Allow ES Modules to export __esModule

internal/bundler/snapshots/snapshots_default.txt

@@ -1835,16 +1835,16 @@ TestMinifiedExportsAndModuleFormatCommonJS
 // foo/test.js
 var t = {};
 f(t, {
-  foo: () => l
+  foo: () => m
 });
-var l = 123;
+var m = 123;
 
 // bar/test.js
 var r = {};
 f(r, {
-  bar: () => m
+  bar: () => b
 });
-var m = 123;
+var b = 123;
 
 // entry.js
 console.log(exports, module.exports, t, r);

internal/bundler/snapshots/snapshots_splitting.txt

@@ -328,7 +328,7 @@ TestSplittingHybridESMAndCJSIssue617
 import {
   foo,
   init_a
-} from "./chunk-ZIIA2BWE.js";
+} from "./chunk-IFICMH5R.js";
 init_a();
 export {
   foo
@@ -338,15 +338,15 @@ export {
 import {
   a_exports,
   init_a
-} from "./chunk-ZIIA2BWE.js";
+} from "./chunk-IFICMH5R.js";
 
 // b.js
 var bar = (init_a(), a_exports);
 export {
   bar
 };
 
----------- /out/chunk-ZIIA2BWE.js ----------
+---------- /out/chunk-IFICMH5R.js ----------
 // a.js
 var a_exports = {};
 __export(a_exports, {
@@ -399,20 +399,20 @@ TestSplittingMissingLazyExport
 ---------- /out/a.js ----------
 import {
   foo
-} from "./chunk-XIEF2OJ5.js";
+} from "./chunk-MN2S3FNS.js";
 
 // a.js
 console.log(foo());
 
 ---------- /out/b.js ----------
 import {
   bar
-} from "./chunk-XIEF2OJ5.js";
+} from "./chunk-MN2S3FNS.js";
 
 // b.js
 console.log(bar());
 
----------- /out/chunk-XIEF2OJ5.js ----------
+---------- /out/chunk-MN2S3FNS.js ----------
 // empty.js
 var empty_exports = {};
 __markAsModule(empty_exports);

internal/js_parser/js_parser.go

@@ -12639,9 +12639,6 @@ func (p *parser) recordExport(loc logger.Loc, alias string, ref js_ast.Ref) {
 			fmt.Sprintf("Multiple exports with the same name %q", alias),
 			[]logger.MsgData{logger.RangeData(&p.tracker, js_lexer.RangeOfIdentifier(p.source, name.AliasLoc),
 				fmt.Sprintf("%q was originally exported here", alias))})
-	} else if alias == "__esModule" {
-		p.log.AddRangeError(&p.tracker, js_lexer.RangeOfIdentifier(p.source, loc),
-			"The export name \"__esModule\" is reserved and cannot be used (it's needed as an export marker when converting ES module syntax to CommonJS)")
 	} else {
 		p.namedExports[alias] = js_ast.NamedExport{AliasLoc: loc, Ref: ref}
 	}

internal/js_parser/js_parser_test.go

@@ -2502,13 +2502,6 @@ func TestExport(t *testing.T) {
 		"<stdin>: error: This export alias is invalid because it contains the unpaired Unicode surrogate U+DC00\n")
 	expectParseErrorTarget(t, 2020, "export * as '' from 'foo'",
 		"<stdin>: error: Using a string as a module namespace identifier name is not supported in the configured target environment\n")
-
-	// Exports with the name "__esModule" are forbidden
-	esModuleError := "<stdin>: error: The export name \"__esModule\" is reserved and cannot be used " +
-		"(it's needed as an export marker when converting ES module syntax to CommonJS)\n"
-	expectParseError(t, "export var __esModule", esModuleError)
-	expectParseError(t, "export {__esModule}; var __esModule", esModuleError)
-	expectParseError(t, "export {__esModule} from 'foo'", esModuleError)
 }
 
 func TestExportDuplicates(t *testing.T) {

internal/runtime/runtime.go

@@ -111,7 +111,7 @@ func code(isES6 bool) string {
 		export var __spreadProps = (a, b) => __defProps(a, __getOwnPropDescs(b))
 
 		// Tells importing modules that this can be considered an ES6 module
-		var __markAsModule = target => __defProp(target, '__esModule', { value: true })
+		var __markAsModule = target => !__hasOwnProp.call(target, '__esModule') && __defProp(target, '__esModule', { value: true })
 
 		// Tells importing modules that this can be considered an ES6 module
 		export var __name = (target, value) => __defProp(target, 'name', { value, configurable: true })
@@ -168,9 +168,9 @@ func code(isES6 bool) string {
 
 		// Used to implement ES6 exports to CommonJS
 		export var __export = (target, all) => {
-			__markAsModule(target)
 			for (var name in all)
 				__defProp(target, name, { get: all[name], enumerable: true })
+			__markAsModule(target)
 		}
 		export var __reExport = (target, module, desc) => {
 			if (module && typeof module === 'object' || typeof module === 'function')

scripts/end-to-end-tests.js

@@ -769,6 +769,10 @@
       'in.js': `const out = require('./foo'); if (!out.__esModule || out.default !== null) throw 'fail'`,
       'foo.js': `export default class x {} x = null`,
     }),
+    test(['--bundle', 'in.js', '--outfile=node.js'], {
+      'in.js': `const out = require('./foo'); if (!out.__esModule) throw 'fail'`,
+      'foo.js': `export const __esModule = true`,
+    }),
     test(['--bundle', 'in.js', '--outfile=node.js'], {
       'in.js': `
         // This is the JavaScript generated by "tsc" for the following TypeScript: