
+}
+
+function aggregateBasenameMatches(parsedPatterns: (ParsedStringPattern | ParsedExpressionPattern)[], result?: string): (ParsedStringPattern | ParsedExpressionPattern)[] {
+    const basenamePatterns = parsedPatterns.filter(parsedPattern => !!(<ParsedStringPattern>parsedPattern).basenames);
+    if (basenamePatterns.length < 2) {
+        return parsedPatterns;
+    }
+
+    const basenames = basenamePatterns.reduce<string[]>((all, current) => all.concat((<ParsedStringPattern>current).basenames!), []);
+    let patterns: string[];
+    if (result) {
+        patterns = [];
+        // tslint:disable-next-line:one-variable-per-declaration
+        for (let i = 0, n = basenames.length; i < n; i++) {
+            patterns.push(result);
+        }
+    } else {
+        patterns = basenamePatterns.reduce((all, current) => all.concat((<ParsedStringPattern>current).patterns!), <string[]>[]);
+    }
+    const aggregate: ParsedStringPattern = function (path, basename): string {
+        if (!path) {
+            return null!;
+        }
+        if (!basename) {
+            let i: number;
+            for (i = path.length; i > 0; i--) {
+                const ch = path.charCodeAt(i - 1);
+                if (ch === CharCode.Slash || ch === CharCode.Backslash) {
+                    break;
+                }
+            }
+            basename = path.substr(i);
+        }
+        const index = basenames.indexOf(basename);
+        return index !== -1 ? patterns[index] : null!;
+    };
+    aggregate.basenames = basenames;
+    aggregate.patterns = patterns;
+    aggregate.allBasenames = basenames;
+
+    const aggregatedPatterns = parsedPatterns.filter(parsedPattern => !(<ParsedStringPattern>parsedPattern).basenames);
+    aggregatedPatterns.push(aggregate);
+    return aggregatedPatterns;
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/paths.ts b/packages/plugin-ext/src/main/browser/custom-editors/paths.ts
new file mode 100644
index 0000000000000..68c538369b4b1
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/paths.ts
@@ -0,0 +1,250 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+// copied from https://github.com/Microsoft/vscode/blob/bf7ac9201e7a7d01741d4e6e64b5dc9f3197d97b/src/vs/base/common/paths.ts
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+/* eslint-disable no-void */
+/* eslint-disable no-null/no-null */
+'use strict';
+import { isWindows } from '@theia/core/lib/common/os';
+import { startsWithIgnoreCase } from '@theia/core/lib/common/strings';
+import { CharCode } from '@theia/core/lib/common/char-code';
+
+/**
+ * The forward slash path separator.
+ */
+export const sep = '/';
+
+/**
+ * The native path separator depending on the OS.
+ */
+export const nativeSep = isWindows ? '\\' : '/';
+
+const _posixBadPath = /(\/\.\.?\/)|(\/\.\.?)$|^(\.\.?\/)|(\/\/+)|(\\)/;
+const _winBadPath = /(\\\.\.?\\)|(\\\.\.?)$|^(\.\.?\\)|(\\\\+)|(\/)/;
+
+function _isNormal(path: string, win: boolean): boolean {
+    return win
+        ? !_winBadPath.test(path)
+        : !_posixBadPath.test(path);
+}
+
+/**
+ * @returns the base name of a path.
+ */
+export function basename(path: string): string {
+    const idx = ~path.lastIndexOf('/') || ~path.lastIndexOf('\\');
+    if (idx === 0) {
+        return path;
+    } else if (~idx === path.length - 1) {
+        return basename(path.substring(0, path.length - 1));
+    } else {
+        return path.substr(~idx + 1);
+    }
+}
+
+/**
+ * @returns `.far` from `boo.far` or the empty string.
+ */
+export function extname(path: string): string {
+    path = basename(path);
+    const idx = ~path.lastIndexOf('.');
+    return idx ? path.substring(~idx) : '';
+}
+
+export function normalize(path: string, toOSPath?: boolean): string {
+    if (path === null || path === void 0) {
+        return path;
+    }
+
+    const len = path.length;
+    if (len === 0) {
+        return '.';
+    }
+
+    const wantsBackslash = isWindows && toOSPath;
+    if (_isNormal(path, wantsBackslash!)) {
+        return path;
+    }
+
+    // eslint-disable-next-line @typescript-eslint/no-shadow
+    const sep = wantsBackslash ? '\\' : '/';
+    const root = getRoot(path, sep);
+
+    // skip the root-portion of the path
+    let start = root.length;
+    let skip = false;
+    let res = '';
+
+    for (let end = root.length; end <= len; end++) {
+
+        // either at the end or at a path-separator character
+        if (end === len || path.charCodeAt(end) === CharCode.Slash || path.charCodeAt(end) === CharCode.Backslash) {
+
+            if (streql(path, start, end, '..')) {
+                // skip current and remove parent (if there is already something)
+                const prev_start = res.lastIndexOf(sep);
+                const prev_part = res.slice(prev_start + 1);
+                if ((root || prev_part.length > 0) && prev_part !== '..') {
+                    res = prev_start === -1 ? '' : res.slice(0, prev_start);
+                    skip = true;
+                }
+            } else if (streql(path, start, end, '.') && (root || res || end < len - 1)) {
+                // skip current (if there is already something or if there is more to come)
+                skip = true;
+            }
+
+            if (!skip) {
+                const part = path.slice(start, end);
+                if (res !== '' && res[res.length - 1] !== sep) {
+                    res += sep;
+                }
+                res += part;
+            }
+            start = end + 1;
+            skip = false;
+        }
+    }
+
+    return root + res;
+}
+function streql(value: string, start: number, end: number, other: string): boolean {
+    return start + other.length === end && value.indexOf(other, start) === start;
+}
+
+/**
+ * Computes the _root_ this path, like `getRoot('c:\files') === c:\`,
+ * `getRoot('files:///files/path') === files:///`,
+ * or `getRoot('\\server\shares\path') === \\server\shares\`
+ */
+// eslint-disable-next-line @typescript-eslint/no-shadow
+export function getRoot(path: string, sep: string = '/'): string {
+
+    if (!path) {
+        return '';
+    }
+
+    const len = path.length;
+    let code = path.charCodeAt(0);
+    if (code === CharCode.Slash || code === CharCode.Backslash) {
+
+        code = path.charCodeAt(1);
+        if (code === CharCode.Slash || code === CharCode.Backslash) {
+            // UNC candidate \\localhost\shares\ddd
+            //               ^^^^^^^^^^^^^^^^^^^
+            code = path.charCodeAt(2);
+            if (code !== CharCode.Slash && code !== CharCode.Backslash) {
+                // eslint-disable-next-line @typescript-eslint/no-shadow
+                let pos = 3;
+                const start = pos;
+                for (; pos < len; pos++) {
+                    code = path.charCodeAt(pos);
+                    if (code === CharCode.Slash || code === CharCode.Backslash) {
+                        break;
+                    }
+                }
+                code = path.charCodeAt(pos + 1);
+                if (start !== pos && code !== CharCode.Slash && code !== CharCode.Backslash) {
+                    pos += 1;
+                    for (; pos < len; pos++) {
+                        code = path.charCodeAt(pos);
+                        if (code === CharCode.Slash || code === CharCode.Backslash) {
+                            return path.slice(0, pos + 1) // consume this separator
+                                .replace(/[\\/]/g, sep);
+                        }
+                    }
+                }
+            }
+        }
+
+        // /user/far
+        // ^
+        return sep;
+
+    } else if ((code >= CharCode.A && code <= CharCode.Z) || (code >= CharCode.a && code <= CharCode.z)) {
+        // check for windows drive letter c:\ or c:
+
+        if (path.charCodeAt(1) === CharCode.Colon) {
+            code = path.charCodeAt(2);
+            if (code === CharCode.Slash || code === CharCode.Backslash) {
+                // C:\fff
+                // ^^^
+                return path.slice(0, 2) + sep;
+            } else {
+                // C:
+                // ^^
+                return path.slice(0, 2);
+            }
+        }
+    }
+
+    // check for URI
+    // scheme://authority/path
+    // ^^^^^^^^^^^^^^^^^^^
+    let pos = path.indexOf('://');
+    if (pos !== -1) {
+        pos += 3; // 3 -> "://".length
+        for (; pos < len; pos++) {
+            code = path.charCodeAt(pos);
+            if (code === CharCode.Slash || code === CharCode.Backslash) {
+                return path.slice(0, pos + 1); // consume this separator
+            }
+        }
+    }
+
+    return '';
+}
+
+export function isEqualOrParent(path: string, candidate: string, ignoreCase?: boolean): boolean {
+    if (path === candidate) {
+        return true;
+    }
+
+    if (!path || !candidate) {
+        return false;
+    }
+
+    if (candidate.length > path.length) {
+        return false;
+    }
+
+    if (ignoreCase) {
+        const beginsWith = startsWithIgnoreCase(path, candidate);
+        if (!beginsWith) {
+            return false;
+        }
+
+        if (candidate.length === path.length) {
+            return true; // same path, different casing
+        }
+
+        let sepOffset = candidate.length;
+        if (candidate.charAt(candidate.length - 1) === nativeSep) {
+            sepOffset--; // adjust the expected sep offset in case our candidate already ends in separator character
+        }
+
+        return path.charAt(sepOffset) === nativeSep;
+    }
+
+    if (candidate.charAt(candidate.length - 1) !== nativeSep) {
+        candidate += nativeSep;
+    }
+
+    return path.indexOf(candidate) === 0;
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/plugin-custom-editor-registry.ts b/packages/plugin-ext/src/main/browser/custom-editors/plugin-custom-editor-registry.ts
new file mode 100644
index 0000000000000..991bcbd35c263
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/plugin-custom-editor-registry.ts
@@ -0,0 +1,142 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+
+import { injectable, inject, postConstruct } from 'inversify';
+import { CustomEditor } from '../../../common';
+import { Disposable, DisposableCollection } from '@theia/core/lib/common/disposable';
+import { CustomEditorOpener } from './custom-editor-opener';
+import { WorkspaceCommands } from '@theia/workspace/lib/browser';
+import { CommandRegistry, Emitter, MenuModelRegistry } from '@theia/core';
+import { SelectionService } from '@theia/core/lib/common';
+import { UriAwareCommandHandler } from '@theia/core/lib/common/uri-command-handler';
+import { NavigatorContextMenu } from '@theia/navigator/lib//browser/navigator-contribution';
+import { ApplicationShell, DefaultOpenerService, WidgetManager } from '@theia/core/lib/browser';
+import { CustomEditorWidget } from './custom-editor-widget';
+
+@injectable()
+export class PluginCustomEditorRegistry {
+    private readonly editors = new Map<string, CustomEditor>();
+    private readonly pendingEditors = new Set<CustomEditorWidget>();
+    private readonly resolvers = new Map<string, (widget: CustomEditorWidget) => void>();
+
+    private readonly onPendingOpenCustomEditorEmitter = new Emitter<string>();
+    readonly onPendingOpenCustomEditor = this.onPendingOpenCustomEditorEmitter.event;
+
+    @inject(DefaultOpenerService)
+    protected readonly defaultOpenerService: DefaultOpenerService;
+
+    @inject(MenuModelRegistry)
+    protected readonly menuModelRegistry: MenuModelRegistry;
+
+    @inject(CommandRegistry)
+    protected readonly commandRegistry: CommandRegistry;
+
+    @inject(SelectionService)
+    protected readonly selectionService: SelectionService;
+
+    @inject(WidgetManager)
+    protected readonly widgetManager: WidgetManager;
+
+    @inject(ApplicationShell)
+    protected readonly shell: ApplicationShell;
+
+    @postConstruct()
+    protected init(): void {
+        this.widgetManager.onDidCreateWidget(({ factoryId, widget }) => {
+            if (factoryId === CustomEditorWidget.FACTORY_ID && widget instanceof CustomEditorWidget) {
+                const restoreState = widget.restoreState.bind(widget);
+
+                widget.restoreState = state => {
+                    if (state.viewType && state.strResource) {
+                        restoreState(state);
+                        this.resolveWidget(widget);
+                    } else {
+                        widget.dispose();
+                    }
+                };
+            }
+        });
+    }
+
+    registerCustomEditor(editor: CustomEditor): Disposable {
+        if (this.editors.has(editor.viewType)) {
+            console.warn('editor with such id already registered: ', JSON.stringify(editor));
+            return Disposable.NULL;
+        }
+        this.editors.set(editor.viewType, editor);
+
+        const toDispose = new DisposableCollection();
+        toDispose.push(Disposable.create(() => this.editors.delete(editor.viewType)));
+
+        const editorOpenHandler = new CustomEditorOpener(
+            editor,
+            this.shell,
+            this.widgetManager
+        );
+        toDispose.push(this.defaultOpenerService.addHandler(editorOpenHandler));
+
+        const openWithCommand = WorkspaceCommands.FILE_OPEN_WITH(editorOpenHandler);
+        toDispose.push(
+            this.menuModelRegistry.registerMenuAction(
+                NavigatorContextMenu.OPEN_WITH,
+                {
+                    commandId: openWithCommand.id,
+                    label: editorOpenHandler.label
+                }
+            )
+        );
+        toDispose.push(
+            this.commandRegistry.registerCommand(
+                openWithCommand,
+                UriAwareCommandHandler.MonoSelect(this.selectionService, {
+                    execute: uri => editorOpenHandler.open(uri),
+                    isEnabled: uri => editorOpenHandler.canHandle(uri) > 0,
+                    isVisible: uri => editorOpenHandler.canHandle(uri) > 0
+                })
+            )
+        );
+        toDispose.push(
+            editorOpenHandler.onOpenCustomEditor(widget => this.resolveWidget(widget))
+        );
+        return toDispose;
+    }
+
+    resolveWidget = (widget: CustomEditorWidget) => {
+        const resolver = this.resolvers.get(widget.viewType);
+        if (resolver) {
+            resolver(widget);
+        } else {
+            this.pendingEditors.add(widget);
+            this.onPendingOpenCustomEditorEmitter.fire(widget.viewType);
+        }
+    };
+
+    registerResolver(viewType: string, resolver: (widget: CustomEditorWidget) => void): Disposable {
+        if (this.resolvers.has(viewType)) {
+            throw new Error(`Resolver for ${viewType} already registered`);
+        }
+
+        for (const editorWidget of this.pendingEditors) {
+            if (editorWidget.viewType === viewType) {
+                resolver(editorWidget);
+                this.pendingEditors.delete(editorWidget);
+            }
+        }
+
+        this.resolvers.set(viewType, resolver);
+        return Disposable.create(() => this.resolvers.delete(viewType));
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/custom-editors/undo-redo-service.ts b/packages/plugin-ext/src/main/browser/custom-editors/undo-redo-service.ts
new file mode 100644
index 0000000000000..99735c0d84898
--- /dev/null
+++ b/packages/plugin-ext/src/main/browser/custom-editors/undo-redo-service.ts
@@ -0,0 +1,120 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+// copied and modified from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/platform/undoRedo/common/undoRedoService.ts#
+
+import { injectable } from 'inversify';
+import URI from '@theia/core/lib/common/uri';
+
+@injectable()
+export class UndoRedoService {
+    private readonly editStacks = new Map<string, ResourceEditStack>();
+
+    pushElement(resource: URI, undo: () => Promise<void>, redo: () => Promise<void>): void {
+        let editStack: ResourceEditStack;
+        if (this.editStacks.has(resource.toString())) {
+            editStack = this.editStacks.get(resource.toString())!;
+        } else {
+            editStack = new ResourceEditStack();
+            this.editStacks.set(resource.toString(), editStack);
+        }
+
+        editStack.pushElement({ undo, redo });
+    }
+
+    removeElements(resource: URI): void {
+        if (this.editStacks.has(resource.toString())) {
+            this.editStacks.delete(resource.toString());
+        }
+    }
+
+    undo(resource: URI): void {
+        if (!this.editStacks.has(resource.toString())) {
+            return;
+        }
+
+        const editStack = this.editStacks.get(resource.toString())!;
+        const element = editStack.getClosestPastElement();
+        if (!element) {
+            return;
+        }
+
+        editStack.moveBackward(element);
+        element.undo();
+    }
+
+    redo(resource: URI): void {
+        if (!this.editStacks.has(resource.toString())) {
+            return;
+        }
+
+        const editStack = this.editStacks.get(resource.toString())!;
+        const element = editStack.getClosestFutureElement();
+        if (!element) {
+            return;
+        }
+
+        editStack.moveForward(element);
+        element.redo();
+    }
+}
+
+interface StackElement {
+    undo(): Promise<void> | void;
+    redo(): Promise<void> | void;
+}
+
+export class ResourceEditStack {
+    private past: StackElement[];
+    private future: StackElement[];
+
+    constructor() {
+        this.past = [];
+        this.future = [];
+    }
+
+    pushElement(element: StackElement): void {
+        this.future = [];
+        this.past.push(element);
+    }
+
+    getClosestPastElement(): StackElement | null {
+        if (this.past.length === 0) {
+            return null;
+        }
+        return this.past[this.past.length - 1];
+    }
+
+    getClosestFutureElement(): StackElement | null {
+        if (this.future.length === 0) {
+            return null;
+        }
+        return this.future[this.future.length - 1];
+    }
+
+    moveBackward(element: StackElement): void {
+        this.past.pop();
+        this.future.push(element);
+    }
+
+    moveForward(element: StackElement): void {
+        this.future.pop();
+        this.past.push(element);
+    }
+}
diff --git a/packages/plugin-ext/src/main/browser/main-context.ts b/packages/plugin-ext/src/main/browser/main-context.ts
index 0aa70f7915ccb..0c600a689b205 100644
--- a/packages/plugin-ext/src/main/browser/main-context.ts
+++ b/packages/plugin-ext/src/main/browser/main-context.ts
@@ -49,11 +49,11 @@ import { MonacoEditorService } from '@theia/monaco/lib/browser/monaco-editor-ser
 import { UntitledResourceResolver } from './editor/untitled-resource';
 import { FileResourceResolver } from '@theia/filesystem/lib/browser';
 import { MainFileSystemEventService } from './main-file-system-event-service';
-import { LabelServiceMainImpl } from './label-service-main';
+import { LabelServiceMainImpl } from '../browser/label-service-main';
 import { TimelineMainImpl } from './timeline-main';
 import { AuthenticationMainImpl } from './authentication-main';
 import { ThemingMainImpl } from './theming-main';
-import { CommentsMainImp } from './comments/comments-main';
+import { CustomEditorsMainImpl } from './custom-editors/custom-editors-main';
 
