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Table of Contents

What is this?

SwiftFormat is a code library and command-line tool for reformatting swift code on macOS or Linux.

SwiftFormat goes above and beyond what you might expect from a code formatter. In addition to adjusting white space it can insert or remove implicit self, remove redundant parentheses, and correct many other deviations from the standard Swift idioms.

Why would I want to do that?

Many programmers have a preferred style for formatting their code, and others seem entirely blind to the existing formatting conventions of a project (to the enragement of their colleagues).

When collaborating on a project, it can be helpful to agree on a common coding style, but enforcing that manually is tedious and error-prone, and can lead to arguments if some participants take it more seriously than others.

Having a tool to automatically enforce a common style eliminates those issues, and lets you focus on the behavior of the code, not its presentation.

How do I install it?

That depends. There are four ways you can use SwiftFormat:

  1. As a command-line tool that you run manually, or as part of some other toolchain
  2. As a Source Editor Extension that you can invoke via the Editor > SwiftFormat menu within Xcode
  3. As a build phase in your Xcode project, so that it runs every time you press Cmd-R or Cmd-B, or
  4. As a Git pre-commit hook, so that it runs on any files you've changed before you check them in

Command-line tool

NOTE: if you are using any of the following methods to install SwiftFormat on macOS 10.14.3 or earlier and are experiencing a crash on launch, you may need to install the Swift 5 Runtime Support for Command Line Tools. See known issues for details.

Installation:

You can install the swiftformat command-line tool on macOS using Homebrew. Assuming you already have Homebrew installed, just type:

$ brew update
$ brew install swiftformat

Alternatively, you can install the tool on macOS or Linux by using Mint as follows:

$ mint install nicklockwood/SwiftFormat

And then run it using:

$ mint run swiftformat

Or if you prefer, you can check out and build SwiftFormat manually on macOS or Linux as follows:

$ git clone https://github.com/nicklockwood/SwiftFormat
$ cd SwiftFormat
$ swift build -c release

If you are installing SwiftFormat into your project directory, you can use CocoaPods on macOS to automatically install the swiftformat binary along with your other pods - see the Xcode build phase instructions below for details.

If you would prefer not to use a package manager, you can build the command-line app manually:

  1. open SwiftFormat.xcodeproj and build the SwiftFormat (Application) scheme.

  2. Drag the swiftformat binary into /usr/local/bin/ (this is a hidden folder, but you can use the Finder's Go > Go to Folder... menu to open it).

  3. Open ~/.bash_profile in your favorite text editor (this is a hidden file, but you can type open ~/.bash_profile in the terminal to open it).

  4. Add the following line to the file: alias swiftformat="/usr/local/bin/swiftformat --indent 4" (you can omit the --indent 4, or replace it with something else. Run swiftformat --help to see the available options).

  5. Save the .bash_profile file and run the command source ~/.bash_profile for the changes to take effect.

Usage:

If you followed the installation instructions above, you can now just type

$ swiftformat .

(that's a space and then a period after the command) in the terminal to format any Swift files in the current directory. In place of the ., you can instead type an absolute or relative path to the file or directory that you want to format.

If you prefer, you can use unix pipes to include SwiftFormat as part of a command chain. For example, this is an alternative way to format a file:

$ cat /path/to/file.swift | swiftformat --output /path/to/file.swift

Omitting the --output /path/to/file.swift will print the formatted file to stdout.

WARNING: swiftformat . will overwrite any Swift files it finds in the current directory, and any subfolders therein. If you run it in your home directory, it will probably reformat every Swift file on your hard drive.

To use it safely, do the following:

  1. Choose a file or directory that you want to apply the changes to.

  2. Make sure that you have committed all your changes to that code safely in git (or whatever source control system you use).

  3. (Optional) In Terminal, type swiftformat --inferoptions "/path/to/your/code/". This will suggest a set of formatting options to use that match your existing project style (but you are free to ignore these and use the defaults, or your own settings if you prefer).

    The path can point to either a single Swift file or a directory of files. It can be either be absolute, or relative to the current directory. The "" quotes around the path are optional, but if the path contains spaces then you either need to use quotes, or escape each space with \. You may include multiple paths separated by spaces.

  4. In Terminal, type swiftformat "/path/to/your/code/". The same rules apply as above with respect to paths, and multiple space-delimited paths are allowed.

    If you used --inferoptions to generate a suggested set of options in step 3, you should copy and paste them into the command, either before or after the path(s) to your source files.

    If you have created a config file, you can specify its path using --config "/path/to/your/config-file/". Alternatively, if you name the file.swiftformat` and place it inside the project you are formatting, it will be picked up automatically.

  5. Press enter to begin formatting. Once the formatting is complete, use your source control system to check the changes, and verify that no undesirable changes have been introduced. If they have, revert the changes, tweak the options and try again.

  6. (Optional) commit the changes.

Following these instructions should ensure that you avoid catastrophic data loss, but in the unlikely event that it wipes your hard drive, please note that I accept no responsibility.

Xcode source editor extension

Installation:

You'll find the latest version of the SwiftFormat for Xcode application inside the EditorExtension folder included in the SwiftFormat repository. Drag it into your Applications folder, then double-click to launch it, and follow the on-screen instructions.

NOTE: The Extension requires Xcode 9.2 and macOS 10.12 (Sierra) or higher.

Usage:

In Xcode, you'll find a SwiftFormat option under the Editor menu. You can use this to format either the current selection or the whole file.

You can configure the formatting rules and options used by the Xcode source editor extension using the host application. There is currently no way to override these per-project, however you can import and export different configurations using the File menu. You will need to do this again each time you switch project.

The format of the configuration file is described in the Config section below.

Note: SwiftFormat for Xcode cannot automatically detect changes to an imported configuration file. If you update the .swiftformat file for your project, you will need to manually re-import that file into SwiftFormat for Xcode in order for the Xcode source editor extension to use the new configuration.

Xcode build phase

To set up SwiftFormat as an Xcode build phase, do the following:

  1. Add the swiftformat binary to your project directory (this is better than referencing a locally installed copy because it means that project will still compile on machines that don't have the swiftformat command-line tool installed). You can install the binary manually, or via CocoaPods, by adding the following line to your Podfile then running pod install:

    pod 'SwiftFormat/CLI'
    

    NOTE: This will only install the pre-built command-line app, not the source code for the SwiftFormat framework.

  2. In the Build Phases section of your project target, add a new Run Script phase before the Compile Sources step. The script should be

    "${SRCROOT}/path/to/swiftformat" "${SRCROOT}/path/to/your/swift/code/"
    

    Both paths should be relative to the directory containing your Xcode project. If you are installing SwiftFormat using Cocoapods, the path will be

    "${PODS_ROOT}/SwiftFormat/CommandLineTool/swiftformat"
    

    NOTE: Adding this script will overwrite your source files as you work on them, which has the annoying side-effect of clearing the undo history. You may wish to add the script to your test target rather than your main target, so that it is invoked only when you run the unit tests, and not every time you build the app.

Alternatively, you can skip installation of the SwiftFormat pod and configure Xcode to use the locally installed swiftformat command-line tool instead by putting the following in your Run Script build phase:

if which swiftformat >/dev/null; then
  swiftformat .
else
  echo "warning: SwiftFormat not installed, download from https://github.com/nicklockwood/SwiftFormat"
fi

This is not recommended for shared projects however, as different team members using different versions of SwiftFormat may result in noise in the commit history as code gets reformatted inconsistently.

Via AppleScript

To run SwiftFormat on the frontmost Xcode document (project or workspace) you can use the following AppleScript:

tell application "Xcode"
	set frontWindow to the first window
	set myPath to path of document of frontWindow
	do shell script "cd " & myPath & ";cd ..; /usr/local/bin/swiftformat ."
end tell

Some Apps you can trigger this from are BetterTouchTool, Alfred or Keyboard Maestro. Another option is to define a QuickAction for Xcode via Automator and then assign a keyboard shortcut for it in the System Preferences.

VSCode plugin

If you prefer to use Microsoft's VSCode editor for writing Swift, Valentin Knabel has created a VSCode plugin for SwiftFormat.

Git pre-commit hook

  1. Follow the instructions for installing the SwiftFormat command-line tool.

  2. Edit or create a .git/hooks/pre-commit file in your project folder. The .git folder is hidden but should already exist if you are using Git with your project, so open in with the terminal, or the Finder's Go > Go to Folder... menu.

