# Development

## Targets 

### Copilot for Xcode

Copilot for Xcode is the host app containing both the XPCService and the editor extension.

### EditorExtension

As its name suggests, the editor extension. Its sole purpose is to forward editor content to the XPCService for processing, and update the editor with the returned content. Due to the sandboxing requirements for editor extensions, it has to communicate with a trusted, non-sandboxed XPCService to bypass the limitations. The XPCService identifier must be included in the `com.apple.security.temporary-exception.mach-lookup.global-name` entitlements.

### ExtensionService

The `ExtensionService` is a program that operates in the background and performs a wide range of tasks. It redirects requests from the `EditorExtension` to the `CopilotService` and returns the updated code back to the extension, or presents it in a GUI outside of Xcode.

### Core

Most of the logics are implemented inside the package `Core`.

- The `CopilotService` is responsible for communicating with the GitHub Copilot LSP.
- The `Service` is responsible for handling the requests from the `EditorExtension`, communicating with the `CopilotService`, update the code blocks and present the GUI.
- The `Client` is basically just a wrapper around the XPCService
- The `SuggestionInjector` is responsible for injecting the suggestions into the code. Used in comment mode to present the suggestions, and all modes to accept suggestions.
- The `Environment` contains some swappable global functions. It is used to make testing easier.
- The `SuggestionWidget` is responsible for presenting the suggestions in floating widget mode.

## Building and Archiving the App

1. Run `make setup` to setup the project. (You may need to install the specific version of python to install the dependencies, please check `Python/site-packages/install.sh` for details.)
2. Build or archive the Copilot for Xcode target.

## Testing Extension

Just run both the `ExtensionService` and the `EditorExtension` Target.

## Unit Tests

To run unit tests, just run test from the `Copilot for Xcode` target.

For new tests, they should be added to the `TestPlan.xctestplan`.

## Chat Plugins

To create a chat plugin, please use the `TerminalChatPlugin` as an example. You should add your plugin to the target `ChatPlugin` and register it in `ChatService`.

## LangChain and Python

The app uses PythonKit to execute Python code.

When running Python code, ensure that you wrap it inside `runPython`. This will automatically insert `GilStateEnsure` and `GilStateRelease` for you.

```swift
import PythonHelper

try runPython {
    // access python here
}
```

Instead of throwing a `PythonError`, `runPython` will throw a `ReadablePythonError`.

If importing a Python module causes the app to crash, it is usually due to the thread's stack size being too small. To resolve this, try importing with `Python.attemptImportOnPythonThread`, which is defined in `PythonHelper`, or simply import from the main thread.

## Code Style

We use SwiftFormat to format the code.

The source code mostly follows the [Ray Wenderlich Style Guide](https://github.com/raywenderlich/swift-style-guide) very closely with the following exception:

- Use the Xcode default of 4 spaces for indentation.

## App Versioning

The app version and all targets' version in controlled by `Version.xcconfig`.