Introduce VSCode companion extension (#3917)

packages/vscode-ide-companion/.vscode/launch.json

@@ -0,0 +1,13 @@
+{
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Run Extension",
+      "type": "extensionHost",
+      "request": "launch",
+      "args": ["--extensionDevelopmentPath=${workspaceFolder}"],
+      "outFiles": ["${workspaceFolder}/out/**/*.js"],
+      "preLaunchTask": "${defaultBuildTask}"
+    }
+  ]
+}

packages/vscode-ide-companion/.vscode/tasks.json

@@ -0,0 +1,18 @@
+{
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "type": "npm",
+      "script": "watch",
+      "problemMatcher": "$tsc-watch",
+      "isBackground": true,
+      "presentation": {
+        "reveal": "never"
+      },
+      "group": {
+        "kind": "build",
+        "isDefault": true
+      }
+    }
+  ]
+}

packages/vscode-ide-companion/README.md

@@ -0,0 +1,9 @@
+# IDE Companion
+
+## Local Development
+
+To test the extension locally, follow these steps:
+
+1. Open the `packages/vscode-ide-companion` directory in VS Code.
+2. Run `npm install`.
+3. Run the extension development host via Run + Debug -> Extension

packages/vscode-ide-companion/esbuild.js

@@ -0,0 +1,62 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+const esbuild = require('esbuild');
+
+const production = process.argv.includes('--production');
+const watch = process.argv.includes('--watch');
+
+/**
+ * @type {import('esbuild').Plugin}
+ */
+const esbuildProblemMatcherPlugin = {
+  name: 'esbuild-problem-matcher',
+
+  setup(build) {
+    build.onStart(() => {
+      console.log('[watch] build started');
+    });
+    build.onEnd((result) => {
+      result.errors.forEach(({ text, location }) => {
+        console.error(`✘ [ERROR] ${text}`);
+        console.error(
+          `    ${location.file}:${location.line}:${location.column}:`,
+        );
+      });
+      console.log('[watch] build finished');
+    });
+  },
+};
+
+async function main() {
+  const ctx = await esbuild.context({
+    entryPoints: ['src/extension.ts'],
+    bundle: true,
+    format: 'cjs',
+    minify: production,
+    sourcemap: !production,
+    sourcesContent: false,
+    platform: 'node',
+    outfile: 'dist/extension.js',
+    external: ['vscode'],
+    logLevel: 'silent',
+    plugins: [
+      /* add to the end of plugins array */
+      esbuildProblemMatcherPlugin,
+    ],
+  });
+  if (watch) {
+    await ctx.watch();
+  } else {
+    await ctx.rebuild();
+    await ctx.dispose();
+  }
+}
+
+main().catch((e) => {
+  console.error(e);
+  process.exit(1);
+});

packages/vscode-ide-companion/eslint.config.mjs

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+import typescriptEslint from '@typescript-eslint/eslint-plugin';
+import tsParser from '@typescript-eslint/parser';
+
+export default [
+  {
+    files: ['**/*.ts'],
+  },
+  {
+    plugins: {
+      '@typescript-eslint': typescriptEslint,
+    },
+
+    languageOptions: {
+      parser: tsParser,
+      ecmaVersion: 2022,
+      sourceType: 'module',
+    },
+
+    rules: {
+      '@typescript-eslint/naming-convention': [
+        'warn',
+        {
+          selector: 'import',
+          format: ['camelCase', 'PascalCase'],
+        },
+      ],
+
+      curly: 'warn',
+      eqeqeq: 'warn',
+      'no-throw-literal': 'warn',
+      semi: 'warn',
+    },
+  },
+];

packages/vscode-ide-companion/package.json

@@ -0,0 +1,45 @@
+{
+  "name": "gemini-cli-vscode-ide-companion",
+  "displayName": "Gemini CLI VSCode IDE Companion",
+  "description": "",
+  "version": "0.0.1",
+  "engines": {
+    "vscode": "^1.101.0"
+  },
+  "categories": [
+    "Other"
+  ],
+  "activationEvents": [
+    "onStartupFinished"
+  ],
+  "main": "./dist/extension.js",
+  "scripts": {
+    "vscode:prepublish": "npm run package",
+    "build": "npm run compile",
+    "compile": "npm run check-types && npm run lint && node esbuild.js",
+    "watch": "npm-run-all -p watch:*",
+    "watch:esbuild": "node esbuild.js --watch",
+    "watch:tsc": "tsc --noEmit --watch --project tsconfig.json",
+    "package": "npm run check-types && npm run lint && node esbuild.js --production",
+    "check-types": "tsc --noEmit",
+    "lint": "eslint src"
+  },
+  "devDependencies": {
+    "@types/cors": "^2.8.19",
+    "@types/express": "^5.0.3",
+    "@types/node": "20.x",
+    "@types/vscode": "^1.101.0",
+    "@typescript-eslint/eslint-plugin": "^8.31.1",
+    "@typescript-eslint/parser": "^8.31.1",
+    "esbuild": "^0.25.3",
+    "eslint": "^9.25.1",
+    "npm-run-all": "^4.1.5",
+    "typescript": "^5.8.3"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "^1.15.1",
+    "cors": "^2.8.5",
+    "express": "^5.1.0",
+    "zod": "^3.25.76"
+  }
+}

