fix(@angular-devkit/build-webpack): fully close Webpack 5 compiler

The Webpack 5 compiler now contains a close function that should be called when the compiler is finished.

(cherry picked from commit dc3cdae)

Author: clydin

packages/angular_devkit/build_webpack/src/webpack/index.ts

@@ -52,6 +52,12 @@ export function runWebpack(
 
   return createWebpack({ ...config, watch: false }).pipe(
     switchMap(webpackCompiler => new Observable<BuildResult>(obs => {
+      // Webpack 5 has a compiler level close function
+      // The close function will crash if caching is disabled
+      const compilerClose = webpackCompiler.options.cache !== false
+        ? (webpackCompiler as { close?(callback: () => void): void }).close
+        : undefined;
+
       const callback = (err?: Error, stats?: webpack.Stats) => {
         if (err) {
           return obs.error(err);
@@ -71,7 +77,11 @@ export function runWebpack(
         } as unknown as BuildResult);
 
         if (!config.watch) {
-          obs.complete();
+          if (compilerClose) {
+            compilerClose(() => obs.complete());
+          } else {
+            obs.complete();
+          }
         }
       };
 
@@ -81,7 +91,10 @@ export function runWebpack(
           const watching = webpackCompiler.watch(watchOptions, callback);
 
           // Teardown logic. Close the watcher when unsubscribed from.
-          return () => watching.close(() => { });
+          return () => {
+            watching.close(() => { });
+            compilerClose?.(() => { });
+          };
         } else {
           webpackCompiler.run(callback);
         }