build: simplify legacy bundle creation and fix build-tooling dependency

The legacy bundle creation relies on `@angular/build-tooling`. As
ideally we don't have any of such scripts, that rely on build tooling
outside of Bazel, we simply add our own simple linker ESBuild plugin,
while we save on complexity by using our existing tsconfig for path
mappings.

if we find more scripts needing build tooling scripts outside of Bazel
that aren't legacy tooling, we should come up with a better solution.

Author: devversion

scripts/create-legacy-tests-bundle.mjs

@@ -1,11 +1,12 @@
 #!/usr/bin/env node
 
-import {createEsbuildAngularOptimizePlugin} from '@angular/build-tooling/shared-scripts/angular-optimization/esbuild-plugin.mjs';
+import babel from '@babel/core';
 import child_process from 'child_process';
 import esbuild from 'esbuild';
 import fs from 'fs';
 import glob from 'glob';
 import module from 'module';
+import path from 'path';
 import {dirname, join, relative} from 'path';
 import * as sass from 'sass';
 import url from 'url';
@@ -48,15 +49,10 @@ async function main() {
   await compileProjectWithNgtsc();
 
   const specEntryPointFile = await createEntryPointSpecFile();
-  const esbuildLinkerPlugin = await createEsbuildAngularOptimizePlugin({
-    enableLinker: {
-      filterPaths: /fesm2022/,
-      linkerOptions: {
-        linkerJitMode: true,
-      },
-    },
-  });
-  const esbuildResolvePlugin = await createResolveEsbuildPlugin();
+
+  // Copy tsconfig so that ESBuild can leverage its path mappings.
+  const esbuildTsconfig = path.join(legacyOutputDir, 'tsconfig-esbuild.json');
+  await fs.promises.cp(path.join(packagesDir, 'bazel-tsconfig-build.json'), esbuildTsconfig);
 
   const result = await esbuild.build({
     bundle: true,
@@ -66,7 +62,9 @@ async function main() {
     target: 'es2015',
     outfile: outFile,
     treeShaking: false,
-    plugins: [esbuildResolvePlugin, esbuildLinkerPlugin],
+    logLevel: 'info',
+    tsconfig: esbuildTsconfig,
+    plugins: [createLinkerEsbuildPlugin()],
     stdin: {contents: specEntryPointFile, resolveDir: projectDir},
   });
 
@@ -168,48 +166,26 @@ function renderSassFile(inputFile) {
   });
 }
 
-/**
- * Creates an ESBuild plugin which maps `@angular/<..>` module names to their
- * locally-built output (for the packages which are built as part of this repo).
- */
-async function createResolveEsbuildPlugin() {
+/** Plugin that links node modules using the Angular compiler CLI. */
+function createLinkerEsbuildPlugin() {
   return {
-    name: 'ng-resolve-esbuild',
+    name: 'ng-link-esbuild',
     setup: build => {
-      build.onResolve({filter: /@angular\//}, async args => {
-        const pkgName = args.path.slice('@angular/'.length);
-        let resolvedPath = join(legacyOutputDir, pkgName);
-        let stats = await statGraceful(resolvedPath);
-
-        // If the resolved path points to a directory, resolve the contained `index.js` file
-        if (stats && stats.isDirectory()) {
-          resolvedPath = join(resolvedPath, 'index.js');
-          stats = await statGraceful(resolvedPath);
-        }
-        // If the resolved path does not exist, check with an explicit JS extension.
-        else if (stats === null) {
-          resolvedPath += '.js';
-          stats = await statGraceful(resolvedPath);
-        }
-
-        return stats !== null ? {path: resolvedPath} : undefined;
+      build.onLoad({filter: /fesm2022/}, async args => {
+        const filePath = args.path;
+        const content = await fs.promises.readFile(filePath, 'utf8');
+        const {code} = await babel.transformAsync(content, {
+          filename: filePath,
+          compact: false,
+          plugins: [['@angular/compiler-cli/linker/babel', {linkerJitMode: true}]],
+        });
+
+        return {contents: code};
       });
     },
   };
 }
 
-/**
- * Retrieves the `fs.Stats` results for the given path gracefully.
- * If the file does not exist, returns `null`.
- */
-async function statGraceful(path) {
-  try {
-    return await fs.promises.stat(path);
-  } catch {
-    return null;
-  }
-}
-
 main().catch(e => {
   console.error(e);
   process.exitCode = 1;