angular · clydin · May 5, 2026
diff --git a/packages/angular/cli/src/commands/mcp/host.ts b/packages/angular/cli/src/commands/mcp/host.ts
@@ -58,7 +58,7 @@ export interface Host {
    * @param encoding The encoding to use.
    * @returns A promise that resolves to the file content.
    */
-  readFile(path: string, encoding: 'utf-8'): Promise<string>;
+  readFile(path: string, encoding: BufferEncoding): Promise<string>;
 
   /**
    * Finds files matching a glob pattern.
@@ -348,7 +348,7 @@ export function createRootRestrictedHost(
 
       return baseHost.existsSync(path);
     },
-    readFile(path: string, encoding: 'utf-8') {
+    readFile(path: string, encoding: BufferEncoding) {
       checkPath(path);
 
       return baseHost.readFile(path, encoding);

diff --git a/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-single-file.ts b/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-single-file.ts
@@ -9,6 +9,7 @@
 import type { RequestHandlerExtra } from '@modelcontextprotocol/sdk/shared/protocol';
 import type { ServerNotification, ServerRequest } from '@modelcontextprotocol/sdk/types';
 import type { SourceFile } from 'typescript';
+import type { Host } from '../../host';
 import { analyzeForUnsupportedZoneUses } from './analyze-for-unsupported-zone-uses';
 import { migrateTestFile } from './migrate-test-file';
 import { generateZonelessMigrationInstructionsForComponent } from './prompts';
@@ -20,12 +21,13 @@ const supportedStrategies: ReadonlySet<string> = new Set(['OnPush', 'Default', '
 
 export async function migrateSingleFile(
   sourceFile: SourceFile,
+  host: Host,
   extras: RequestHandlerExtra<ServerRequest, ServerNotification>,
 ): Promise<MigrationResponse | null> {
   const testBedSpecifier = await getImportSpecifier(sourceFile, '@angular/core/testing', 'TestBed');
   const isTestFile = sourceFile.fileName.endsWith('.spec.ts') || !!testBedSpecifier;
   if (isTestFile) {
-    return migrateTestFile(sourceFile);
+    return migrateTestFile(sourceFile, host);
   }
 
   const unsupportedZoneUseResponse = await analyzeForUnsupportedZoneUses(sourceFile);

diff --git a/.../angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-single-file_spec.ts b/.../angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-single-file_spec.ts
@@ -9,6 +9,7 @@
 import type { RequestHandlerExtra } from '@modelcontextprotocol/sdk/shared/protocol';
 import type { ServerNotification, ServerRequest } from '@modelcontextprotocol/sdk/types';
 import ts from 'typescript';
+import { createMockHost } from '../../testing/test-utils';
 import { migrateSingleFile } from './migrate-single-file';
 
 const fakeExtras = {
@@ -17,11 +18,13 @@ const fakeExtras = {
 } as unknown as RequestHandlerExtra<ServerRequest, ServerNotification>;
 
 describe('migrateSingleFile', () => {
+  const mockHost = createMockHost();
+
   it('should identify test files by extension', async () => {
     const fileName = 'test.spec.ts';
     const sourceFile = ts.createSourceFile(fileName, '', ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result?.content[0].text).toContain(
       'The test file `test.spec.ts` is not yet configured for zoneless change detection.' +
@@ -34,7 +37,7 @@ describe('migrateSingleFile', () => {
     const content = `import { TestBed } from '@angular/core/testing';`;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result?.content[0].text).toContain(
       'The test file `test.ts` is not yet configured for zoneless change detection.' +
@@ -59,7 +62,7 @@ describe('migrateSingleFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result?.content[0].text).toContain(
       'The component uses NgZone APIs that are incompatible with zoneless applications',
@@ -80,7 +83,7 @@ describe('migrateSingleFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result).toBeNull();
   });
@@ -99,7 +102,7 @@ describe('migrateSingleFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result).toBeNull();
   });
@@ -117,7 +120,7 @@ describe('migrateSingleFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result?.content[0].text).toContain(
       'The component does not currently use a change detection strategy, which means it may rely on Zone.js',
@@ -134,7 +137,7 @@ describe('migrateSingleFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result).toBeNull();
   });
@@ -144,7 +147,7 @@ describe('migrateSingleFile', () => {
     const content = ``;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateSingleFile(sourceFile, fakeExtras);
+    const result = await migrateSingleFile(sourceFile, mockHost, fakeExtras);
 
     expect(result).toBeNull();
   });

diff --git a/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-test-file.ts b/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-test-file.ts
@@ -6,19 +6,21 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import { existsSync, readFileSync } from 'node:fs';
-import { glob } from 'node:fs/promises';
-import { dirname, join } from 'node:path';
+import { join } from 'node:path';
 import type { SourceFile } from 'typescript';
+import { type Host } from '../../host';
 import { findAngularJsonDir } from '../../workspace-utils';
 import { createFixResponseForZoneTests, createProvideZonelessForTestsSetupPrompt } from './prompts';
 import { loadTypescript } from './ts-utils';
 import { MigrationResponse } from './types';
 
