refactor: use cjs-module-lexer

packages/yarnpkg-pnp/package.json

@@ -16,6 +16,7 @@
     "@yarnpkg/builder": "workspace:^2.1.3",
     "@yarnpkg/libzip": "workspace:^2.2.1",
     "@yarnpkg/monorepo": "workspace:0.0.0",
+    "cjs-module-lexer": "^1.0.0",
     "enhanced-resolve": "^5.4.1",
     "rollup": "^2.35.1",
     "typescript": "4.1.0-beta",

packages/yarnpkg-pnp/sources/esm-loader/loader.ts

@@ -1,6 +1,7 @@
+import {parse, init}                            from 'cjs-module-lexer';
 import {ResolverFactory, CachedInputFileSystem} from 'enhanced-resolve';
 import fs                                       from 'fs';
-import {builtinModules, createRequire}          from 'module';
+import {builtinModules}                         from 'module';
 import path                                     from 'path';
 import {fileURLToPath, pathToFileURL, URL}      from 'url';
 
@@ -149,6 +150,16 @@ export async function getFormat(resolved: string, context: any, defaultGetFormat
   throw new Error(`Unable to get module type of '${resolved}'`);
 }
 
+let parserInit: Promise<void> | null = init().then(() => {
+  parserInit = null;
+});
+
+async function parseExports(filePath: string) {
+  const {exports} = parse(await readFile(filePath));
+  // https://github.com/nodejs/node/blob/4d22dd329b5890387356806e45cc007b7004ee65/lib/internal/modules/esm/translators.js#L186-L188
+  return exports.includes(`default`) ? exports : [`default`, ...exports];
+}
+
 export async function getSource(urlString: string, context: any, defaultGetSource: any) {
   const url = new URL(urlString);
   if (url.protocol !== `file:`) return defaultGetSource(url, context, defaultGetSource);
@@ -161,30 +172,32 @@ export async function getSource(urlString: string, context: any, defaultGetSourc
     };
   }
 
-  const fakeModulePath = path.join(path.dirname(urlString), `noop.js`);
+  if (parserInit !== null) await parserInit;
 
-  const require = createRequire(fakeModulePath);
-  const dynModule = require(urlString);
+  const exports = await parseExports(urlString);
 
-  let exportStrings: Array<string> = [];
-  if (dynModule.__esModule === true) {
-    exportStrings = Object.getOwnPropertyNames(dynModule).map(propKey => {
-      if (propKey === `default`) {
-        return `export default cjs['default']`;
+  let exportStrings = ``;
+
+  if (exports.length !== 0) {
+    for (const exportName of exports) {
+      if (exportName === `default`) {
+        exportStrings += `export default cjs['default']\n`;
       } else {
-        return `const __${propKey} = cjs['${propKey}'];\n export { __${propKey} as ${propKey} }`;
+        exportStrings += `const __${exportName} = cjs['${exportName}'];\n export { __${exportName} as ${exportName} }\n`;
       }
-    });
+    }
   } else {
-    exportStrings = [`export default cjs`];
+    exportStrings = `export default cjs`;
   }
 
+  const fakeModulePath = path.join(path.dirname(urlString), `noop.js`);
+
   const code = `
   import {createRequire} from 'module';
   const require = createRequire('${fakeModulePath.replace(/\\/g,`/`)}');
   const cjs = require('${urlString.replace(/\\/g,`/`)}');
   
-  ${exportStrings.join(`\n`)}
+  ${exportStrings}
   `;
 
   return {

yarn.lock

@@ -6300,6 +6300,7 @@ __metadata:
     "@yarnpkg/fslib": "workspace:^2.4.0"
     "@yarnpkg/libzip": "workspace:^2.2.1"
     "@yarnpkg/monorepo": "workspace:0.0.0"
+    cjs-module-lexer: ^1.0.0
     enhanced-resolve: ^5.4.1
     rollup: ^2.35.1
     tslib: ^1.13.0
@@ -8772,6 +8773,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"cjs-module-lexer@npm:^1.0.0":
+  version: 1.0.0
+  resolution: "cjs-module-lexer@npm:1.0.0"
+  checksum: 5460ba5ac64ab7014b2263a2743a2b5e29a9add758fe22a84407581b59d916cc25758e34fb17d56d9911e27403aa7f090b474eb6e69f86c8df4aa77cb6aff908
+  languageName: node
+  linkType: hard
+
 "class-utils@npm:^0.3.5":
   version: 0.3.6
   resolution: "class-utils@npm:0.3.6"