fix(@angular/build): ensure recreated files are watched

When deleting a file and then recreating a file that is
again referenced in the application, the watch state
will now be correctly synchronized. Previously the
application builder would consider the previously deleted
file as still watched which would prevent it from being
watched again. This situation can happen when switching
source control branches while a build is active watching.

packages/angular/build/src/builders/application/build-action.ts

@@ -180,6 +180,9 @@ export async function* runEsBuildBuildAction(
         logger.info(changes.toDebugString());
       }
 
+      // Clear removed files from current watch files
+      changes.removed.forEach((removedPath) => currentWatchFiles.delete(removedPath));
+
       result = await withProgress('Changes detected. Rebuilding...', () =>
         action(result.createRebuildState(changes)),
       );

packages/angular/build/src/builders/application/tests/behavior/rebuild-general_spec.ts

@@ -0,0 +1,111 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import { concatMap, count, take, timeout } from 'rxjs';
+import { buildApplication } from '../../index';
+import { APPLICATION_BUILDER_INFO, BASE_OPTIONS, describeBuilder } from '../setup';
+
+/**
+ * Maximum time in milliseconds for single build/rebuild
+ * This accounts for CI variability.
+ */
+export const BUILD_TIMEOUT = 30_000;
+
+describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
+  describe('Behavior: "Rebuild updates in general cases"', () => {
+    it('detects changes after a file was deleted and recreated', async () => {
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+        watch: true,
+      });
+
+      const fileAContent = `
+        console.log('FILE-A');
+        export {};
+      `;
+
+      // Create a file and add to application
+      await harness.writeFile('src/app/file-a.ts', fileAContent);
+      await harness.writeFile(
+        'src/app/app.component.ts',
+        `
+        import { Component } from '@angular/core';
+        import './file-a';
+        @Component({
+          selector: 'app-root',
+          template: 'App component',
+        })
+        export class AppComponent { }
+      `,
+      );
+
+      const buildCount = await harness
+        .execute({ outputLogsOnFailure: false })
+        .pipe(
+          timeout(BUILD_TIMEOUT),
+          concatMap(async ({ result, logs }, index) => {
+            switch (index) {
+              case 0:
+                expect(result?.success).toBeTrue();
+                harness.expectFile('dist/browser/main.js').content.toContain('FILE-A');
+
+                // Delete the imported file
+                await harness.removeFile('src/app/file-a.ts');
+
+                break;
+              case 1:
+                // Should fail from missing import
+                expect(result?.success).toBeFalse();
+
+                // Remove the failing import
+                await harness.modifyFile('src/app/app.component.ts', (content) =>
+                  content.replace(`import './file-a';`, ''),
+                );
+
+                break;
+              case 2:
+                expect(result?.success).toBeTrue();
+
+                harness.expectFile('dist/browser/main.js').content.not.toContain('FILE-A');
+
+                // Recreate the file and the import
+                await harness.writeFile('src/app/file-a.ts', fileAContent);
+                await harness.modifyFile(
+                  'src/app/app.component.ts',
+                  (content) => `import './file-a';\n` + content,
+                );
+
+                break;
+              case 3:
+                expect(result?.success).toBeTrue();
+
+                harness.expectFile('dist/browser/main.js').content.toContain('FILE-A');
+
+                // Change the imported file
+                await harness.modifyFile('src/app/file-a.ts', (content) =>
+                  content.replace('FILE-A', 'FILE-B'),
+                );
+
+                break;
+              case 4:
+                expect(result?.success).toBeTrue();
+
+                harness.expectFile('dist/browser/main.js').content.toContain('FILE-B');
+
+                break;
+            }
+          }),
+          take(5),
+          count(),
+        )
+        .toPromise();
+
+      expect(buildCount).toBe(5);
+    });
+  });
+});