Add a command line option to enable and list extensions (#3191)

8 files changed, 220 insertions, 10 deletions

diff --git a/docs/cli/configuration.md b/docs/cli/configuration.md
index 5f0514b0..1b2f9680 100644
--- a/docs/cli/configuration.md
+++ b/docs/cli/configuration.md
@@ -311,6 +311,12 @@ Arguments passed directly when running the CLI can override other configurations
   - Enables logging of prompts for telemetry. See [telemetry](../telemetry.md) for more information.
 - **`--checkpointing`**:
   - Enables [checkpointing](./commands.md#checkpointing-commands).
+- **`--extensions <extension_name ...>`** (**`-e <extension_name ...>`**):
+  - Specifies a list of extensions to use for the session. If not provided, all available extensions are used.
+  - Use the special term `gemini -e none` to disable all extensions.
+  - Example: `gemini -e my-extension -e my-other-extension`
+- **`--list-extensions`** (**`-l`**):
+  - Lists all available extensions and exits.
 - **`--version`**:
   - Displays the version of the CLI.
 
diff --git a/packages/cli/src/config/config.test.ts b/packages/cli/src/config/config.test.ts
index ca5c9fdf..1ea48760 100644
--- a/packages/cli/src/config/config.test.ts
+++ b/packages/cli/src/config/config.test.ts
@@ -555,3 +555,41 @@ describe('loadCliConfig with allowed-mcp-server-names', () => {
     expect(config.getMcpServers()).toEqual(baseSettings.mcpServers);
   });
 });
+
+describe('loadCliConfig extensions', () => {
+  const mockExtensions: Extension[] = [
+    {
+      config: { name: 'ext1', version: '1.0.0' },
+      contextFiles: ['/path/to/ext1.md'],
+    },
+    {
+      config: { name: 'ext2', version: '1.0.0' },
+      contextFiles: ['/path/to/ext2.md'],
+    },
+  ];
+
+  it('should not filter extensions if --extensions flag is not used', async () => {
+    process.argv = ['node', 'script.js'];
+    const settings: Settings = {};
+    const config = await loadCliConfig(
+      settings,
+      mockExtensions,
+      'test-session',
+    );
+    expect(config.getExtensionContextFilePaths()).toEqual([
+      '/path/to/ext1.md',
+      '/path/to/ext2.md',
+    ]);
+  });
+
+  it('should filter extensions if --extensions flag is used', async () => {
+    process.argv = ['node', 'script.js', '--extensions', 'ext1'];
+    const settings: Settings = {};
+    const config = await loadCliConfig(
+      settings,
+      mockExtensions,
+      'test-session',
+    );
+    expect(config.getExtensionContextFilePaths()).toEqual(['/path/to/ext1.md']);
+  });
+});
diff --git a/packages/cli/src/config/config.ts b/packages/cli/src/config/config.ts
index b79d20fc..7d1af7e1 100644
--- a/packages/cli/src/config/config.ts
+++ b/packages/cli/src/config/config.ts
@@ -20,7 +20,7 @@ import {
 } from '@google/gemini-cli-core';
 import { Settings } from './settings.js';
 
-import { Extension } from './extension.js';
+import { Extension, filterActiveExtensions } from './extension.js';
 import { getCliVersion } from '../utils/version.js';
 import { loadSandboxConfig } from './sandboxConfig.js';
 
@@ -49,6 +49,8 @@ interface CliArgs {
   telemetryOtlpEndpoint: string | undefined;
   telemetryLogPrompts: boolean | undefined;
   'allowed-mcp-server-names': string | undefined;
+  extensions: string[] | undefined;
+  listExtensions: boolean | undefined;
 }
 
 async function parseArguments(): Promise<CliArgs> {
@@ -133,6 +135,18 @@ async function parseArguments(): Promise<CliArgs> {
       type: 'string',
       description: 'Allowed MCP server names',
     })
+    .option('extensions', {
+      alias: 'e',
+      type: 'array',
+      string: true,
+      description:
+        'A list of extensions to use. If not provided, all extensions are used.',
+    })
+    .option('list-extensions', {
+      alias: 'l',
+      type: 'boolean',
+      description: 'List all available extensions and exit.',
+    })
     .version(await getCliVersion()) // This will enable the --version flag based on package.json
     .alias('v', 'version')
     .help()
@@ -174,6 +188,11 @@ export async function loadCliConfig(
   const argv = await parseArguments();
   const debugMode = argv.debug || false;
 
+  const activeExtensions = filterActiveExtensions(
+    extensions,
+    argv.extensions || [],
+  );
+
   // Set the context filename in the server's memoryTool module BEFORE loading memory
   // TODO(b/343434939): This is a bit of a hack. The contextFileName should ideally be passed
   // directly to the Config constructor in core, and have core handle setGeminiMdFilename.
@@ -185,7 +204,9 @@ export async function loadCliConfig(
     setServerGeminiMdFilename(getCurrentGeminiMdFilename());
   }
 
