From 11928c7f57d4b1229ebf759940a7332be872b6de Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 12:06:28 -0700
Subject: [PATCH 01/10] module: custom --conditions flag option

---
 doc/api/cli.md                                | 15 ++++++++++
 doc/node.1                                    |  4 +++
 lib/internal/modules/cjs/loader.js            | 28 +++++++------------
 lib/internal/modules/esm/resolve.js           |  3 +-
 src/node_options.cc                           |  5 ++++
 src/node_options.h                            |  1 +
 test/es-module/test-esm-custom-exports.mjs    | 10 +++++++
 .../pkgexports/custom-condition.js            |  1 +
 .../node_modules/pkgexports/package.json      |  5 +++-
 9 files changed, 52 insertions(+), 20 deletions(-)
 create mode 100644 test/es-module/test-esm-custom-exports.mjs
 create mode 100644 test/fixtures/node_modules/pkgexports/custom-condition.js

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 899c28f6f76675..493e40a79c5db5 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -76,6 +76,21 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
+### `-cc`, `--conditions=conditionA,conditionB`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Enable experimental support for custom conditional exports resolution
+conditions.
+
+Any custom comma-separated string condition names are permitted.
+
+The default Node.js conditions of `"node"`, `"default"`, `"import"` and
+`"require"` will always apply as defined.
+
 ### `--cpu-prof`
 <!-- YAML
 added: v12.0.0
diff --git a/doc/node.1 b/doc/node.1
index 3da44752bd38eb..e35dd697638bd6 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -78,6 +78,10 @@ Aborting instead of exiting causes a core file to be generated for analysis.
 .It Fl -completion-bash
 Print source-able bash completion script for Node.js.
 .
+.It Fl cc , Fl -conditions Ar string
+Use custom conditional exports conditions
+.Ar string
+.
 .It Fl -cpu-prof
 Start the V8 CPU profiler on start up, and write the CPU profile to disk
 before exit. If
diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index de24f6c409c498..c47f43b238094e 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -85,6 +85,7 @@ const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
 const { compileFunction } = internalBinding('contextify');
+const userConditions = (getOptionValue('--conditions') || '').split(',');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
@@ -625,23 +626,14 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
           'contain numeric property keys.');
     }
     for (const p of keys) {
-      switch (p) {
-        case 'node':
-        case 'require':
-          try {
-            return resolveExportsTarget(baseUrl, target[p], subpath,
-                                        mappingKey);
-          } catch (e) {
-            if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
-          }
-          break;
-        case 'default':
-          try {
-            return resolveExportsTarget(baseUrl, target.default, subpath,
-                                        mappingKey);
-          } catch (e) {
-            if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
-          }
+      if (cjsConditions.has(p) || p === 'default') {
+        try {
+          return resolveExportsTarget(baseUrl, target[p], subpath,
+                                      mappingKey);
+        } catch (e) {
+          if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
+        }
+        break;
       }
     }
     throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
@@ -1006,7 +998,7 @@ Module._load = function(request, parent, isMain) {
 };
 
 // TODO: Use this set when resolving pkg#exports conditions.
-const cjsConditions = new SafeSet(['require', 'node']);
+const cjsConditions = new SafeSet(['require', 'node', ...userConditions]);
 Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.canBeRequiredByUsers(request)) {
     return request;
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index 7ea59f30c6894e..f998f28ddf08d1 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -51,7 +51,8 @@ const {
 const { Module: CJSModule } = require('internal/modules/cjs/loader');
 
 const packageJsonReader = require('internal/modules/package_json_reader');
-const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import']);
+const userConditions = (getOptionValue('--conditions') || '').split(',');
+const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
 
diff --git a/src/node_options.cc b/src/node_options.cc
index 737c4c147d3bcb..541eb2b1906d57 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -281,6 +281,11 @@ DebugOptionsParser::DebugOptionsParser() {
 }
 