 export function setUpPluginApi(rpc: RPCProtocol, container: interfaces.Container): void {
     const authenticationMain = new AuthenticationMainImpl(rpc, container);
@@ -122,6 +122,9 @@ export function setUpPluginApi(rpc: RPCProtocol, container: interfaces.Container
     const webviewsMain = new WebviewsMainImpl(rpc, container);
     rpc.set(PLUGIN_RPC_CONTEXT.WEBVIEWS_MAIN, webviewsMain);
 
+    const customEditorsMain = new CustomEditorsMainImpl(rpc, container, webviewsMain);
+    rpc.set(PLUGIN_RPC_CONTEXT.CUSTOM_EDITORS_MAIN, customEditorsMain);
+
     const storageMain = new StorageMainImpl(container);
     rpc.set(PLUGIN_RPC_CONTEXT.STORAGE_MAIN, storageMain);
 
@@ -164,7 +167,4 @@ export function setUpPluginApi(rpc: RPCProtocol, container: interfaces.Container
 
     const themingMain = new ThemingMainImpl(rpc);
     rpc.set(PLUGIN_RPC_CONTEXT.THEMING_MAIN, themingMain);
-
-    const commentsMain = new CommentsMainImp(rpc, container);
-    rpc.set(PLUGIN_RPC_CONTEXT.COMMENTS_MAIN, commentsMain);
 }
diff --git a/packages/plugin-ext/src/main/browser/menus/menus-contribution-handler.ts b/packages/plugin-ext/src/main/browser/menus/menus-contribution-handler.ts
index 54cb4be97a34f..122fced865369 100644
--- a/packages/plugin-ext/src/main/browser/menus/menus-contribution-handler.ts
+++ b/packages/plugin-ext/src/main/browser/menus/menus-contribution-handler.ts
@@ -43,7 +43,6 @@ import { Navigatable } from '@theia/core/lib/browser/navigatable';
 import { ContextKeyService } from '@theia/core/lib/browser/context-key-service';
 import { TIMELINE_ITEM_CONTEXT_MENU } from '@theia/timeline/lib/browser/timeline-tree-widget';
 import { TimelineItem } from '@theia/timeline/lib/common/timeline-model';
-import { COMMENT_CONTEXT, COMMENT_THREAD_CONTEXT, COMMENT_TITLE } from '../comments/comment-thread-widget';
 
 type CodeEditorWidget = EditorWidget | WebviewWidget;
 @injectable()
@@ -164,45 +163,6 @@ export class MenusContributionPointHandler {
                         })
                     ));
                 }
-            } else if (location === 'comments/commentThread/context') {
-                for (const menu of allMenus[location]) {
-                    toDispose.push(this.registerMenuAction(COMMENT_THREAD_CONTEXT, menu,
-                        command => ({
-                            execute: (...args) => this.commands.executeCommand(command, ...this.toCommentArgs(...args)),
-                            isEnabled: () => {
-                                const commandContributions = plugin.contributes?.commands;
-                                if (commandContributions) {
-                                    const commandContribution = commandContributions.find(c => c.command === command);
-                                    if (commandContribution && commandContribution.enablement) {
-                                        return this.contextKeyService.match(commandContribution.enablement);
-                                    }
-                                }
-                                return true;
-                            },
-                            isVisible: (...args) => this.commands.isVisible(command, ...this.toCommentArgs(...args))
-                        })
-                    ));
-                }
-            } else if (location === 'comments/comment/title') {
-                for (const menu of allMenus[location]) {
-                    toDispose.push(this.registerMenuAction(COMMENT_TITLE, menu,
-                        command => ({
-                            execute: (...args) => this.commands.executeCommand(command, ...this.toCommentArgs(...args)),
-                            isEnabled: (...args) => this.commands.isEnabled(command, ...this.toCommentArgs(...args)),
-                            isVisible: (...args) => this.commands.isVisible(command, ...this.toCommentArgs(...args))
-                        })
-                    ));
-                }
-            } else if (location === 'comments/comment/context') {
-                for (const menu of allMenus[location]) {
-                    toDispose.push(this.registerMenuAction(COMMENT_CONTEXT, menu,
-                        command => ({
-                            execute: (...args) => this.commands.executeCommand(command, ...this.toCommentArgs(...args)),
-                            isEnabled: () => true,
-                            isVisible: (...args) => this.commands.isVisible(command, ...this.toCommentArgs(...args))
-                        })
-                    ));
-                }
             } else if (location === 'debug/callstack/context') {
                 for (const menu of allMenus[location]) {
                     for (const menuPath of [DebugStackFramesWidget.CONTEXT_MENU, DebugThreadsWidget.CONTEXT_MENU]) {
@@ -362,30 +322,6 @@ export class MenusContributionPointHandler {
         };
     }
 
-    protected toCommentArgs(...args: any[]): any[] {
-        const arg = args[0];
-        if ('text' in arg) {
-            if ('commentUniqueId' in arg) {
-                return [{
-                    commentControlHandle: arg.thread.controllerHandle,
-                    commentThreadHandle: arg.thread.commentThreadHandle,
-                    text: arg.text,
-                    commentUniqueId: arg.commentUniqueId
-                }];
-            }
-            return [{
-                commentControlHandle: arg.thread.controllerHandle,
-                commentThreadHandle: arg.thread.commentThreadHandle,
-                text: arg.text
-            }];
-        }
-        return [{
-            commentControlHandle: arg.thread.controllerHandle,
-            commentThreadHandle: arg.thread.commentThreadHandle,
-            commentUniqueId: arg.commentUniqueId
-        }];
-    }
-
     protected registerGlobalMenuAction(menuPath: MenuPath, menu: Menu): Disposable {
         const selectedResource = () => {
             const selection = this.selectionService.selection;
diff --git a/packages/plugin-ext/src/main/browser/plugin-contribution-handler.ts b/packages/plugin-ext/src/main/browser/plugin-contribution-handler.ts
index fa48da1159b03..d57d5ce4acad2 100644
--- a/packages/plugin-ext/src/main/browser/plugin-contribution-handler.ts
+++ b/packages/plugin-ext/src/main/browser/plugin-contribution-handler.ts
@@ -19,6 +19,7 @@ import { ITokenTypeMap, IEmbeddedLanguagesMap, StandardTokenType } from 'vscode-
 import { TextmateRegistry, getEncodedLanguageId, MonacoTextmateService, GrammarDefinition } from '@theia/monaco/lib/browser/textmate';
 import { MenusContributionPointHandler } from './menus/menus-contribution-handler';
 import { PluginViewRegistry } from './view/plugin-view-registry';
+import { PluginCustomEditorRegistry } from './custom-editors/plugin-custom-editor-registry';
 import { PluginContribution, IndentationRules, FoldingRules, ScopeMap, DeployedPlugin, GrammarsContribution } from '../../common';
 import {
     DefaultUriLabelProviderContribution,
@@ -51,6 +52,9 @@ export class PluginContributionHandler {
     @inject(PluginViewRegistry)
     private readonly viewRegistry: PluginViewRegistry;
 
+    @inject(PluginCustomEditorRegistry)
+    private readonly customEditorRegistry: PluginCustomEditorRegistry;
+
     @inject(MenusContributionPointHandler)
     private readonly menusContributionHandler: MenusContributionPointHandler;
 
@@ -117,7 +121,6 @@ export class PluginContributionHandler {
         const toDispose = new DisposableCollection(Disposable.create(() => { /* mark as not disposed */ }));
         /* eslint-disable @typescript-eslint/no-explicit-any */
         const logError = (message: string, ...args: any[]) => console.error(`[${clientId}][${plugin.metadata.model.id}]: ${message}`, ...args);
-        const logWarning = (message: string, ...args: any[]) => console.warn(`[${clientId}][${plugin.metadata.model.id}]: ${message}`, ...args);
         const pushContribution = (id: string, contribute: () => Disposable) => {
             if (toDispose.disposed) {
                 return;
@@ -211,7 +214,7 @@ export class PluginContributionHandler {
                     const language = grammar.language!;
                     pushContribution(`grammar.language.${language}.scope`, () => this.grammarsRegistry.mapLanguageIdToTextmateGrammar(language, grammar.scope));
                     pushContribution(`grammar.language.${language}.configuration`, () => this.grammarsRegistry.registerGrammarConfiguration(language, {
-                        embeddedLanguages: this.convertEmbeddedLanguages(grammar.embeddedLanguages, logWarning),
+                        embeddedLanguages: this.convertEmbeddedLanguages(grammar.embeddedLanguages, logError),
                         tokenTypes: this.convertTokenTypes(grammar.tokenTypes)
                     }));
                 }
@@ -232,6 +235,14 @@ export class PluginContributionHandler {
         pushContribution('menus', () => this.menusContributionHandler.handle(plugin));
         pushContribution('keybindings', () => this.keybindingsContributionHandler.handle(contributions));
 
+        if (contributions.customEditors) {
+            for (const customEditor of contributions.customEditors) {
+                pushContribution(`customEditors.${customEditor.viewType}`,
+                    () => this.customEditorRegistry.registerCustomEditor(customEditor)
+                );
+            }
+        }
+
         if (contributions.viewsContainers) {
             for (const location in contributions.viewsContainers) {
                 if (contributions.viewsContainers!.hasOwnProperty(location)) {
@@ -494,7 +505,7 @@ export class PluginContributionHandler {
         return result;
     }
 
-    private convertEmbeddedLanguages(languages: ScopeMap | undefined, logWarning: (warning: string) => void): IEmbeddedLanguagesMap | undefined {
+    private convertEmbeddedLanguages(languages: ScopeMap | undefined, logError: (error: string) => void): IEmbeddedLanguagesMap | undefined {
         if (typeof languages === 'undefined' || languages === null) {
             return undefined;
         }
@@ -506,7 +517,7 @@ export class PluginContributionHandler {
             const langId = languages[scope];
             result[scope] = getEncodedLanguageId(langId);
             if (!result[scope]) {
-                logWarning(`Language for '${scope}' not found.`);
+                logError(`Language for '${scope}' not found.`);
             }
         }
         return result;
diff --git a/packages/plugin-ext/src/main/browser/plugin-ext-deploy-command.ts b/packages/plugin-ext/src/main/browser/plugin-ext-deploy-command.ts
index d6ac84bf19371..ce35bcfc0e7d0 100644
--- a/packages/plugin-ext/src/main/browser/plugin-ext-deploy-command.ts
+++ b/packages/plugin-ext/src/main/browser/plugin-ext-deploy-command.ts
@@ -65,15 +65,11 @@ export class PluginExtDeployCommandService implements QuickOpenModel {
     public async onType(lookFor: string, acceptor: (items: QuickOpenItem[]) => void): Promise<void> {
         this.items = [];
         if (lookFor || lookFor.length > 0) {
-            this.items.push(this.createDeployQuickOpenItem(lookFor, 'Deploy this plugin'));
+            this.items.push(new DeployQuickOpenItem(lookFor, this.pluginServer, 'Deploy this plugin'));
         }
         acceptor(this.items);
     }
 
