fix(@angular/build): prevent deleting parent directories of project root

packages/angular/build/src/utils/delete-output-dir.ts

@@ -7,7 +7,7 @@
  */
 
 import { readdir, rm } from 'node:fs/promises';
-import { join, resolve } from 'node:path';
+import { isAbsolute, join, relative, resolve } from 'node:path';
 
 /**
  * Delete an output directory, but error out if it's the root of the project.
@@ -18,8 +18,13 @@ export async function deleteOutputDir(
   emptyOnlyDirectories?: string[],
 ): Promise<void> {
   const resolvedOutputPath = resolve(root, outputPath);
-  if (resolvedOutputPath === root) {
-    throw new Error('Output path MUST not be project root directory!');
+  const relativePath = relative(resolvedOutputPath, root);
+  // When relative() returns an absolute path, the paths are on different drives/roots
+  // (e.g. Windows drive letters or UNC paths), so it cannot be an ancestor.
+  if (!relativePath || (!isAbsolute(relativePath) && !relativePath.startsWith('..'))) {
+    throw new Error(
+      `Output path "${resolvedOutputPath}" MUST not be the project root directory or its parent.`,
+    );
   }
 
   const directoriesToEmpty = emptyOnlyDirectories

packages/angular/build/src/utils/delete-output-dir_spec.ts

@@ -0,0 +1,68 @@
+/**
+ * @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.dev/license
+ */
+
+import { mkdir, mkdtemp, readdir, writeFile } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { deleteOutputDir } from './delete-output-dir';
+
+describe('deleteOutputDir', () => {
+  let root: string;
+
+  beforeEach(async () => {
+    root = await mkdtemp(join(tmpdir(), 'ng-test-'));
+  });
+
+  it('should throw when output path is the project root', async () => {
+    await expectAsync(deleteOutputDir(root, '.')).toBeRejectedWithError(
+      /MUST not be the project root directory or its parent/,
+    );
+  });
+
+  it('should throw when output path is a parent of the project root', async () => {
+    await expectAsync(deleteOutputDir(root, '..')).toBeRejectedWithError(
+      /MUST not be the project root directory or its parent/,
+    );
+  });
+
+  it('should throw when output path is a grandparent of the project root', async () => {
+    await expectAsync(deleteOutputDir(root, '../..')).toBeRejectedWithError(
+      /MUST not be the project root directory or its parent/,
+    );
+  });
+
+  it('should not throw when output path is a child of the project root', async () => {
+    const outputDir = join(root, 'dist');
+    await mkdir(outputDir, { recursive: true });
+    await writeFile(join(outputDir, 'old-file.txt'), 'content');
+
+    await expectAsync(deleteOutputDir(root, 'dist')).toBeResolved();
+  });
+
+  it('should delete contents of a valid output directory', async () => {
+    const outputDir = join(root, 'dist');
+    await mkdir(outputDir, { recursive: true });
+    await writeFile(join(outputDir, 'old-file.txt'), 'content');
+
+    await deleteOutputDir(root, 'dist');
+
+    const entries = await readdir(outputDir);
+    expect(entries.length).toBe(0);
+  });
+
+  it('should not throw when output directory does not exist', async () => {
+    await expectAsync(deleteOutputDir(root, 'nonexistent')).toBeResolved();
+  });
+
+  it('should not throw when output path is an absolute path outside the project', async () => {
+    const externalDir = await mkdtemp(join(tmpdir(), 'ng-test-external-'));
+    await writeFile(join(externalDir, 'old-file.txt'), 'content');
+
+    await expectAsync(deleteOutputDir(root, externalDir)).toBeResolved();
+  });
+});