 EnvironmentOptionsParser::EnvironmentOptionsParser() {
+  AddOption("--conditions",
+            "set the conditional exports conditions",
+            &EnvironmentOptions::conditions,
+            kAllowedInEnvironment);
+  AddAlias("-cc", "--conditions");
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",
diff --git a/src/node_options.h b/src/node_options.h
index fe20022bb2f357..c668abb0b61303 100644
--- a/src/node_options.h
+++ b/src/node_options.h
@@ -100,6 +100,7 @@ class DebugOptions : public Options {
 class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
+  std::string conditions;
   bool enable_source_maps = false;
   bool experimental_json_modules = false;
   bool experimental_modules = false;
diff --git a/test/es-module/test-esm-custom-exports.mjs b/test/es-module/test-esm-custom-exports.mjs
new file mode 100644
index 00000000000000..227b4652588a5f
--- /dev/null
+++ b/test/es-module/test-esm-custom-exports.mjs
@@ -0,0 +1,10 @@
+// Flags: --conditions=custom-condition,another
+import { mustCall } from '../common/index.mjs';
+import { strictEqual } from 'assert';
+import { requireFixture, importFixture } from '../fixtures/pkgexports.mjs';
+[requireFixture, importFixture].forEach((loadFixture) => {
+  loadFixture('pkgexports/condition')
+    .then(mustCall((actual) => {
+      strictEqual(actual.default, 'from custom condition');
+    }));
+});
diff --git a/test/fixtures/node_modules/pkgexports/custom-condition.js b/test/fixtures/node_modules/pkgexports/custom-condition.js
new file mode 100644
index 00000000000000..63d77460d8d6b7
--- /dev/null
+++ b/test/fixtures/node_modules/pkgexports/custom-condition.js
@@ -0,0 +1 @@
+module.exports = 'from custom condition';
diff --git a/test/fixtures/node_modules/pkgexports/package.json b/test/fixtures/node_modules/pkgexports/package.json
index b99e5c7b79f6a8..71406a407c453d 100644
--- a/test/fixtures/node_modules/pkgexports/package.json
+++ b/test/fixtures/node_modules/pkgexports/package.json
@@ -21,7 +21,10 @@
     "./nofallback2": [null, {}, "builtin:x"],
     "./nodemodules": "./node_modules/internalpkg/x.js",
     "./condition": [{
-      "custom-condition": "./custom-condition.mjs",
+      "custom-condition": {
+        "import": "./custom-condition.mjs",
+        "require": "./custom-condition.js"
+      },
       "import": "///overridden",
       "require": {
         "require": {

From 5dc585dd669a9a0b959afb292d6f5658dc95bac2 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 12:39:59 -0700
Subject: [PATCH 02/10] fixup resolution bugs

---
 lib/internal/modules/cjs/loader.js  | 52 ++++++++++++++++++-----------
 lib/internal/modules/esm/resolve.js | 10 +++---
 2 files changed, 36 insertions(+), 26 deletions(-)

diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index c47f43b238094e..8aa20119c91b62 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -85,7 +85,8 @@ const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
 const { compileFunction } = internalBinding('contextify');
-const userConditions = (getOptionValue('--conditions') || '').split(',');
+const userConditions = getOptionValue('--conditions') &&
+    getOptionValue('--conditions').split(',');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
@@ -498,8 +499,12 @@ function applyExports(basePath, expansion) {
   if (typeof pkgExports === 'object') {
     if (ObjectPrototypeHasOwnProperty(pkgExports, mappingKey)) {
       const mapping = pkgExports[mappingKey];
-      return resolveExportsTarget(pathToFileURL(basePath + '/'), mapping, '',
-                                  mappingKey);
+      const resolved = resolveExportsTarget(
+        pathToFileURL(basePath + '/'), mapping, '', mappingKey);
+      if (resolved === null || resolved === undefined)
+        throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
+          basePath, mappingKey);
+      return resolved;
     }
 