-    protected createDeployQuickOpenItem(name: string, description: string): DeployQuickOpenItem {
-        return new DeployQuickOpenItem(name, this.pluginServer, description);
-    }
-
 }
 
 export class DeployQuickOpenItem extends QuickOpenItem {
diff --git a/packages/plugin-ext/src/main/browser/plugin-ext-frontend-module.ts b/packages/plugin-ext/src/main/browser/plugin-ext-frontend-module.ts
index dbb005c6952ef..87503134c3655 100644
--- a/packages/plugin-ext/src/main/browser/plugin-ext-frontend-module.ts
+++ b/packages/plugin-ext/src/main/browser/plugin-ext-frontend-module.ts
@@ -16,7 +16,6 @@
 
 import '../../../src/main/style/status-bar.css';
 import '../../../src/main/browser/style/index.css';
-import '../../../src/main/browser/style/comments.css';
 
 import { ContainerModule } from 'inversify';
 import {
@@ -65,10 +64,12 @@ import { WebviewResourceCache } from './webview/webview-resource-cache';
 import { PluginIconThemeService, PluginIconThemeFactory, PluginIconThemeDefinition, PluginIconTheme } from './plugin-icon-theme-service';
 import { PluginTreeViewNodeLabelProvider } from './view/plugin-tree-view-node-label-provider';
 import { WebviewWidgetFactory } from './webview/webview-widget-factory';
-import { CommentsService, PluginCommentService } from './comments/comments-service';
-import { CommentingRangeDecorator } from './comments/comments-decorator';
-import { CommentsContribution } from './comments/comments-contribution';
-import { CommentsContextKeyService } from './comments/comments-context-key-service';
+import { CustomEditorContribution } from './custom-editors/custom-editor-contribution';
+import { PluginCustomEditorRegistry } from './custom-editors/plugin-custom-editor-registry';
+import { CustomEditorWidgetFactory } from '../browser/custom-editors/custom-editor-widget-factory';
+import { CustomEditorWidget } from './custom-editors/custom-editor-widget';
+import { CustomEditorService } from './custom-editors/custom-editor-service';
+import { UndoRedoService } from './custom-editors/undo-redo-service';
 
 export default new ContainerModule((bind, unbind, isBound, rebind) => {
 
@@ -161,6 +162,17 @@ export default new ContainerModule((bind, unbind, isBound, rebind) => {
     bind(WebviewWidgetFactory).toDynamicValue(ctx => new WebviewWidgetFactory(ctx.container)).inSingletonScope();
     bind(WidgetFactory).toService(WebviewWidgetFactory);
 
+    bind(CustomEditorContribution).toSelf().inSingletonScope();
+    bind(CommandContribution).toService(CustomEditorContribution);
+
+    bind(PluginCustomEditorRegistry).toSelf().inSingletonScope();
+    bind(CustomEditorService).toSelf().inSingletonScope();
+    bind(CustomEditorWidget).toSelf();
+    bind(CustomEditorWidgetFactory).toDynamicValue(ctx => new CustomEditorWidgetFactory(ctx.container)).inSingletonScope();
+    bind(WidgetFactory).toService(CustomEditorWidgetFactory);
+
+    bind(UndoRedoService).toSelf().inSingletonScope();
+
     bind(PluginViewWidget).toSelf();
     bind(WidgetFactory).toDynamicValue(({ container }) => ({
         id: PLUGIN_VIEW_FACTORY_ID,
@@ -204,9 +216,4 @@ export default new ContainerModule((bind, unbind, isBound, rebind) => {
     rebind(DebugSessionContributionRegistry).toService(PluginDebugSessionContributionRegistry);
 
     bind(ViewColumnService).toSelf().inSingletonScope();
-
-    bind(CommentsService).to(PluginCommentService).inSingletonScope();
-    bind(CommentingRangeDecorator).toSelf().inSingletonScope();
-    bind(CommentsContribution).toSelf().inSingletonScope();
-    bind(CommentsContextKeyService).toSelf().inSingletonScope();
 });
diff --git a/packages/plugin-ext/src/main/browser/style/comments.css b/packages/plugin-ext/src/main/browser/style/comments.css
deleted file mode 100644
index d0fdd31c40f62..0000000000000
--- a/packages/plugin-ext/src/main/browser/style/comments.css
+++ /dev/null
@@ -1,339 +0,0 @@
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-/* some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/contrib/comments/browser/media/review.css */
-
-.comment-range-glyph {
-    margin-left: 5px;
-    cursor: pointer;
-}
-.comment-range-glyph:before {
-    position: absolute;
-    content: '';
-    height: 100%;
-    width: 0;
-    left: -2px;
-    transition: width 80ms linear, left 80ms linear;
-}
-
-.monaco-editor .margin-view-overlays > div:hover > .comment-range-glyph.comment-diff-added:before,
-.monaco-editor .comment-range-glyph.comment-thread:before {
-    position: absolute;
-    height: 100%;
-    width: 9px;
-    left: -6px;
-    z-index: 10;
-    color: black;
-    text-align: center;
-    display: flex;
-    flex-direction: row;
-    align-items: center;
-    justify-content: center;
-}
-
-.monaco-editor .comment-diff-added {
-    border-left: 3px solid var(--theia-editorGutter-commentRangeForeground);
-    transition: opacity 0.5s;
-}
-.monaco-editor .comment-diff-added:before {
-    background: var(--theia-editorGutter-commentRangeForeground);
-}
-
-.monaco-editor .margin-view-overlays > div:hover > .comment-range-glyph.comment-diff-added:before {
-    content: "+";
-}
-
-.monaco-editor .comment-range-glyph.comment-thread {
-    z-index: 20;
-    border-left: 3px solid #000;
-}
-
-.monaco-editor .comment-thread:before {
-    background: var(--theia-editorGutter-commentRangeForeground);
-}
-
-.monaco-editor .comment-range-glyph.comment-thread:before {
-    content: "◆";
-    font-size: 10px;
-    line-height: 100%;
-    z-index: 20;
-}
-
-.monaco-editor .review-widget .body {
-    overflow: hidden;
-}
-
-.monaco-editor .review-widget .head {
-    box-sizing: border-box;
-    display: flex;
-    height: 100%;
-}
-
-.monaco-editor .review-widget .head .review-title {
-    display: inline-block;
-    font-size: 13px;
-    margin-left: 20px;
-    cursor: default;
-}
-
-.monaco-editor .review-widget .head .review-actions {
-    flex: 1;
-    text-align: right;
-    padding-right: 2px;
-}
-
-.monaco-editor .review-widget .head .review-actions > .monaco-action-bar {
-    display: inline-block;
-}
-
-.monaco-editor .review-widget .head .review-actions > .monaco-action-bar,
-.monaco-editor .review-widget .head .review-actions > .monaco-action-bar > .actions-container {
-    height: 100%;
-}
-
-.monaco-editor .review-widget .action-item {
-    min-width: 18px;
-    min-height: 20px;
-    margin-left: 4px;
-}
-
-.monaco-editor .review-widget .head .review-actions > .monaco-action-bar .action-label {
-    width: 16px;
-    height: 100%;
-    margin: 0;
-    color: var(--theia-editorWidget-foreground);
-    line-height: inherit;
-    background-repeat: no-repeat;
-    background-position: center center;
-}
-
-.monaco-editor .review-widget>.body {
-    border-top: 1px solid;
-    position: relative;
-}
-
-.monaco-editor .review-widget .body .comment-form {
-    margin: 8px 20px;
-}
-
-.monaco-editor .review-widget .body .review-comment {
-    padding: 8px 16px 8px 20px;
-    display: flex;
-}
-
-.monaco-editor .review-widget .body .review-comment .avatar-container {
-    margin-top: 4px !important;
-}
-
-.monaco-editor .review-widget .body .review-comment .avatar-container img.avatar {
-    height: 28px;
-    width: 28px;
-    display: inline-block;
-    overflow: hidden;
-    line-height: 1;
-    vertical-align: middle;
-    border-radius: 3px;
-    border-style: none;
-}
-
-.monaco-editor .review-widget .body .review-comment .review-comment-contents {
-    padding-left: 20px;
-    user-select: text;
-    -webkit-user-select: text;
-    width: 100%;
-    overflow: hidden;
-}
-
-.monaco-editor .review-widget .body .review-comment .review-comment-contents .author {
-    line-height: 22px;
-}
-
-.monaco-editor .review-widget .body .review-comment .review-comment-contents .isPending {
-    margin: 0 5px 0 5px;
-    padding: 0 2px 0 2px;
-    font-style: italic;
-}
-
-.monaco-editor .review-widget .body .review-comment .review-comment-contents .comment-body {
-    padding-top: 4px;
-}
-
-.monaco-editor .review-widget .body .review-comment .comment-title {
-    display: flex;
-    width: 100%;
-}
-
-.monaco-editor .review-widget .body .comment-form .theia-comments-input-message-container {
-    display: none;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .theia-comments-input-message-container,
-.edit-textarea .theia-comments-input-message-container {
-    display: flex;
-    flex-direction: column;
-    margin: 0px 0px 7px 0px;
-    max-height: 400px;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .theia-comments-input-message-container textarea,
-.edit-textarea .theia-comments-input-message-container textarea {
-    line-height: var(--theia-content-line-height);
-    background: var(--theia-editor-background);
-    resize: none;
-    height: 90px;
-    box-sizing: border-box;
-    min-height: 32px;
-    padding: 4px;
-    border: none;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .theia-comments-input-message-container textarea:placeholder-shown,
-.edit-textarea .theia-comments-input-message-container textarea:placeholder-shown {
-    overflow: hidden;
-    text-overflow: ellipsis;
-    white-space: nowrap;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .theia-comments-input-message-container textarea:not(:focus),
-.edit-textarea .theia-comments-input-message-container textarea:not(:focus) {
-    border: var(--theia-border-width) solid var(--theia-editor-background);
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .theia-comments-input-message-container textarea:focus,
-.edit-textarea .theia-comments-input-message-container textarea:focus {
-    border: var(--theia-border-width) solid var(--theia-focusBorder);
-}
-
-.theia-comments-input-message {
-    width: 100%;
-}
-
-.monaco-editor .review-widget .body .comment-body p,
-.monaco-editor .review-widget .body .comment-body ul {
-    margin: 8px 0;
-}
-
-.monaco-editor .review-widget .body .comment-body p:first-child,
-.monaco-editor .review-widget .body .comment-body ul:first-child {
-    margin-top: 0;
-}
-
-.monaco-editor .review-widget .body .comment-body p:last-child,
-.monaco-editor .review-widget .body.comment-body ul:last-child {
-    margin-bottom: 0;
-}
-
-.monaco-editor .review-widget .body .comment-body ul {
-    padding-left: 20px;
-}
-
-.monaco-editor .review-widget .body .comment-body li > p {
-    margin-bottom: 0;
-}
-
-.monaco-editor .review-widget .body .comment-body li > ul {
-    margin-top: 0;
-}
-
-.monaco-editor .review-widget .body .comment-body code {
-    border-radius: 3px;
-    padding: 0 0.4em;
-}
-
-.monaco-editor .review-widget .body .comment-body span {
-    white-space: pre;
-}
-
-.monaco-editor .review-widget .body .comment-body img {
-    max-width: 100%;
-}
-
-.monaco-editor .review-widget .body .comment-form .form-actions {
-    display: none;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .form-actions {
-    display: block;
-    box-sizing: content-box;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .review-thread-reply-button {
-    display: none;
-}
-
-.monaco-editor .review-widget .body .comment-form .review-thread-reply-button {
-    text-align: left;
-    display: block;
-    width: 100%;
-    resize: vertical;
-    background: var(--theia-editor-background);
-    color: var(--theia-input-foreground);
-    cursor: text;
-    font-size: var(--theia-ui-font-size1);
-    border-radius: 0;
-    box-sizing: border-box;
-    padding: 6px 12px;
-    font-weight: 600;
-    line-height: 20px;
-    white-space: nowrap;
-    border: 0px;
-    outline: 1px solid transparent;
-}
-
-.monaco-editor .review-widget .body .comment-form .review-thread-reply-button:focus {
-    outline-style: solid;
-    outline-width: 1px;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .form-actions,
-.monaco-editor .review-widget .body .edit-container .form-actions {
-    overflow: auto;
-    padding: 10px 0;
-}
-
-.monaco-editor .review-widget .body .edit-container .form-actions {
-    display: flex;
-    justify-content: flex-end;
-}
-
-.monaco-editor .review-widget .body .edit-textarea {
-    margin: 5px 0 10px 0;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .comments-text-button,
-.monaco-editor .review-widget .body .edit-container .comments-text-button {
-    width: auto;
-    padding: 4px 10px;
-    margin-left: 5px;
-    margin-bottom: 5px;
-}
-
-.monaco-editor .review-widget .body .comment-form.expand .comments-text-button {
-    float: right;
-}
-
-.theia-comments-inline-actions-container {
-    display: flex;
-    justify-content: flex-end;
-    margin-left: auto;
-    min-height: 16px;
-}
-
-.theia-comments-inline-actions {
-    display: flex;
-    margin: 0 3px;
-}
-
-.theia-comments-inline-actions a {
-    color: var(--theia-icon-foreground);
-}
-
-.theia-comments-inline-action {
-    padding: 0px 3px;
-    font-size: var(--theia-ui-font-size1);
-    margin: 0 2px;
-    cursor: pointer;
-    display: flex;
-    align-items: center;
-}
diff --git a/packages/plugin-ext/src/main/browser/webview/pre/main.js b/packages/plugin-ext/src/main/browser/webview/pre/main.js
index 58560f55b57bd..0c1bb0894cc9f 100644
--- a/packages/plugin-ext/src/main/browser/webview/pre/main.js
+++ b/packages/plugin-ext/src/main/browser/webview/pre/main.js
@@ -34,13 +34,13 @@
 (function () {
     'use strict';
 
