Read and write files through Zed (#6169)

Co-authored-by: Agus Zubiaga <agus@zed.dev>

packages/core/src/services/fileSystemService.test.ts

@@ -0,0 +1,59 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import fs from 'fs/promises';
+import { StandardFileSystemService } from './fileSystemService.js';
+
+vi.mock('fs/promises');
+
+describe('StandardFileSystemService', () => {
+  let fileSystem: StandardFileSystemService;
+
+  beforeEach(() => {
+    vi.resetAllMocks();
+    fileSystem = new StandardFileSystemService();
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  describe('readTextFile', () => {
+    it('should read file content using fs', async () => {
+      const testContent = 'Hello, World!';
+      vi.mocked(fs.readFile).mockResolvedValue(testContent);
+
+      const result = await fileSystem.readTextFile('/test/file.txt');
+
+      expect(fs.readFile).toHaveBeenCalledWith('/test/file.txt', 'utf-8');
+      expect(result).toBe(testContent);
+    });
+
+    it('should propagate fs.readFile errors', async () => {
+      const error = new Error('ENOENT: File not found');
+      vi.mocked(fs.readFile).mockRejectedValue(error);
+
+      await expect(fileSystem.readTextFile('/test/file.txt')).rejects.toThrow(
+        'ENOENT: File not found',
+      );
+    });
+  });
+
+  describe('writeTextFile', () => {
+    it('should write file content using fs', async () => {
+      vi.mocked(fs.writeFile).mockResolvedValue();
+
+      await fileSystem.writeTextFile('/test/file.txt', 'Hello, World!');
+
+      expect(fs.writeFile).toHaveBeenCalledWith(
+        '/test/file.txt',
+        'Hello, World!',
+        'utf-8',
+      );
+    });
+  });
+});

packages/core/src/services/fileSystemService.ts

@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import fs from 'fs/promises';
+
+/**
+ * Interface for file system operations that may be delegated to different implementations
+ */
+export interface FileSystemService {
+  /**
+   * Read text content from a file
+   *
+   * @param filePath - The path to the file to read
+   * @returns The file content as a string
+   */
+  readTextFile(filePath: string): Promise<string>;
+
+  /**
+   * Write text content to a file
+   *
+   * @param filePath - The path to the file to write
+   * @param content - The content to write
+   */
+  writeTextFile(filePath: string, content: string): Promise<void>;
+}
+
+/**
+ * Standard file system implementation
+ */
+export class StandardFileSystemService implements FileSystemService {
+  async readTextFile(filePath: string): Promise<string> {
+    return fs.readFile(filePath, 'utf-8');
+  }
+
+  async writeTextFile(filePath: string, content: string): Promise<void> {
+    await fs.writeFile(filePath, content, 'utf-8');
+  }
+}