feat(aws-cdk-lib): reduce JavaScript load time, second attempt (#27362)

This is a re-roll of #27217 which had to be reverted (first attempt to fix forward in #27314, then reverted in #27353).

The issue with the previous change were:

- The mutation was accidentally switched off at the last second.
- It did not work for ESM modules, because the code were were generating was not recognized as a CommonJS export by `cjs-module-lexer`.

We now generate code that passes the `cjs-module-lexer`, and have tests in place to prove it.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk-testing/cli-integ/tests/init-javascript/init-javascript.integtest.ts

@@ -25,8 +25,10 @@ integTest('Test importing CDK from ESM', withTemporaryDirectory(withPackages(asy
 
  // Rewrite some files
  await fs.writeFile(path.join(context.integTestDir, 'new-entrypoint.mjs'), `
-// Test two styles of imports
-import { Stack, aws_sns as sns, aws_sns_subscriptions as subs, aws_sqs as sqs } from 'aws-cdk-lib';
+// Test multiple styles of imports
+import { Stack, aws_sns as sns } from 'aws-cdk-lib';
+import { SqsSubscription } from 'aws-cdk-lib/aws-sns-subscriptions';
+import * as sqs from 'aws-cdk-lib/aws-sqs';
 import * as cdk from 'aws-cdk-lib';
 
 class TestjsStack extends Stack {
@@ -39,7 +41,7 @@ class TestjsStack extends Stack {
 
  const topic = new sns.Topic(this, 'TestjsTopic');
 
- topic.addSubscription(new subs.SqsSubscription(queue));
+ topic.addSubscription(new SqsSubscription(queue));
  }
 }
 

tools/@aws-cdk/lazify/lib/index.ts

@@ -139,6 +139,8 @@ export function transformFileContents(filename: string, contents: string, progre
 
  file = ts.transform(file, [(ctx: ts.TransformationContext): ts.Transformer<ts.SourceFile> => {
  const factory = ctx.factory;
+ const alreadyEmittedExports = new Set<string>();
+
  const visit: ts.Visitor = node => {
  if (node.parent && ts.isSourceFile(node.parent)
  && ts.isExpressionStatement(node)
@@ -159,8 +161,8 @@ export function transformFileContents(filename: string, contents: string, progre
  const module = require(file);
  const entries = Object.keys(module);
 
- return entries.map((entry) =>
- createModuleGetter(factory, entry, requiredModule, (mod) =>
+ return entries.flatMap((entry) =>
+ createModuleGetterOnce(alreadyEmittedExports)(factory, entry, requiredModule, (mod) =>
  factory.createPropertyAccessExpression(mod, entry))
  );
  }
@@ -180,7 +182,7 @@ export function transformFileContents(filename: string, contents: string, progre
 
  const exportName = node.expression.left.name.text;
  const moduleName = node.expression.right.arguments[0].text;
- return createModuleGetter(factory, exportName, moduleName, (x) => x);
+ return createModuleGetterOnce(alreadyEmittedExports)(factory, exportName, moduleName, (x) => x);
  }
 
  return ts.visitEachChild(node, child => visit(child), ctx);
@@ -212,25 +214,67 @@ function createAssignment(factory: ts.NodeFactory, name: string, expression: ts.
  expression));
 }
 
+/**
+ * Create an lazy getter for a particular value at the module level
+ *
+ * Since Node statically analyzes CommonJS modules to determine its exports
+ * (using the `cjs-module-lexer` module), we need to trick it into recognizing
+ * these exports as legitimate.
+ *
+ * We do that by generating one form it will recognize that doesn't do anything,
+ * in combination with a form that actually works, that doesn't disqualify the
+ * export name.
+ */
 function createModuleGetter(
  factory: ts.NodeFactory,
  exportName: string,
  moduleName: string,
  moduleFormatter: (x: ts.Expression) => ts.Expression,
 ) {
- return factory.createExpressionStatement(factory.createCallExpression(
- factory.createPropertyAccessExpression(factory.createIdentifier('Object'), factory.createIdentifier('defineProperty')),
- undefined,
- [
- factory.createIdentifier('exports'),
- factory.createStringLiteral(exportName),
- factory.createObjectLiteralExpression([
- factory.createPropertyAssignment('configurable', factory.createTrue()),
- factory.createPropertyAssignment('get',
- factory.createArrowFunction(undefined, undefined, [], undefined, undefined,
- moduleFormatter(
- factory.createCallExpression(factory.createIdentifier('require'), undefined, [factory.createStringLiteral(moduleName)])))),
- ]),
- ]
- ));
+ return [
+ // exports.<name> = void 0;
+ factory.createExpressionStatement(factory.createBinaryExpression(
+ factory.createPropertyAccessExpression(
+ factory.createIdentifier('exports'),
+ factory.createIdentifier(exportName)),
+ ts.SyntaxKind.EqualsToken,
+ factory.createVoidZero())),
+ // Object.defineProperty(exports, "<n>" + "<ame>", { get: () => });
+ factory.createExpressionStatement(factory.createCallExpression(
+ factory.createPropertyAccessExpression(factory.createIdentifier('Object'), factory.createIdentifier('defineProperty')),
+ undefined,
+ [
+ factory.createIdentifier('exports'),
+ factory.createBinaryExpression(
+ factory.createStringLiteral(exportName.substring(0, 1)),
+ ts.SyntaxKind.PlusToken,
+ factory.createStringLiteral(exportName.substring(1)),
+ ),
+ factory.createObjectLiteralExpression([
+ factory.createPropertyAssignment('enumerable', factory.createTrue()),
+ factory.createPropertyAssignment('configurable', factory.createTrue()),
+ factory.createPropertyAssignment('get',
+ factory.createArrowFunction(undefined, undefined, [], undefined, undefined,
+ moduleFormatter(
+ factory.createCallExpression(factory.createIdentifier('require'), undefined, [factory.createStringLiteral(moduleName)])))),
+ ]),
+ ]
+ )
+ )];
+}
+
+/**
+ * Prevent emitting an export if it has already been emitted before
+ *
+ * This assumes that the symbols have the same definition, and are only duplicated because of
+ * accidental multiple `export *`s.
+ */
+function createModuleGetterOnce(alreadyEmittedExports: Set<string>): typeof createModuleGetter {
+ return (factory, exportName, moduleName, moduleFormatter) => {
+ if (alreadyEmittedExports.has(exportName)) {
+ return [];
+ }
+ alreadyEmittedExports.add(exportName);
+ return createModuleGetter(factory, exportName, moduleName, moduleFormatter);
+ };
 }

