feat(@ngtools/webpack): support multiple plugin instances per compilation

This change allows multiple instances of the `AngularWebpackPlugin` to be present in a Webpack configuration.
Each plugin instance should reference a different TypeScript configuration file (`tsconfig.json`) and the TypeScript configuration files should be setup to not include source files present in the other TypeScript configuration files. If files are included in more than one TypeScript configuration, the first plugin present in the Webpack configuration that can emit the file will be used.

Closes: angular#5072

Author: clydin

packages/ngtools/webpack/src/ivy/loader.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import * as path from 'path';
-import { AngularPluginSymbol, FileEmitter } from './symbol';
+import { AngularPluginSymbol, FileEmitterCollection } from './symbol';
 
 export function angularWebpackLoader(
   this: import('webpack').loader.LoaderContext,
@@ -20,8 +20,8 @@ export function angularWebpackLoader(
     throw new Error('Invalid webpack version');
   }
 
-  const emitFile = this._compilation[AngularPluginSymbol] as FileEmitter;
-  if (typeof emitFile !== 'function') {
+  const fileEmitter = this._compilation[AngularPluginSymbol] as FileEmitterCollection;
+  if (typeof fileEmitter !== 'object') {
     if (this.resourcePath.endsWith('.js')) {
       // Passthrough for JS files when no plugin is used
       this.callback(undefined, content, map);
@@ -34,7 +34,7 @@ export function angularWebpackLoader(
     return;
   }
 
-  emitFile(this.resourcePath)
+  fileEmitter.emit(this.resourcePath)
     .then((result) => {
       if (!result) {
         if (this.resourcePath.endsWith('.js')) {

packages/ngtools/webpack/src/ivy/plugin.ts

@@ -27,7 +27,7 @@ import {
   augmentProgramWithVersioning,
 } from './host';
 import { externalizePath, normalizePath } from './paths';
-import { AngularPluginSymbol, EmitFileResult, FileEmitter } from './symbol';
+import { AngularPluginSymbol, EmitFileResult, FileEmitter, FileEmitterCollection } from './symbol';
 import { InputFileSystemSync, createWebpackSystem } from './system';
 import { createAotTransformers, createJitTransformers, mergeTransformers } from './transformation';
 
@@ -54,7 +54,7 @@ interface WebpackCompilation extends compilation.Compilation {
   // tslint:disable-next-line: no-any
   compilationDependencies: { add(item: string): any };
   rebuildModule(module: compilation.Module, callback: () => void): void;
-  [AngularPluginSymbol]: FileEmitter;
+  [AngularPluginSymbol]: FileEmitterCollection;
 }
 
 function initializeNgccProcessor(
@@ -156,6 +156,12 @@ export class AngularWebpackPlugin {
     compiler.hooks.thisCompilation.tap(PLUGIN_NAME, (thisCompilation) => {
       const compilation = thisCompilation as WebpackCompilation;
 
+      // Register plugin to ensure deterministic emit order in multi-plugin usage
+      if (!compilation[AngularPluginSymbol]) {
+        compilation[AngularPluginSymbol] = new FileEmitterCollection();
+      }
+      const emitRegistration = compilation[AngularPluginSymbol].register();
+
       // Store watch mode; assume true if not present (webpack < 4.23.0)
       this.watchMode = compiler.watchMode ?? true;
 
@@ -294,7 +300,7 @@ export class AngularWebpackPlugin {
       });
 
       // Store file emitter for loader usage
-      compilation[AngularPluginSymbol] = fileEmitter;
+      emitRegistration.update(fileEmitter);
     });
   }
 
@@ -538,7 +544,7 @@ export class AngularWebpackPlugin {
       // tslint:disable-next-line: no-any
       (angularProgram as any).reuseTsProgram =
         // tslint:disable-next-line: no-any
-        angularCompiler?.getNextProgram() || (angularCompiler as any)?.getCurrentProgram();
+        angularCompiler.getNextProgram?.() || (angularCompiler as any).getCurrentProgram?.();
 
       return this.createFileEmitter(
         builder,

packages/ngtools/webpack/src/ivy/symbol.ts

@@ -15,3 +15,43 @@ export interface EmitFileResult {
 }
 
 export type FileEmitter = (file: string) => Promise<EmitFileResult | undefined>;
+
+export class FileEmitterRegistration {
+  #fileEmitter?: FileEmitter;
+
+  update(emitter: FileEmitter): void {
+    this.#fileEmitter = emitter;
+  }
+
+  emit(file: string): Promise<EmitFileResult | undefined> {
+    if (!this.#fileEmitter) {
+      throw new Error('Emit attempted before Angular Webpack plugin initialization.');
+    }
+
+    return this.#fileEmitter(file);
+  }
+}
+
+export class FileEmitterCollection {
+  #registrations: FileEmitterRegistration[] = [];
+
+  register(): FileEmitterRegistration {
+    const registration = new FileEmitterRegistration();
+    this.#registrations.push(registration);
+
+    return registration;
+  }
+
+  async emit(file: string): Promise<EmitFileResult | undefined> {
+    if (this.#registrations.length === 1) {
+      return this.#registrations[0].emit(file);
+    }
+
+    for (const registration of this.#registrations) {
+      const result = await registration.emit(file);
+      if (result) {
+        return result;
+      }
+    }
+  }
+}