fix(@angular-devkit/build-angular): retain symlinks to output platform directories on builds

The `deleteOutputPath` option will now empty specific build artifact directories instead of
removing them completely. This allows for symlinking or mounting the directories via Docker.
This is similar to the current behavior of emptying the root output path to allow similar
actions. All previous files will still be removed when the `deleteOutputPath` option is enabled.
This is useful in situations were the browser output files may be symlinked onto another
location on disk that is setup as a development server, or a Docker configuration mounts the browser
and server output to different locations on the host machine.

Author: clydin

packages/angular_devkit/build_angular/src/builders/application/build-action.ts

@@ -53,7 +53,7 @@ export async function* runEsBuildBuildAction(
   } = options;
 
   if (deleteOutputPath && writeToFileSystem) {
-    await deleteOutputDir(workspaceRoot, outputPath);
+    await deleteOutputDir(workspaceRoot, outputPath, ['browser', 'server']);
   }
 
   const withProgress: typeof withSpinner = progress ? withSpinner : withNoProgress;

packages/angular_devkit/build_angular/src/builders/application/tests/options/delete-output-path_spec.ts

@@ -15,8 +15,9 @@ describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
       // Application code is not needed for asset tests
       await harness.writeFile('src/main.ts', 'console.log("TEST");');
 
-      // Add file in output
-      await harness.writeFile('dist/dummy.txt', '');
+      // Add files in output
+      await harness.writeFile('dist/a.txt', 'A');
+      await harness.writeFile('dist/browser/b.txt', 'B');
     });
 
     it(`should delete the output files when 'deleteOutputPath' is true`, async () => {
@@ -27,7 +28,10 @@ describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
 
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
-      harness.expectFile('dist/dummy.txt').toNotExist();
+      harness.expectDirectory('dist').toExist();
+      harness.expectFile('dist/a.txt').toNotExist();
+      harness.expectDirectory('dist/browser').toExist();
+      harness.expectFile('dist/browser/b.txt').toNotExist();
     });
 
     it(`should delete the output files when 'deleteOutputPath' is not set`, async () => {
@@ -38,7 +42,10 @@ describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
 
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
-      harness.expectFile('dist/dummy.txt').toNotExist();
+      harness.expectDirectory('dist').toExist();
+      harness.expectFile('dist/a.txt').toNotExist();
+      harness.expectDirectory('dist/browser').toExist();
+      harness.expectFile('dist/browser/b.txt').toNotExist();
     });
 
     it(`should not delete the output files when 'deleteOutputPath' is false`, async () => {
@@ -49,7 +56,23 @@ describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
 
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
-      harness.expectFile('dist/dummy.txt').toExist();
+      harness.expectFile('dist/a.txt').toExist();
+      harness.expectFile('dist/browser/b.txt').toExist();
+    });
+
+    it(`should not delete empty only directories when 'deleteOutputPath' is true`, async () => {
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+        deleteOutputPath: true,
+      });
+
+      // Add an error to prevent the build from writing files
+      await harness.writeFile('src/main.ts', 'INVALID_CODE');
+
+      const { result } = await harness.executeOnce({ outputLogsOnFailure: false });
+      expect(result?.success).toBeFalse();
+      harness.expectDirectory('dist').toExist();
+      harness.expectDirectory('dist/browser').toExist();
     });
   });
 });

packages/angular_devkit/build_angular/src/utils/delete-output-dir.ts

@@ -12,12 +12,20 @@ import { join, resolve } from 'node:path';
 /**
  * Delete an output directory, but error out if it's the root of the project.
  */
-export async function deleteOutputDir(root: string, outputPath: string): Promise<void> {
+export async function deleteOutputDir(
+  root: string,
+  outputPath: string,
+  emptyOnlyDirectories?: string[],
+): Promise<void> {
   const resolvedOutputPath = resolve(root, outputPath);
   if (resolvedOutputPath === root) {
     throw new Error('Output path MUST not be project root directory!');
   }
 
+  const directoriesToEmpty = emptyOnlyDirectories
+    ? new Set(emptyOnlyDirectories.map((directory) => join(resolvedOutputPath, directory)))
+    : undefined;
+
   // Avoid removing the actual directory to avoid errors in cases where the output
   // directory is mounted or symlinked. Instead the contents are removed.
   let entries;
@@ -31,6 +39,14 @@ export async function deleteOutputDir(root: string, outputPath: string): Promise
   }
 
   for (const entry of entries) {
-    await rm(join(resolvedOutputPath, entry), { force: true, recursive: true, maxRetries: 3 });
+    const fullEntry = join(resolvedOutputPath, entry);
+
+    // Leave requested directories. This allows symlinks to continue to function.
+    if (directoriesToEmpty?.has(fullEntry)) {
+      await deleteOutputDir(resolvedOutputPath, fullEntry);
+      continue;
+    }
+
+    await rm(fullEntry, { force: true, recursive: true, maxRetries: 3 });
   }
 }