     let dirMatch = '';
@@ -516,6 +521,9 @@ function applyExports(basePath, expansion) {
       const subpath = StringPrototypeSlice(mappingKey, dirMatch.length);
       const resolved = resolveExportsTarget(pathToFileURL(basePath + '/'),
                                             mapping, subpath, mappingKey);
+      if (resolved === null || resolved === undefined)
+        throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
+          basePath, mappingKey + subpath);
       // Extension searching for folder exports only
       const rc = stat(resolved);
       if (rc === 0) return resolved;
@@ -603,21 +611,29 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
     throw new ERR_INVALID_MODULE_SPECIFIER(mappingKey + subpath, reason);
   } else if (ArrayIsArray(target)) {
     if (target.length === 0)
-      throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-        baseUrl.pathname, mappingKey + subpath);
+      return null;
     let lastException;
     for (const targetValue of target) {
+      let resolved;
       try {
-        return resolveExportsTarget(baseUrl, targetValue, subpath, mappingKey);
+        resolved = resolveExportsTarget(baseUrl, targetValue, subpath,
+                                        mappingKey);
       } catch (e) {
         lastException = e;
-        if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED' &&
-            e.code !== 'ERR_INVALID_PACKAGE_TARGET')
+        if (e.code !== 'ERR_INVALID_PACKAGE_TARGET')
           throw e;
       }
+      if (resolved === undefined)
+        continue;
+      if (resolved === null) {
+        lastException = null;
+        continue;
+      }
+      return resolved;
     }
     // Throw last fallback error
-    assert(lastException !== undefined);
+    if (lastException === undefined || lastException === null)
+      return lastException;
     throw lastException;
   } else if (typeof target === 'object' && target !== null) {
     const keys = ObjectKeys(target);
@@ -627,20 +643,16 @@ function resolveExportsTarget(baseUrl, target, subpath, mappingKey) {
     }
     for (const p of keys) {
       if (cjsConditions.has(p) || p === 'default') {
-        try {
-          return resolveExportsTarget(baseUrl, target[p], subpath,
-                                      mappingKey);
-        } catch (e) {
-          if (e.code !== 'ERR_PACKAGE_PATH_NOT_EXPORTED') throw e;
-        }
-        break;
+        const resolved = resolveExportsTarget(baseUrl, target[p], subpath,
+                                              mappingKey);
+        if (resolved === undefined)
+          continue;
+        return resolved;
       }
     }
-    throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-      baseUrl.pathname, mappingKey + subpath);
+    return undefined;
   } else if (target === null) {
-    throw new ERR_PACKAGE_PATH_NOT_EXPORTED(
-      baseUrl.pathname, mappingKey + subpath);
+    return null;
   }
   throw new ERR_INVALID_PACKAGE_TARGET(baseUrl.pathname, mappingKey, target);
 }
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index f998f28ddf08d1..fec0ee181c7e28 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -51,7 +51,8 @@ const {
 const { Module: CJSModule } = require('internal/modules/cjs/loader');
 
 const packageJsonReader = require('internal/modules/package_json_reader');
-const userConditions = (getOptionValue('--conditions') || '').split(',');
+const userConditions = getOptionValue('--conditions') &&
+    getOptionValue('--conditions').split(',');
 const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
@@ -360,12 +361,9 @@ function isArrayIndex(key) {
 function resolvePackageTarget(
   packageJSONUrl, target, subpath, packageSubpath, base, internal, conditions) {
   if (typeof target === 'string') {
-    const resolved = resolvePackageTargetString(
+    return finalizeResolution(resolvePackageTargetString(
       target, subpath, packageSubpath, packageJSONUrl, base, internal,
-      conditions);
-    if (resolved === null)
-      return null;
-    return finalizeResolution(resolved, base);
+      conditions), base);
   } else if (ArrayIsArray(target)) {
     if (target.length === 0)
       return null;

From 936a2135c31191ee1242b793c2c762421557a090 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 12:49:59 -0700
Subject: [PATCH 03/10] remove condition alias for now

