[extensions] Add extension management install command (#6703)

packages/cli/src/commands/extensions.tsx

@@ -0,0 +1,22 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { CommandModule } from 'yargs';
+import { installCommand } from './extensions/install.js';
+
+export const extensionsCommand: CommandModule = {
+  command: 'extensions <command>',
+  describe: 'Manage Gemini CLI extensions.',
+  builder: (yargs) =>
+    yargs
+      .command(installCommand)
+      .demandCommand(1, 'You need at least one command before continuing.')
+      .version(false),
+  handler: () => {
+    // This handler is not called when a subcommand is provided.
+    // Yargs will show the help menu.
+  },
+};

packages/cli/src/commands/extensions/install.test.ts

@@ -0,0 +1,25 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect } from 'vitest';
+import { installCommand } from './install.js';
+import yargs from 'yargs';
+
+describe('extensions install command', () => {
+  it('should fail if no source is provided', () => {
+    const validationParser = yargs([]).command(installCommand).fail(false);
+    expect(() => validationParser.parse('install')).toThrow(
+      'Either a git URL --source or a --path must be provided.',
+    );
+  });
+
+  it('should fail if both git source and local path are provided', () => {
+    const validationParser = yargs([]).command(installCommand).fail(false);
+    expect(() =>
+      validationParser.parse('install --source some-url --path /some/path'),
+    ).toThrow('Arguments source and path are mutually exclusive');
+  });
+});

packages/cli/src/commands/extensions/install.ts

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+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { CommandModule } from 'yargs';
+import {
+  installExtension,
+  ExtensionInstallMetadata,
+} from '../../config/extension.js';
+
+interface InstallArgs {
+  source?: string;
+  path?: string;
+}
+
+export async function handleInstall(args: InstallArgs) {
+  try {
+    const installMetadata: ExtensionInstallMetadata = {
+      source: (args.source || args.path) as string,
+      type: args.source ? 'git' : 'local',
+    };
+    const extensionName = await installExtension(installMetadata);
+    console.log(
+      `Extension "${extensionName}" installed successfully and enabled.`,
+    );
+  } catch (error) {
+    console.error((error as Error).message);
+    process.exit(1);
+  }
+}
+
+export const installCommand: CommandModule = {
+  command: 'install [--source | --path ]',
+  describe: 'Installs an extension from a git repository or a local path.',
+  builder: (yargs) =>
+    yargs
+      .option('source', {
+        describe: 'The git URL of the extension to install.',
+        type: 'string',
+      })
+      .option('path', {
+        describe: 'Path to a local extension directory.',
+        type: 'string',
+      })
+      .conflicts('source', 'path')
+      .check((argv) => {
+        if (!argv.source && !argv.path) {
+          throw new Error(
+            'Either a git URL --source or a --path must be provided.',
+          );
+        }
+        return true;
+      }),
+  handler: async (argv) => {
+    await handleInstall({
+      source: argv['source'] as string | undefined,
+      path: argv['path'] as string | undefined,
+    });
+  },
+};