feat(extension): resolve environment variables in extension configuration (#7213)

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

packages/cli/src/config/extension.test.ts

@@ -216,6 +216,100 @@ describe('loadExtensions', () => {
     );
     expect(loadedConfig.mcpServers?.['test-server'].cwd).toBe(expectedCwd);
   });
+
+  it('should resolve environment variables in extension configuration', () => {
+    process.env.TEST_API_KEY = 'test-api-key-123';
+    process.env.TEST_DB_URL = 'postgresql://localhost:5432/testdb';
+
+    try {
+      const workspaceExtensionsDir = path.join(
+        tempWorkspaceDir,
+        EXTENSIONS_DIRECTORY_NAME,
+      );
+      fs.mkdirSync(workspaceExtensionsDir, { recursive: true });
+
+      const extDir = path.join(workspaceExtensionsDir, 'test-extension');
+      fs.mkdirSync(extDir);
+
+      // Write config to a separate file for clarity and good practices
+      const configPath = path.join(extDir, EXTENSIONS_CONFIG_FILENAME);
+      const extensionConfig = {
+        name: 'test-extension',
+        version: '1.0.0',
+        mcpServers: {
+          'test-server': {
+            command: 'node',
+            args: ['server.js'],
+            env: {
+              API_KEY: '$TEST_API_KEY',
+              DATABASE_URL: '${TEST_DB_URL}',
+              STATIC_VALUE: 'no-substitution',
+            },
+          },
+        },
+      };
+      fs.writeFileSync(configPath, JSON.stringify(extensionConfig));
+
+      const extensions = loadExtensions(tempWorkspaceDir);
+
+      expect(extensions).toHaveLength(1);
+      const extension = extensions[0];
+      expect(extension.config.name).toBe('test-extension');
+      expect(extension.config.mcpServers).toBeDefined();
+
+      const serverConfig = extension.config.mcpServers?.['test-server'];
+      expect(serverConfig).toBeDefined();
+      expect(serverConfig?.env).toBeDefined();
+      expect(serverConfig?.env?.API_KEY).toBe('test-api-key-123');
+      expect(serverConfig?.env?.DATABASE_URL).toBe(
+        'postgresql://localhost:5432/testdb',
+      );
+      expect(serverConfig?.env?.STATIC_VALUE).toBe('no-substitution');
+    } finally {
+      delete process.env.TEST_API_KEY;
+      delete process.env.TEST_DB_URL;
+    }
+  });
+
+  it('should handle missing environment variables gracefully', () => {
+    const workspaceExtensionsDir = path.join(
+      tempWorkspaceDir,
+      EXTENSIONS_DIRECTORY_NAME,
+    );
+    fs.mkdirSync(workspaceExtensionsDir, { recursive: true });
+
+    const extDir = path.join(workspaceExtensionsDir, 'test-extension');
+    fs.mkdirSync(extDir);
+
+    const extensionConfig = {
+      name: 'test-extension',
+      version: '1.0.0',
+      mcpServers: {
+        'test-server': {
+          command: 'node',
+          args: ['server.js'],
+          env: {
+            MISSING_VAR: '$UNDEFINED_ENV_VAR',
+            MISSING_VAR_BRACES: '${ALSO_UNDEFINED}',
+          },
+        },
+      },
+    };
+
+    fs.writeFileSync(
+      path.join(extDir, EXTENSIONS_CONFIG_FILENAME),
+      JSON.stringify(extensionConfig),
+    );
+
+    const extensions = loadExtensions(tempWorkspaceDir);
+
+    expect(extensions).toHaveLength(1);
+    const extension = extensions[0];
+    const serverConfig = extension.config.mcpServers!['test-server'];
+    expect(serverConfig.env).toBeDefined();
+    expect(serverConfig.env!.MISSING_VAR).toBe('$UNDEFINED_ENV_VAR');
+    expect(serverConfig.env!.MISSING_VAR_BRACES).toBe('${ALSO_UNDEFINED}');
+  });
 });
 