-	/**
-	 * Use polling to track focus of main webview and iframes within the webview
-	 *
-	 * @param {Object} handlers
-	 * @param {() => void} handlers.onFocus
-	 * @param {() => void} handlers.onBlur
-	 */
+    /**
+     * Use polling to track focus of main webview and iframes within the webview
+     *
+     * @param {Object} handlers
+     * @param {() => void} handlers.onFocus
+     * @param {() => void} handlers.onBlur
+     */
     const trackFocus = ({ onFocus, onBlur }) => {
         const interval = 50;
         let isFocused = document.hasFocus();
@@ -140,10 +140,10 @@
 		background-color: var(--vscode-scrollbarSlider-activeBackground);
 	}`;
 
-	/**
-	 * @param {*} [state]
-	 * @return {string}
-	 */
+    /**
+     * @param {*} [state]
+     * @return {string}
+     */
     function getVsCodeApiScript(state) {
         return `
 			const acquireVsCodeApi = (function() {
@@ -180,9 +180,9 @@
 		`;
     }
 
-	/**
-	 * @param {WebviewHost} host
-	 */
+    /**
+     * @param {WebviewHost} host
+     */
     function createWebviewManager(host) {
         // state
         let firstLoad = true;
@@ -194,10 +194,10 @@
         };
 
 
-		/**
-		 * @param {HTMLDocument?} document
-		 * @param {HTMLElement?} body
-		 */
+        /**
+         * @param {HTMLDocument?} document
+         * @param {HTMLElement?} body
+         */
         const applyStyles = (document, body) => {
             if (!document) {
                 return;
@@ -215,9 +215,9 @@
             }
         };
 
-		/**
-		 * @param {MouseEvent} event
-		 */
+        /**
+         * @param {MouseEvent} event
+         */
         const handleInnerClick = (event) => {
             if (!event || !event.view || !event.view.document) {
                 return;
@@ -245,9 +245,9 @@
             }
         };
 
-		/**
-		 * @param {MouseEvent} event
-		 */
+        /**
+         * @param {MouseEvent} event
+         */
         const handleAuxClick =
             (event) => {
                 // Prevent middle clicks opening a broken link in the browser
@@ -267,9 +267,9 @@
                 }
             };
 
-		/**
-		 * @param {KeyboardEvent} e
-		 */
+        /**
+         * @param {KeyboardEvent} e
+         */
         const handleInnerKeydown = (e) => {
             preventDefaultBrowserHotkeys(e);
 
@@ -318,10 +318,10 @@
         };
 
         function preventDefaultBrowserHotkeys(e) {
-            var isOSX = navigator.platform.toUpperCase().indexOf('MAC')>=0;
+            var isOSX = navigator.platform.toUpperCase().indexOf('MAC') >= 0;
 
-            // F1 or CtrlCmd+P
-            if (e.keyCode === 112 || (((e.ctrlKey && !isOSX) || (e.metaKey && isOSX)) && e.keyCode === 80)) {
+            // F1 or CtrlCmd+P or CtrlCmd+S
+            if (e.keyCode === 112 || (((e.ctrlKey && !isOSX) || (e.metaKey && isOSX)) && (e.keyCode === 80 || e.keyCode === 83))) {
                 e.preventDefault();
             }
         }
@@ -351,9 +351,9 @@
             });
         };
 
-		/**
-		 * @return {string}
-		 */
+        /**
+         * @return {string}
+         */
         function toContentHtml(data) {
             const options = data.options;
             const text = data.contents;
@@ -539,9 +539,9 @@
                     }
                 };
 
-				/**
-				 * @param {HTMLIFrameElement} newFrame
-				 */
+                /**
+                 * @param {HTMLIFrameElement} newFrame
+                 */
                 function hookupOnLoadHandlers(newFrame) {
                     const timeoutDelay = 5000;
                     clearTimeout(loadTimeout);
diff --git a/packages/plugin-ext/src/main/browser/webviews-main.ts b/packages/plugin-ext/src/main/browser/webviews-main.ts
index 9c2524d10b16d..d68480a85708b 100644
--- a/packages/plugin-ext/src/main/browser/webviews-main.ts
+++ b/packages/plugin-ext/src/main/browser/webviews-main.ts
@@ -29,6 +29,7 @@ import { JSONExt } from '@phosphor/coreutils/lib/json';
 import { Mutable } from '@theia/core/lib/common/types';
 import { HostedPluginSupport } from '../../hosted/browser/hosted-plugin';
 import { IconUrl } from '../../common/plugin-protocol';
+import { CustomEditorWidget } from './custom-editors/custom-editor-widget';
 
 export class WebviewsMainImpl implements WebviewsMain, Disposable {
 
@@ -75,7 +76,7 @@ export class WebviewsMainImpl implements WebviewsMain, Disposable {
         this.addOrReattachWidget(view, showOptions);
     }
 
-    protected hookWebview(view: WebviewWidget): void {
+    hookWebview(view: WebviewWidget): void {
         const handle = view.identifier.id;
         this.toDispose.push(view.onDidChangeVisibility(() => this.updateViewState(view)));
         this.toDispose.push(view.onMessage(data => this.proxy.$onMessage(handle, data)));
@@ -87,7 +88,7 @@ export class WebviewsMainImpl implements WebviewsMain, Disposable {
         });
     }
 
-    private addOrReattachWidget(widget: WebviewWidget, showOptions: WebviewPanelShowOptions): void {
+    addOrReattachWidget(widget: WebviewWidget, showOptions: WebviewPanelShowOptions): void {
         const widgetOptions: ApplicationShell.WidgetOptions = { area: showOptions.area ? showOptions.area : 'main' };
 
         let mode = 'open-to-right';
@@ -217,7 +218,10 @@ export class WebviewsMainImpl implements WebviewsMain, Disposable {
     }
 
     protected readonly updateViewStates = debounce(() => {
-        for (const widget of this.widgetManager.getWidgets(WebviewWidget.FACTORY_ID)) {
+        const widgets = this.widgetManager.getWidgets(WebviewWidget.FACTORY_ID);
+        const customEditors = this.widgetManager.getWidgets(CustomEditorWidget.FACTORY_ID);
+
+        for (const widget of widgets.concat(customEditors)) {
             if (widget instanceof WebviewWidget) {
                 this.updateViewState(widget);
             }
@@ -251,7 +255,9 @@ export class WebviewsMainImpl implements WebviewsMain, Disposable {
     }
 
     private async tryGetWebview(id: string): Promise<WebviewWidget | undefined> {
-        return this.widgetManager.getWidget<WebviewWidget>(WebviewWidget.FACTORY_ID, <WebviewWidgetIdentifier>{ id });
+        const webview = await this.widgetManager.getWidget<WebviewWidget>(WebviewWidget.FACTORY_ID, <WebviewWidgetIdentifier>{ id })
+            || await this.widgetManager.getWidget<CustomEditorWidget>(CustomEditorWidget.FACTORY_ID, <WebviewWidgetIdentifier>{ id });
+        return webview;
     }
 
 }
diff --git a/packages/plugin-ext/src/main/electron-browser/plugin-ext-frontend-electron-module.ts b/packages/plugin-ext/src/main/electron-browser/plugin-ext-frontend-electron-module.ts
index 063d29909eb11..2a89707ebe024 100644
--- a/packages/plugin-ext/src/main/electron-browser/plugin-ext-frontend-electron-module.ts
+++ b/packages/plugin-ext/src/main/electron-browser/plugin-ext-frontend-electron-module.ts
@@ -16,8 +16,10 @@
 
 import { ContainerModule } from 'inversify';
 import { WebviewWidgetFactory } from '../browser/webview/webview-widget-factory';
-import { ElectronWebviewWidgetFactory } from './webview/electron-webview-widget-factory';
+import { CustomEditorWidgetFactory } from '../browser/custom-editors/custom-editor-widget-factory';
+import { ElectronCustomEditorWidgetFactory, ElectronWebviewWidgetFactory } from './webview/electron-webview-widget-factory';
 
 export default new ContainerModule((bind, unbind, isBound, rebind) => {
     rebind(WebviewWidgetFactory).toDynamicValue(ctx => new ElectronWebviewWidgetFactory(ctx.container)).inSingletonScope();
+    rebind(CustomEditorWidgetFactory).toDynamicValue(ctx => new ElectronCustomEditorWidgetFactory(ctx.container)).inSingletonScope();
 });
diff --git a/packages/plugin-ext/src/main/electron-browser/webview/electron-webview-widget-factory.ts b/packages/plugin-ext/src/main/electron-browser/webview/electron-webview-widget-factory.ts
index 9ba5a26fde40b..7230af0eff04a 100644
--- a/packages/plugin-ext/src/main/electron-browser/webview/electron-webview-widget-factory.ts
+++ b/packages/plugin-ext/src/main/electron-browser/webview/electron-webview-widget-factory.ts
@@ -18,6 +18,8 @@ import { remote } from 'electron';
 import { ElectronSecurityToken } from '@theia/core/lib/electron-common/electron-token';
 import { WebviewWidgetFactory } from '../../browser/webview/webview-widget-factory';
 import { WebviewWidgetIdentifier, WebviewWidget } from '../../browser/webview/webview';
+import { CustomEditorWidgetFactory } from '../../browser/custom-editors/custom-editor-widget-factory';
+import { CustomEditorWidget } from '../../browser/custom-editors/custom-editor-widget';
 
 export class ElectronWebviewWidgetFactory extends WebviewWidgetFactory {
 
@@ -42,3 +44,27 @@ export class ElectronWebviewWidgetFactory extends WebviewWidgetFactory {
     }
 
