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apple/swift-format swift-5.9.2-RELEASE
Formatting technology for Swift source code
⭐️ 2,247
🕓 10 weeks ago
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.package(url: "https://github.com/apple/swift-format.git", from: "swift-5.9.2-RELEASE")


swift-format provides the formatting technology for SourceKit-LSP and the building blocks for doing code formatting transformations.

This package 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 default Swift code style guidelines have yet been proposed. The style that is currently applied 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.

Matching swift-format to Your Swift Version

Swift 5.8 and later

As of Swift 5.8, swift-format depends on the version of SwiftSyntax whose parser has been rewritten in Swift and no longer has dependencies on libraries in the Swift toolchain.

This change allows swift-format to be built, developed, and run using any version of Swift that can compile it, decoupling it from the version that supported a particular syntax. However, earlier versions of swift-format will still not be able to recognize new syntax added in later versions of the language and parser.

Note also that the version numbering scheme has changed to match SwiftSyntax; the 5.8 release of swift-format is 508.0.0, not 0.50800.0.

Swift 5.7 and earlier

swift-format versions 0.50700.0 and earlier depend on versions of SwiftSyntax that used a standalone parsing library distributed as part of the Swift toolchain. When using these versions, you should check out and build swift-format from the release tag or branch that is compatible with the version of Swift you are using.

The major and minor version components of swift-format and SwiftSyntax must be the same—this is expressed in the SwiftSyntax dependency in Package.swift—and those version components must match the Swift toolchain that is installed and used to build and run the formatter:

Xcode Release Swift Version swift-format Branch / Tags
Swift at main main
Xcode 14.0 Swift 5.7 release/5.7 / 0.50700.x
Xcode 13.3 Swift 5.6 release/5.6 / 0.50600.x
Xcode 13.0–13.2 Swift 5.5 swift-5.5-branch / 0.50500.x
Xcode 12.5 Swift 5.4 swift-5.4-branch / 0.50400.x
Xcode 12.0–12.4 Swift 5.3 swift-5.3-branch / 0.50300.x
Xcode 11.4–11.7 Swift 5.2 swift-5.2-branch / 0.50200.x
Xcode 11.0–11.3 Swift 5.1 swift-5.1-branch

For example, if you are using Xcode 13.3 (Swift 5.6), you will need swift-format 0.50600.0.

Getting swift-format

If you are mainly interested in using swift-format (rather than developing it), then you can get swift-format either via Homebrew or by checking out the source and building it.

Installing via Homebrew

Run brew install swift-format to install the latest version.

Building from source

Install swift-format using the following commands:

VERSION=509.0.0  # replace this with the version you need
git clone https://github.com/apple/swift-format.git
cd swift-format
git checkout "tags/$VERSION"
swift build -c release

Note that the git checkout command above will leave the repository in a "detached HEAD" state. This is fine if building and running the tool is all you want to do.

Once the build has finished, the swift-format executable will be located at .build/release/swift-format.

To test that the formatter was built successfully and is compatible with your Swift toolchain, you can also run the following command:

swift test --parallel

We recommend using the --parallel flag to speed up the test run since there are a large number of tests.

Command Line Usage

The general invocation syntax for swift-format is as follows:

swift-format [SUBCOMMAND] [OPTIONS...] [FILES...]

The tool supports a number of subcommands, each of which has its own options and are described below. Descriptions of the subcommands that are available can also be obtained by running swift-format --help, and the description of a specific subcommand can be obtained by using the --help flag after the subcommand name; for example, swift-format lint --help.


swift-format [format] [OPTIONS...] [FILES...]

The format subcommand formats one or more Swift source files (or source code from standard input if no file paths are given on the command line). Writing out the format subcommand is optional; it is the default behavior if no other subcommand is given.

This subcommand supports all of the common lint and format options, as well as the formatting-only options below:

  • -i/--in-place: Overwrites the input files when formatting instead of printing the results to standard output. No backup of the original file is made before it is overwritten.


swift-format lint [OPTIONS...] [FILES...]

The lint subcommand checks one or more Swift source files (or source code from standard input if no file paths are given on the command line) for style violations and prints diagnostics to standard error for any violations that are detected.

This subcommand supports all of the common lint and format options, as well as the linting-only options below:

  • -s/--strict: If this option is specified, lint warnings will cause the tool to exit with a non-zero exit code (failure). By default, lint warnings do not prevent a successful exit; only fatal errors (for example, trying to lint a file that does not exist) cause the tool to exit unsuccessfully.

Options Supported by Formatting and Linting

The following options are supported by both the format and lint subcommands:

  • --assume-filename <path>: The file path that should be used in diagnostics when linting or formatting from standard input. If this option is not provided, then <stdin> will be used as the filename printed in diagnostics.

