docs(ide ext): add companion extension specification (#8262)

2026-03-10 14:10:37 -07:00 · 2025-09-12 17:08:31 -04:00
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+# Gemini CLI Companion Extension: Interface Specification
+
+This document defines the contract for building a companion extension to enable Gemini CLI's IDE mode. For VS Code, these features (native diffing, context awareness) are provided by the official extension ([marketplace](https://marketplace.visualstudio.com/items?itemName=Google.gemini-cli-vscode-ide-companion)). This specification is for contributors who wish to bring similar functionality to other editors like JetBrains IDEs, Sublime Text, etc.
+
+## I. The Communication Interface
+
+The foundation of the IDE integration is a local communication channel between Gemini CLI and the IDE extension.
+
+### 1. Transport Layer: MCP over HTTP
+
+The extension **MUST** run a local HTTP server that implements the **Model Context Protocol (MCP)**.
+
+- **Protocol:** The server must be a valid MCP server. We recommend using an existing MCP SDK for your language of choice if available.
+- **Endpoint:** The server should expose a single endpoint (e.g., `/mcp`) for all MCP communication.
+- **Port:** The server **MUST** listen on a dynamically assigned port (i.e., listen on port `0`).
+
+### 2. Discovery Mechanism: The Port File
+
+For Gemini CLI to connect, it needs to discover which IDE instance it's running in and what port your server is using. The extension **MUST** facilitate this by creating a "discovery file."
+
+- **How the CLI Finds the File:** The CLI determines the Process ID (PID) of the IDE it's running in by traversing the process tree. It then looks for a discovery file that contains this PID in its name.
+- **File Location:** The file must be created in a specific directory: `os.tmpdir()/gemini/ide/`. Your extension must create this directory if it doesn't exist.
+- **File Naming Convention:** The filename is critical and **MUST** follow the pattern:
+  `gemini-ide-server-${PID}-${PORT}.json`
+  - `${PID}`: The process ID of the parent IDE process. Your extension must determine this PID and include it in the filename.
+  - `${PORT}`: The port your MCP server is listening on.
+- **File Content & Workspace Validation:** The file **MUST** contain a JSON object with the following structure:
+  ```json
+  {
+    "port": 12345,
+    "workspacePath": "/path/to/project1:/path/to/project2"
+  }
+  ```
+  - `port` (number): The port of the MCP server.
+  - `workspacePath` (string): A list of all open workspace root paths, delimited by the OS-specific path separator (`:` for Linux/macOS, `;` for Windows). The CLI uses this path to ensure it's running in the same project folder that's open in the IDE. If the CLI's current working directory is not a sub-directory of `workspacePath`, the connection will be rejected. Your extension **MUST** provide the correct, absolute path(s) to the root of the open workspace(s).
+- **Tie-Breaking with Environment Variables (Recommended):** For the most reliable experience, your extension **SHOULD** both create the discovery file and set the `GEMINI_CLI_IDE_SERVER_PORT` and `GEMINI_CLI_IDE_WORKSPACE_PATH` environment variables in the integrated terminal. The file serves as the primary discovery mechanism, but the environment variables are crucial for tie-breaking. If a user has multiple IDE windows open for the same workspace, the CLI uses the `GEMINI_CLI_IDE_SERVER_PORT` variable to identify and connect to the correct window's server.
+  - For prototyping, you may opt to _only_ set the environment variables. However, this is not a robust solution for a production extension, as environment variables may not be reliably set in all terminal sessions (e.g., restored terminals), which can lead to connection failures.
+- **Authentication:** (TBD)
+
+## II. The Context Interface
+
+A powerful capability of the extension is to provide the CLI with real-time information about the user's activity in the IDE.
+
+### `ide/contextUpdate` Notification
+
+The extension **MAY** send an `ide/contextUpdate` [notification](https://modelcontextprotocol.io/specification/2025-06-18/basic/index#notifications) to the CLI whenever the user's context changes.
+
+- **Triggering Events:** This notification should be sent (with a recommended debounce of 50ms) when:
+  - A file is opened, closed, or focused.
+  - The user's cursor position or text selection changes in the active file.
+- **Payload (`IdeContext`):** The notification parameters **MUST** be an `IdeContext` object (`@packages/core/src/ide/types.ts`):
+
+  ```typescript
+  interface IdeContext {
+    workspaceState?: {
+      openFiles?: File[];
+      isTrusted?: boolean;
+    };
+  }
+
+  interface File {
+    path: string; // Absolute path to the file
+    timestamp: number; // Last focused Unix timestamp (for ordering)
+    isActive?: boolean; // True if this is the currently focused file
+    cursor?: {
+      line: number; // 1-based line number
+      character: number; // 1-based character number
+    };
+    selectedText?: string; // The text currently selected by the user
+  }
+  ```
+
