fix(@angular-devkit/build-angular): empty output directory instead of removing

When the `deleteOutputPath` option is enabled (default is enabled), the configured
`outputPath` for the project was previously removed directly. This was problematic
for cases such as when the path was mounted via a Docker setup. To alleviate these
issues, the contents of the output path will now be removed instead. This maintains
the existing output path directory itself but ensures an empty location to place the
new build output.

Author: clydin

packages/angular_devkit/build_angular/src/builders/browser/specs/output-path_spec.ts

@@ -21,7 +21,7 @@ describe('Browser Builder output path', () => {
   });
   afterEach(async () => host.restore().toPromise());
 
-  it('deletes output path', async () => {
+  it('deletes output path content', async () => {
     // Write a file to the output path to later verify it was deleted.
     await host
       .write(join(host.root(), 'dist/file.txt'), virtualFs.stringToFileBuffer('file'))
@@ -34,14 +34,14 @@ describe('Browser Builder output path', () => {
     const run = await architect.scheduleTarget(target);
     const output = await run.result;
     expect(output.success).toBe(false);
-    expect(await host.exists(join(host.root(), 'dist')).toPromise()).toBe(false);
+    expect(await host.exists(join(host.root(), 'dist/file.txt')).toPromise()).toBe(false);
     await run.stop();
   });
 
-  it('deletes output path and unlink symbolic link', async () => {
+  it('deletes output path content and unlink symbolic link', async () => {
     // Write a file to the output path to later verify it was deleted.
     host.writeMultipleFiles({
-      'src-link/dummy.txt': '',
+      'src-link/a.txt': '',
       'dist/file.txt': virtualFs.stringToFileBuffer('file'),
     });
 
@@ -63,8 +63,8 @@ describe('Browser Builder output path', () => {
     const output = await run.result;
     expect(output.success).toBe(false);
 
-    expect(await host.exists(join(host.root(), 'dist')).toPromise()).toBe(false);
-    expect(await host.exists(join(host.root(), 'src-link')).toPromise()).toBe(true);
+    expect(await host.exists(join(host.root(), 'dist/file.txt')).toPromise()).toBe(false);
+    expect(await host.exists(join(host.root(), 'src-link/a.txt')).toPromise()).toBe(true);
     await run.stop();
   });
 

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

@@ -7,7 +7,7 @@
  */
 
 import * as fs from 'fs';
-import { resolve } from 'path';
+import { join, resolve } from 'path';
 
 /**
  * Delete an output directory, but error out if it's the root of the project.
@@ -18,5 +18,19 @@ export function deleteOutputDir(root: string, outputPath: string): void {
     throw new Error('Output path MUST not be project root directory!');
   }
 
-  fs.rmSync(resolvedOutputPath, { force: true, recursive: true, maxRetries: 3 });
+  // 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;
+  try {
+    entries = fs.readdirSync(resolvedOutputPath);
+  } catch (error) {
+    if (error instanceof Error && 'code' in error && error.code === 'ENOENT') {
+      return;
+    }
+    throw error;
+  }
+
+  for (const entry of entries) {
+    fs.rmSync(join(resolvedOutputPath, entry), { force: true, recursive: true, maxRetries: 3 });
+  }
 }