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Developing swift-format

Keeping the Pipeline and Tests Updated

Since Swift does not yet have a runtime reflection system, we use code generation to keep the linting/formatting pipeline up-to-date. If you add or remove any rules from the SwiftFormat module, or if you add or remove any visit methods from an existing rule in that module, you must run the generate-swift-format tool update the pipeline and configuration sources.

The easiest way to do this is to run the following command in your terminal:

swift run generate-swift-format

If successful, this tool will update the files Pipelines+Generated.swift, RuleNameCache+Generated.swift, and RuleRegistry+Generated.swift in the Sources/SwiftFormat/Core directory.

Command Line Options for Debugging

swift-format provides some hidden command line options to facilitate debugging the tool during development:

  • --debug-disable-pretty-print: Disables the pretty-printing pass of the formatter, causing only the syntax tree transformations in the first phase pipeline to run.

  • --debug-dump-token-stream: Dumps a human-readable indented structure representing the pseudotoken stream constructed by the pretty printing phase.

Support Scripts

The Scripts directory contains a format-diff.sh script that some developers may find useful. When invoked, it rebuilds swift-format (if necessary to pick up any recent changes) and lets you view a side-by-side diff with the original file on the left side and the formatted output on the right side.

This script will use colordiff if it is installed on your PATH; otherwise, it will fall back to diff.