---
 doc/api/cli.md      | 3 ++-
 doc/node.1          | 2 +-
 src/node_options.cc | 1 -
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 493e40a79c5db5..805198c9516cd7 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -76,7 +76,7 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
-### `-cc`, `--conditions=conditionA,conditionB`
+### `--conditions=conditionA,conditionB`
 <!-- YAML
 added: REPLACEME
 -->
@@ -1247,6 +1247,7 @@ node --require "./a.js" --require "./b.js"
 
 Node.js options that are allowed are:
 <!-- node-options-node start -->
+* `--conditions`
 * `--diagnostic-dir`
 * `--disable-proto`
 * `--enable-fips`
diff --git a/doc/node.1 b/doc/node.1
index e35dd697638bd6..b6b062cd346b5b 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -78,7 +78,7 @@ Aborting instead of exiting causes a core file to be generated for analysis.
 .It Fl -completion-bash
 Print source-able bash completion script for Node.js.
 .
-.It Fl cc , Fl -conditions Ar string
+.It Fl -conditions Ar string
 Use custom conditional exports conditions
 .Ar string
 .
diff --git a/src/node_options.cc b/src/node_options.cc
index 541eb2b1906d57..d61ea6bec25085 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -285,7 +285,6 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "set the conditional exports conditions",
             &EnvironmentOptions::conditions,
             kAllowedInEnvironment);
-  AddAlias("-cc", "--conditions");
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",

From e1a91c85d0f040b49ded26a0b46f5a788eca1e95 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 12:52:08 -0700
Subject: [PATCH 04/10] todo is done

---
 lib/internal/modules/cjs/loader.js | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index 8aa20119c91b62..1b7abb26dbd0f1 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -1009,7 +1009,6 @@ Module._load = function(request, parent, isMain) {
   return module.exports;
 };
 
-// TODO: Use this set when resolving pkg#exports conditions.
 const cjsConditions = new SafeSet(['require', 'node', ...userConditions]);
 Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.canBeRequiredByUsers(request)) {

From ed6923507f9664044eac688a490843f247a84109 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 12:58:53 -0700
Subject: [PATCH 05/10] -m alias, docs

---
 doc/api/cli.md      |  4 ++--
 doc/api/esm.md      | 11 +++++++++++
 doc/node.1          |  2 +-
 src/node_options.cc |  1 +
 4 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 805198c9516cd7..d19e0628f1889b 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -76,7 +76,7 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
-### `--conditions=conditionA,conditionB`
+### `-m`, `--conditions=conditionA,conditionB`
 <!-- YAML
 added: REPLACEME
 -->
@@ -1247,7 +1247,7 @@ node --require "./a.js" --require "./b.js"
 
 Node.js options that are allowed are:
 <!-- node-options-node start -->
-* `--conditions`
+* `--conditions`, `-m`
 * `--diagnostic-dir`
 * `--disable-proto`
 * `--enable-fips`
diff --git a/doc/api/esm.md b/doc/api/esm.md
index 551eef604eac0e..0a75edf2ad56bc 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -475,6 +475,17 @@ order to support packages with conditional exports. For this reason, using
 `"node"` and `"default"` condition branches is usually preferable to using
 `"node"` and `"browser"` condition branches.
 
+When running Node.js, custom comma-separated conditions can be set with the
+`--conditions` or `-m` flag:
+
+```bash
+node --conditions=development main.js
+```
+
+which would then resolve the `"development"` condition in exports, along with
+the existing `"node"`, `"default"`, `"import"` and `"require"` conditions as
+appropriate.
+
 #### Nested conditions
 
 In addition to direct mappings, Node.js also supports nested condition objects.
diff --git a/doc/node.1 b/doc/node.1
index b6b062cd346b5b..caf1705fa9f704 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -78,7 +78,7 @@ Aborting instead of exiting causes a core file to be generated for analysis.
 .It Fl -completion-bash
 Print source-able bash completion script for Node.js.
 .
-.It Fl -conditions Ar string
+.It Fl m , Fl -conditions Ar string
 Use custom conditional exports conditions
 .Ar string
 .
diff --git a/src/node_options.cc b/src/node_options.cc
index d61ea6bec25085..ea2943812680a0 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -285,6 +285,7 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "set the conditional exports conditions",
             &EnvironmentOptions::conditions,
             kAllowedInEnvironment);
+  AddAlias("-m", "--conditions");
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",