  3. Add the following line in the pre-commit file (unlike the Xcode build phase approach, this uses your locally installed version of SwiftFormat, not a separate copy in your project repository)

    #!/bin/bash
    git diff --diff-filter=d --staged --name-only | grep -e '\(.*\).swift$' | while read line; do
      swiftformat "${line}";
      git add "$line";
    done
    
  4. enable the hook by typing chmod +x .git/hooks/pre-commit in the terminal

The pre-commit hook will now run whenever you run git commit. Running git commit --no-verify will skip the pre-commit hook.

NOTE: If you are using Git via a GUI client such as Tower, additional steps may be needed.

NOTE (2): Unlike the Xcode build phase approach, git pre-commit hook won't be checked in to source control, and there's no way to guarantee that all users of the project are using the same version of SwiftFormat. For a collaborative project, you might want to consider a post-commit hook instead, which would run on your continuous integration server.

On CI using Danger

To setup SwiftFormat to be used by your continuous integration system using Danger, do the following:

  1. Follow the instructions to setup Danger.

  2. Add the danger-swiftformat plugin to your Gemfile.

  3. Add the following to your Dangerfile:

    swiftformat.binary_path = "/path/to/swiftformat" # optional
    swiftformat.additional_args = "--indent tab --self insert" # optional
    swiftformat.check_format(fail_on_error: true)
    

    NOTE: It is recommended to add the swiftformat binary to your project directory to ensure the same version is used each time (see the Xcode build phase instructions above).

Configuration

SwiftFormat's configuration is split between rules and options. Rules are functions in the SwiftFormat library that apply changes to the code. Options are settings that control the behavior of the rules.

Options

The options available in SwiftFormat can be displayed using the --options command-line argument. The default value for each option is indicated in the help text.

Rules are configured by adding --[option_name] [value] to your command-line arguments, or by creating a .swiftformat config file and placing it in your project directory.

A given option may affect multiple rules. Use --ruleinfo [rule_name] command for details about which options affect a given rule, or see the Rules.md file.

Rules

SwiftFormat includes over 50 rules, and new ones are added all the time. An up-to-date list can be found in Rules.md along with documentation for how they are used.

The list of available rules can be displayed within the command-line app using the --rules argument. Rules can be either enabled or disabled. Most are enabled by default. Disabled rules are marked with "(disabled)" when displayed using --rules.

You can use the --ruleinfo [rule_name] command to get information about a specific rule. Pass a comma-delimited list of rule names to get information for multiple rules at once, or use --ruleinfo with no argument for info on all rules.

You can disable rules individually using --disable followed by a list of one or more comma-delimited rule names, or enable opt-in rules using --enable followed by the rule names:

--disable redundantSelf,trailingClosures
--enable isEmpty

If you prefer, you can place your enabled/disabled rules on separate lines instead of using commas:

--disable indent
--disable linebreaks
--disable redundantSelf

To avoid automatically opting-in to new rules when SwiftFormat is updated, you can use the--rules argument to only enable the rules you specify:

--rules indent,linebreaks

To see exactly which rules were applied to a given file, you can use the --verbose command-line option to force SwiftFormat to print a more detailed log as it applies the formatting. NOTE: running in verbose mode is slower than the default mode.

You can disable rules for specific files or code ranges by using swiftformat: directives in comments inside your Swift files. To temporarily disable one or more rules inside a source file, use:

// swiftformat:disable <rule1> [<rule2> [rule<3> ...]]

To enable the rule(s) again, use:

// swiftformat:enable <rule1> [<rule2> [rule<3> ...]]

To disable all rules use:

// swiftformat:disable all

And to enable them all again, use:

// swiftformat:enable all

To temporarily prevent one or more rules being applied to just the next line, use:

// swiftformat:disable:next <rule1> [<rule2> [rule<3> ...]]
let foo = bar // rule(s) will be disabled for this line
let bar = baz // rule(s) will be re-enabled for this line

There is no need to manually re-enable a rule after using the next directive.

NOTE: The swiftformat:enable directives only serves to counter a previous swiftformat:disable directive in the same file. It is not possible to use swiftformat:enable to enable a rule that was not already enabled when formatting started.