-export async function migrateTestFile(sourceFile: SourceFile): Promise<MigrationResponse | null> {
+export async function migrateTestFile(
+  sourceFile: SourceFile,
+  host: Host,
+): Promise<MigrationResponse | null> {
   const ts = await loadTypescript();
   // Check if tests use zoneless either by default through `initTestEnvironment` or by explicitly calling `provideZonelessChangeDetection`.
-  let testsUseZonelessChangeDetection = await searchForGlobalZoneless(sourceFile.fileName);
+  let testsUseZonelessChangeDetection = await searchForGlobalZoneless(sourceFile.fileName, host);
   if (!testsUseZonelessChangeDetection) {
     ts.forEachChild(sourceFile, function visit(node) {
       if (
@@ -42,18 +44,19 @@ export async function migrateTestFile(sourceFile: SourceFile): Promise<Migration
   return createFixResponseForZoneTests(sourceFile);
 }
 
-export async function searchForGlobalZoneless(startPath: string): Promise<boolean> {
-  const angularJsonDir = findAngularJsonDir(startPath);
+export async function searchForGlobalZoneless(startPath: string, host: Host): Promise<boolean> {
+  const angularJsonDir = findAngularJsonDir(startPath, host);
   if (!angularJsonDir) {
     // Cannot determine project root, fallback to original behavior or assume false.
     // For now, let's assume no global setup if angular.json is not found.
     return false;
   }
 
   try {
-    const files = glob(`${angularJsonDir}/**/*.ts`);
+    const files = host.glob('**/*.ts', { cwd: angularJsonDir });
     for await (const file of files) {
-      const content = readFileSync(file, 'utf-8');
+      const fullPath = join(file.parentPath, file.name);
+      const content = await host.readFile(fullPath, 'utf-8');
       if (
         content.includes('initTestEnvironment') &&
         content.includes('provideZonelessChangeDetection')

diff --git a/...es/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-test-file_spec.ts b/...es/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/migrate-test-file_spec.ts
@@ -7,14 +7,16 @@
  */
 
 import ts from 'typescript';
+import { createMockHost } from '../../testing/test-utils';
 import { migrateTestFile } from './migrate-test-file';
 
 describe('migrateTestFile', () => {
+  const mockHost = createMockHost();
   it('should return setup prompt when zoneless is not detected', async () => {
     const fileName = 'test.spec.ts';
     const sourceFile = ts.createSourceFile(fileName, '', ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateTestFile(sourceFile);
+    const result = await migrateTestFile(sourceFile, mockHost);
 
     expect(result?.content[0].text).toContain(
       'The test file `test.spec.ts` is not yet configured for zoneless change detection.',
@@ -33,7 +35,7 @@ describe('migrateTestFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateTestFile(sourceFile);
+    const result = await migrateTestFile(sourceFile, mockHost);
 
     expect(result).toBeNull();
   });
@@ -60,7 +62,7 @@ describe('migrateTestFile', () => {
     `;
     const sourceFile = ts.createSourceFile(fileName, content, ts.ScriptTarget.ESNext, true);
 
-    const result = await migrateTestFile(sourceFile);
+    const result = await migrateTestFile(sourceFile, mockHost);
 
     expect(result?.content[0].text).toContain(
       'You must refactor these tests to work in a zoneless environment and remove the `provideZoneChangeDetection` calls.',

diff --git a/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/ts-utils.ts b/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/ts-utils.ts
@@ -6,8 +6,8 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import { readFileSync } from 'node:fs';
 import type ts from 'typescript';
+import type { Host } from '../../host';
 
 let typescriptModule: typeof ts;
 
@@ -116,8 +116,8 @@ export function findImportSpecifier(
 }
 
 /** Creates a TypeScript source file from a file path. */
-export async function createSourceFile(file: string) {
-  const content = readFileSync(file, 'utf8');
+export async function createSourceFile(file: string, host: Host) {
+  const content = await host.readFile(file, 'utf8');
 
   const ts = await loadTypescript();
 

diff --git a/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/zoneless-migration.ts b/packages/angular/cli/src/commands/mcp/tools/onpush-zoneless-migration/zoneless-migration.ts
@@ -8,10 +8,10 @@
 
 import type { RequestHandlerExtra } from '@modelcontextprotocol/sdk/shared/protocol';
 import type { ServerNotification, ServerRequest } from '@modelcontextprotocol/sdk/types';
-import { existsSync, statSync } from 'node:fs';
-import { glob } from 'node:fs/promises';
+import { join } from 'node:path';
 import type { SourceFile } from 'typescript';
 import { z } from 'zod';
+import type { Host } from '../../host';
 import { declareTool } from '../tool-registry';
 import { analyzeForUnsupportedZoneUses } from './analyze-for-unsupported-zone-uses';
 import { migrateSingleFile } from './migrate-single-file';
@@ -61,19 +61,20 @@ most important action to take in the migration journey.
       ),
   },
   factory:
-    () =>
+    ({ host }) =>
     ({ fileOrDirPath }, requestHandlerExtra) =>
-      registerZonelessMigrationTool(fileOrDirPath, requestHandlerExtra),
+      registerZonelessMigrationTool(fileOrDirPath, host, requestHandlerExtra),
 });
 