 }
+
+export class ElectronCustomEditorWidgetFactory extends CustomEditorWidgetFactory {
+
+    async createWidget(identifier: WebviewWidgetIdentifier): Promise<CustomEditorWidget> {
+        const widget = await super.createWidget(identifier);
+        await this.attachElectronSecurityCookie(widget.externalEndpoint);
+        return widget;
+    }
+
+    /**
+     * Attach the ElectronSecurityToken to a cookie that will be sent with each webview request.
+     *
+     * @param endpoint cookie's target url
+     */
+    protected async attachElectronSecurityCookie(endpoint: string): Promise<void> {
+        await remote.session.defaultSession!.cookies.set({
+            url: endpoint,
+            name: ElectronSecurityToken,
+            value: JSON.stringify(this.container.get(ElectronSecurityToken)),
+            httpOnly: true
+        });
+    }
+
+}
diff --git a/packages/plugin-ext/src/plugin/comments.ts b/packages/plugin-ext/src/plugin/comments.ts
deleted file mode 100644
index db0517aed0d06..0000000000000
--- a/packages/plugin-ext/src/plugin/comments.ts
+++ /dev/null
@@ -1,502 +0,0 @@
-/********************************************************************************
- * Copyright (C) 2020 Red Hat, Inc. and others.
- *
- * This program and the accompanying materials are made available under the
- * terms of the Eclipse Public License v. 2.0 which is available at
- * http://www.eclipse.org/legal/epl-2.0.
- *
- * This Source Code may also be made available under the following Secondary
- * Licenses when the conditions for such availability set forth in the Eclipse
- * Public License v. 2.0 are satisfied: GNU General Public License, version 2
- * with the GNU Classpath Exception which is available at
- * https://www.gnu.org/software/classpath/license.html.
- *
- * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
- ********************************************************************************/
-
-import * as theia from '@theia/plugin';
-import { RPCProtocol } from '../common/rpc-protocol';
-import { CommandRegistryImpl } from './command-registry';
-import { UriComponents } from '../common/uri-components';
-import { URI } from 'vscode-uri';
-import {
-    Range,
-    Comment,
-    CommentThreadCollapsibleState as CommentThreadCollapsibleStateModel,
-    CommentOptions
-} from '../common/plugin-api-rpc-model';
-import { DocumentsExtImpl } from './documents';
-import { Emitter } from '@theia/core/lib/common/event';
-import { Disposable, DisposableCollection } from '@theia/core/lib/common/disposable';
-import { fromMarkdown, fromRange, toRange } from './type-converters';
-import { CommentThreadCollapsibleState } from './types-impl';
-import {
-    CommentsCommandArg, CommentsContextCommandArg, CommentsEditCommandArg,
-    CommentsExt,
-    CommentsMain,
-    CommentThreadChanges,
-    Plugin as InternalPlugin,
-    PLUGIN_RPC_CONTEXT
-} from '../common/plugin-api-rpc';
-
-/*---------------------------------------------------------------------------------------------
- *  Copyright (c) Microsoft Corporation. All rights reserved.
- *  Licensed under the MIT License. See License.txt in the project root for license information.
- *--------------------------------------------------------------------------------------------*/
-// some code copied and modified from https://github.com/microsoft/vscode/blob/1.49.3/src/vs/workbench/api/common/extHostComments.ts
-
-type ProviderHandle = number;
-
-export class CommentsExtImpl implements CommentsExt {
-    private handle = 0;
-    private readonly proxy: CommentsMain;
-    private readonly commentControllers: Map<ProviderHandle, CommentController> = new Map<ProviderHandle, CommentController>();
-    private readonly commentControllersByExtension: Map<string, CommentController[]> = new Map<string, CommentController[]>();
-
-    constructor(readonly rpc: RPCProtocol, readonly commands: CommandRegistryImpl, readonly _documents: DocumentsExtImpl) {
-        this.proxy = rpc.getProxy(PLUGIN_RPC_CONTEXT.COMMENTS_MAIN);
-
-        commands.registerArgumentProcessor({
-            processArgument: arg => {
-                if (CommentsCommandArg.is(arg)) {
-                    const commentController = this.commentControllers.get(arg.commentControlHandle);
-
-                    if (!commentController) {
-                        return arg;
-                    }
-
-                    const commentThread = commentController.getCommentThread(arg.commentThreadHandle);
-
-                    if (!commentThread) {
-                        return arg;
-                    }
-
-                    return {
-                        thread: commentThread,
-                        text: arg.text
-                    };
-                } else if (CommentsContextCommandArg.is(arg)) {
-                    const commentController = this.commentControllers.get(arg.commentControlHandle);
-
-                    if (!commentController) {
-                        return arg;
-                    }
-
-                    const commentThread = commentController.getCommentThread(arg.commentThreadHandle);
-
-                    if (!commentThread) {
-                        return arg;
-                    }
-
-                    const comment = commentThread.getCommentByUniqueId(arg.commentUniqueId);
-
-                    if (!comment) {
-                        return arg;
-                    }
-
-                    return comment;
-                } else if (CommentsEditCommandArg.is(arg)) {
-                    const commentController = this.commentControllers.get(arg.commentControlHandle);
-
-                    if (!commentController) {
-                        return arg;
-                    }
-
-                    const commentThread = commentController.getCommentThread(arg.commentThreadHandle);
-
-                    if (!commentThread) {
-                        return arg;
-                    }
-
-                    const comment = commentThread.getCommentByUniqueId(arg.commentUniqueId);
-
-                    if (!comment) {
-                        return arg;
-                    }
-
-                    comment.body = arg.text;
-                    return comment;
-                }
-
-                return arg;
-            }
-        });
-    }
-
-    createCommentController(plugin: InternalPlugin, id: string, label: string): theia.CommentController {
-        const handle = this.handle++;
-        const commentController = new CommentController(plugin.model.id, this.proxy, handle, id, label);
-        this.commentControllers.set(commentController.handle, commentController);
-
-        const commentControllers = this.commentControllersByExtension.get(plugin.model.id.toLowerCase()) || [];
-        commentControllers.push(commentController);
-        this.commentControllersByExtension.set(plugin.model.id.toLowerCase(), commentControllers);
-
-        return commentController;
-    }
-
-    $createCommentThreadTemplate(commentControllerHandle: number, uriComponents: UriComponents, range: Range): void {
-        const commentController = this.commentControllers.get(commentControllerHandle);
-
-        if (!commentController) {
-            return;
-        }
-
-        commentController.$createCommentThreadTemplate(uriComponents, range);
-    }
-
-    async $updateCommentThreadTemplate(commentControllerHandle: number, threadHandle: number, range: Range): Promise<void> {
-        const commentController = this.commentControllers.get(commentControllerHandle);
-
-        if (!commentController) {
-            return;
-        }
-
-        commentController.$updateCommentThreadTemplate(threadHandle, range);
-    }
-
-    async $deleteCommentThread(commentControllerHandle: number, commentThreadHandle: number): Promise<void> {
-        const commentController = this.commentControllers.get(commentControllerHandle);
-
-        if (commentController) {
-            commentController.$deleteCommentThread(commentThreadHandle);
-        }
-    }
-
-    async $provideCommentingRanges(commentControllerHandle: number, uriComponents: UriComponents, token: theia.CancellationToken): Promise<Range[] | undefined> {
-        const commentController = this.commentControllers.get(commentControllerHandle);
-
-        if (!commentController || !commentController.commentingRangeProvider) {
-            return Promise.resolve(undefined);
-        }
-
-        const documentData = this._documents.getDocumentData(URI.revive(uriComponents));
-        if (documentData) {
-            const ranges: theia.Range[] | undefined = await commentController.commentingRangeProvider!.provideCommentingRanges(documentData.document, token);
-            if (ranges) {
-                return ranges.map(x => fromRange(x));
-            }
-        }
-    }
-}
-
-type CommentThreadModification = Partial<{
-    range: theia.Range,
-    label: string | undefined,
-    contextValue: string | undefined,
-    comments: theia.Comment[],
-    collapsibleState: theia.CommentThreadCollapsibleState
-}>;
-
-export class ExtHostCommentThread implements theia.CommentThread, theia.Disposable {
-    private static _handlePool: number = 0;
-    readonly handle = ExtHostCommentThread._handlePool++;
-    public commentHandle: number = 0;
-
-    private modifications: CommentThreadModification = Object.create(null);
-
-    set threadId(id: string) {
-        this._id = id;
-    }
-
-    get threadId(): string {
-        return this._id!;
-    }
-
-    get id(): string {
-        return this._id!;
-    }
-
-    get resource(): theia.Uri {
-        return this._uri;
-    }
-
-    get uri(): theia.Uri {
-        return this._uri;
-    }
-
-    private readonly _onDidUpdateCommentThread = new Emitter<void>();
-    readonly onDidUpdateCommentThread = this._onDidUpdateCommentThread.event;
-
-    set range(range: theia.Range) {
-        if (!range.isEqual(this._range)) {
-            this._range = range;
-            this.modifications.range = range;
-            this._onDidUpdateCommentThread.fire();
-        }
-    }
-
-    get range(): theia.Range {
-        return this._range;
-    }
-
-    private _label: string | undefined;
-
-    get label(): string | undefined {
-        return this._label;
-    }
-
-    set label(label: string | undefined) {
-        this._label = label;
-        this.modifications.label = label;
-        this._onDidUpdateCommentThread.fire();
-    }
-
-    private _contextValue: string | undefined;
-
-    get contextValue(): string | undefined {
-        return this._contextValue;
-    }
-
-    set contextValue(context: string | undefined) {
-        this._contextValue = context;
-        this.modifications.contextValue = context;
-        this._onDidUpdateCommentThread.fire();
-    }
-
-    get comments(): theia.Comment[] {
-        return this._comments;
-    }
-
-    set comments(newComments: theia.Comment[]) {
-        this._comments = newComments;
-        this.modifications.comments = newComments;
-        this._onDidUpdateCommentThread.fire();
-    }
-
-    private collapseState?: theia.CommentThreadCollapsibleState;
-
-    get collapsibleState(): theia.CommentThreadCollapsibleState {
-        return this.collapseState!;
-    }
-
-    set collapsibleState(newState: theia.CommentThreadCollapsibleState) {
-        this.collapseState = newState;
-        this.modifications.collapsibleState = newState;
-        this._onDidUpdateCommentThread.fire();
-    }
-
-    private localDisposables: Disposable[];
-
-    private _isDisposed: boolean;
-
-    public get isDisposed(): boolean {
-        return this._isDisposed;
-    }
-
-    private commentsMap: Map<theia.Comment, number> = new Map<theia.Comment, number>();
-
-    private acceptInputDisposables = new DisposableCollection();
-
-    constructor(
-        private proxy: CommentsMain,
-        private commentController: CommentController,
-        private _id: string | undefined,
-        private _uri: theia.Uri,
-        private _range: theia.Range,
-        private _comments: theia.Comment[],
-        extensionId: string
-    ) {
-        if (this._id === undefined) {
-            this._id = `${commentController.id}.${this.handle}`;
-        }
-
-        this.proxy.$createCommentThread(
-            this.commentController.handle,
-            this.handle,
-            this._id,
-            this._uri,
-            fromRange(this._range),
-            extensionId
-        );
-
-        this.localDisposables = [];
-        this._isDisposed = false;
-
-        this.localDisposables.push(this.onDidUpdateCommentThread(() => {
-            this.eventuallyUpdateCommentThread();
-        }));
-
-        // set up comments after ctor to batch update events.
-        this.comments = _comments;
-    }
-
-    eventuallyUpdateCommentThread(): void {
-        if (this._isDisposed) {
-            return;
-        }
-
-        const modified = (value: keyof CommentThreadModification): boolean =>
-            Object.prototype.hasOwnProperty.call(this.modifications, value);
-
-        const formattedModifications: CommentThreadChanges = {};
-        if (modified('range')) {
-            formattedModifications.range = fromRange(this._range);
-        }
-        if (modified('label')) {
-            formattedModifications.label = this.label;
-        }
-        if (modified('contextValue')) {
-            formattedModifications.contextValue = this.contextValue;
-        }
-        if (modified('comments')) {
-            formattedModifications.comments =
-                this._comments.map(cmt => convertToModeComment(this, this.commentController, cmt, this.commentsMap));
-        }
-        if (modified('collapsibleState')) {
-            formattedModifications.collapseState = convertToCollapsibleState(this.collapseState);
-        }
-        this.modifications = {};
-
-        this.proxy.$updateCommentThread(
-            this.commentController.handle,
-            this.handle,
-            this._id!,
-            this._uri,
-            formattedModifications
-        );
-    }
-
-    getCommentByUniqueId(uniqueId: number): theia.Comment | undefined {
-        for (const key of this.commentsMap) {
-            const comment = key[0];
-            const id = key[1];
-            if (uniqueId === id) {
-                return comment;
-            }
-        }
-
-        return;
-    }
-
-    dispose(): void {
-        this._isDisposed = true;
-        this.acceptInputDisposables.dispose();
-        this.localDisposables.forEach(disposable => disposable.dispose());
-        this.proxy.$deleteCommentThread(
-            this.commentController.handle,
-            this.handle
-        );
-    }
-}
-
-class CommentController implements theia.CommentController {
-
-    constructor(
-        private extension: string,
-        private proxy: CommentsMain,
-        private _handle: number,
-        private _id: string,
-        private _label: string
-    ) {
-        this.proxy.$registerCommentController(this.handle, _id, _label);
-    }
-
-    private readonly threads: Map<number, ExtHostCommentThread> = new Map<number, ExtHostCommentThread>();
-    readonly commentingRangeProvider?: theia.CommentingRangeProvider;
-
-    get id(): string {
-        return this._id;
-    }
-
-    get label(): string {
-        return this._label;
-    }
-
-    get handle(): number {
-        return this._handle;
-    }
-
-    private _options: CommentOptions | undefined;
-
-    get options(): CommentOptions | undefined {
-        return this._options;
-    }
-
-    set options(options: CommentOptions | undefined) {
-        this._options = options;
-
-        this.proxy.$updateCommentControllerFeatures(this.handle, { options: this._options });
-    }
-
-    createCommentThread(resource: theia.Uri, range: theia.Range, comments: theia.Comment[]): theia.CommentThread;
-    createCommentThread(arg0: theia.Uri | string, arg1: theia.Uri | theia.Range, arg2: theia.Range | theia.Comment[], arg3?: theia.Comment[]): theia.CommentThread {
-        if (typeof arg0 === 'string') {
-            const commentThread = new ExtHostCommentThread(this.proxy, this, arg0, arg1 as theia.Uri, arg2 as theia.Range, arg3 as theia.Comment[], this.extension);
-            this.threads.set(commentThread.handle, commentThread);
-            return commentThread;
-        } else {
-            const commentThread = new ExtHostCommentThread(this.proxy, this, undefined, arg0 as theia.Uri, arg1 as theia.Range, arg2 as theia.Comment[], this.extension);
-            this.threads.set(commentThread.handle, commentThread);
-            return commentThread;
-        }
-    }
-
-    $createCommentThreadTemplate(uriComponents: UriComponents, range: Range): ExtHostCommentThread {
-        const commentThread = new ExtHostCommentThread(this.proxy, this, undefined, URI.revive(uriComponents), toRange(range), [], this.extension);
-        commentThread.collapsibleState = CommentThreadCollapsibleStateModel.Expanded;
-        this.threads.set(commentThread.handle, commentThread);
-        return commentThread;
-    }
-
-    $updateCommentThreadTemplate(threadHandle: number, range: Range): void {
-        const thread = this.threads.get(threadHandle);
-        if (thread) {
-            thread.range = toRange(range);
-        }
-    }
-
-    $deleteCommentThread(threadHandle: number): void {
-        const thread = this.threads.get(threadHandle);
-
-        if (thread) {
-            thread.dispose();
-        }
-
-        this.threads.delete(threadHandle);
-    }
-