Swift version

Most SwiftFormat rules are version-agnostic, but some are applicable only to newer Swift versions. These rules will be disabled automatically if the Swift version is not specified, so to make sure that the full functionality is available you should specify the version of Swift that is used by your project.

You can specify the Swift version in one of two ways:

The preferred option is to add a .swift-version file to your project directory. This is a text file that should contain the minimum Swift version supported by your project, and is a standard already used by other tools.

The .swift-version file applies hierarchically; If you have submodules in your project that use a different Swift version, you can add separate .swift-version files to those directories.

The other option to specify the Swift version using the --swiftversion command line argument. Note that this will be overridden by any .swift-version files encountered while processing.

Config file

Although it is possible to configure SwiftFormat directly by using the command-line options and rules detailed above, it is sometimes more convenient to create a configuration file, which can be added to your project and shared with other developers.

A SwiftFormat configuration file consists of one or more command-line options, split onto separate lines, e.g:

--allman true
--indent tabs
--disable elseOnSameLine,semicolons

While formatting, SwiftFormat will automatically check inside each subdirectory for the presence of a .swiftformat file and will apply any options that it finds there to the files in that directory.

This allows you to override certain rules or formatting options just for a particular directory of files. You can also specify excluded files relative to that directory using --exclude, which may be more convenient than specifying them at the top-level:

--exclude Pods,Generated

The --exclude option takes a comma-delimited list of file or directory paths to exclude from formatting. Excluded paths are relative to the config file containing the --exclude command. The excluded paths can include wildcards, specified using Unix "Glob" syntax, as documented below.

Config files named ".swiftformat" will be processed automatically, however you can select an additional configuration file to use for formatting using the --config "path/to/config/file" command-line argument. A configuration file selected using --config does not need to be named ".swiftformat", and can be located outside of the project directory.

The config file format is designed to be edited by hand. You may include blank lines for readability, and can also add comments using a hash prefix (#), e.g.

# format options
--allman true
--indent tabs # tabs FTW!

# file options
--exclude Pods

# rules
--disable elseOnSameLine,semicolons

If you would prefer not to edit the configuration file by hand, you can use the SwiftFormat for Xcode app to edit the configuration and export a configuration file. You can also use the swiftformat command-line-tool's --inferoptions command to generate a config file from your existing project, like this:

$ cd /path/to/project
$ swiftformat --inferoptions . --output .swiftformat

Globs

When excluding files from formatting using the --exclude option, you may wish to make use of wildcard paths (aka "Globs") to match all files that match a particular naming convention without having to manually list them all.

SwiftFormat's glob syntax is based on Ruby's implementation, which varies slightly from the Unix standard. The following patterns are supported:

  • * - A single star matches zero or more characters in a filename, but not a /.

  • ** - A double star will match anything, including one or more /.

  • ? - A question mark will match any single character except /.

  • [abc] - Matches any single character inside the brackets.

  • [a-z] - Matches a single character in the specified range in the brackets.

  • {foo,bar} - Matches any one of the comma-delimited strings inside the braces.

Examples:

  • foo.swift - Matches the file "foo.swift" in the same directory as the config file.

  • *.swift - Matches any swift file in the same directory as the config file.

  • foo/bar.swift - Matches the file "bar.swift" in the directory "foo".

  • **/foo.swift - Matches any file named "foo.swift" in the project.

  • **/*.swift - Matches any swift file in the project.

  • **/Generated - Matches any folder called Generated in the project.

  • **/*_generated.swift - Matches any Swift file with the suffix "_generated" in the project.

Linting

SwiftFormat is primarily designed as a formatter rather than a linter, i.e. it is designed to fix your code rather than tell you what's wrong with it. However, sometimes it can be useful to verify that code has been formatted in a context where it is not desirable to actually change it.

A typical example would be as part of a CI (Continuous Integration) process, where you may wish to have an automated script that checks committed code for style violations. While you can use a separate tool such as SwiftLint for this, it makes sense to be able to validate the formatting against the exact same rules as you are using to apply it.

In order to run SwiftFormat as a linter, you can use the --lint command-line option:

$ swiftformat --lint path/to/project

This works exactly the same way as when running in format mode, and all the same configuration options apply, however no files will be modified. SwiftFormat will simply format each file in memory and then compare the result against the input and report the files that required changes.

