Do not start OmniSharp server in Live Share scenarios

src/omnisharp/launcher.ts

@@ -17,7 +17,8 @@ export enum LaunchTargetKind {
     ProjectJson,
     Folder,
     Csx,
-    Cake
+    Cake,
+    LiveShare
 }
 
 /**
@@ -31,6 +32,24 @@ export interface LaunchTarget {
     kind: LaunchTargetKind;
 }
 
+export const vslsTarget: LaunchTarget = {
+    label: "VSLS",
+    description: "Visual Studio Live Share",
+    directory: "",
+    target: "",
+    kind: LaunchTargetKind.LiveShare
+};
+
+/** Live share scheme */
+export const vsls = 'vsls';
+
+/*
+ * File scheme for which OmniSharp language feature should be disabled
+ */
+export const disabledSchemes = new Set([
+    vsls,
+]);
+
 /**
  * Returns a list of potential targets on which OmniSharp can be launched.
  * This includes `project.json` files, `*.sln` files (if any `*.csproj` files are found), and the root folder
@@ -55,7 +74,7 @@ export async function findLaunchTargets(options: Options): Promise<LaunchTarget[
     return resourcesToLaunchTargets(projectFiles.concat(csFiles));
 }
 
-function resourcesToLaunchTargets(resources: vscode.Uri[]): LaunchTarget[] {
+export function resourcesToLaunchTargets(resources: vscode.Uri[]): LaunchTarget[] {
     // The list of launch targets is calculated like so:
     //   * If there are .csproj files, .sln files are considered as launch targets.
     //   * Any project.json file is considered a launch target.
@@ -67,13 +86,20 @@ function resourcesToLaunchTargets(resources: vscode.Uri[]): LaunchTarget[] {
     //   * It should be possible to choose a .sln file even when no .csproj files are found
     //     within the root.
 
-    if (!Array.isArray(resources)) {
+    if (!Array.isArray(resources) || resources.length === 0) {
         return [];
     }
 
+    // Since language server functionality is run on the server instance there is no need
+    // to start OmniSharp on the LiveShare client.
+    const localResources = resources.filter(resource => !disabledSchemes.has(resource.scheme));
+    if (localResources.length === 0) {
+        return [vslsTarget];
+    }
+
     let workspaceFolderToUriMap = new Map<number, vscode.Uri[]>();
 
-    for (let resource of resources) {
+    for (let resource of localResources) {
         let folder = vscode.workspace.getWorkspaceFolder(resource);
         if (folder) {
             let buckets: vscode.Uri[];

src/omnisharp/server.ts

@@ -11,7 +11,7 @@ import * as utils from '../common';
 import * as serverUtils from '../omnisharp/utils';
 import { vscode, CancellationToken } from '../vscodeAdapter';
 import { ChildProcess, exec } from 'child_process';
-import { LaunchTarget, findLaunchTargets } from './launcher';
+import { LaunchTarget, findLaunchTargets, LaunchTargetKind } from './launcher';
 import { ReadLine, createInterface } from 'readline';
 import { Request, RequestQueueCollection } from './requestQueue';
 import { DelayTracker } from './delayTracker';
@@ -246,6 +246,11 @@ export class OmniSharpServer {
 
     private async _start(launchTarget: LaunchTarget, options: Options): Promise<void> {
 
+        if (launchTarget.kind === LaunchTargetKind.LiveShare) {
+            this.eventStream.post(new ObservableEvents.OmnisharpServerMessage("During Live Share sessions language services are provided by the Live Share server."));
+            return;
+        }
+
         let disposables = new CompositeDisposable();
 
         disposables.add(this.onServerError(err =>

test/integrationTests/launcher.test.ts

@@ -0,0 +1,41 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import { assert } from "chai";
+import { resourcesToLaunchTargets, vsls, vslsTarget } from "../../src/omnisharp/launcher";
+
+const chai = require('chai');
+chai.use(require('chai-arrays'));
+chai.use(require('chai-fs'));
+
+suite(`launcher:`, () => {
+
+    test(`Returns the LiveShare launch target when processing vsls resources`, () => {
+        const testResources: vscode.Uri[] = [
+            vscode.Uri.parse(`${vsls}:/test.sln`),
+            vscode.Uri.parse(`${vsls}:/test/test.csproj`),
+            vscode.Uri.parse(`${vsls}:/test/Program.cs`),
+        ];
+
+        const launchTargets = resourcesToLaunchTargets(testResources);
+
+        const liveShareTarget = launchTargets.find(target => target === vslsTarget);
+        assert.exists(liveShareTarget, "Launch targets was not the Visual Studio Live Share target.");
+    });
+
+    test(`Does not return the LiveShare launch target when processing local resources`, () => {
+        const testResources: vscode.Uri[] = [
+            vscode.Uri.parse(`/test.sln`),
+            vscode.Uri.parse(`/test/test.csproj`),
+            vscode.Uri.parse(`/test/Program.cs`),
+        ];
+
+        const launchTargets = resourcesToLaunchTargets(testResources);
+
+        const liveShareTarget = launchTargets.find(target => target === vslsTarget);
+        assert.notExists(liveShareTarget, "Launch targets contained the Visual Studio Live Share target.");
+    });
+});