-    getCommentThread(handle: number): ExtHostCommentThread | undefined {
-        return this.threads.get(handle);
-    }
-
-    dispose(): void {
-        this.threads.forEach(value => {
-            value.dispose();
-        });
-
-        this.proxy.$unregisterCommentController(this.handle);
-    }
-}
-
-function convertToModeComment(thread: ExtHostCommentThread, commentController: CommentController, theiaComment: theia.Comment, commentsMap: Map<theia.Comment, number>): Comment {
-    let commentUniqueId = commentsMap.get(theiaComment)!;
-    if (!commentUniqueId) {
-        commentUniqueId = ++thread.commentHandle;
-        commentsMap.set(theiaComment, commentUniqueId);
-    }
-
-    const iconPath = theiaComment.author && theiaComment.author.iconPath ? theiaComment.author.iconPath.toString() : undefined;
-
-    return {
-        mode: theiaComment.mode,
-        contextValue: theiaComment.contextValue,
-        uniqueIdInThread: commentUniqueId,
-        body: fromMarkdown(theiaComment.body),
-        userName: theiaComment.author.name,
-        userIconPath: iconPath,
-        label: theiaComment.label,
-    };
-}
-
-function convertToCollapsibleState(kind: theia.CommentThreadCollapsibleState | undefined): CommentThreadCollapsibleStateModel {
-    if (kind !== undefined) {
-        switch (kind) {
-            case CommentThreadCollapsibleState.Expanded:
-                return CommentThreadCollapsibleStateModel.Expanded;
-            case CommentThreadCollapsibleState.Collapsed:
-                return CommentThreadCollapsibleStateModel.Collapsed;
-        }
-    }
-    return CommentThreadCollapsibleStateModel.Collapsed;
-}
diff --git a/packages/plugin-ext/src/plugin/custom-editors.ts b/packages/plugin-ext/src/plugin/custom-editors.ts
new file mode 100644
index 0000000000000..f5636168b3ab8
--- /dev/null
+++ b/packages/plugin-ext/src/plugin/custom-editors.ts
@@ -0,0 +1,376 @@
+/********************************************************************************
+ * Copyright (c) 2020 SAP SE or an SAP affiliate company and others.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * This Source Code may also be made available under the following Secondary
+ * Licenses when the conditions for such availability set forth in the Eclipse
+ * Public License v. 2.0 are satisfied: GNU General Public License, version 2
+ * with the GNU Classpath Exception which is available at
+ * https://www.gnu.org/software/classpath/license.html.
+ *
+ * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+ ********************************************************************************/
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+// copied and modified from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/workbench/api/common/extHostCustomEditors.ts
+
+import { CustomEditorsExt, CustomEditorsMain, PLUGIN_RPC_CONTEXT } from '../common/plugin-api-rpc';
+import * as theia from '@theia/plugin';
+import { RPCProtocol } from '../common/rpc-protocol';
+import { Plugin } from '../common/plugin-api-rpc';
+import { URI } from 'vscode-uri';
+import { UriComponents } from '../common/uri-components';
+import { DocumentsExtImpl } from './documents';
+import { WebviewImpl, WebviewsExtImpl } from './webviews';
+import { CancellationToken, CancellationTokenSource } from '@theia/core/lib/common/cancellation';
+import { DisposableCollection } from '@theia/core/lib/common/disposable';
+import { Disposable } from './types-impl';
+import { WorkspaceExtImpl } from './workspace';
+
+export class CustomEditorsExtImpl implements CustomEditorsExt {
+    private readonly proxy: CustomEditorsMain;
+    private readonly editorProviders = new EditorProviderStore();
+    private readonly documents = new CustomDocumentStore();
+
+    constructor(
+        rpc: RPCProtocol,
+        private readonly documentExt: DocumentsExtImpl,
+        private readonly webviewExt: WebviewsExtImpl,
+        private readonly workspace: WorkspaceExtImpl
+    ) {
+        this.proxy = rpc.getProxy(PLUGIN_RPC_CONTEXT.CUSTOM_EDITORS_MAIN);
+    }
+
+    registerCustomEditorProvider(
+        viewType: string,
+        provider: theia.CustomReadonlyEditorProvider | theia.CustomTextEditorProvider,
+        options: { webviewOptions?: theia.WebviewPanelOptions, supportsMultipleEditorsPerDocument?: boolean },
+        plugin: Plugin
+    ): theia.Disposable {
+        const disposables = new DisposableCollection();
+        if ('resolveCustomTextEditor' in provider) {
+            disposables.push(this.editorProviders.addTextProvider(viewType, plugin, provider));
+            this.proxy.$registerTextEditorProvider(viewType, options.webviewOptions || {}, {
+                supportsMove: !!provider.moveCustomTextEditor,
+            });
+        } else {
+            disposables.push(this.editorProviders.addCustomProvider(viewType, plugin, provider));
+
+            if (this.supportEditing(provider)) {
+                disposables.push(provider.onDidChangeCustomDocument(e => {
+                    const entry = this.getCustomDocumentEntry(viewType, e.document.uri);
+                    if (isEditEvent(e)) {
+                        const editId = entry.addEdit(e);
+                        this.proxy.$onDidEdit(e.document.uri, viewType, editId, e.label);
+                    } else {
+                        this.proxy.$onContentChange(e.document.uri, viewType);
+                    }
+                }));
+            }
+
+            this.proxy.$registerCustomEditorProvider(viewType, options.webviewOptions || {}, !!options.supportsMultipleEditorsPerDocument);
+        }
+
+        return Disposable.from(
+            disposables,
+            Disposable.create(() => {
+                this.proxy.$unregisterEditorProvider(viewType);
+            })
+        );
+    }
+
+    async $createCustomDocument(resource: UriComponents, viewType: string, backupId: string | undefined, cancellation: CancellationToken): Promise<{
+        editable: boolean;
+    }> {
+        const entry = this.editorProviders.get(viewType);
+        if (!entry) {
+            throw new Error(`No provider found for '${viewType}'`);
+        }
+
+        if (entry.type !== CustomEditorType.Custom) {
+            throw new Error(`Invalid provide type for '${viewType}'`);
+        }
+
+        const revivedResource = URI.revive(resource);
+        const document = await entry.provider.openCustomDocument(revivedResource, { backupId }, cancellation);
+        this.documents.add(viewType, document);
+
+        return { editable: this.supportEditing(entry.provider) };
+    }
+
+    async $disposeCustomDocument(resource: UriComponents, viewType: string): Promise<void> {
+        const entry = this.editorProviders.get(viewType);
+        if (!entry) {
+            throw new Error(`No provider found for '${viewType}'`);
+        }
+
+        if (entry.type !== CustomEditorType.Custom) {
+            throw new Error(`Invalid provider type for '${viewType}'`);
+        }
+
+        const revivedResource = URI.revive(resource);
+        const { document } = this.getCustomDocumentEntry(viewType, revivedResource);
+        this.documents.delete(viewType, document);
+        document.dispose();
+    }
+
+    async $resolveCustomEditorWebview(
+        handler: string,
+        viewType: string,
+        resource: URI,
+        title: string,
+        options: theia.WebviewPanelOptions & theia.WebviewOptions,
+        cancellation: CancellationToken
+    ): Promise<void> {
+        const entry = this.editorProviders.get(viewType);
+        if (!entry) {
+            throw new Error(`No provider found for '${viewType}'`);
+        }
+        const panel = this.webviewExt.createWebviewPanel(viewType, title, {}, options, entry.plugin, handler);
+        const webviewOptions = WebviewImpl.toWebviewOptions(options, this.workspace, entry.plugin);
+        await this.proxy.$createCustomEditorPanel(handler, title, webviewOptions);
+
+        const revivedResource = URI.revive(resource);
+
+        switch (entry.type) {
+            case CustomEditorType.Custom: {
+                const { document } = this.getCustomDocumentEntry(viewType, revivedResource);
+                return entry.provider.resolveCustomEditor(document, panel, cancellation);
+            }
+            case CustomEditorType.Text: {
+                const document = this.documentExt.getDocument(revivedResource);
+                return entry.provider.resolveCustomTextEditor(document, panel, cancellation);
+            }
+            default: {
+                throw new Error('Unknown webview provider type');
+            }
+        }
+    }
+
+    getCustomDocumentEntry(viewType: string, resource: UriComponents): CustomDocumentStoreEntry {
+        const entry = this.documents.get(viewType, URI.revive(resource));
+        if (!entry) {
+            throw new Error('No custom document found');
+        }
+        return entry;
+    }
+
+    $disposeEdits(resourceComponents: UriComponents, viewType: string, editIds: number[]): void {
+        const document = this.getCustomDocumentEntry(viewType, resourceComponents);
+        document.disposeEdits(editIds);
+    }
+
+    async $onMoveCustomEditor(handle: string, newResourceComponents: UriComponents, viewType: string): Promise<void> {
+        const entry = this.editorProviders.get(viewType);
+        if (!entry) {
+            throw new Error(`No provider found for '${viewType}'`);
+        }
+
+        if (!(entry.provider as theia.CustomTextEditorProvider).moveCustomTextEditor) {
+            throw new Error(`Provider does not implement move '${viewType}'`);
+        }
+
+        const webview = this.webviewExt.getWebviewPanel(handle);
+        if (!webview) {
+            throw new Error('No webview found');
+        }
+
+        const resource = URI.revive(newResourceComponents);
+        const document = this.documentExt.getDocument(resource);
+        const cancellationSource = new CancellationTokenSource();
+        await (entry.provider as theia.CustomTextEditorProvider).moveCustomTextEditor!(document, webview, cancellationSource.token);
+    }
+
+    async $undo(resourceComponents: UriComponents, viewType: string, editId: number, isDirty: boolean): Promise<void> {
+        const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
+        return entry.undo(editId, isDirty);
+    }
+
+    async $redo(resourceComponents: UriComponents, viewType: string, editId: number, isDirty: boolean): Promise<void> {
+        const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
+        return entry.redo(editId, isDirty);
+    }
+
+    async $revert(resourceComponents: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void> {
+        const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
+        const provider = this.getCustomEditorProvider(viewType);
+        await provider.revertCustomDocument(entry.document, cancellation);
+    }
+
+    async $onSave(resourceComponents: UriComponents, viewType: string, cancellation: CancellationToken): Promise<void> {
+        const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
+        const provider = this.getCustomEditorProvider(viewType);
+        await provider.saveCustomDocument(entry.document, cancellation);
+    }
+
+    async $onSaveAs(resourceComponents: UriComponents, viewType: string, targetResource: UriComponents, cancellation: CancellationToken): Promise<void> {
+        const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
+        const provider = this.getCustomEditorProvider(viewType);
+        return provider.saveCustomDocumentAs(entry.document, URI.revive(targetResource), cancellation);
+    }
+
+    private getCustomEditorProvider(viewType: string): theia.CustomEditorProvider {
+        const entry = this.editorProviders.get(viewType);
+        const provider = entry?.provider;
+        if (!provider || !this.supportEditing(provider)) {
+            throw new Error('Custom document is not editable');
+        }
+        return provider;
+    }
+
+    private supportEditing(
+        provider: theia.CustomTextEditorProvider | theia.CustomEditorProvider | theia.CustomReadonlyEditorProvider
+    ): provider is theia.CustomEditorProvider {
+        return !!(provider as theia.CustomEditorProvider).onDidChangeCustomDocument;
+    }
+
+}
+
+function isEditEvent(e: theia.CustomDocumentContentChangeEvent | theia.CustomDocumentEditEvent): e is theia.CustomDocumentEditEvent {
+    return typeof (e as theia.CustomDocumentEditEvent).undo === 'function'
+        && typeof (e as theia.CustomDocumentEditEvent).redo === 'function';
+}
+
+class CustomDocumentStoreEntry {
+
+    constructor(
+        readonly document: theia.CustomDocument,
+    ) { }
+
+    private readonly edits = new Cache<theia.CustomDocumentEditEvent>('custom documents');
+
+    addEdit(item: theia.CustomDocumentEditEvent): number {
+        return this.edits.add([item]);
+    }
+
+    async undo(editId: number, isDirty: boolean): Promise<void> {
+        await this.getEdit(editId).undo();
+    }
+
+    async redo(editId: number, isDirty: boolean): Promise<void> {
+        await this.getEdit(editId).redo();
+    }
+
+    disposeEdits(editIds: number[]): void {
+        for (const id of editIds) {
+            this.edits.delete(id);
+        }
+    }
+
+    private getEdit(editId: number): theia.CustomDocumentEditEvent {
+        const edit = this.edits.get(editId, 0);
+        if (!edit) {
+            throw new Error('No edit found');
+        }
+        return edit;
+    }
+}
+
+const enum CustomEditorType {
+    Text,
+    Custom
+}
+
+type ProviderEntry = {
+    readonly plugin: Plugin;
+    readonly type: CustomEditorType.Text;
+    readonly provider: theia.CustomTextEditorProvider;
+} | {
+    readonly plugin: Plugin;
+    readonly type: CustomEditorType.Custom;
+    readonly provider: theia.CustomReadonlyEditorProvider;
+};
+
+class EditorProviderStore {
+    private readonly providers = new Map<string, ProviderEntry>();
+
+    addTextProvider(viewType: string, plugin: Plugin, provider: theia.CustomTextEditorProvider): theia.Disposable {
+        return this.add(CustomEditorType.Text, viewType, plugin, provider);
+    }
+
+    addCustomProvider(viewType: string, plugin: Plugin, provider: theia.CustomReadonlyEditorProvider): theia.Disposable {
+        return this.add(CustomEditorType.Custom, viewType, plugin, provider);
+    }
+
+    get(viewType: string): ProviderEntry | undefined {
+        return this.providers.get(viewType);
+    }
+
+    private add(type: CustomEditorType, viewType: string,
+        plugin: Plugin, provider: theia.CustomTextEditorProvider | theia.CustomReadonlyEditorProvider): theia.Disposable {
+        if (this.providers.has(viewType)) {
+            throw new Error(`Provider for viewType:${viewType} already registered`);
+        }
+        this.providers.set(viewType, { type, plugin: plugin, provider } as ProviderEntry);
+        return new Disposable(() => this.providers.delete(viewType));
+    }
+}
+
+class CustomDocumentStore {
+    private readonly documents = new Map<string, CustomDocumentStoreEntry>();
+
+    get(viewType: string, resource: theia.Uri): CustomDocumentStoreEntry | undefined {
+        return this.documents.get(this.key(viewType, resource));
+    }
+
+    add(viewType: string, document: theia.CustomDocument): CustomDocumentStoreEntry {
+        const key = this.key(viewType, document.uri);
+        if (this.documents.has(key)) {
+            throw new Error(`Document already exists for viewType:${viewType} resource:${document.uri}`);
+        }
+        const entry = new CustomDocumentStoreEntry(document);
+        this.documents.set(key, entry);
+        return entry;
+    }
+
+    delete(viewType: string, document: theia.CustomDocument): void {
+        const key = this.key(viewType, document.uri);
+        this.documents.delete(key);
+    }
+
+    private key(viewType: string, resource: theia.Uri): string {
+        return `${viewType}@@@${resource}`;
+    }
+
+}
+
+// copied from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/workbench/api/common/cache.ts
+class Cache<T> {
+
+    private static readonly enableDebugLogging = false;
+
+    private readonly _data = new Map<number, readonly T[]>();
+    private _idPool = 1;
+
+    constructor(
+        private readonly id: string
+    ) { }
+
+    add(item: readonly T[]): number {
+        const id = this._idPool++;
+        this._data.set(id, item);
+        this.logDebugInfo();
+        return id;
+    }
+
+    get(pid: number, id: number): T | undefined {
+        return this._data.has(pid) ? this._data.get(pid)![id] : undefined;
+    }
+
+    delete(id: number): void {
+        this._data.delete(id);
+        this.logDebugInfo();
+    }
+
+    private logDebugInfo(): void {
+        if (!Cache.enableDebugLogging) {
+            return;
+        }
+        console.log(`${this.id} cache size — ${this._data.size}`);
+    }
+}
diff --git a/packages/plugin-ext/src/plugin/plugin-context.ts b/packages/plugin-ext/src/plugin/plugin-context.ts
index d5a4058acea6a..1932c4fba282f 100644
--- a/packages/plugin-ext/src/plugin/plugin-context.ts
+++ b/packages/plugin-ext/src/plugin/plugin-context.ts
@@ -164,7 +164,7 @@ import { ExtHostFileSystemEventService } from './file-system-event-service-ext-i
 import { LabelServiceExtImpl } from '../plugin/label-service';
 import { TimelineExtImpl } from './timeline';
 import { ThemingExtImpl } from './theming';
-import { CommentsExtImpl } from './comments';
+import { CustomEditorsExtImpl } from './custom-editors';
 