The --lint option is very similar to --dryrun, except that --lint will return a nonzero error code if any changes are detected, which is useful if you want it to fail a build step on your CI server.

By default, --lint will only report the number of files that were changed, but you can use the additional --verbose flag to display a detailed report about which specific rules were applied to which specific files.

Cache

SwiftFormat uses a cache file to avoid reformatting files that haven't changed. For a large project, this can significantly reduce processing time.

By default, the cache is stored in ~/Library/Caches/com.charcoaldesign.swiftformat on macOS, or /var/tmp/com.charcoaldesign.swiftformat on Linux. Use the command-line option --cache ignore to ignore the cached version and re-apply formatting to all files. Alternatively, you can use --cache clear to delete the cache (or you can just manually delete the cache file).

The cache is shared between all projects. The file is fairly small, as it only stores the path and size for each file, not the contents. If you do start experiencing slowdown due to the cache growing too large, you might want to consider using a separate cache file for each project.

You can specify a custom cache file location by passing a path as the --cache option value. For example, you might want to store the cache file inside your project directory. It is fine to check in the cache file if you want to share it between different users of your project, as the paths stored in the cache are relative to the location of the formatted files.

File headers

SwiftFormat can be configured to strip or replace the header comments in every file with a template. The "header comment" is defined as a comment block that begins on the first nonblank line in the file, and is followed by at least one blank line. This may consist of a single comment body, or multiple comments on consecutive lines:

// This is a header comment
// This is a regular comment
func foo(bar: Int) -> Void { ... }

The header template is a string that you provide using the --header command-line option. Passing a value of ignore (the default) will leave the header comments unmodified. Passing strip or an empty string "" will remove them. If you wish to provide a custom header template, the format is as follows:

For a single-line template: --header "Copyright (c) 2017 Foobar Industries"

For a multiline comment, mark linebreaks with \n: --header "First line\nSecond line"

You can optionally include Swift comment markup in the template if you wish: --header "/*--- Header comment ---*/"

If you do not include comment markup, each line in the template will be prepended with // and a single space.

It is common practice to include the file name, creation date and/or the current year in a comment header copyright notice. To do that, you can use the following placeholders:

  • {file} - the name of the file
  • {year} - the current year
  • {created} - the date on which the file was created
  • {created.year} - the year in which the file was created

For example, a header template of:

--header "{file}\nCopyright (c) {year} Foobar Industries\nCreated by John Smith on {created}."

Will be formatted as:

// SomeFile.swift
// Copyright (c) 2019 Foobar Industries
// Created by John Smith on 01/02/2016.

NOTE: the {year} value and {created} date format are determined from the current locale and timezone of the machine running the script.

FAQ

Q. How is this different from SwiftLint?

A. SwiftLint is primarily designed to find and report code smells and style violations in your code. SwiftFormat is designed to fix them. While SwiftLint can autocorrect some issues, and SwiftFormat has some support for linting, their primary functions are different.

Q. Can SwiftFormat and SwiftLint be used together?

A. Absolutely! The style rules encouraged by both tools are quite similar, and SwiftFormat even fixes some style violations that SwiftLint warns about but can't currently autocorrect.

Q. What platforms does SwiftFormat support?

A. SwiftFormat works on macOS 10.12 (Sierra) and above, and also runs on Ubuntu Linux.

Q. What versions of Swift are supported?

A. The SwiftFormat framework and command-line tool can be compiled using Swift 4.0 and above, and can format programs written in Swift 3.x, 4.x or 5. Swift 2.x is no longer actively supported. If you are still using Swift 2.x, and find that SwiftFormat breaks your code, the best solution is probably to revert to an earlier SwiftFormat release, or enable only a small subset of rules.

Q. SwiftFormat made changes I didn't want it to. How can I find out which rules to disable?

A. If you run SwiftFormat using the --verbose option, it will tell you which rules were applied to each file. You can then selectively disable certain rules using the --disable argument (see below).

Q. How can I modify the formatting rules?

A. Many configuration options are exposed in the command-line interface or .swiftformat configuration file. You can either set these manually, or use the --inferoptions argument to automatically generate the configuration from your existing project.

