From 382d66c92b0d04c96ea804991dd27d71039ad1f2 Mon Sep 17 00:00:00 2001
From: Antoine du HAMEL <duhamelantoine1995@gmail.com>
Date: Sun, 8 Mar 2020 23:28:23 +0100
Subject: [PATCH] esm: implement import.meta.main

Boolean value to check if a module is run as entry point of the current
process.

Fixes: https://gtihub.com/nodejs/modules/issues/274
---
 doc/api/esm.md                                |  7 ++++++-
 lib/internal/modules/esm/translators.js       |  9 +++++++--
 test/es-module/test-esm-import-meta-main.mjs  | 11 +++++++++++
 test/es-module/test-esm-import-meta.mjs       |  2 +-
 test/fixtures/es-modules/import-meta-main.mjs |  1 +
 5 files changed, 26 insertions(+), 4 deletions(-)
 create mode 100644 test/es-module/test-esm-import-meta-main.mjs
 create mode 100644 test/fixtures/es-modules/import-meta-main.mjs

diff --git a/doc/api/esm.md b/doc/api/esm.md
index 3215cc100df651..598f748d236c6d 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -784,8 +784,10 @@ import _ from 'data:application/json,"world!"';
 * {Object}
 
 The `import.meta` metaproperty is an `Object` that contains the following
-property:
+properties:
 
+* `main` {boolean} `true` when the current module is the entry point of
+  the current process.
 * `url` {string} The absolute `file:` URL of the module.
 
 ## Differences Between ES Modules and CommonJS
@@ -820,6 +822,8 @@ const __filename = fileURLToPath(import.meta.url);
 const __dirname = dirname(__filename);
 ```
 
+Equivalent of `require.main === module` is [`import.meta.main`][].
+
 ### No `require.resolve`
 
 Former use cases relying on `require.resolve` to determine the resolved path
@@ -1694,6 +1698,7 @@ success!
 [`getFormat` hook]: #esm_code_getformat_code_hook
 [`import()`]: #esm_import-expressions
 [`import.meta.url`]: #esm_import_meta
+[`import.meta.main`]: #esm_import_meta
 [`import`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import
 [`module.createRequire()`]: modules.html#modules_module_createrequire_filename
 [`module.syncBuiltinESMExports()`]: modules.html#modules_module_syncbuiltinesmexports
diff --git a/lib/internal/modules/esm/translators.js b/lib/internal/modules/esm/translators.js
index 497f90ed94475b..b416a5180131ed 100644
--- a/lib/internal/modules/esm/translators.js
+++ b/lib/internal/modules/esm/translators.js
@@ -3,6 +3,8 @@
 /* global WebAssembly */
 
 const {
+  Boolean,
+  FunctionPrototypeBind,
   JSONParse,
   ObjectKeys,
   SafeMap,
@@ -66,11 +68,12 @@ function initializeImportMeta(meta, { url }) {
   // Alphabetical
   if (experimentalImportMetaResolve)
     meta.resolve = createImportMetaResolve(url);
+  meta.main = Boolean(this?.isMain);
   meta.url = url;
 }
 
 // Strategy for loading a standard JavaScript module
-translators.set('module', async function moduleStrategy(url) {
+translators.set('module', async function moduleStrategy(url, isMain) {
   let { source } = await this._getSource(
     url, { format: 'module' }, defaultGetSource);
   source = `${source}`;
@@ -80,7 +83,9 @@ translators.set('module', async function moduleStrategy(url) {
   debug(`Translating StandardModule ${url}`);
   const module = new ModuleWrap(url, undefined, source, 0, 0);
   moduleWrap.callbackMap.set(module, {
-    initializeImportMeta,
+    initializeImportMeta: isMain ?
+      FunctionPrototypeBind(initializeImportMeta, { isMain }) :
+      initializeImportMeta,
     importModuleDynamically,
   });
   return module;
diff --git a/test/es-module/test-esm-import-meta-main.mjs b/test/es-module/test-esm-import-meta-main.mjs
new file mode 100644
index 00000000000000..bd079ec2364e26
--- /dev/null
+++ b/test/es-module/test-esm-import-meta-main.mjs
@@ -0,0 +1,11 @@
+import { mustCall } from '../common/index.mjs';
+import fixtures from '../common/fixtures.js';
+import assert from 'assert';
+
+assert.strictEqual(import.meta.main, true);
+
+import(fixtures.path('/es-modules/import-meta-main.mjs')).then(
+  mustCall(({ isMain }) => {
+    assert.strictEqual(isMain, false);
+  })
+);
diff --git a/test/es-module/test-esm-import-meta.mjs b/test/es-module/test-esm-import-meta.mjs
index 0151177b21c302..4d3fc9f357baec 100644
--- a/test/es-module/test-esm-import-meta.mjs
+++ b/test/es-module/test-esm-import-meta.mjs
@@ -3,7 +3,7 @@ import assert from 'assert';
 
 assert.strictEqual(Object.getPrototypeOf(import.meta), null);
 
-const keys = ['url'];
+const keys = ['main', 'url'];
 assert.deepStrictEqual(Reflect.ownKeys(import.meta), keys);
 
 const descriptors = Object.getOwnPropertyDescriptors(import.meta);
diff --git a/test/fixtures/es-modules/import-meta-main.mjs b/test/fixtures/es-modules/import-meta-main.mjs
new file mode 100644
index 00000000000000..bee2c8e2651335
--- /dev/null
+++ b/test/fixtures/es-modules/import-meta-main.mjs
@@ -0,0 +1 @@
+export const isMain = import.meta.main;