 describe('annotateActiveExtensions', () => {

packages/cli/src/config/extension.ts

@@ -17,6 +17,7 @@ import { SettingScope, loadSettings } from '../config/settings.js';
 import { getErrorMessage } from '../utils/errors.js';
 import { recursivelyHydrateStrings } from './extensions/variables.js';
 import { isWorkspaceTrusted } from './trustedFolders.js';
+import { resolveEnvVarsInObject } from '../utils/envVarResolver.js';
 
 export const EXTENSIONS_DIRECTORY_NAME = path.join(GEMINI_DIR, 'extensions');
 
@@ -184,7 +185,7 @@ export function loadExtension(extensionDir: string): Extension | null {
 
   try {
     const configContent = fs.readFileSync(configFilePath, 'utf-8');
-    const config = recursivelyHydrateStrings(JSON.parse(configContent), {
+    let config = recursivelyHydrateStrings(JSON.parse(configContent), {
       extensionPath: extensionDir,
       '/': path.sep,
       pathSeparator: path.sep,
@@ -196,6 +197,8 @@ export function loadExtension(extensionDir: string): Extension | null {
       return null;
     }
 
+    config = resolveEnvVarsInObject(config);
+
     const contextFiles = getContextFileNames(config)
       .map((contextFileName) => path.join(extensionDir, contextFileName))
       .filter((contextFilePath) => fs.existsSync(contextFilePath));

packages/cli/src/config/settings.ts

@@ -8,6 +8,7 @@ import * as fs from 'node:fs';
 import * as path from 'node:path';
 import { homedir, platform } from 'node:os';
 import * as dotenv from 'dotenv';
+import process from 'node:process';
 import {
   GEMINI_CONFIG_DIR as GEMINI_DIR,
   getErrorMessage,
@@ -18,6 +19,7 @@ import { DefaultLight } from '../ui/themes/default-light.js';
 import { DefaultDark } from '../ui/themes/default.js';
 import { isWorkspaceTrusted } from './trustedFolders.js';
 import type { Settings, MemoryImportFormat } from './settingsSchema.js';
+import { resolveEnvVarsInObject } from '../utils/envVarResolver.js';
 import { mergeWith } from 'lodash-es';
 
 export type { Settings, MemoryImportFormat };
@@ -462,48 +464,6 @@ export class LoadedSettings {
   }
 }
 
-function resolveEnvVarsInString(value: string): string {
-  const envVarRegex = /\$(?:(\w+)|{([^}]+)})/g; // Find $VAR_NAME or ${VAR_NAME}
-  return value.replace(envVarRegex, (match, varName1, varName2) => {
-    const varName = varName1 || varName2;
-    if (process && process.env && typeof process.env[varName] === 'string') {
-      return process.env[varName]!;
-    }
-    return match;
-  });
-}
-
-function resolveEnvVarsInObject<T>(obj: T): T {
-  if (
-    obj === null ||
-    obj === undefined ||
-    typeof obj === 'boolean' ||
-    typeof obj === 'number'
-  ) {
-    return obj;
-  }
-
-  if (typeof obj === 'string') {
-    return resolveEnvVarsInString(obj) as unknown as T;
-  }
-
-  if (Array.isArray(obj)) {
-    return obj.map((item) => resolveEnvVarsInObject(item)) as unknown as T;
-  }
-
-  if (typeof obj === 'object') {
-    const newObj = { ...obj } as T;
-    for (const key in newObj) {
-      if (Object.prototype.hasOwnProperty.call(newObj, key)) {
-        newObj[key] = resolveEnvVarsInObject(newObj[key]);
-      }
-    }
-    return newObj;
-  }
-
-  return obj;
-}
-
 function findEnvFile(startDir: string): string | null {
   let currentDir = path.resolve(startDir);
   while (true) {