tools/@aws-cdk/lazify/package.json

@@ -20,7 +20,8 @@
  "@aws-cdk/cdk-build-tools": "0.0.0",
  "jest": "^29",
  "ts-jest": "^29",
- "typescript": "^4.5.5"
+ "typescript": "^4.5.5",
+ "cjs-module-lexer": "^1.2.3"
  },
  "dependencies": {
  "esbuild": "^0.19.4",

tools/@aws-cdk/lazify/test/export-star.test.ts

@@ -1,6 +1,7 @@
 import * as fs from 'fs-extra';
 import * as path from 'path';
 import { transformFileContents } from '../lib';
+import { parse } from 'cjs-module-lexer';
 
 // Write a .js file in this directory that will be imported by tests below
 beforeEach(async () => {
@@ -12,21 +13,47 @@ beforeEach(async () => {
 
 test('replace __exportStar with getters', () => {
  const fakeFile = path.join(__dirname, 'index.ts');
- expect(transformFileContents(fakeFile, [
+
+ const transformed = transformFileContents(fakeFile, [
  '__exportStar(require("./some-module"), exports);'
- ].join('\n'))).toMatchInlineSnapshot(`
-"Object.defineProperty(exports, "foo", { configurable: true, get: () => require("./some-module").foo });
-Object.defineProperty(exports, "bar", { configurable: true, get: () => require("./some-module").bar });
-"
-`);
+ ].join('\n'));
+
+ expect(parse(transformed).exports).toEqual([
+ 'foo',
+ 'bar',
+ ]);
+
+ const mod = evalModule(transformed);
+ expect(mod.foo()).toEqual('foo');
+ expect(mod.bar).toEqual(5);
 });
 
 test('replace re-export with getter', () => {
  const fakeFile = path.join(__dirname, 'index.ts');
- expect(transformFileContents(fakeFile, [
+ const transformed = transformFileContents(fakeFile, [
  'exports.some_module = require("./some-module");',
- ].join('\n'))).toMatchInlineSnapshot(`
-"Object.defineProperty(exports, "some_module", { configurable: true, get: () => require("./some-module") });
-"
-`);
-});
+ ].join('\n'));
+
+ expect(parse(transformed).exports).toEqual([
+ 'some_module',
+ ]);
+
+ const mod = evalModule(transformed);
+ expect(mod.some_module.foo()).toEqual('foo');
+ expect(mod.some_module.bar).toEqual(5);
+});
+
+/**
+ * Fake NodeJS evaluation of a module
+ */
+function evalModule(x: string) {
+ const code = [
+ '(function() {',
+ 'const exports = {};',
+ 'const module = { exports };',
+ x,
+ 'return exports;',
+ '})()',
+ ].join('\n');
+ return eval(code);
+}

yarn.lock

@@ -5468,7 +5468,7 @@ cidr-regex@^3.1.1:
  dependencies:
  ip-regex "^4.1.0"
 
-cjs-module-lexer@^1.0.0:
+cjs-module-lexer@^1.0.0, cjs-module-lexer@^1.2.3:
  version "1.2.3"
  resolved "https://registry.npmjs.org/cjs-module-lexer/-/cjs-module-lexer-1.2.3.tgz#6c370ab19f8a3394e318fe682686ec0ac684d107"
  integrity sha512-0TNiGstbQmCFwt4akjjBg5pLRTSyj/PkWQ1ZoO2zntmg9yLqSRxwEa4iCfQLGjqhiqBfOJa7W/E8wfGrTDmlZQ==