fix(@ngtools/webpack): display unused file warning once per file

Author: alan-agius4

packages/angular_devkit/build_angular/test/browser/unused-files-warning_spec_large.ts

@@ -11,7 +11,7 @@ import { debounceTime, take, tap } from 'rxjs/operators';
 import { BrowserBuilderOutput } from '../../src/browser/index';
 import { createArchitect, host, ivyEnabled } from '../utils';
 
-
+// tslint:disable-next-line:no-big-function
 describe('Browser Builder unused files warnings', () => {
   const warningMessageSuffix = `is part of the TypeScript compilation but it's unused`;
   const targetSpec = { project: 'app', target: 'build' };
@@ -162,4 +162,56 @@ describe('Browser Builder unused files warnings', () => {
     await run.stop();
   });
 
+  it('should only show warning once per file', async () => {
+    if (!ivyEnabled) {
+      // TODO: https://github.com/angular/angular-cli/issues/15056
+      pending('Only supported in Ivy.');
+
+      return;
+    }
+
+    host.replaceInFile(
+      'src/tsconfig.app.json',
+      '"**/*.d.ts"',
+      '"**/*.d.ts", "testing/**/*.ts"',
+    );
+
+    // Write a used file
+    host.writeMultipleFiles({
+      'src/testing/type.ts': 'export type MyType = number;',
+    });
+
+    const logger = new TestLogger('unused-files-warnings');
+    let buildNumber = 0;
+    const run = await architect.scheduleTarget(targetSpec, { watch: true }, { logger });
+
+    await run.output
+      .pipe(
+        debounceTime(1000),
+        tap(buildEvent => {
+          expect(buildEvent.success).toBe(true);
+
+          buildNumber ++;
+          switch (buildNumber) {
+            case 1:
+              // The first should have type.ts as unused.
+              expect(logger.includes(`type.ts ${warningMessageSuffix}`)).toBe(true, `Case ${buildNumber} failed.`);
+
+              // touch a file to trigger a rebuild
+              host.appendToFile('src/main.ts', '');
+              break;
+            case 2:
+              // The second should should have type.ts as unused but shouldn't warn.
+              expect(logger.includes(warningMessageSuffix)).toBe(false, `Case ${buildNumber} failed.`);
+              break;
+          }
+
+          logger.clear();
+        }),
+        take(2),
+      )
+      .toPromise();
+    await run.stop();
+  });
+
 });

packages/ngtools/webpack/src/angular_compiler_plugin.ts

@@ -111,6 +111,7 @@ export class AngularCompilerPlugin {
   // This is needed because if the first build fails we need to do a full emit
   // even whe only a single file gets updated.
   private _hadFullJitEmit: boolean | undefined;
+  private _unusedFiles = new Set<string>();
   private _changedFileExtensions = new Set(['ts', 'tsx', 'html', 'css', 'js', 'json']);
 
   // Webpack plugin.
@@ -626,12 +627,18 @@ export class AngularCompilerPlugin {
       }
     }
 
-    const unusedFilesWarning = program.getSourceFiles()
-      .filter(({ fileName }) => !fileExcludeRegExp.test(fileName) && !usedFiles.has(fileName))
-      .map(({ fileName }) => `${fileName} is part of the TypeScript compilation but it's unused.`);
+    const sourceFiles = program.getSourceFiles();
+    for (const { fileName } of sourceFiles) {
+      if (
+        fileExcludeRegExp.test(fileName)
+        || usedFiles.has(fileName)
+        || this._unusedFiles.has(fileName)
+      ) {
+        continue;
+      }
 
-    if (unusedFilesWarning.length) {
-      compilation.warnings.push(...unusedFilesWarning);
+      compilation.warnings.push(`${fileName} is part of the TypeScript compilation but it's unused.`);
+      this._unusedFiles.add(fileName);
     }
   }