 export function createAPIFactory(
     rpc: RPCProtocol,
@@ -201,7 +201,7 @@ export function createAPIFactory(
     const labelServiceExt = rpc.set(MAIN_RPC_CONTEXT.LABEL_SERVICE_EXT, new LabelServiceExtImpl(rpc));
     const timelineExt = rpc.set(MAIN_RPC_CONTEXT.TIMELINE_EXT, new TimelineExtImpl(rpc, commandRegistry));
     const themingExt = rpc.set(MAIN_RPC_CONTEXT.THEMING_EXT, new ThemingExtImpl(rpc));
-    const commentsExt = rpc.set(MAIN_RPC_CONTEXT.COMMENTS_EXT, new CommentsExtImpl(rpc, commandRegistry, documents));
+    const customEditorExt = rpc.set(MAIN_RPC_CONTEXT.CUSTOM_EDITORS_EXT, new CustomEditorsExtImpl(rpc, documents, webviewExt, workspaceExt));
     rpc.set(MAIN_RPC_CONTEXT.DEBUG_EXT, debugExt);
 
     return function (plugin: InternalPlugin): typeof theia {
@@ -396,6 +396,11 @@ export function createAPIFactory(
             registerWebviewPanelSerializer(viewType: string, serializer: theia.WebviewPanelSerializer): theia.Disposable {
                 return webviewExt.registerWebviewPanelSerializer(viewType, serializer, plugin);
             },
+            registerCustomEditorProvider(viewType: string,
+                provider: theia.CustomTextEditorProvider | theia.CustomReadonlyEditorProvider,
+                options: { webviewOptions?: theia.WebviewPanelOptions, supportsMultipleEditorsPerDocument?: boolean } = {}): theia.Disposable {
+                return customEditorExt.registerCustomEditorProvider(viewType, provider, options, plugin);
+            },
             get state(): theia.WindowState {
                 return windowStateExt.getWindowState();
             },
@@ -813,7 +818,22 @@ export function createAPIFactory(
 
         const comments: typeof theia.comments = {
             createCommentController(id: string, label: string): theia.CommentController {
-                return commentsExt.createCommentController(plugin, id, label);
+                // TODO replace the dummy implementation, see https://github.com/eclipse-theia/theia/issues/8492
+                return {
+                    id, label,
+                    createCommentThread(uri: Uri, range: Range, commentsArray: theia.Comment[]): theia.CommentThread {
+                        return {
+                            uri,
+                            range,
+                            comments: commentsArray,
+                            collapsibleState: 0,
+                            dispose(): void {
+                            }
+                        };
+                    },
+                    dispose(): void {
+                    }
+                };
             }
         };
 
diff --git a/packages/plugin-ext/src/plugin/plugin-manager.ts b/packages/plugin-ext/src/plugin/plugin-manager.ts
index 274da9e107af5..cf9a894ae22f1 100644
--- a/packages/plugin-ext/src/plugin/plugin-manager.ts
+++ b/packages/plugin-ext/src/plugin/plugin-manager.ts
@@ -82,7 +82,8 @@ export class PluginManagerExtImpl implements PluginManagerExt, PluginManager {
         'onView',
         'onUri',
         'onWebviewPanel',
-        'onFileSystem'
+        'onFileSystem',
+        'onCustomEditor'
     ]);
 
     private configStorage: ConfigStorage | undefined;
diff --git a/packages/plugin-ext/src/plugin/webviews.ts b/packages/plugin-ext/src/plugin/webviews.ts
index 76d189afc51df..98bb068c20067 100644
--- a/packages/plugin-ext/src/plugin/webviews.ts
+++ b/packages/plugin-ext/src/plugin/webviews.ts
@@ -104,13 +104,26 @@ export class WebviewsExtImpl implements WebviewsExt {
         options: theia.WebviewPanelOptions & theia.WebviewOptions,
         plugin: Plugin
     ): theia.WebviewPanel {
+        const viewId = v4();
+        const webviewShowOptions = toWebviewPanelShowOptions(showOptions);
+        const webviewOptions = WebviewImpl.toWebviewOptions(options, this.workspace, plugin);
+        this.proxy.$createWebviewPanel(viewId, viewType, title, webviewShowOptions, webviewOptions);
+        const panel = this.createWebviewPanel(viewType, title, showOptions, options, plugin, viewId);
+        return panel;
+    }
+
+    createWebviewPanel(
+        viewType: string,
+        title: string,
+        showOptions: theia.ViewColumn | theia.WebviewPanelShowOptions,
+        options: theia.WebviewPanelOptions & theia.WebviewOptions,
+        plugin: Plugin,
+        viewId: string
+    ): WebviewPanelImpl {
         if (!this.initData) {
             throw new Error('Webviews are not initialized');
         }
         const webviewShowOptions = toWebviewPanelShowOptions(showOptions);
-        const viewId = v4();
-        this.proxy.$createWebviewPanel(viewId, viewType, title, webviewShowOptions, WebviewImpl.toWebviewOptions(options, this.workspace, plugin));
-
         const webview = new WebviewImpl(viewId, this.proxy, options, this.initData, this.workspace, plugin);
         const panel = new WebviewPanelImpl(viewId, this.proxy, viewType, title, webviewShowOptions, options, webview);
         this.webviewPanels.set(viewId, panel);
@@ -135,7 +148,7 @@ export class WebviewsExtImpl implements WebviewsExt {
         });
     }
 
-    private getWebviewPanel(viewId: string): WebviewPanelImpl | undefined {
+    getWebviewPanel(viewId: string): WebviewPanelImpl | undefined {
         if (this.webviewPanels.has(viewId)) {
             return this.webviewPanels.get(viewId);
         }
@@ -195,7 +208,7 @@ export class WebviewImpl implements theia.Webview {
         this.checkIsDisposed();
         if (this._html !== value) {
             this._html = value;
-            this.proxy.$setHtml(this.viewId, this._html);
+            this.proxy.$setHtml(this.viewId, value);
         }
     }
 
diff --git a/packages/plugin/src/theia-proposed.d.ts b/packages/plugin/src/theia-proposed.d.ts
index fef39a9b1d105..6384e514e4675 100644
--- a/packages/plugin/src/theia-proposed.d.ts
+++ b/packages/plugin/src/theia-proposed.d.ts
@@ -505,6 +505,30 @@ declare module '@theia/plugin' {
 
     // #endregion
 
+    // #region Custom editor move https://github.com/microsoft/vscode/issues/86146
+    // copied from https://github.com/microsoft/vscode/blob/53eac52308c4611000a171cc7bf1214293473c78/src/vs/vscode.proposed.d.ts#L986-L1007
+
+    // TODO: Also for custom editor
+
+    export interface CustomTextEditorProvider {
+
+        /**
+         * Handle when the underlying resource for a custom editor is renamed.
+         *
+         * This allows the webview for the editor be preserved throughout the rename. If this method is not implemented,
+         * Theia will destory the previous custom editor and create a replacement one.
+         *
+         * @param newDocument New text document to use for the custom editor.
+         * @param existingWebviewPanel Webview panel for the custom editor.
+         * @param token A cancellation token that indicates the result is no longer needed.
+         *
+         * @return Thenable indicating that the webview editor has been moved.
+         */
+        moveCustomTextEditor?(newDocument: TextDocument, existingWebviewPanel: WebviewPanel, token: CancellationToken): Thenable<void>;
+    }
+
+    // #endregion
+
     export interface ResourceLabelFormatter {
         scheme: string;
         authority?: string;
diff --git a/packages/plugin/src/theia.d.ts b/packages/plugin/src/theia.d.ts
index 651b18ea31f5e..feaaf2f8c7e97 100644
--- a/packages/plugin/src/theia.d.ts
+++ b/packages/plugin/src/theia.d.ts
@@ -3459,6 +3459,257 @@ declare module '@theia/plugin' {
         handleUri(uri: Uri): ProviderResult<void>;
     }
 
+    /**
+     * Provider for text based custom editors.
+     *
+     * Text based custom editors use a [`TextDocument`](#TextDocument) as their data model. This considerably simplifies
+     * implementing a custom editor as it allows Theia to handle many common operations such as
+     * undo and backup. The provider is responsible for synchronizing text changes between the webview and the `TextDocument`.
+    */
+    export interface CustomTextEditorProvider {
+
+        /**
+         * Resolve a custom editor for a given text resource.
+         *
+         * This is called when a user first opens a resource for a `CustomTextEditorProvider`, or if they reopen an
+         * existing editor using this `CustomTextEditorProvider`.
+         *
+         *
+         * @param document Document for the resource to resolve.
+         *
+         * @param webviewPanel The webview panel used to display the editor UI for this resource.
+         *
+         * During resolve, the provider must fill in the initial html for the content webview panel and hook up all
+         * the event listeners on it that it is interested in. The provider can also hold onto the `WebviewPanel` to
+         * use later for example in a command. See [`WebviewPanel`](#WebviewPanel) for additional details.
+         *
+         * @param token A cancellation token that indicates the result is no longer needed.
+         *
+         * @return Thenable indicating that the custom editor has been resolved.
+         */
+        resolveCustomTextEditor(document: TextDocument, webviewPanel: WebviewPanel, token: CancellationToken): Thenable<void> | void;
+    }
+
+    /**
+     * Represents a custom document used by a [`CustomEditorProvider`](#CustomEditorProvider).
+     *
+     * Custom documents are only used within a given `CustomEditorProvider`. The lifecycle of a `CustomDocument` is
+     * managed by Theia. When no more references remain to a `CustomDocument`, it is disposed of.
+     */
+    interface CustomDocument {
+        /**
+         * The associated uri for this document.
+         */
+        readonly uri: Uri;
+
+        /**
+         * Dispose of the custom document.
+         *
+         * This is invoked by Theia when there are no more references to a given `CustomDocument` (for example when
+         * all editors associated with the document have been closed.)
+         */
+        dispose(): void;
+    }
+
+    /**
+ * Event triggered by extensions to signal that an edit has occurred on an [`CustomDocument`](#CustomDocument).
+ *
+ * @see [`CustomDocumentProvider.onDidChangeCustomDocument`](#CustomDocumentProvider.onDidChangeCustomDocument).
+ */
+    interface CustomDocumentEditEvent<T extends CustomDocument = CustomDocument> {
+
+        /**
+         * The document that the edit is for.
+         */
+        readonly document: T;
+
+        /**
+         * Undo the edit operation.
+         *
+         * This is invoked by Theia when the user undoes this edit. To implement `undo`, your
+         * extension should restore the document and editor to the state they were in just before this
+         * edit was added to Theia's internal edit stack by `onDidChangeCustomDocument`.
+         */
+        undo(): Thenable<void> | void;
+
+        /**
+         * Redo the edit operation.
+         *
+         * This is invoked by Theia when the user redoes this edit. To implement `redo`, your
+         * extension should restore the document and editor to the state they were in just after this
+         * edit was added to Theia's internal edit stack by `onDidChangeCustomDocument`.
+         */
+        redo(): Thenable<void> | void;
+
+        /**
+         * Display name describing the edit.
+         *
+         * This will be shown to users in the UI for undo/redo operations.
+         */
+        readonly label?: string;
+    }
+
+    /**
+     * Event triggered by extensions to signal to Theia that the content of a [`CustomDocument`](#CustomDocument)
+     * has changed.
+     *
+     * @see [`CustomDocumentProvider.onDidChangeCustomDocument`](#CustomDocumentProvider.onDidChangeCustomDocument).
+     */
+    interface CustomDocumentContentChangeEvent<T extends CustomDocument = CustomDocument> {
+        /**
+         * The document that the change is for.
+         */
+        readonly document: T;
+    }
+
+    /**
+     * Additional information about the opening custom document.
+     */
+    interface CustomDocumentOpenContext {
+        /**
+         * The id of the backup to restore the document from or `undefined` if there is no backup.
+         *
+         * If this is provided, your extension should restore the editor from the backup instead of reading the file
+         * from the user's workspace.
+         */
+        readonly backupId?: string;
+    }
+
+    /**
+     * Provider for readonly custom editors that use a custom document model.
+     *
+     * Custom editors use [`CustomDocument`](#CustomDocument) as their document model instead of a [`TextDocument`](#TextDocument).
+     *
+     * You should use this type of custom editor when dealing with binary files or more complex scenarios. For simple
+     * text based documents, use [`CustomTextEditorProvider`](#CustomTextEditorProvider) instead.
+     *
+     * @param T Type of the custom document returned by this provider.
+     */
+    export interface CustomReadonlyEditorProvider<T extends CustomDocument = CustomDocument> {
+
+        /**
+         * Create a new document for a given resource.
+         *
+         * `openCustomDocument` is called when the first time an editor for a given resource is opened. The opened
+         * document is then passed to `resolveCustomEditor` so that the editor can be shown to the user.
+         *
+         * Already opened `CustomDocument` are re-used if the user opened additional editors. When all editors for a
+         * given resource are closed, the `CustomDocument` is disposed of. Opening an editor at this point will
+         * trigger another call to `openCustomDocument`.
+         *
+         * @param uri Uri of the document to open.
+         * @param openContext Additional information about the opening custom document.
+         * @param token A cancellation token that indicates the result is no longer needed.
+         *
+         * @return The custom document.
+         */
+        openCustomDocument(uri: Uri, openContext: CustomDocumentOpenContext, token: CancellationToken): Thenable<T> | T;
+
+        /**
+         * Resolve a custom editor for a given resource.
+         *
+         * This is called whenever the user opens a new editor for this `CustomEditorProvider`.
+         *
+         * @param document Document for the resource being resolved.
+         *
+         * @param webviewPanel The webview panel used to display the editor UI for this resource.
+         *
+         * During resolve, the provider must fill in the initial html for the content webview panel and hook up all
+         * the event listeners on it that it is interested in. The provider can also hold onto the `WebviewPanel` to
+         * use later for example in a command. See [`WebviewPanel`](#WebviewPanel) for additional details.
+         *
+         * @param token A cancellation token that indicates the result is no longer needed.
+         *
+         * @return Optional thenable indicating that the custom editor has been resolved.
+         */
+        resolveCustomEditor(document: T, webviewPanel: WebviewPanel, token: CancellationToken): Thenable<void> | void;
+    }
+
+    /**
+     * Provider for editable custom editors that use a custom document model.
+     *
+     * Custom editors use [`CustomDocument`](#CustomDocument) as their document model instead of a [`TextDocument`](#TextDocument).
+     * This gives extensions full control over actions such as edit, save, and backup.
+     *
+     * You should use this type of custom editor when dealing with binary files or more complex scenarios. For simple
+     * text based documents, use [`CustomTextEditorProvider`](#CustomTextEditorProvider) instead.
+     *
+     * @param T Type of the custom document returned by this provider.
+     */
+    export interface CustomEditorProvider<T extends CustomDocument = CustomDocument> extends CustomReadonlyEditorProvider<T> {
+        /**
+         * Signal that an edit has occurred inside a custom editor.
+         *
+         * This event must be fired by your extension whenever an edit happens in a custom editor. An edit can be
+         * anything from changing some text, to cropping an image, to reordering a list. Your extension is free to
+         * define what an edit is and what data is stored on each edit.
+         *
+         * Firing `onDidChange` causes Theia to mark the editors as being dirty. This is cleared when the user either
+         * saves or reverts the file.
+         *
+         * Editors that support undo/redo must fire a `CustomDocumentEditEvent` whenever an edit happens. This allows
+         * users to undo and redo the edit using Theia's standard Theia keyboard shortcuts. Theia will also mark
+         * the editor as no longer being dirty if the user undoes all edits to the last saved state.
+         *
+         * Editors that support editing but cannot use Theia's standard undo/redo mechanism must fire a `CustomDocumentContentChangeEvent`.
+         * The only way for a user to clear the dirty state of an editor that does not support undo/redo is to either
+         * `save` or `revert` the file.
+         *
+         * An editor should only ever fire `CustomDocumentEditEvent` events, or only ever fire `CustomDocumentContentChangeEvent` events.
+         */
+        readonly onDidChangeCustomDocument: Event<CustomDocumentContentChangeEvent<T>> | Event<CustomDocumentEditEvent<T>>;
+
+        /**
+         * Save a custom document.
+         *
+         * This method is invoked by Theia when the user saves a custom editor. This can happen when the user
+         * triggers save while the custom editor is active, by commands such as `save all`, or by auto save if enabled.
+         *
+         * To implement `save`, the implementer must persist the custom editor. This usually means writing the
+         * file data for the custom document to disk. After `save` completes, any associated editor instances will
+         * no longer be marked as dirty.
+         *
+         * @param document Document to save.
+         * @param cancellation Token that signals the save is no longer required (for example, if another save was triggered).
+         *
+         * @return Thenable signaling that saving has completed.
+         */
+        saveCustomDocument(document: T, cancellation: CancellationToken): Thenable<void>;
+
+        /**
+         * Save a custom document to a different location.
+         *
+         * This method is invoked by Theia when the user triggers 'save as' on a custom editor. The implementer must
+         * persist the custom editor to `destination`.
+         *
+         * When the user accepts save as, the current editor is be replaced by an non-dirty editor for the newly saved file.
+         *
+         * @param document Document to save.
+         * @param destination Location to save to.
+         * @param cancellation Token that signals the save is no longer required.
+         *
+         * @return Thenable signaling that saving has completed.
+         */
+        saveCustomDocumentAs(document: T, destination: Uri, cancellation: CancellationToken): Thenable<void>;
+
+        /**
+         * Revert a custom document to its last saved state.
+         *
+         * This method is invoked by Theia when the user triggers `File: Revert File` in a custom editor. (Note that
+         * this is only used using Theia's `File: Revert File` command and not on a `git revert` of the file).
+         *
+         * To implement `revert`, the implementer must make sure all editor instances (webviews) for `document`
+         * are displaying the document in the same state is saved in. This usually means reloading the file from the
+         * workspace.
+         *
+         * @param document Document to revert.
+         * @param cancellation Token that signals the revert is no longer required.
+         *
+         * @return Thenable signaling that the change has completed.
+         */
+        revertCustomDocument(document: T, cancellation: CancellationToken): Thenable<void>;
+    }
+
     /**
      * Common namespace for dealing with window and editor, showing messages and user input.
      */
@@ -3793,6 +4044,44 @@ declare module '@theia/plugin' {
          */
         export function registerWebviewPanelSerializer(viewType: string, serializer: WebviewPanelSerializer): Disposable;
 