From 0180f8648527f64a4a00f4bc1daffeb1660ba52d Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 13:04:00 -0700
Subject: [PATCH 06/10] doc reorder

---
 doc/api/esm.md | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/doc/api/esm.md b/doc/api/esm.md
index 0a75edf2ad56bc..2ada58dfadc59c 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -475,17 +475,6 @@ order to support packages with conditional exports. For this reason, using
 `"node"` and `"default"` condition branches is usually preferable to using
 `"node"` and `"browser"` condition branches.
 
-When running Node.js, custom comma-separated conditions can be set with the
-`--conditions` or `-m` flag:
-
-```bash
-node --conditions=development main.js
-```
-
-which would then resolve the `"development"` condition in exports, along with
-the existing `"node"`, `"default"`, `"import"` and `"require"` conditions as
-appropriate.
-
 #### Nested conditions
 
 In addition to direct mappings, Node.js also supports nested condition objects.
@@ -512,6 +501,19 @@ a nested conditional does not have any mapping it will continue checking
 the remaining conditions of the parent condition. In this way nested
 conditions behave analogously to nested JavaScript `if` statements.
 
+#### Executing custom conditions
+
+When running Node.js, custom comma-separated conditions can be set with the
+`--conditions` or `-m` flag:
+
+```bash
+node --conditions=development main.js
+```
+
+which would then resolve the `"development"` condition in exports, along with
+the existing `"node"`, `"default"`, `"import"` and `"require"` conditions as
+appropriate.
+
 #### Self-referencing a package using its name
 
 Within a package, the values defined in the package’s

From dba70c16578c04fe530c6a2db68bd160b62f4f31 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 13:04:48 -0700
Subject: [PATCH 07/10] rename heading

---
 doc/api/esm.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/api/esm.md b/doc/api/esm.md
index 2ada58dfadc59c..97c8c23bbe1def 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -501,7 +501,7 @@ a nested conditional does not have any mapping it will continue checking
 the remaining conditions of the parent condition. In this way nested
 conditions behave analogously to nested JavaScript `if` statements.
 
-#### Executing custom conditions
+#### Resolving custom conditions
 
 When running Node.js, custom comma-separated conditions can be set with the
 `--conditions` or `-m` flag:

From 52f216cd0506de9cfca2b40dfd137a94e3e17c92 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 13:43:40 -0700
Subject: [PATCH 08/10] use -u short flag

---
 doc/api/cli.md      | 4 ++--
 doc/node.1          | 2 +-
 src/node_options.cc | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/doc/api/cli.md b/doc/api/cli.md
index d19e0628f1889b..3b56f2390d4684 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -76,7 +76,7 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
-### `-m`, `--conditions=conditionA,conditionB`
+### `-u`, `--conditions=conditionA,conditionB`
 <!-- YAML
 added: REPLACEME
 -->
@@ -1247,7 +1247,7 @@ node --require "./a.js" --require "./b.js"
 
 Node.js options that are allowed are:
 <!-- node-options-node start -->
-* `--conditions`, `-m`
+* `--conditions`, `-u`
 * `--diagnostic-dir`
 * `--disable-proto`
 * `--enable-fips`
diff --git a/doc/node.1 b/doc/node.1
index caf1705fa9f704..7eb877bb1c8b4d 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -78,7 +78,7 @@ Aborting instead of exiting causes a core file to be generated for analysis.
 .It Fl -completion-bash
 Print source-able bash completion script for Node.js.
 .
-.It Fl m , Fl -conditions Ar string
+.It Fl u , Fl -conditions Ar string
 Use custom conditional exports conditions
 .Ar string
 .
diff --git a/src/node_options.cc b/src/node_options.cc
index ea2943812680a0..f5dcc18b105a10 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -285,7 +285,7 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "set the conditional exports conditions",
             &EnvironmentOptions::conditions,
             kAllowedInEnvironment);
-  AddAlias("-m", "--conditions");
+  AddAlias("-u", "--conditions");
   AddOption("--diagnostic-dir",
             "set dir for all output files"
             " (default: current working directory)",

