fix: aws-cdk-lib imports from ESM modules are broken

packages/aws-cdk-lib/.gitignore

@@ -6,6 +6,9 @@
 !NOTICE
 !README.md
 !scripts/
+!scripts/*.ts
+!scripts/*.sh
+scripts/*.d.ts
 
 .LAST_BUILD
 *.snk

packages/aws-cdk-lib/.npmignore

@@ -36,3 +36,5 @@ junit.xml
 exports.d.ts
 exports.js
 exports.js.map
+
+scripts

packages/aws-cdk-lib/package.json

@@ -41,7 +41,8 @@
       "cp exports.js index.js",
       "node ./scripts/verify-imports-resolve-same.js",
       "node ./scripts/verify-imports-shielded.js",
-      "/bin/bash ./scripts/minify-sources.sh"
+      "/bin/bash ./scripts/minify-sources.sh",
+      "node ./scripts/verify-esm-exports.js"
     ]
   },
   "cdk-package": {
@@ -384,7 +385,8 @@
     "esbuild": "^0.16.16",
     "fs-extra": "^9.1.0",
     "ts-node": "^9.1.1",
-    "typescript": "~3.8.3"
+    "typescript": "~3.8.3",
+    "cjs-module-lexer": "^1.2.2"
   },
   "peerDependencies": {
     "constructs": "^10.0.0"

packages/aws-cdk-lib/scripts/minify-sources.sh

@@ -16,7 +16,7 @@
 scriptdir=$(cd $(dirname $0) && pwd)
 cd ${scriptdir}/..
 
-find . -name '*.js' ! -name 'exports.js' ! -name '.eslintrc.js' ! -path '*node_modules*' | xargs npx esbuild \
+find . -name '*.js' ! -name 'index.js' ! -name 'exports.js' ! -name '.eslintrc.js' ! -path '*node_modules*' | xargs npx esbuild \
   --sourcemap \
   --platform=node \
   --format=cjs \

packages/aws-cdk-lib/scripts/verify-esm-exports.ts

@@ -0,0 +1,28 @@
+/* eslint-disable import/no-extraneous-dependencies */
+// This script is executed post packaging to verify that the JS trickery we do to make
+// lazy exports show up in an ESM import actually works.
+//
+import * as console from 'console';
+import * as lexer from 'cjs-module-lexer';
+import * as fs from 'fs-extra';
+
+async function main() {
+  console.log('🧐 Checking the CJS exports for index.js...');
+
+  const indexJs = await fs.readFile('index.js', { encoding: 'utf-8' });
+
+  const result = lexer.parse(indexJs);
+
+  if (!result.exports.includes('aws_cognito')) {
+    throw new Error('The lexer did not find aws_cognito in the set of exports of index.js');
+  }
+  if (!result.reexports.includes('./core')) {
+    throw new Error('The lexer did not find ./core in the set of -reexports of index.js');
+  }
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exitCode = 1;
+});
+

tools/@aws-cdk/ubergen/bin/ubergen.ts

@@ -299,13 +299,16 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
       indexStatements.push(`export * from './${library.shortName}';`);
       exportsStatements.unshift(`export * from './${library.shortName}';`);
     } else {
-      indexStatements.push(`export * as ${library.shortName.replace(/-/g, '_')} from './${library.shortName}';`);
-      exportsStatements.push(`Object.defineProperty(exports, '${library.shortName.replace(/-/g, '_')}', { get: function () { return require('./${library.shortName}'); } });`);
+      const exportName = library.shortName.replace(/-/g, '_');
+
+      indexStatements.push(`export * as ${exportName} from './${library.shortName}';`);
+      addLazyExport(exportsStatements, `./${library.shortName}`, exportName);
     }
     copySubmoduleExports(packageJson.exports, library, library.shortName);
   }
 
   // make the exports.ts file pass linting
+  exportsStatements.unshift('const DUMMY = undefined;');
   exportsStatements.unshift('/* eslint-disable @typescript-eslint/no-require-imports */');
 
   await fs.writeFile(path.join(libRoot, 'index.ts'), indexStatements.join('\n'), { encoding: 'utf8' });
@@ -314,6 +317,40 @@ async function prepareSourceFiles(libraries: readonly LibraryReference[], packag
   console.log('\t🍺 Success!');
 }
 
+
+/**
+ * Make this module available under the given exportName, but make it lazily loaded
+ *
+ * If we don't do this, Node is going to load all submodules upon import (even if you don't use
+ * any of their contents), which takes a long time.
+ *
+ * We need to do a little hack here to support this export style from ESM modules. The
+ * ESM loader will lex any imported CJS files to detect named exports using a NPM package
+ * called `cjs-module-lexer` (source: https://nodejs.org/api/packages.html#modules-loaders). This
+ * lexer tries to avoid recognizing exports that may have side effects, and it will refuse to
+ * recognize:
+ *
+ *    Object.defineProperty(..., 'myExport', get: () => require('./module'))
+ *
+ * Because we know our exports are safe and side-effect free, we trick it by hiding the
+ * name in a string concatenation, and then add a plain export of something it WILL
+ * recognize, but make sure it's a no-op:
+ *
+ *    Object.defineProperty(..., 'my' + 'Export', get: () => require('./module'))
+ *    if (false) {
+ *       exports.myExport = DUMMY;
+ *    }
+ *
+ * The effect is the same but we bypass the lexer and everything works out at runtime.
+ */
+function addLazyExport(into: string[], moduleName: string, exportName: string) {
+  const firstChar = exportName.substr(0, 1);
+  const rest = exportName.substr(1);
+
+  into.push(`Object.defineProperty(exports, '${firstChar}' + '${rest}', { get: function () { return require('${moduleName}'); } });`);
+  into.push(`if (false) { exports.${exportName} = DUMMY; }`);
+}
+
 /**
  * Copy the sublibrary's exports into the 'exports' of the main library.
  *

yarn.lock

@@ -3411,7 +3411,7 @@ cint@^8.2.1:
   resolved "https://registry.npmjs.org/cint/-/cint-8.2.1.tgz#70386b1b48e2773d0d63166a55aff94ef4456a12"
   integrity sha512-gyWqJHXgDFPNx7PEyFJotutav+al92TTC3dWlMFyTETlOyKBQMZb7Cetqmj3GlrnSILHwSJRwf4mIGzc7C5lXw==
 
-cjs-module-lexer@^1.0.0:
+cjs-module-lexer@^1.0.0, cjs-module-lexer@^1.2.2:
   version "1.2.2"
   resolved "https://registry.npmjs.org/cjs-module-lexer/-/cjs-module-lexer-1.2.2.tgz#9f84ba3244a512f3a54e5277e8eef4c489864e40"
   integrity sha512-cOU9usZw8/dXIXKtwa8pM0OTJQuJkxMN6w30csNRUerHfeQ5R6U3kkU/FtJeIf3M202OHfY2U8ccInBG7/xogA==