-  const extensionContextFilePaths = extensions.flatMap((e) => e.contextFiles);
+  const extensionContextFilePaths = activeExtensions.flatMap(
+    (e) => e.contextFiles,
+  );
 
   const fileService = new FileDiscoveryService(process.cwd());
   // Call the (now wrapper) loadHierarchicalGeminiMemory which calls the server's version
@@ -196,8 +217,8 @@ export async function loadCliConfig(
     extensionContextFilePaths,
   );
 
-  let mcpServers = mergeMcpServers(settings, extensions);
-  const excludeTools = mergeExcludeTools(settings, extensions);
+  let mcpServers = mergeMcpServers(settings, activeExtensions);
+  const excludeTools = mergeExcludeTools(settings, activeExtensions);
 
   if (argv['allowed-mcp-server-names']) {
     const allowedNames = new Set(
@@ -262,6 +283,11 @@ export async function loadCliConfig(
     bugCommand: settings.bugCommand,
     model: argv.model!,
     extensionContextFilePaths,
+    listExtensions: argv.listExtensions || false,
+    activeExtensions: activeExtensions.map((e) => ({
+      name: e.config.name,
+      version: e.config.version,
+    })),
   });
 }
 
diff --git a/packages/cli/src/config/extension.test.ts b/packages/cli/src/config/extension.test.ts
index 7d299c78..ab68e3f5 100644
--- a/packages/cli/src/config/extension.test.ts
+++ b/packages/cli/src/config/extension.test.ts
@@ -11,6 +11,7 @@ import * as path from 'path';
 import {
   EXTENSIONS_CONFIG_FILENAME,
   EXTENSIONS_DIRECTORY_NAME,
+  filterActiveExtensions,
   loadExtensions,
 } from './extension.js';
 
@@ -85,6 +86,47 @@ describe('loadExtensions', () => {
   });
 });
 
+describe('filterActiveExtensions', () => {
+  const extensions = [
+    { config: { name: 'ext1', version: '1.0.0' }, contextFiles: [] },
+    { config: { name: 'ext2', version: '1.0.0' }, contextFiles: [] },
+    { config: { name: 'ext3', version: '1.0.0' }, contextFiles: [] },
+  ];
+
+  it('should return all extensions if no enabled extensions are provided', () => {
+    const activeExtensions = filterActiveExtensions(extensions, []);
+    expect(activeExtensions).toHaveLength(3);
+  });
+
+  it('should return only the enabled extensions', () => {
+    const activeExtensions = filterActiveExtensions(extensions, [
+      'ext1',
+      'ext3',
+    ]);
+    expect(activeExtensions).toHaveLength(2);
+    expect(activeExtensions.some((e) => e.config.name === 'ext1')).toBe(true);
+    expect(activeExtensions.some((e) => e.config.name === 'ext3')).toBe(true);
+  });
+
+  it('should return no extensions when "none" is provided', () => {
+    const activeExtensions = filterActiveExtensions(extensions, ['none']);
+    expect(activeExtensions).toHaveLength(0);
+  });
+
+  it('should handle case-insensitivity', () => {
+    const activeExtensions = filterActiveExtensions(extensions, ['EXT1']);
+    expect(activeExtensions).toHaveLength(1);
+    expect(activeExtensions[0].config.name).toBe('ext1');
+  });
+
+  it('should log an error for unknown extensions', () => {
+    const consoleSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+    filterActiveExtensions(extensions, ['ext4']);
+    expect(consoleSpy).toHaveBeenCalledWith('Extension not found: ext4');
+    consoleSpy.mockRestore();
+  });
+});
+
 function createExtension(
   extensionsDir: string,
   name: string,
diff --git a/packages/cli/src/config/extension.ts b/packages/cli/src/config/extension.ts
index 57e6632b..aa540cfd 100644
--- a/packages/cli/src/config/extension.ts
+++ b/packages/cli/src/config/extension.ts
@@ -31,19 +31,17 @@ export function loadExtensions(workspaceDir: string): Extension[] {
     ...loadExtensionsFromDir(os.homedir()),
   ];
 
-  const uniqueExtensions: Extension[] = [];
-  const seenNames = new Set<string>();
+  const uniqueExtensions = new Map<string, Extension>();
   for (const extension of allExtensions) {
-    if (!seenNames.has(extension.config.name)) {
+    if (!uniqueExtensions.has(extension.config.name)) {
       console.log(
         `Loading extension: ${extension.config.name} (version: ${extension.config.version})`,
       );
-      uniqueExtensions.push(extension);
-      seenNames.add(extension.config.name);
+      uniqueExtensions.set(extension.config.name, extension);
     }
   }
 
