Image you want to write a developer tool for Swift. You probably want to parse, inspect, generate and transform Swift source code.

What are your best options?

Old School: SourceKit / SourceKitten

Apple provides SourceKit as a framework for supporting IDE features like indexing, syntax-coloring, code-completion, etc. That's how Xcode gets its intelligence. Here is a really good article if you wanna know more about SourceKit.

The gold standard is (was?) SourceKitten , a open source and community-maintained library which significantly reduces the complexity to communicate with SourceKit directly.

It is very popular (~ 1.9k stars on Github) and is used by well-known tools for Swift developers like

• SwiftLint : A tool to enforce Swift style and conventions.
• Jazzy : Soulful docs for Swift & Objective-C.
• Sourcery: Meta-programming for Swift, stop writing boilerplate code.

But wait! Sourcery recently switched from SourceKit/SourceKitten to SwiftSyntax and announced significant performance improvements.

The new kid: SwiftSyntax

SwiftSyntax is a set of Swift bindings for the libSyntax library. It allows for Swift tools to parse, inspect, generate, and transform Swift source code.

According to Apple:

Its API is designed for performance critical applications. It uses value types almost exclusively and aims to avoid existential conversions where possible.

There is a really nice Swift Abstract Syntax Tree (AST) visualizer

It looks for me that SwiftSyntax can provide information, which were previously very expensive to obtain in SourceKit/SourceKitten, much faster. For example, SourceKit/SourceKitten has to ask the Swift compiler to determine the runtime name of an inferred type (var hasBasket = false // type is Bool) or to determine the used types within a typealias.

I am planning to evaluate and probably switch from SourceKitten to SwiftSyntax for my open source project SwiftPlantUML.

Then I'll provide feedback about my experience with SwiftSyntax.

This is merely a teaser :)