+
+        /**
+         * Register a provider for custom editors for the `viewType` contributed by the `customEditors` extension point.
+         *
+         * When a custom editor is opened, Theia fires an `onCustomEditor:viewType` activation event. Your extension
+         * must register a [`CustomTextEditorProvider`](#CustomTextEditorProvider), [`CustomReadonlyEditorProvider`](#CustomReadonlyEditorProvider),
+         * [`CustomEditorProvider`](#CustomEditorProvider)for `viewType` as part of activation.
+         *
+         * @param viewType Unique identifier for the custom editor provider. This should match the `viewType` from the
+         *   `customEditors` contribution point.
+         * @param provider Provider that resolves custom editors.
+         * @param options Options for the provider.
+         *
+         * @return Disposable that unregisters the provider.
+         */
+        export function registerCustomEditorProvider(viewType: string, provider: CustomTextEditorProvider | CustomReadonlyEditorProvider | CustomEditorProvider, options?: {
+            /**
+             * Content settings for the webview panels created for this custom editor.
+             */
+            readonly webviewOptions?: WebviewPanelOptions;
+
+            /**
+             * Only applies to `CustomReadonlyEditorProvider | CustomEditorProvider`.
+             *
+             * Indicates that the provider allows multiple editor instances to be open at the same time for
+             * the same resource.
+             *
+             * By default, Theia only allows one editor instance to be open at a time for each resource. If the
+             * user tries to open a second editor instance for the resource, the first one is instead moved to where
+             * the second one was to be opened.
+             *
+             * When `supportsMultipleEditorsPerDocument` is enabled, users can split and create copies of the custom
+             * editor. In this case, the custom editor must make sure it can properly synchronize the states of all
+             * editor instances for a resource so that they are consistent.
+             */
+            readonly supportsMultipleEditorsPerDocument?: boolean;
+        }): Disposable;
+
         /**
          * Represents the current window's state.
          *
diff --git a/packages/preferences/src/browser/preferences-json-schema-contribution.ts b/packages/preferences/src/browser/preferences-json-schema-contribution.ts
index 51b6300e45a31..b25f2c0ab47b0 100644
--- a/packages/preferences/src/browser/preferences-json-schema-contribution.ts
+++ b/packages/preferences/src/browser/preferences-json-schema-contribution.ts
@@ -20,14 +20,10 @@ import { InMemoryResources } from '@theia/core';
 import { JsonSchemaRegisterContext, JsonSchemaContribution } from '@theia/core/lib/browser/json-schema-store';
 import { PreferenceSchemaProvider } from '@theia/core/lib/browser/preferences/preference-contribution';
 import { PreferenceConfigurations } from '@theia/core/lib/browser/preferences/preference-configurations';
-import { PreferenceScope } from '@theia/core/lib/browser';
-
-const PREFERENCE_URI_PREFIX = 'vscode://schemas/settings/';
-const USER_STORAGE_PREFIX = 'user_storage:/';
+import { UserStorageUri } from '@theia/userstorage/lib/browser/user-storage-uri';
 
 @injectable()
 export class PreferencesJsonSchemaContribution implements JsonSchemaContribution {
-    private serializeSchema = (scope: PreferenceScope) => JSON.stringify(this.schemaProvider.getSchema(scope));
 
     @inject(PreferenceSchemaProvider)
     protected readonly schemaProvider: PreferenceSchemaProvider;
@@ -39,39 +35,18 @@ export class PreferencesJsonSchemaContribution implements JsonSchemaContribution
     protected readonly preferenceConfigurations: PreferenceConfigurations;
 
     registerSchemas(context: JsonSchemaRegisterContext): void {
-        this.registerSchema(PreferenceScope.Default, context);
-        this.registerSchema(PreferenceScope.User, context);
-        this.registerSchema(PreferenceScope.Workspace, context);
-        this.registerSchema(PreferenceScope.Folder, context);
-
-        this.schemaProvider.onDidPreferenceSchemaChanged(() => this.updateInMemoryResources());
-    }
-
-    private registerSchema(scope: PreferenceScope, context: JsonSchemaRegisterContext): void {
-        const scopeStr = PreferenceScope[scope].toLowerCase();
-        const uri = new URI(PREFERENCE_URI_PREFIX + scopeStr);
-
-        this.inmemoryResources.add(uri, this.serializeSchema(scope));
-
+        const serializeSchema = () => JSON.stringify(this.schemaProvider.getCombinedSchema());
+        const uri = new URI('vscode://schemas/settings/user');
+        this.inmemoryResources.add(uri, serializeSchema());
+        const baseName = this.preferenceConfigurations.getConfigName() + '.json';
+        const fileMatch = [baseName, UserStorageUri.resolve(baseName).toString()];
         context.registerSchema({
-            fileMatch: this.getFileMatch(scopeStr),
+            fileMatch,
             url: uri.toString()
         });
+        this.schemaProvider.onDidPreferenceSchemaChanged(() =>
+            this.inmemoryResources.update(uri, serializeSchema())
+        );
     }
 
-    private updateInMemoryResources(): void {
-        this.inmemoryResources.update(new URI(PREFERENCE_URI_PREFIX + PreferenceScope[PreferenceScope.Default].toLowerCase()),
-            this.serializeSchema(+PreferenceScope.Default));
-        this.inmemoryResources.update(new URI(PREFERENCE_URI_PREFIX + PreferenceScope[PreferenceScope.User].toLowerCase()),
-            this.serializeSchema(+PreferenceScope.User));
-        this.inmemoryResources.update(new URI(PREFERENCE_URI_PREFIX + PreferenceScope[PreferenceScope.Workspace].toLowerCase()),
-            this.serializeSchema(+PreferenceScope.Workspace));
-        this.inmemoryResources.update(new URI(PREFERENCE_URI_PREFIX + PreferenceScope[PreferenceScope.Folder].toLowerCase()),
-            this.serializeSchema(+PreferenceScope.Folder));
-    }
-
-    private getFileMatch(scope: string): string[] {
-        const baseName = this.preferenceConfigurations.getConfigName() + '.json';
-        return [baseName, new URI(USER_STORAGE_PREFIX + scope).resolve(baseName).toString()];
-    }
 }
diff --git a/packages/task/src/node/process/process-task-runner.ts b/packages/task/src/node/process/process-task-runner.ts
index 25e984c5e8ab8..412752bfa5891 100644
--- a/packages/task/src/node/process/process-task-runner.ts
+++ b/packages/task/src/node/process/process-task-runner.ts
@@ -116,6 +116,11 @@ export class ProcessTaskRunner implements TaskRunner {
         }
 
         const options = systemSpecificCommand.options;
+        // sanity checks:
+        // - we expect the cwd to be set by the client.
+        if (!options || !options.cwd) {
+            throw new Error("Can't run a task when 'cwd' is not provided by the client");
+        }
 
         // Use task's cwd with spawned process and pass node env object to
         // new process, so e.g. we can re-use the system path
diff --git a/packages/terminal/src/browser/terminal-widget-impl.ts b/packages/terminal/src/browser/terminal-widget-impl.ts
index 9f442189bf03d..4850b5436e228 100644
--- a/packages/terminal/src/browser/terminal-widget-impl.ts
+++ b/packages/terminal/src/browser/terminal-widget-impl.ts
@@ -382,7 +382,7 @@ export class TerminalWidgetImpl extends TerminalWidget implements StatefulWidget
         if (IBaseTerminalServer.validateId(terminalId)) {
             return terminalId;
         }
-        this.logger.warn(`Failed attaching to terminal id ${id}, the terminal is most likely gone. Starting up a new terminal instead.`);
+        this.logger.error(`Error attaching to terminal id ${id}, the terminal is most likely gone. Starting up a new terminal instead.`);
         if (this.kind === 'user') {
             return this.createTerminal();
         } else {
diff --git a/packages/terminal/src/node/base-terminal-server.ts b/packages/terminal/src/node/base-terminal-server.ts
index 564155128dd87..b5c0285da00cf 100644
--- a/packages/terminal/src/node/base-terminal-server.ts
+++ b/packages/terminal/src/node/base-terminal-server.ts
@@ -63,7 +63,7 @@ export abstract class BaseTerminalServer implements IBaseTerminalServer {
         if (term && term instanceof TerminalProcess) {
             return term.id;
         } else {
-            this.logger.warn(`Couldn't attach - can't find terminal with id: ${id} `);
+            this.logger.error(`Couldn't attach - can't find terminal with id: ${id} `);
             return -1;
         }
     }
@@ -116,7 +116,7 @@ export abstract class BaseTerminalServer implements IBaseTerminalServer {
         if (term && term instanceof TerminalProcess) {
             term.resize(cols, rows);
         } else {
-            console.warn("Couldn't resize terminal " + id + ", because it doesn't exist.");
+            console.error("Couldn't resize terminal " + id + ", because it doesn't exist.");
         }
     }
 
diff --git a/packages/workspace/src/browser/workspace-commands.ts b/packages/workspace/src/browser/workspace-commands.ts
index 3c1c0751ab176..8142907f19560 100644
--- a/packages/workspace/src/browser/workspace-commands.ts
+++ b/packages/workspace/src/browser/workspace-commands.ts
@@ -212,16 +212,7 @@ export class WorkspaceCommandContribution implements CommandContribution {
     }
 
     registerCommands(registry: CommandRegistry): void {
-        this.openerService.getOpeners().then(openers => {
-            for (const opener of openers) {
-                const openWithCommand = WorkspaceCommands.FILE_OPEN_WITH(opener);
-                registry.registerCommand(openWithCommand, this.newUriAwareCommandHandler({
-                    execute: uri => opener.open(uri),
-                    isEnabled: uri => opener.canHandle(uri) > 0,
-                    isVisible: uri => opener.canHandle(uri) > 0 && this.areMultipleOpenHandlersPresent(openers, uri)
-                }));
-            }
-        });
+        this.registerOpenWith(registry);
         registry.registerCommand(WorkspaceCommands.NEW_FILE, this.newWorkspaceRootUriAwareCommandHandler({
             execute: uri => this.getDirectory(uri).then(parent => {
                 if (parent) {
@@ -342,6 +333,24 @@ export class WorkspaceCommandContribution implements CommandContribution {
         });
     }
 
+    openers: OpenHandler[];
+    protected async registerOpenWith(registry: CommandRegistry): Promise<void> {
+        if (this.openerService.onOpenersStateChanged) {
+            this.openerService.onOpenersStateChanged(async e => {
+                this.openers = await this.openerService.getOpeners();
+            });
+        }
+        const openers = await this.openerService.getOpeners();
+        for (const opener of openers) {
+            const openWithCommand = WorkspaceCommands.FILE_OPEN_WITH(opener);
+            registry.registerCommand(openWithCommand, this.newUriAwareCommandHandler({
+                execute: uri => opener.open(uri),
+                isEnabled: uri => opener.canHandle(uri) > 0,
+                isVisible: uri => opener.canHandle(uri) > 0 && this.areMultipleOpenHandlersPresent(uri)
+            }));
+        }
+    }
+
     protected newUriAwareCommandHandler(handler: UriCommandHandler<URI>): UriAwareCommandHandler<URI> {
         return UriAwareCommandHandler.MonoSelect(this.selectionService, handler);
     }
@@ -476,9 +485,9 @@ export class WorkspaceCommandContribution implements CommandContribution {
         }
     }
 
-    protected areMultipleOpenHandlersPresent(openers: OpenHandler[], uri: URI): boolean {
+    protected areMultipleOpenHandlersPresent(uri: URI): boolean {
         let count = 0;
-        for (const opener of openers) {
+        for (const opener of this.openers) {
             if (opener.canHandle(uri) > 0) {
                 count++;
             }