What is this?

SwiftFormat is a code library and command line tool for reformatting swift code.

It applies a set of rules to the whitespace around the code, leaving the meaning intact.

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 bad feeling 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 operation of the code, not its presentation.

How do I install it?

1. The latest binary version of the swiftformat command-line tool is included in the CommandLineTool folder. You can either use that, or build it yourself from source. To build it yourself, 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.

How do I use it?

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.

WARNING: swiftformat . will overwrite any swift files it finds in the current directory, and any subfolders therein. If you run it from 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. If you don't use source control, rethink your life choices).

3. In Terminal, type swiftformat "/path/to/your/code/" (the path can 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 \).

4. Use your source control system to check the changes, and verify that no undesirable changes have been introduced (if they have, file a bug).

5. (Optional) commit the changes.

This 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.

If you prefer, you can also 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.

That seems like a cumbersome process - can I automate it?

Yes. Once you are confident that SwiftFormat isn't going to wreck your code, there are a couple of approaches you can take to run it automatically:

1. As a build phase in your Xcode project, so that it runs every time you press Cmd-R or Cmd-B, or
2. As a Git pre-commit hook, so that it runs on any files you've changed before you check them in

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 your local copy because it ensures that everyone who checks out the project will be using the same version).

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).

NOTE: This will slightly increase your build time, but shouldn't impact it too much, as SwiftFormat is quite fast compared to compilation. If you find that it has a noticeable impact, file a bug report and I'll try to diagnose why.

Git pre-commit hook

1. 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.

2. Add the following line in the pre-commit file (this assumes you have already installed the swiftformat command-line tool as instructed in the "How do I install it?" section above - unlike the Xcode build phase approach, this uses your locally installed version of swiftformat)

    #!/bin/bash
    git status --porcelain | grep -e '^[AM]\(.*\).swift$' | cut -c 3- | while read line; do
      swiftformat ${line};
      git add $line;
    done
   

3. 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: 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.

So what does SwiftFormat actually do?

Here are all the rules that SwiftFormat currently applies:

spaceAroundParens - contextually adjusts the space around ( ). For example:

init (foo)    -->   init(foo)

switch(x){    -->   switch (x) {

spaceInsideParens - removes the space inside ( ). For example:

( a, b )    -->    (a, b)

spaceAroundBrackets - contextually adjusts the space around [ ]. For example:

foo as[String]   -->   foo as [String]

foo = bar [5]    -->   foo = bar[5]

spaceInsideBrackets - removes the space inside [ ]. For example:

[ 1, 2, 3 ]    -->    [1, 2, 3]

spaceAroundBraces - contextually adds space around { }. For example:

foo.filter{ return true }.map{ $0 }   -->   foo.filter { return true }.map { $0 }

foo({})   							  -->   foo({})

spaceInsideBraces - adds space inside { }. For example:

foo.filter {return true}    -->    foo.filter { return true }

spaceAroundGenerics - removes the space around < >. For example:

Foo <Bar> ()    -->    Foo<Bar>()

spaceInsideGenerics - removes the space inside < >. For example:

Foo< Bar, Baz >    -->    Foo<Bar, Baz>

spaceAroundOperators - contextually adjusts the space around infix operators:

foo . bar()   -->    foo.bar()

a+b+c         -->    a + b + c

spaceAroundComments - adds space around /* ... */ comments and before // comments:

let a = 5// assignment     -->   let a = 5 // assignment

func foo() {/* no-op */}   -->   func foo() { /* no-op */ }

spaceInsideComments - adds space inside /* ... */ comments and at the start of // comments:

let a = 5 //assignment     -->   let a = 5 // assignment

func foo() { /*no-op*/ }   -->   func foo() { /* no-op */ }

consecutiveSpaces - reduces a sequence of spaces to a single space:

let  foo =  5    -->    let foo = 5

trailingWhitespace - removes the whitespace at the end of a line

consecutiveBlankLines - reduces multiple sequential blank lines to a single blank line