From acbe3ee460e24e46d7d64dd729d7fa99783e8844 Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 14:10:23 -0700
Subject: [PATCH 09/10] Apply suggestions from code review

Co-authored-by: Jordan Harband <ljharb@gmail.com>
Co-authored-by: Jan Olaf Krems <jan.krems@gmail.com>
---
 doc/api/cli.md                      | 2 +-
 doc/api/esm.md                      | 4 ++--
 lib/internal/modules/cjs/loader.js  | 2 +-
 lib/internal/modules/esm/resolve.js | 2 +-
 src/node_options.cc                 | 2 +-
 5 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 3b56f2390d4684..077239efe03d14 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -88,7 +88,7 @@ conditions.
 
 Any custom comma-separated string condition names are permitted.
 
-The default Node.js conditions of `"node"`, `"default"`, `"import"` and
+The default Node.js conditions of `"node"`, `"default"`, `"import"`, and
 `"require"` will always apply as defined.
 
 ### `--cpu-prof`
diff --git a/doc/api/esm.md b/doc/api/esm.md
index 97c8c23bbe1def..bf6ceb20908611 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -504,14 +504,14 @@ conditions behave analogously to nested JavaScript `if` statements.
 #### Resolving custom conditions
 
 When running Node.js, custom comma-separated conditions can be set with the
-`--conditions` or `-m` flag:
+`--conditions` or `-u` flag:
 
 ```bash
 node --conditions=development main.js
 ```
 
 which would then resolve the `"development"` condition in exports, along with
-the existing `"node"`, `"default"`, `"import"` and `"require"` conditions as
+the existing `"node"`, `"default"`, `"import"`, and `"require"` conditions as
 appropriate.
 
 #### Self-referencing a package using its name
diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index 1b7abb26dbd0f1..b058e6ccd4e8ff 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -86,7 +86,7 @@ const manifest = getOptionValue('--experimental-policy') ?
   null;
 const { compileFunction } = internalBinding('contextify');
 const userConditions = getOptionValue('--conditions') &&
-    getOptionValue('--conditions').split(',');
+    StringPrototypeSplit(getOptionValue('--conditions'), ',');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index fec0ee181c7e28..5fb5dd72f6f04c 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -52,7 +52,7 @@ const { Module: CJSModule } = require('internal/modules/cjs/loader');
 
 const packageJsonReader = require('internal/modules/package_json_reader');
 const userConditions = getOptionValue('--conditions') &&
-    getOptionValue('--conditions').split(',');
+    StringPrototypeSplit(getOptionValue('--conditions'), ',');
 const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
diff --git a/src/node_options.cc b/src/node_options.cc
index f5dcc18b105a10..d3fdc459de1ee2 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -282,7 +282,7 @@ DebugOptionsParser::DebugOptionsParser() {
 
 EnvironmentOptionsParser::EnvironmentOptionsParser() {
   AddOption("--conditions",
-            "set the conditional exports conditions",
+            "additional user conditions for conditional exports and imports",
             &EnvironmentOptions::conditions,
             kAllowedInEnvironment);
   AddAlias("-u", "--conditions");

From 1ed44a4f144cfc0209cf3a3b1866f20b9ee38e4e Mon Sep 17 00:00:00 2001
From: Guy Bedford <guybedford@gmail.com>
Date: Wed, 5 Aug 2020 14:31:31 -0700
Subject: [PATCH 10/10] use multiple flags over comma separated

