Don’t emit __esModule on CJS files that didn’t use ESM syntax (microsoft#58169)

Author: andrewbranch

src/compiler/transformers/module/module.ts

@@ -56,6 +56,7 @@ import {
     getOriginalNodeId,
     getStrictOptionValue,
     getTextOfIdentifierOrLiteral,
+    hasJSFileExtension,
     hasJsonModuleEmitEnabled,
     hasSyntacticModifier,
     Identifier,
@@ -243,6 +244,9 @@ export function transformModule(context: TransformationContext): (x: SourceFile
     }
 
     function shouldEmitUnderscoreUnderscoreESModule() {
+        if (hasJSFileExtension(currentSourceFile.fileName) && currentSourceFile.commonJsModuleIndicator && (!currentSourceFile.externalModuleIndicator || currentSourceFile.externalModuleIndicator === true)) {
+            return false;
+        }
         if (!currentModuleInfo.exportEquals && isExternalModule(currentSourceFile)) {
             return true;
         }

tests/baselines/reference/nodeModulesAllowJsExportAssignment(module=node16).js

@@ -35,7 +35,6 @@ const a = {};
 module.exports = a;
 //// [file.js]
 "use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
 // cjs format file
 const a = {};
 module.exports = a;

tests/baselines/reference/nodeModulesAllowJsExportAssignment(module=nodenext).js

@@ -35,7 +35,6 @@ const a = {};
 module.exports = a;
 //// [file.js]
 "use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
 // cjs format file
 const a = {};
 module.exports = a;

tests/baselines/reference/nodeModulesCJSEmit1.errors.txt

@@ -0,0 +1,27 @@
+/3.cjs(2,1): error TS2304: Cannot find name 'exports'.
+/5.cjs(2,8): error TS1192: Module '"/3"' has no default export.
+
+
+==== /1.cjs (0 errors) ====
+    module.exports = {};
+    
+==== /2.cjs (0 errors) ====
+    exports.foo = 0;
+    
+==== /3.cjs (1 errors) ====
+    import "foo";
+    exports.foo = {};
+    ~~~~~~~
+!!! error TS2304: Cannot find name 'exports'.
+    
+==== /4.cjs (0 errors) ====
+    ;
+    
+==== /5.cjs (1 errors) ====
+    import two from "./2.cjs";   // ok
+    import three from "./3.cjs"; // error
+           ~~~~~
+!!! error TS1192: Module '"/3"' has no default export.
+    two.foo;
+    three.foo;
+    

tests/baselines/reference/nodeModulesCJSEmit1.js

@@ -0,0 +1,47 @@
+//// [tests/cases/conformance/node/nodeModulesCJSEmit1.ts] ////
+
+//// [1.cjs]
+module.exports = {};
+
+//// [2.cjs]
+exports.foo = 0;
+
+//// [3.cjs]
+import "foo";
+exports.foo = {};
+
+//// [4.cjs]
+;
+
+//// [5.cjs]
+import two from "./2.cjs";   // ok
+import three from "./3.cjs"; // error
+two.foo;
+three.foo;
+
+
+//// [1.cjs]
+"use strict";
+module.exports = {};
+//// [2.cjs]
+"use strict";
+exports.foo = 0;
+//// [3.cjs]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+require("foo");
+exports.foo = {};
+//// [4.cjs]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+;
+//// [5.cjs]
+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+const _2_cjs_1 = __importDefault(require("./2.cjs")); // ok
+const _3_cjs_1 = __importDefault(require("./3.cjs")); // error
+_2_cjs_1.default.foo;
+_3_cjs_1.default.foo;

tests/cases/conformance/node/nodeModulesCJSEmit1.ts

@@ -0,0 +1,23 @@
+// @module: nodenext
+// @checkJs: true
+// @outDir: dist
+// @noTypesAndSymbols: true
+
+// @Filename: /1.cjs
+module.exports = {};
+
+// @Filename: /2.cjs
+exports.foo = 0;
+
+// @Filename: /3.cjs
+import "foo";
+exports.foo = {};
+
+// @Filename: /4.cjs
+;
+
+// @Filename: /5.cjs
+import two from "./2.cjs";   // ok
+import three from "./3.cjs"; // error
+two.foo;
+three.foo;