refactor(@angular/build): allow Bazel to inject a custom esbuild plugin

Introduces a mechanism to dynamically load a custom esbuild plugin when the application builder is executed within a Bazel environment.

This is enabled by a new `bazelEsbuildPluginPath` option, which is derived from the `NG_INTERNAL_ESBUILD_PLUGINS_DO_NOT_USE` environment variable. The path is only resolved if the `BAZEL_BINDIR` and `JS_BINARY__EXECROOT` environment variables are also present, ensuring the logic is only active during a Bazel build.

The builder dynamically imports the plugin from the specified path and adds it to the esbuild pipeline, allowing for build-system-specific customizations.

Author: clydin

packages/angular/build/src/builders/application/index.ts

@@ -14,7 +14,7 @@ import { BuildOutputFileType } from '../../tools/esbuild/bundler-context';
 import { createJsonBuildManifest, emitFilesToDisk } from '../../tools/esbuild/utils';
 import { colors as ansiColors } from '../../utils/color';
 import { deleteOutputDir } from '../../utils/delete-output-dir';
-import { useJSONBuildLogs } from '../../utils/environment-options';
+import { bazelEsbuildPluginPath, useJSONBuildLogs } from '../../utils/environment-options';
 import { purgeStaleBuildCache } from '../../utils/purge-cache';
 import { assertCompatibleAngularVersion } from '../../utils/version';
 import { runEsBuildBuildAction } from './build-action';
@@ -56,6 +56,14 @@ export async function* buildApplicationInternal(
     return;
   }
 
+  if (bazelEsbuildPluginPath) {
+    extensions ??= {};
+    extensions.codePlugins ??= [];
+
+    const { default: bazelEsbuildPlugin } = await import(bazelEsbuildPluginPath);
+    extensions.codePlugins.push(bazelEsbuildPlugin);
+  }
+
   const normalizedOptions = await normalizeOptions(context, projectName, options, extensions);
 
   if (!normalizedOptions.outputOptions.ignoreServer) {

packages/angular/build/src/utils/environment-options.ts

@@ -165,3 +165,11 @@ export const useComponentTemplateHmr = parseTristate(process.env['NG_HMR_TEMPLAT
  * When `NG_BUILD_PARTIAL_SSR` is enabled, a partial server-side rendering build will be performed.
  */
 export const usePartialSsrBuild = parseTristate(process.env['NG_BUILD_PARTIAL_SSR']) === true;
+
+const bazelBinDirectory = process.env['BAZEL_BINDIR'];
+const bazelExecRoot = process.env['JS_BINARY__EXECROOT'];
+
+export const bazelEsbuildPluginPath =
+  bazelBinDirectory && bazelExecRoot
+    ? process.env['NG_INTERNAL_ESBUILD_PLUGINS_DO_NOT_USE']
+    : undefined;