From e87d6f5a35641da157dff001befbc9759583e7a4 Mon Sep 17 00:00:00 2001
From: sapphi-red <49056869+sapphi-red@users.noreply.github.com>
Date: Sun, 30 Mar 2025 16:37:56 +0900
Subject: [PATCH] module: add module.customConditions

Add module.customConditions which exposes the
custom resolution conditions specified by the
user.

Fixes: https://github.com/nodejs/node/issues/55824
---
 doc/api/module.md                             | 40 +++++++++++++++++++
 lib/module.js                                 | 16 ++++++++
 .../test-module-customConditions-empty.js     |  7 ++++
 .../test-module-customConditions-multiple.js  | 12 ++++++
 .../test-module-customConditions-single.js    |  9 +++++
 5 files changed, 84 insertions(+)
 create mode 100644 test/parallel/test-module-customConditions-empty.js
 create mode 100644 test/parallel/test-module-customConditions-multiple.js
 create mode 100644 test/parallel/test-module-customConditions-single.js

diff --git a/doc/api/module.md b/doc/api/module.md
index f4259a35cd0d50..34429c41eb9c8a 100644
--- a/doc/api/module.md
+++ b/doc/api/module.md
@@ -66,6 +66,46 @@ const require = createRequire(import.meta.url);
 const siblingModule = require('./sibling-module');
 ```
 
+### `module.customConditions`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* Type: {Set<string>}
+
+The custom resolution conditions specified by the user. The default Node.js conditions are not included.
+
+For example, assuming the following script for `module-customconditions.js`:
+
+```mjs
+import module from 'node:module';
+
+if (module.customConditions.has('development')) {
+  console.warn('warning: running in development mode');
+}
+```
+
+```cjs
+const module = require('node:module');
+
+if (module.customConditions.has('development')) {
+  console.warn('warning: running in development mode');
+}
+```
+
+Launching the Node.js process as:
+
+```console
+$ node -C development module-customconditions.js
+```
+
+Would generate the output:
+
+```text
+warning: running in development mode
+```
+
 ### `module.findPackageJSON(specifier[, base])`
 
 <!-- YAML
diff --git a/lib/module.js b/lib/module.js
index 1217172afb3ccb..a310522a878e61 100644
--- a/lib/module.js
+++ b/lib/module.js
@@ -1,5 +1,11 @@
 'use strict';
 
+const {
+  ObjectDefineProperty,
+  SafeArrayIterator,
+  Set,
+} = primordials;
+const { getOptionValue } = require('internal/options');
 const {
   findSourceMap,
   getSourceMapsSupport,
@@ -23,6 +29,16 @@ const { stripTypeScriptTypes } = require('internal/modules/typescript');
 
 Module.register = register;
 Module.constants = constants;
+ObjectDefineProperty(Module, 'customConditions', {
+  __proto__: null,
+  get() {
+    const value = new Set(new SafeArrayIterator(getOptionValue('--conditions')));
+    ObjectDefineProperty(this, 'customConditions', { __proto__: null, value, configurable: false });
+    return value;
+  },
+  enumerable: true,
+  configurable: true,
+});
 Module.enableCompileCache = enableCompileCache;
 Module.findPackageJSON = findPackageJSON;
 Module.flushCompileCache = flushCompileCache;
diff --git a/test/parallel/test-module-customConditions-empty.js b/test/parallel/test-module-customConditions-empty.js
new file mode 100644
index 00000000000000..fc99804911ad5d
--- /dev/null
+++ b/test/parallel/test-module-customConditions-empty.js
@@ -0,0 +1,7 @@
+'use strict';
+
+require('../common');
+const assert = require('node:assert');
+const { customConditions } = require('module');
+
+assert.deepStrictEqual(customConditions, new Set());
diff --git a/test/parallel/test-module-customConditions-multiple.js b/test/parallel/test-module-customConditions-multiple.js
new file mode 100644
index 00000000000000..fc75ea8618178b
--- /dev/null
+++ b/test/parallel/test-module-customConditions-multiple.js
@@ -0,0 +1,12 @@
+'use strict';
+
+// Flags: -C additional -C additional2
+
+require('../common');
+const assert = require('node:assert');
+const { customConditions } = require('module');
+
+assert.deepStrictEqual(
+  customConditions,
+  new Set(['additional', 'additional2'])
+);
diff --git a/test/parallel/test-module-customConditions-single.js b/test/parallel/test-module-customConditions-single.js
new file mode 100644
index 00000000000000..d654c42f9ff6ce
--- /dev/null
+++ b/test/parallel/test-module-customConditions-single.js
@@ -0,0 +1,9 @@
+'use strict';
+
+// Flags: -C additional
+
+require('../common');
+const assert = require('node:assert');
+const { customConditions } = require('module');
+
+assert.deepStrictEqual(customConditions, new Set(['additional']));