Add MCP Roots support (#5856)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/core/src/tools/mcp-client.test.ts

@@ -13,6 +13,7 @@ import {
   discoverTools,
   discoverPrompts,
   hasValidTypes,
+  connectToMcpServer,
 } from './mcp-client.js';
 import { SSEClientTransport } from '@modelcontextprotocol/sdk/client/sse.js';
 import * as SdkClientStdioLib from '@modelcontextprotocol/sdk/client/stdio.js';
@@ -23,6 +24,8 @@ import { AuthProviderType } from '../config/config.js';
 import { PromptRegistry } from '../prompts/prompt-registry.js';
 
 import { DiscoveredMCPTool } from './mcp-tool.js';
+import { WorkspaceContext } from '../utils/workspaceContext.js';
+import { pathToFileURL } from 'node:url';
 
 vi.mock('@modelcontextprotocol/sdk/client/stdio.js');
 vi.mock('@modelcontextprotocol/sdk/client/index.js');
@@ -276,6 +279,56 @@ describe('mcp-client', () => {
     });
   });
 
+  describe('connectToMcpServer', () => {
+    it('should register a roots/list handler', async () => {
+      const mockedClient = {
+        registerCapabilities: vi.fn(),
+        setRequestHandler: vi.fn(),
+        callTool: vi.fn(),
+        connect: vi.fn(),
+      };
+      vi.mocked(ClientLib.Client).mockReturnValue(
+        mockedClient as unknown as ClientLib.Client,
+      );
+      vi.spyOn(SdkClientStdioLib, 'StdioClientTransport').mockReturnValue(
+        {} as SdkClientStdioLib.StdioClientTransport,
+      );
+      const mockWorkspaceContext = {
+        getDirectories: vi
+          .fn()
+          .mockReturnValue(['/test/dir', '/another/project']),
+      } as unknown as WorkspaceContext;
+
+      await connectToMcpServer(
+        'test-server',
+        {
+          command: 'test-command',
+        },
+        false,
+        mockWorkspaceContext,
+      );
+
+      expect(mockedClient.registerCapabilities).toHaveBeenCalledWith({
+        roots: {},
+      });
+      expect(mockedClient.setRequestHandler).toHaveBeenCalledOnce();
+      const handler = mockedClient.setRequestHandler.mock.calls[0][1];
+      const roots = await handler();
+      expect(roots).toEqual({
+        roots: [
+          {
+            uri: pathToFileURL('/test/dir').toString(),
+            name: 'dir',
+          },
+          {
+            uri: pathToFileURL('/another/project').toString(),
+            name: 'project',
+          },
+        ],
+      });
+    });
+  });
+
   describe('discoverPrompts', () => {
     const mockedPromptRegistry = {
       registerPrompt: vi.fn(),
@@ -486,7 +539,9 @@ describe('mcp-client', () => {
     });
 
     it('should connect via command', async () => {
-      const mockedTransport = vi.mocked(SdkClientStdioLib.StdioClientTransport);
+      const mockedTransport = vi
+        .spyOn(SdkClientStdioLib, 'StdioClientTransport')
+        .mockReturnValue({} as SdkClientStdioLib.StdioClientTransport);
 
       await createTransport(
         'test-server',

packages/core/src/tools/mcp-client.ts

@@ -20,6 +20,7 @@ import {
   ListPromptsResultSchema,
   GetPromptResult,
   GetPromptResultSchema,
+  ListRootsRequestSchema,
 } from '@modelcontextprotocol/sdk/types.js';
 import { parse } from 'shell-quote';
 import { AuthProviderType, MCPServerConfig } from '../config/config.js';
@@ -33,6 +34,9 @@ import { MCPOAuthProvider } from '../mcp/oauth-provider.js';
 import { OAuthUtils } from '../mcp/oauth-utils.js';
 import { MCPOAuthTokenStorage } from '../mcp/oauth-token-storage.js';
 import { getErrorMessage } from '../utils/errors.js';
+import { basename } from 'node:path';
+import { pathToFileURL } from 'node:url';
+import { WorkspaceContext } from '../utils/workspaceContext.js';
 
 export const MCP_DEFAULT_TIMEOUT_MSEC = 10 * 60 * 1000; // default to 10 minutes
 
@@ -306,6 +310,7 @@ export async function discoverMcpTools(
   toolRegistry: ToolRegistry,
   promptRegistry: PromptRegistry,
   debugMode: boolean,
+  workspaceContext: WorkspaceContext,
 ): Promise<void> {
   mcpDiscoveryState = MCPDiscoveryState.IN_PROGRESS;
   try {
@@ -319,6 +324,7 @@ export async function discoverMcpTools(
           toolRegistry,
           promptRegistry,
           debugMode,
+          workspaceContext,
         ),
     );
     await Promise.all(discoveryPromises);
@@ -363,6 +369,7 @@ export async function connectAndDiscover(
   toolRegistry: ToolRegistry,
   promptRegistry: PromptRegistry,
   debugMode: boolean,
+  workspaceContext: WorkspaceContext,
 ): Promise<void> {
   updateMCPServerStatus(mcpServerName, MCPServerStatus.CONNECTING);
 
@@ -372,6 +379,7 @@ export async function connectAndDiscover(
       mcpServerName,
       mcpServerConfig,
       debugMode,
+      workspaceContext,
     );
 
     mcpClient.onerror = (error) => {
@@ -655,12 +663,30 @@ export async function connectToMcpServer(
   mcpServerName: string,
   mcpServerConfig: MCPServerConfig,
   debugMode: boolean,
+  workspaceContext: WorkspaceContext,
 ): Promise<Client> {
   const mcpClient = new Client({
     name: 'gemini-cli-mcp-client',
     version: '0.0.1',
   });
 
+  mcpClient.registerCapabilities({
+    roots: {},
+  });
+
+  mcpClient.setRequestHandler(ListRootsRequestSchema, async () => {
+    const roots = [];
+    for (const dir of workspaceContext.getDirectories()) {
+      roots.push({
+        uri: pathToFileURL(dir).toString(),
+        name: basename(dir),
+      });
+    }
+    return {
+      roots,
+    };
+  });
+
   // patch Client.callTool to use request timeout as genai McpCallTool.callTool does not do it
   // TODO: remove this hack once GenAI SDK does callTool with request options
   if ('callTool' in mcpClient) {

packages/core/src/tools/tool-registry.test.ts

@@ -336,6 +336,7 @@ describe('ToolRegistry', () => {
         toolRegistry,
         config.getPromptRegistry(),
         false,
+        expect.any(Object),
       );
     });
 
@@ -359,6 +360,7 @@ describe('ToolRegistry', () => {
         toolRegistry,
         config.getPromptRegistry(),
         false,
+        expect.any(Object),
       );
     });
   });

packages/core/src/tools/tool-registry.ts

@@ -178,6 +178,7 @@ export class ToolRegistry {
       this,
       this.config.getPromptRegistry(),
       this.config.getDebugMode(),
+      this.config.getWorkspaceContext(),
     );
   }
 
@@ -199,6 +200,7 @@ export class ToolRegistry {
       this,
       this.config.getPromptRegistry(),
       this.config.getDebugMode(),
+      this.config.getWorkspaceContext(),
     );
   }
 
@@ -225,6 +227,7 @@ export class ToolRegistry {
         this,
         this.config.getPromptRegistry(),
         this.config.getDebugMode(),
+        this.config.getWorkspaceContext(),
       );
     }
   }