-  return uniqueExtensions;
+  return Array.from(uniqueExtensions.values());
 }
 
 function loadExtensionsFromDir(dir: string): Extension[] {
@@ -114,3 +112,48 @@ function getContextFileNames(config: ExtensionConfig): string[] {
   }
   return config.contextFileName;
 }
+
+export function filterActiveExtensions(
+  extensions: Extension[],
+  enabledExtensionNames: string[],
+): Extension[] {
+  if (enabledExtensionNames.length === 0) {
+    return extensions;
+  }
+
+  const lowerCaseEnabledExtensions = new Set(
+    enabledExtensionNames.map((e) => e.trim().toLowerCase()),
+  );
+
+  if (
+    lowerCaseEnabledExtensions.size === 1 &&
+    lowerCaseEnabledExtensions.has('none')
+  ) {
+    if (extensions.length > 0) {
+      console.log('All extensions are disabled.');
+    }
+    return [];
+  }
+
+  const activeExtensions: Extension[] = [];
+  const notFoundNames = new Set(lowerCaseEnabledExtensions);
+
+  for (const extension of extensions) {
+    const lowerCaseName = extension.config.name.toLowerCase();
+    if (lowerCaseEnabledExtensions.has(lowerCaseName)) {
+      console.log(
+        `Activated extension: ${extension.config.name} (version: ${extension.config.version})`,
+      );
+      activeExtensions.push(extension);
+      notFoundNames.delete(lowerCaseName);
+    } else {
+      console.log(`Disabled extension: ${extension.config.name}`);
+    }
+  }
+
+  for (const requestedName of notFoundNames) {
+    console.log(`Extension not found: ${requestedName}`);
+  }
+
+  return activeExtensions;
+}
diff --git a/packages/cli/src/gemini.tsx b/packages/cli/src/gemini.tsx
index 7e86a8ca..89f5eb3a 100644
--- a/packages/cli/src/gemini.tsx
+++ b/packages/cli/src/gemini.tsx
@@ -103,6 +103,14 @@ export async function main() {
   const extensions = loadExtensions(workspaceRoot);
   const config = await loadCliConfig(settings.merged, extensions, sessionId);
 
+  if (config.getListExtensions()) {
+    console.log('Installed extensions:');
+    for (const extension of extensions) {
+      console.log(`- ${extension.config.name}`);
+    }
+    process.exit(0);
+  }
+
   // Set a default auth type if one isn't set for a couple of known cases.
   if (!settings.merged.selectedAuthType) {
     if (process.env.GEMINI_API_KEY) {
diff --git a/packages/cli/src/ui/hooks/slashCommandProcessor.ts b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
index c174b8a4..66cf4e39 100644
--- a/packages/cli/src/ui/hooks/slashCommandProcessor.ts
+++ b/packages/cli/src/ui/hooks/slashCommandProcessor.ts
@@ -494,6 +494,34 @@ export const useSlashCommandProcessor = (
         },
       },
       {
+        name: 'extensions',
+        description: 'list active extensions',
+        action: async () => {
+          const activeExtensions = config?.getActiveExtensions();
+          if (!activeExtensions || activeExtensions.length === 0) {
+            addMessage({
+              type: MessageType.INFO,
+              content: 'No active extensions.',
+              timestamp: new Date(),
+            });
+            return;
+          }
+
+          let message = 'Active extensions:\n\n';
+          for (const ext of activeExtensions) {
+            message += `  - \u001b[36m${ext.name} (v${ext.version})\u001b[0m\n`;
+          }
+          // Make sure to reset any ANSI formatting at the end to prevent it from affecting the terminal
+          message += '\u001b[0m';
+
+          addMessage({
+            type: MessageType.INFO,
+            content: message,
+            timestamp: new Date(),
+          });
+        },
+      },
+      {
         name: 'tools',
         description: 'list available Gemini CLI tools',
         action: async (_mainCommand, _subCommand, _args) => {
diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index ca0714f0..2cea70ca 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -66,6 +66,11 @@ export interface TelemetrySettings {
   logPrompts?: boolean;
 }
 
+export interface ActiveExtension {
+  name: string;
+  version: string;
+}
+
 export class MCPServerConfig {
   constructor(
     // For stdio transport
@@ -133,6 +138,8 @@ export interface ConfigParameters {
   bugCommand?: BugCommandSettings;
   model: string;
   extensionContextFilePaths?: string[];
+  listExtensions?: boolean;
+  activeExtensions?: ActiveExtension[];
 }
 
 export class Config {
@@ -172,6 +179,8 @@ export class Config {
   private readonly model: string;
   private readonly extensionContextFilePaths: string[];
   private modelSwitchedDuringSession: boolean = false;
+  private readonly listExtensions: boolean;
+  private readonly _activeExtensions: ActiveExtension[];
   flashFallbackHandler?: FlashFallbackHandler;
 
   constructor(params: ConfigParameters) {
@@ -214,6 +223,8 @@ export class Config {
     this.bugCommand = params.bugCommand;
     this.model = params.model;
     this.extensionContextFilePaths = params.extensionContextFilePaths ?? [];
+    this.listExtensions = params.listExtensions ?? false;
+    this._activeExtensions = params.activeExtensions ?? [];
 
     if (params.contextFileName) {
       setGeminiMdFilename(params.contextFileName);
@@ -446,6 +457,14 @@ export class Config {
     return this.extensionContextFilePaths;
   }
 
+  getListExtensions(): boolean {
+    return this.listExtensions;
+  }
+
+  getActiveExtensions(): ActiveExtension[] {
+    return this._activeExtensions;
+  }
+
   async getGitService(): Promise<GitService> {
     if (!this.gitService) {
       this.gitService = new GitService(this.targetDir);