blankLinesAtEndOfScope - removes trailing bank lines from inside braces, brackets, parens or chevrons:

func foo() {         func foo() {
    //foo      -->       //foo
                     }
}

array = [            array = [
    foo,                 foo,
    bar,       -->       bar,
    baz,                 baz,
                     }
]

blankLinesBetweenScopes - adds a blank line before each class, struct, enum, extension, protocol or function:

func foo() {         func foo() {
    //foo      -->       //foo
}                    }
func bar() {         
    //bar      -->   func bar() {
}                        //bar
                     }

linebreakAtEndOfFile - ensures that the last line of the file is empty

indent - adjusts leading whitespace based on scope and line wrapping:

if x {               if x {
 //foo                   //foo
} else {       -->   } else {
    //bar                //bar
   }                 }
   
let array = [        let array = [
       foo,              foo,
      bar,     -->       bar,
     baz                 baz
   ]                 ]

knrBraces - implements K&R style braces, where the opening brace is on the same line as related code:

if x                 if x {
{                        //foo
    //foo            } 
}    	       -->   else {
else                     //bar
{                    }
	//bar
}

elseOnSameLine - ensures the else following an if statement appears on the same line as the closing }

if x {               if x {
    //foo                //foo
}              -->   } else {
else {                   //bar
    //bar            }
}

trailingCommas - adds a trailing , to the last line in a multiline array or dictionary literal:

let array = [        let array = [
    foo,                 foo,
    bar,       -->       bar,
    baz                  baz,
]                    ]

todos - ensures that TODO:, MARK: and FIXME: comments include the trailing colon (else they're ignored by Xcode)

/* TODO fix this properly */    -->   /* TODO: fix this properly */

// MARK - UIScrollViewDelegate  -->   // MARK: - UIScrollViewDelegate

semicolons - removes semicolons at the end of lines and (optionally) replaces inline semicolons with a linebreak:

let foo = 5;              -->  let foo = 5

let foo = 5; let bar = 6  -->  let foo = 5
                               let bar = 6
                               
return; 	              -->  return;
goto(fail)                     goto(fail)

linebreaks - normalizes all linebreaks to use the same character, as specified in options (either CR, LF or CRLF).

specifiers - normalizes the order for access specifiers, and other property/function/class/etc. specifiers:

lazy public weak private(set) var foo: UIView?    -->    private(set) public lazy weak var foo: UIView?

public override final func foo()                  -->    final override public func foo() 

convenience private init()                        -->    private convenience init() 

FAQ

There haven't been many questions yet, but here's what I'd like to think people are wondering:

Q. Does SwiftFormat support Swift 3?

A. Probably. I've fixed some specific issues with Swift 3, but I've only tested it extensively with Swift 2.3 code.

Q. Can I compile it with Swift 3?

A. Hahahahahahahahahahahahahahahahahahahaha no.

Q. I don't like how SwiftFormat formatted my code

A. That's not a question (but see below).

Q. How can I modify the formatting rules?

A. Most of the rules are hard-coded right now, with a handful of options exposed in the FormatOptions struct. If you look in Rules.swift you will find a list of all the rules that are applied by default. You can easily remove rules you don't want and build a new version of the command line tool.

With a bit more effort, you can also edit the existing rules or create new ones. If you think your changes might be generally useful, make a pull request.

Q. Why did you write yet another Swift formatting tool?

A. Surprisingly, there really aren't that many other options out there, and none of them currently support all the rules I wanted. The only other comparable ones I'm aware of are Realm's SwiftLint and Jintin's Swimat - you might want to try those if SwiftFormat doesn't meet your requirements.

Q. Does it use SourceKit?

A. No.

Q. Why would you write a parser from scratch instead of just using SourceKit?

A. The fact that there aren't already dozens of full-featured Swift formatters using SourceKit would suggest that the "just" isn't warranted.

Q. You wrote a Swift parser from scratch!? Are you a wizard?

A. Yes. Yes I am.

Q. How does it work?

A. First it loops through the source file character-by-character and breaks it into tokens, such as Number, Identifier, Whitespace, etc. That's handled by the functions in Tokenizer.swift.

