SwiftFormat is a mature, rule-based Swift source code formatter and linter. It operates as a command-line tool, an Xcode source editor extension, and a Swift Package Manager plugin. The core engine tokenizes Swift source code and applies a configurable set of formatting rules, each defined as a static `FormatRule` with help text, options, and a closure that manipulates the token stream via a `Formatter` API. The architecture is modular: rules are isolated in individual files under `Sources/Rules/`, the formatter provides reusable token manipulation primitives, and reporters (JSON, XML, SARIF, GitHub Actions) handle output. Configuration is hierarchical via `.swiftformat` files, inline directives, and command-line options. The system's primary data flow is: source file → tokenization → rule application (ordered by dependencies) → token stream mutation → output. Rules can be disabled, version-gated, or run once. The test suite uses a shared `testFormatting` helper that verifies formatting output, lint idempotency, and change tracking. The project also includes an Xcode extension with a preferences UI and an SPM plugin for build-time formatting. External dependencies are minimal (Foundation, XcodeKit for the extension, and git for header metadata). Key entry points include `CommandLineTool/main.swift` (CLI), `EditorExtension/Extension/FormatFileCommand.swift` (Xcode), and `Plugins/SwiftFormatPlugin/SwiftFormatPlugin.swift` (SPM). The library target `SwiftFormat` exposes `format()` and `lint()` APIs for programmatic use. The codebase demonstrates high craftsmanship with a declarative rule DSL, auto-updating declaration tracking, and a comprehensive test infrastructure that catches regressions across real-world Swift projects (vendored as snapshot fixtures).
Copilot for Xcode is a macOS application that integrates multiple AI code completion and chat services (GitHub Copilot, Codeium, OpenAI, Claude, Google Gemini, Ollama) directly into Xcode as a source editor extension. It provides inline code suggestions, a chat panel with context-aware memory, a prompt-to-code feature, and custom command execution. The architecture is a multi-process system: a host app manages settings and lifecycle, an XPC extension service handles AI requests and workspace state, and an Accessibility-powered widget overlays suggestion and chat panels on Xcode windows. The codebase is heavily modularized into Swift packages (Core, Tool, OverlayWindow) and uses the Composable Architecture (TCA) for state management. While primarily an application, it includes data-centric components like embedding services, vector stores (USearch), and a LangChain-inspired chain abstraction for retrieval-augmented generation, giving it a hybrid character.