Allow simple extensions for registering MCPservers (#890)

packages/cli/src/config/extension.ts

@@ -0,0 +1,87 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { MCPServerConfig } from '@gemini-cli/core';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+
+export const EXTENSIONS_DIRECTORY_NAME = path.join('.gemini', 'extensions');
+export const EXTENSIONS_CONFIG_FILENAME = 'gemini-extension.json';
+
+export interface ExtensionConfig {
+  name: string;
+  version: string;
+  mcpServers?: Record<string, MCPServerConfig>;
+  contextFileName?: string;
+}
+
+export function loadExtensions(workspaceDir: string): ExtensionConfig[] {
+  const allExtensions = [
+    ...loadExtensionsFromDir(workspaceDir),
+    ...loadExtensionsFromDir(os.homedir()),
+  ];
+
+  const uniqueExtensions: ExtensionConfig[] = [];
+  const seenNames = new Set<string>();
+  for (const extension of allExtensions) {
+    if (!seenNames.has(extension.name)) {
+      console.log(
+        `Loading extension: ${extension.name} (version: ${extension.version})`,
+      );
+      uniqueExtensions.push(extension);
+      seenNames.add(extension.name);
+    }
+  }
+
+  return uniqueExtensions;
+}
+
+function loadExtensionsFromDir(dir: string): ExtensionConfig[] {
+  const extensionsDir = path.join(dir, EXTENSIONS_DIRECTORY_NAME);
+  if (!fs.existsSync(extensionsDir)) {
+    return [];
+  }
+
+  const extensions: ExtensionConfig[] = [];
+  for (const subdir of fs.readdirSync(extensionsDir)) {
+    const extensionDir = path.join(extensionsDir, subdir);
+
+    if (!fs.statSync(extensionDir).isDirectory()) {
+      console.error(
+        `Warning: unexpected file ${extensionDir} in extensions directory.`,
+      );
+      continue;
+    }
+
+    const extensionPath = path.join(extensionDir, EXTENSIONS_CONFIG_FILENAME);
+    if (!fs.existsSync(extensionPath)) {
+      console.error(
+        `Warning: extension directory ${extensionDir} does not contain a config file ${extensionPath}.`,
+      );
+      continue;
+    }
+
+    try {
+      const fileContent = fs.readFileSync(extensionPath, 'utf-8');
+      const extensionConfig = JSON.parse(fileContent) as ExtensionConfig;
+      if (!extensionConfig.name || !extensionConfig.version) {
+        console.error(
+          `Invalid extension config in ${extensionPath}: missing name or version.`,
+        );
+        continue;
+      }
+      extensions.push(extensionConfig);
+    } catch (e) {
+      console.error(
+        `Failed to load extension config from ${extensionPath}:`,
+        e,
+      );
+    }
+  }
+
+  return extensions;
+}