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Alex Rupérez

Published: 05 Mar 15:13
I starred NSHipster/swift-format at GitHub.
Pitch: an Official Style Guide and Formatter for Swift
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swift-format formats and diagnoses Swift source code according to a set of style guidelines. It can be used as a command line tool or linked into other applications as a Swift Package Manager dependency and invoked via an API.

NOTE: No official Swift style guide has yet been proposed. The style that is currently enforced by swift-format is just one possibility, and the code is provided so that it can be tested on real-world code and experiments can be made by modifying it.

Command Line Usage

swift-format [OPTIONS] FILE...

The swift-format tool can be invoked with one or more .swift source files, as well as the following command line options:

  • -v/--version: Prints the swift-format version and exits.

  • -m/--mode <format|lint|dump-configuration>: The mode in which to run swift-format. The format mode formats source files. The lint mode only prints diagnostics indicating style violations. The dump-configuration mode dumps the default swift-format configuration to standard output.

    If unspecified, the default mode is format.

  • --configuration <file>: The path to a JSON file that contains configurable settings for swift-format. If omitted, a default configuration is use (which can be seen by running --mode dump-configuration).

  • -i/--in-place: Overwrites the input files when formatting instead of printing the results to standard output.

The command line tool also provides some hidden debugging options for use when developing swift-format.


For any source file being checked or formatted, swift-format looks for a JSON-formatted file named .swift-format in the same directory. If one is found, then that file is loaded to determine the tool's configuration. If the file is not found, then it looks in the parent directory, and so on.

If no configuration file is found, a default configuration is used. The settings in the default configuration can be viewed by running swift-format --mode dump-configuration, which will dump it to standard output.

If the --configuration <file> option is passed to swift-format, then that configuration will be used unconditionally and the file system will not be searched.

See Documentation/ for a description of the configuration file format and the settings that are available.

API Usage

swift-format can be easily integrated into other tools written in Swift. Instead of invoking the formatter by spawning a subprocess, users can depend on swift-format as a Swift Package Manager dependency and import the SwiftFormat module, which contains the entry points into the formatter's diagnostic and correction behavior.

Formatting behavior is provided by the SwiftFormatter class and linting behavior is provided by the SwiftLinter class. These APIs can be passed either a Swift source file URL or a Syntax node representing a SwiftSyntax syntax tree. The latter capability is particularly useful for writing code generators, since it significantly reduces the amount of trivia that the generator needs to be concerned about adding to the syntax nodes it creates. Instead, it can pass the in-memory syntax tree to the SwiftFormat API and receive perfectly formatted code as output.

Please see the documentation in the SwiftFormatter and SwiftLinter classes for more information about their usage.