  • --color-diagnostics/--no-color-diagnostics: By default, swift-format will print diagnostics in color if standard error is connected to a terminal and without color otherwise (for example, if standard error is being redirected to a file). These flags can be used to force colors on or off respectively, regardless of whether the output is going to a terminal.

  • --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 swift-format dump-configuration).

  • --ignore-unparsable-files: If this option is specified and a source file contains syntax errors or can otherwise not be parsed successfully by the Swift syntax parser, it will be ignored (no diagnostics will be emitted and it will not be formatted). Without this option, an error will be emitted for any unparsable files.

  • -p/--parallel: Process files in parallel, simultaneously across multiple cores.

  • -r/--recursive: If specified, then the tool will process .swift source files in any directories listed on the command line and their descendants. Without this flag, it is an error to list a directory on the command line.

Viewing the Default Configuration

swift-format dump-configuration

The dump-configuration subcommand dumps the default configuration in JSON format to standard output. This can be used to simplify generating a custom configuration, by redirecting it to a file and editing it.

Configuring the Command Line Tool

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 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/Configuration.md for a description of the configuration file format and the settings that are available.


Running swift-format -v or swift-format --version will print version information about swift-format version and then exit.

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.

Checking Out the Source Code for Development

The main branch is used for development. Pull requests should be created to merge into the main branch; changes that are low-risk and compatible with the latest release branch may be cherry-picked into that branch after they have been merged into main.

If you are interested in developing swift-format, there is additional documentation about that here.


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Release Notes

23 weeks ago

This release is compatible with Swift 5.9.

Significant changes since the last release:

New rules

  • AlwaysUseLiteralForEmptyCollectionInit: transforms no-argument initializer calls on collection types to use the empty collection literal instead. For example, let x = [Int]() will be transformed into let x: [Int] = []. This rule is opt-in (disabled by default).
  • NoPlaygroundLiterals: emits lint findings when the playground literals (#colorLiteral, #fileLiteral, #imageLiteral) are used in code. Enabled by default.
  • OmitExplicitReturns: removes unnecessary return keywords from single-expression function/closure/subscript/accessor bodies. This rule is opt-in (disabled by default).
  • ReplaceForEachWithForLoop: emits lint findings when the forEach method is called with a closure literal at the end of a member access chain, indicating that it should be replaced by a for loop instead. Enabled by default.
  • TypeNamesShouldBeCapitalized: emits lint findings when a type is declared with a name that is not UpperCamelCase. Enabled by default.

New configuration settings

  • multiElementCollectionTrailingCommas (boolean): When set to false, the last element of a multi-element array or dictionary literal will not have a trailing comma, even when the literal wraps across multiple lines. Defaults to true (preserving the behavior of previous releases).

Bug fixes and behavior changes

  • swift-format no longer crashes when formatting a case block that contains no statements.
  • In multi-statement closures, there is now always a line break between the in keyword and the first statement.
  • Attributes before import statements are no longer wrapped.
  • The NoParensAroundConditions rule no longer removes parentheses around an immediately called closure.
  • The NoAssignmentInExpressions rule can be configured to ignore assignments that occur inside certain function calls. The default configuration ignores assignments inside XCTAssertNoThrow.
  • When an editor placeholder is found in the source, this is now treated as a warning instead of an error. This allows formatting to continue, treating the placeholder as a regular identifier.
  • Keypath literals are properly wrapped and indented.
  • Postfix-#if expressions are no longer indented too far when they follow a closing parenthesis.
  • Indentation of multiline strings has been fixed in a number of locations.
  • Documentation comment parsing has improved for rules like BeginDocumentationCommentWithOneLineSummary, UseTripleSlashForDocumentationComments, and ValidateDocumentationComments.
  • Diagnostic messages throughout swift-format have been cleaned up and improved.
  • The UseShorthandTypeNames rule properly parenthesizes optional some/any types; for example, Optional<any P> becomes (any P)?, not any P? (which is invalid).
  • The UseSynthesizedInitializer rule no longer warns that an initializer is redundant if it is declared with any attributes.
  • The lint/format plugins for SPM now default to processing all targets if the --target argument is not specified.
  • swift-format now emits a warning if you configure a rule that does not exist. This is meant to help catch typos in the configuration file.
  • swift-format now does nothing if its input is empty (i.e., a zero-byte file). This suppresses a single trailing newline that would have otherwise been added in this case.

API changes

For developers using swift-format as a library, the types in the SwiftFormatConfiguration module have been folded into the SwiftFormat module. The SwiftFormat module is now the sole module you should import to use the linter/formatter APIs.

The SwiftFormatConfiguration module still exists to re-export the types for backwards compatibility, but this will be removed in the 510.0.0 release.

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