 export async function registerZonelessMigrationTool(
   fileOrDirPath: string,
+  host: Host,
   extras: RequestHandlerExtra<ServerRequest, ServerNotification>,
 ) {
   let filesWithComponents, componentTestFiles, zoneFiles, categorizationErrors;
   try {
     ({ filesWithComponents, componentTestFiles, zoneFiles, categorizationErrors } =
-      await discoverAndCategorizeFiles(fileOrDirPath, extras));
+      await discoverAndCategorizeFiles(fileOrDirPath, host, extras));
   } catch (e) {
     return createResponse(
       `Error: Could not access the specified path. Please ensure the following path is correct ` +
@@ -97,15 +98,15 @@ export async function registerZonelessMigrationTool(
         : Array.from(filesWithComponents);
 
     for (const file of rankedFiles) {
-      const result = await migrateSingleFile(file, extras);
+      const result = await migrateSingleFile(file, host, extras);
       if (result !== null) {
         return result;
       }
     }
   }
 
   for (const file of componentTestFiles) {
-    const result = await migrateTestFile(file);
+    const result = await migrateTestFile(file, host);
     if (result !== null) {
       return result;
     }
@@ -124,6 +125,7 @@ export async function registerZonelessMigrationTool(
 
 async function discoverAndCategorizeFiles(
   fileOrDirPath: string,
+  host: Host,
   extras: RequestHandlerExtra<ServerRequest, ServerNotification>,
 ) {
   const filePaths: string[] = [];
@@ -134,19 +136,20 @@ async function discoverAndCategorizeFiles(
 
   let isDirectory: boolean;
   try {
-    isDirectory = statSync(fileOrDirPath).isDirectory();
+    isDirectory = (await host.stat(fileOrDirPath)).isDirectory();
   } catch (e) {
     // Re-throw to be handled by the main function as a user input error
     throw new Error(`Failed to access path: ${fileOrDirPath}`, { cause: e });
   }
 
   if (isDirectory) {
-    for await (const file of glob(`${fileOrDirPath}/**/*.ts`)) {
-      filePaths.push(file);
+    const files = host.glob('**/*.ts', { cwd: fileOrDirPath });
+    for await (const file of files) {
+      filePaths.push(join(file.parentPath, file.name));
     }
   } else {
     filePaths.push(fileOrDirPath);
-    const maybeTestFile = await getTestFilePath(fileOrDirPath);
+    const maybeTestFile = await getTestFilePath(fileOrDirPath, host);
     if (maybeTestFile) {
       // Eagerly add the test file path for categorization.
       filePaths.push(maybeTestFile);
@@ -159,8 +162,8 @@ async function discoverAndCategorizeFiles(
     const batch = filesToProcess.splice(0, CONCURRENCY_LIMIT);
     const results = await Promise.allSettled(
       batch.map(async (filePath) => {
-        const sourceFile = await createSourceFile(filePath);
-        await categorizeFile(sourceFile, extras, {
+        const sourceFile = await createSourceFile(filePath, host);
+        await categorizeFile(sourceFile, host, extras, {
           filesWithComponents,
           componentTestFiles,
           zoneFiles,
@@ -183,6 +186,7 @@ async function discoverAndCategorizeFiles(
 
 async function categorizeFile(
   sourceFile: SourceFile,
+  host: Host,
   extras: RequestHandlerExtra<ServerRequest, ServerNotification>,
   categorizedFiles: {
     filesWithComponents: Set<SourceFile>;
@@ -214,9 +218,9 @@ async function categorizeFile(
       );
     }
 
-    const testFilePath = await getTestFilePath(sourceFile.fileName);
+    const testFilePath = await getTestFilePath(sourceFile.fileName, host);
     if (testFilePath) {
-      componentTestFiles.add(await createSourceFile(testFilePath));
+      componentTestFiles.add(await createSourceFile(testFilePath, host));
     }
   } else if (zoneSpecifier) {
     zoneFiles.add(sourceFile);
@@ -271,9 +275,9 @@ async function rankComponentFilesForMigration(
   return componentFiles; // Fallback to original order if the response fails
 }
 
-async function getTestFilePath(filePath: string): Promise<string | undefined> {
+async function getTestFilePath(filePath: string, host: Host): Promise<string | undefined> {
   const testFilePath = filePath.replace(/\.ts$/, '.spec.ts');
-  if (existsSync(testFilePath)) {
+  if (host.existsSync(testFilePath)) {
     return testFilePath;
   }