---
 doc/api/cli.md                             |  4 ++--
 doc/api/esm.md                             | 12 +++++++-----
 lib/internal/modules/cjs/loader.js         |  3 +--
 lib/internal/modules/esm/resolve.js        |  3 +--
 src/node_options.h                         |  2 +-
 test/es-module/test-esm-custom-exports.mjs |  2 +-
 6 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 077239efe03d14..413784538d289d 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -76,7 +76,7 @@ $ node --completion-bash > node_bash_completion
 $ source node_bash_completion
 ```
 
-### `-u`, `--conditions=conditionA,conditionB`
+### `-u`, `--conditions=condition`
 <!-- YAML
 added: REPLACEME
 -->
@@ -86,7 +86,7 @@ added: REPLACEME
 Enable experimental support for custom conditional exports resolution
 conditions.
 
-Any custom comma-separated string condition names are permitted.
+Any number of custom string condition names are permitted.
 
 The default Node.js conditions of `"node"`, `"default"`, `"import"`, and
 `"require"` will always apply as defined.
diff --git a/doc/api/esm.md b/doc/api/esm.md
index bf6ceb20908611..adbb55f0d82f0d 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -501,18 +501,20 @@ a nested conditional does not have any mapping it will continue checking
 the remaining conditions of the parent condition. In this way nested
 conditions behave analogously to nested JavaScript `if` statements.
 
-#### Resolving custom conditions
+#### Resolving user conditions
 
-When running Node.js, custom comma-separated conditions can be set with the
+When running Node.js, custom user conditions can be added with the
 `--conditions` or `-u` flag:
 
 ```bash
 node --conditions=development main.js
 ```
 
-which would then resolve the `"development"` condition in exports, along with
-the existing `"node"`, `"default"`, `"import"`, and `"require"` conditions as
-appropriate.
+which would then resolve the `"development"` condition in package imports and
+exports, while resolving the existing `"node"`, `"default"`, `"import"`, and
+`"require"` conditions as appropriate.
+
+Any number of custom conditions can be set with repeat flags.
 
 #### Self-referencing a package using its name
 
diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index b058e6ccd4e8ff..44b373f3e76063 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -85,8 +85,7 @@ const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
 const { compileFunction } = internalBinding('contextify');
-const userConditions = getOptionValue('--conditions') &&
-    StringPrototypeSplit(getOptionValue('--conditions'), ',');
+const userConditions = getOptionValue('--conditions');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
diff --git a/lib/internal/modules/esm/resolve.js b/lib/internal/modules/esm/resolve.js
index 5fb5dd72f6f04c..7cf3552948194d 100644
--- a/lib/internal/modules/esm/resolve.js
+++ b/lib/internal/modules/esm/resolve.js
@@ -51,8 +51,7 @@ const {
 const { Module: CJSModule } = require('internal/modules/cjs/loader');
 
 const packageJsonReader = require('internal/modules/package_json_reader');
-const userConditions = getOptionValue('--conditions') &&
-    StringPrototypeSplit(getOptionValue('--conditions'), ',');
+const userConditions = getOptionValue('--conditions');
 const DEFAULT_CONDITIONS = ObjectFreeze(['node', 'import', ...userConditions]);
 const DEFAULT_CONDITIONS_SET = new SafeSet(DEFAULT_CONDITIONS);
 
diff --git a/src/node_options.h b/src/node_options.h
index c668abb0b61303..3258d4b3f0df0c 100644
--- a/src/node_options.h
+++ b/src/node_options.h
@@ -100,7 +100,7 @@ class DebugOptions : public Options {
 class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
-  std::string conditions;
+  std::vector<std::string> conditions;
   bool enable_source_maps = false;
   bool experimental_json_modules = false;
   bool experimental_modules = false;
diff --git a/test/es-module/test-esm-custom-exports.mjs b/test/es-module/test-esm-custom-exports.mjs
index 227b4652588a5f..ad81abfdafd861 100644
--- a/test/es-module/test-esm-custom-exports.mjs
+++ b/test/es-module/test-esm-custom-exports.mjs
@@ -1,4 +1,4 @@
-// Flags: --conditions=custom-condition,another
+// Flags: --conditions=custom-condition -u another
 import { mustCall } from '../common/index.mjs';
 import { strictEqual } from 'assert';
 import { requireFixture, importFixture } from '../fixtures/pkgexports.mjs';