+  **Note:** The `openFiles` list should only include files that exist on disk. Virtual files (e.g., unsaved files without a path, editor settings pages) **MUST** be excluded.
+
+### How the CLI Uses This Context
+
+After receiving the `IdeContext` object, the CLI performs several normalization and truncation steps before sending the information to the model.
+
+- **File Ordering:** The CLI uses the `timestamp` field to determine the most recently used files. It sorts the `openFiles` list based on this value. Therefore, your extension **MUST** provide an accurate Unix timestamp for when a file was last focused.
+- **Active File:** The CLI considers only the most recent file (after sorting) to be the "active" file. It will ignore the `isActive` flag on all other files and clear their `cursor` and `selectedText` fields. Your extension should focus on setting `isActive: true` and providing cursor/selection details only for the currently focused file.
+- **Truncation:** To manage token limits, the CLI truncates both the file list (to 10 files) and the `selectedText` (to 16KB).
+
+While the CLI handles the final truncation, it is highly recommended that your extension also limits the amount of context it sends.
+
+## III. Supporting Additional IDEs
+
+To add support for a new IDE, two main components in the Gemini CLI codebase need to be updated: the detection logic and the installer logic.
+
+### 1. IDE Detection (`@packages/core/src/ide/detect-ide.ts`)
+
+// TODO(skeshive): Determine whether we should discover the IDE via the port file
+
+The CLI must be able to identify when it is running inside a specific IDE's integrated terminal. This is primarily done by checking for unique environment variables. As a fallback, it can also inspect process information (like the command name) to help distinguish between IDEs if a unique environment variable is not available.
+
+- **Add to `DetectedIde` Enum:** First, add your new IDE to the `DetectedIde` enum.
+- **Update `detectIdeFromEnv`:** Add a check in this function for an environment variable specific to your IDE (e.g., `if (process.env['MY_IDE_VAR']) { return DetectedIde.MyIde; }`).
+- **Update `detectIde` (Optional):** If your IDE lacks a unique environment variable, you can add logic to the `detectIde` function to inspect `ideProcessInfo` (e.g., `ideProcessInfo.command`) as a secondary detection mechanism.
+
+### 2. Extension Installation (`@packages/core/src/ide/ide-installer.ts`)
+
+The CLI provides a command (`/ide install`) to help users automatically install the companion extension. While optional, implementing an `IdeInstaller` for your IDE is highly recommended to provide a seamless setup experience.
+
+- **Create an Installer Class:** Create a new class that implements the `IdeInstaller` interface.
+- **Implement `install()`:** The `install` method should:
+  1.  Locate the IDE's command-line executable. The `VsCodeInstaller` provides a good example of searching common installation paths for different operating systems.
+  2.  Execute the command to install the extension by its marketplace ID (e.g., `"path/to/my-ide-cli" --install-extension my-publisher.my-extension-id`).
+  3.  Return a result object indicating success or failure.
+- **Update `getIdeInstaller`:** Add a case to the `switch` statement in this factory function to return an instance of your new installer class when your `DetectedIde` enum is matched.
+
+## IV. The Lifecycle Interface
+
+The extension **MUST** manage its resources and the discovery file correctly based on the IDE's lifecycle.
+
+- **On Activation (IDE startup/extension enabled):**
+  1.  Start the MCP server.
+  2.  Create the discovery file.
+- **On Deactivation (IDE shutdown/extension disabled):**
+  1.  Stop the MCP server.
+  2.  Delete the discovery file.
--- a/docs/ide-integration.md
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@@ -2,7 +2,7 @@

 Gemini CLI can integrate with your IDE to provide a more seamless and context-aware experience. This integration allows the CLI to understand your workspace better and enables powerful features like native in-editor diffing.

-Currently, the only supported IDE is [Visual Studio Code](https://code.visualstudio.com/) and other editors that support VS Code extensions.
+Currently, the only supported IDE is [Visual Studio Code](https://code.visualstudio.com/) and other editors that support VS Code extensions. To build support for other editors, see the [IDE Companion Extension Spec](./ide-companion-spec.md).

 ## Features

--- a/docs/index.md
+++ b/docs/index.md
@@ -19,6 +19,7 @@ This documentation is organized into the following sections:
  - **[Checkpointing](./checkpointing.md):** Documentation for the checkpointing feature.
  - **[Extensions](./extension.md):** How to extend the CLI with new functionality.
  - **[IDE Integration](./ide-integration.md):** Connect the CLI to your editor.
+  - **[IDE Companion Extension Spec](./ide-companion-spec.md):** Spec for building IDE companion extensions.
  - **[Telemetry](./telemetry.md):** Overview of telemetry in the CLI.
 - **Core Details:** Documentation for `packages/core`.
  - **[Core Introduction](./core/index.md):** Overview of the core component.