feat(@angular/cli): automatic formatting files modified by schematics

packages/angular/cli/src/command-builder/schematics-command-module.ts

@@ -29,6 +29,7 @@ import {
   OtherOptions,
 } from './command-module';
 import { Option, parseJsonSchemaToOptions } from './utilities/json-schema';
+import { formatFiles } from './utilities/prettier';
 import { SchematicEngineHost } from './utilities/schematic-engine-host';
 import { subscribeToWorkflow } from './utilities/schematic-workflow';
 
@@ -361,7 +362,24 @@ export abstract class SchematicsCommandModule
 
       if (executionOptions.dryRun) {
         logger.warn(`\nNOTE: The "--dry-run" option means no changes were made.`);
+
+        return 0;
       }
+
+      if (files.size) {
+        // Note: we could use a task executor to format the files but this is simpler.
+        try {
+          await formatFiles(this.context.root, files);
+        } catch (error) {
+          assertIsError(error);
+
+          logger.warn(
+            `WARNING: Formatting of files failed with the following error: ${error.message}`,
+          );
+        }
+      }
+
+      return 0;
     } catch (err) {
       // In case the workflow was not successful, show an appropriate error message.
       if (err instanceof UnsuccessfulWorkflowExecution) {
@@ -376,8 +394,6 @@ export abstract class SchematicsCommandModule
     } finally {
       unsubscribe();
     }
-
-    return 0;
   }
 
   private getProjectName(): string | undefined {

packages/angular/cli/src/command-builder/utilities/prettier.ts

@@ -0,0 +1,73 @@
+/**
+ * @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 { execFile } from 'node:child_process';
+import { readFile } from 'node:fs/promises';
+import { createRequire } from 'node:module';
+import { dirname, extname, join, relative } from 'node:path';
+import { promisify } from 'node:util';
+
+const execFileAsync = promisify(execFile);
+let prettierCliPath: string | null | undefined;
+
+/**
+ * File types that can be formatted using Prettier.
+ */
+const fileTypes: ReadonlySet<string> = new Set([
+  '.ts',
+  '.html',
+  '.js',
+  '.mjs',
+  '.cjs',
+  '.json',
+  '.css',
+  '.less',
+  '.scss',
+  '.sass',
+]);
+
+/**
+ * Formats files using Prettier.
+ * @param cwd The current working directory.
+ * @param files The files to format.
+ */
+export async function formatFiles(cwd: string, files: Set<string>): Promise<void> {
+  if (!files.size) {
+    return;
+  }
+
+  if (prettierCliPath === undefined) {
+    try {
+      const prettierPath = createRequire(cwd + '/').resolve('prettier/package.json');
+      const prettierPackageJson = JSON.parse(await readFile(prettierPath, 'utf-8')) as {
+        bin: string;
+      };
+      prettierCliPath = join(dirname(prettierPath), prettierPackageJson.bin);
+    } catch {
+      // Prettier is not installed.
+      prettierCliPath = null;
+    }
+  }
+
+  if (!prettierCliPath) {
+    return;
+  }
+
+  const filesToFormat: string[] = [];
+  for (const file of files) {
+    if (fileTypes.has(extname(file))) {
+      filesToFormat.push(relative(cwd, file));
+    }
+  }
+
+  if (!filesToFormat.length) {
+    return;
+  }
+
+  await execFileAsync(prettierCliPath, ['--write', ...filesToFormat], { cwd });
+}

tests/e2e/tests/commands/add/add-tailwindcss.ts

@@ -13,7 +13,7 @@ export default async function () {
   try {
     await ng('add', 'tailwindcss', '--skip-confirmation');
     await expectFileToExist('.postcssrc.json');
-    await expectFileToMatch('src/styles.css', /@import "tailwindcss";/);
+    await expectFileToMatch('src/styles.css', /@import 'tailwindcss';/);
     await expectFileToMatch('package.json', /"tailwindcss":/);
     await expectFileToMatch('package.json', /"@tailwindcss\/postcss":/);
     await expectFileToMatch('package.json', /"postcss":/);

tests/e2e/tests/test/karma-junit-output.ts

@@ -9,7 +9,7 @@ const E2E_CUSTOM_LAUNCHER = `
       flags: ['--no-sandbox', '--headless', '--disable-gpu', '--disable-dev-shm-usage'],
     },
   },
-  restartOnFileChange: true,
+  restartOnFileChange: true
 `;
 
 export default async function () {