If there is a rule that you don't like, and which cannot be configured to your liking via the command-line options, you can disable one or more rules by using the --disable argument, followed by the name of the rules, separated by commas. You can display a list of all supported rules using the --rules argument, and their behaviors are documented above this section in the README.

If you are using the Xcode source editor extension, rules and options can be configured using the SwiftFormat for Xcode host application. Unfortunately, due to limitation of the Extensions API, there is no way to configure these on a per-project basis.

If the options you want aren't exposed, and disabling the rule doesn't solve the problem, the rules are implemented in the file Rules.swift, so you can modify them and build a new version of the command-line tool. If you think your changes might be generally useful, make a pull request.

Q. I don't want to be surprised by new rules added when I upgrade SwiftFormat. How can I prevent this?

A. You can use the --rules argument to specify an exclusive list of rules to run. If new rules are added, they won't be enabled if you have specified a --rules list in your SwiftFormat configuration.

Q. Why can't I set the indent width or choose between tabs/spaces in the SwiftFormat for Xcode options?

Indent width and tabs/spaces can be configured in Xcode on a per project-basis. You'll find the option under "Text Settings" in the right-hand sidebar.

Q. After applying SwiftFormat, my code won't compile. Is that a bug?

A. SwiftFormat should ideally never break your code. Check the known issues, and if it's not already listed there, or the suggested workaround doesn't solve your problem, please open an issue on Github.

Q. Can I use SwiftFormat to lint my code without changing it?

A. Yes, see the linting section above for details.

Q. Can I use the SwiftFormat.framework inside another app?

A. Yes, the SwiftFormat framework can be included in an app or test target, and used for many kinds of parsing and processing of Swift source code besides formatting. The SwiftFormat framework is available as a CocoaPod for easy integration.

Known issues

  • When running a version of SwiftFormat built using Xcode 10.2 on macOS 10.14.3 or earlier, you may experience a crash with the error "dyld: Library not loaded: @rpath/libswiftCore.dylib". To fix this, you need to install the Swift 5 Runtime Support for Command Line Tools. These tools are included by default in macOS 10.14.4 and later.

  • When using the --self remove option, the redundantSelf rule will remove references to self in autoclosure arguments, which may change the meaning of the code, or cause it not to compile. To work around this issue, use the --selfrequired option to provide a comma-delimited list of methods to be excluded from the rule. The expect() function from the popular Nimble unit testing framework is already excluded by default. If you are using the --self insert option then this is not an issue.

  • If you assign SomeClass.self to a variable and then instantiate an instance of the class using that variable, Swift requires that you use an explicit .init(), however the redundantInit rule is not currently capable of detecting this situation and will remove the .init. To work around this issue, use the // swiftformat:disable:next redundantInit comment directive to disable the rule for any affected lines of code (or just disable the redundantInit rule completely).

  • The --self insert option can only recognize locally declared member variables, not ones inherited from superclasses or extensions in other files, so it cannot insert missing self references for those. Note that the reverse is not true: --self remove should remove all redundant self references.

  • The trailingClosures rule can generate ambiguous code if a function has multiple optional closure arguments, or if multiple functions have signatures differing only by the name of the closure argument. For this reason, the rule is limited to anonymous closure arguments by default, with a whitelist for exceptions.

  • The isEmpty rule will convert count == 0 to isEmpty even for types that do not have an isEmpty method, such as NSArray/NSDictionary/etc. Use of Foundation collections in Swift code is pretty rare, but just in case, the rule is disabled by default.

  • If a file begins with a comment, the stripHeaders rule will remove it if it is followed by a blank line. To avoid this, make sure that the first comment is directly followed by a line of code.

  • The formatted file cache is based on a hash of the file contents, so it's possible (though unlikely) that an edited file will have the exact same hash as the previously formatted version, causing SwiftFormat to incorrectly identify it as not having changed, and fail to update it.

    To fix this, you can use the command-line option --cache ignore to force SwiftFormat to ignore the cache for this run, or just type an extra space in the file (which SwiftFormat will then remove again when it applies the correct formatting).

  • When running on Linux, the --symlinks option has no effect, and some of the fileHeader placeholders are not supported.

Credits

(Full list of contributors)