packages/vscode-ide-companion/src/extension.ts

@@ -0,0 +1,14 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+import { startIDEServer } from './ide-server';
+
+export async function activate(context: vscode.ExtensionContext) {
+  startIDEServer(context);
+}
+
+export function deactivate() {}

packages/vscode-ide-companion/src/ide-server.ts

@@ -0,0 +1,109 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import * as vscode from 'vscode';
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/streamableHttp.js';
+import express, { Request, Response } from 'express';
+
+export async function startIDEServer(_context: vscode.ExtensionContext) {
+  const app = express();
+  app.use(express.json());
+
+  const mcpServer = createMcpServer();
+  const transport = new StreamableHTTPServerTransport({
+    sessionIdGenerator: undefined,
+    enableJsonResponse: true,
+  });
+
+  mcpServer.connect(transport);
+
+  app.post('/mcp', async (req: Request, res: Response) => {
+    console.log('Received MCP request:', req.body);
+    try {
+      await transport.handleRequest(req, res, req.body);
+    } catch (error) {
+      console.error('Error handling MCP request:', error);
+      if (!res.headersSent) {
+        res.status(500).json({
+          jsonrpc: '2.0',
+          error: {
+            code: -32603,
+            message: 'Internal server error',
+          },
+          id: null,
+        });
+      }
+    }
+  });
+
+  // Handle GET requests for SSE streams
+  app.get('/mcp', async (req: Request, res: Response) => {
+    res.status(405).set('Allow', 'POST').send('Method Not Allowed');
+  });
+
+  // Start the server
+  // TODO(#3918): Generate dynamically and write to env variable
+  const PORT = 3000;
+  app.listen(PORT, (error) => {
+    if (error) {
+      console.error('Failed to start server:', error);
+      vscode.window.showErrorMessage(
+        `Companion server failed to start on port ${PORT}: ${error.message}`,
+      );
+    }
+    console.log(`MCP Streamable HTTP Server listening on port ${PORT}`);
+  });
+}
+
+const createMcpServer = () => {
+  const server = new McpServer({
+    name: 'vscode-ide-server',
+    version: '1.0.0',
+  });
+  server.registerTool(
+    'getActiveFile',
+    {
+      description:
+        '(IDE Tool) Get the path of the file currently active in VS Code.',
+      inputSchema: {},
+    },
+    async () => {
+      try {
+        const activeEditor = vscode.window.activeTextEditor;
+        const filePath = activeEditor
+          ? activeEditor.document.uri.fsPath
+          : undefined;
+        if (filePath) {
+          return {
+            content: [{ type: 'text', text: `Active file: ${filePath}` }],
+          };
+        } else {
+          return {
+            content: [
+              {
+                type: 'text',
+                text: 'No file is currently active in the editor.',
+              },
+            ],
+          };
+        }
+      } catch (error) {
+        return {
+          content: [
+            {
+              type: 'text',
+              text: `Failed to get active file: ${
+                (error as Error).message || 'Unknown error'
+              }`,
+            },
+          ],
+        };
+      }
+    },
+  );
+  return server;
+};

packages/vscode-ide-companion/tsconfig.json

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+{
+  "compilerOptions": {
+    "module": "Node16",
+    "target": "ES2022",
+    "lib": ["ES2022", "dom"],
+    "sourceMap": true,
+    "rootDir": "src",
+    "strict": true /* enable all strict type-checking options */
+    /* Additional Checks */
+    // "noImplicitReturns": true, /* Report error when not all code paths in function return a value. */
+    // "noFallthroughCasesInSwitch": true, /* Report errors for fallthrough cases in switch statement. */
+    // "noUnusedParameters": true,  /* Report errors on unused parameters. */
+  }
+}