Next, it applies a series of formatting rules to the token array, such as "remove whitespace at the end of a line", or "ensure each opening brace appears on the same line as the preceding non-whitespace token". Each rule is designed to be relatively independent of the others, so they can be enabled or disabled individually (the order matters though). The rules are all defined as floating functions in Rules.swift.

Finally, the modified token array is stitched back together to re-generate the source file.

Q. Why aren't you using regular expressions?

A. See https://xkcd.com/1171/ for details.

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

A. I only created the framework to facilitate testing, so to be honest I've no idea if it will work in an app, but you're welcome to try. If you need to make adjustments to the public/private flags or namespaces to get it working, put up a pull request.

Known issues

SwiftFormat currently reformats multiline comment blocks without regard for the original indenting. That means

/* some documentation

      func codeExample() {
          print("Hello World")
      }

 */

Will become

/* some documentation

 func codeExample() {
 print("Hello World")
 }
 
 */

To work around that, either use blocks of single-line comments...

// some documentation
//
//    func codeExample() {
//        print("Hello World")
//    }
//
//

Or begin each line with a * (or any other non-whitespace character)

/* some documentation
 *
 *    func codeExample() {
 *        print("Hello World")
 *    }
 *  
 */

What's next?

There are a bunch of additional rules I'd like to add, such as consistent placement of blank lines in and around functions, and correctly formatting headerdoc comments.

At some point I should probably add an intermediate parsing stage that identifies high-level constructs such as classes and functions and assembles them into a syntax tree. I didn't bother doing this originally because I thought it would be easier to implement formatting at the token level, but in fact this just meant that the logic for distinguishing between syntax constructs had to be split between the tokenizer and the formatting rules, making both of them more complex than they ought to be.

With a syntax tree in place, it should become possible to add much more sophisticated rules, such as converting uppercase enums to lowercase for Swift 3, etc.

Release notes

Version 0.9.6

• Fixed parsing error when switch statement is followed by enum
• Fixed formatting of guard case statements

Version 0.9.5

• Fixed a number of cases where the use of keywords as identifiers was not being handled correctly

Version 0.9.4

• Fixed bug where parsing would fail if a switch/case statement contained default or case indentifiers (valid in Swift 3)

Version 0.9.3

• Fixed bug where functions would be prefixed with an additional blank line if the preceding line had a trailing comment

Version 0.9.2

• Fixed bug where case expressions containing a colon would not be parsed correctly

Version 0.9.1

• Fixed bug where trailingCommas rule would place comma after a comment instead of before it

Version 0.9

• Added blankLinesBetweenScopes rule that adds a blank line before each class, struct, enum, extension, protocol or function
• Added specifiers rule, for normalizing the order of access modifiers, etc
• Fixed indent bugs when wrapping code before or after a where or else keyword
• Fixed indent bugs when using an operator as a value (e.g. let greaterThan = >)

Version 0.8.2

• Fixed bug where consecutive spaces would not be removed in lines that appeared after a // comment
• SwiftFormat will no longer try to format code containing unbalanced braces
• Added pre-commit hook instructions

Version 0.8.1

• Fixed formatting of /*! ... */ and //! headerdoc comments, and /*: ... */ and //: Swift Playground comments

Version 0.8

• Added new ranges rules that adds or removes the spaces around range operators (e.g. 0 ..< count, "a"..."z")
• Added a new --ranges command-line option, which can be used to configure the spacing around range operators
• Added new spaceAroundComments rule, which adds a space around /* ... */ comments and before // comments
• Added new spaceInsideComments rule, which adds a space inside /* ... */ comments and at the start of // comments
• Added new blankLinesAtEndOfScope rule, which removes blank lines at the end of braces, brackets and parens
• Removed double blank line at end of file

Version 0.7.1

• Fixed critical bug where failable generic init (e.g. init?<T>()) was not handled correctly

Version 0.7

• swiftformat command-line tool now correctly handles paths with \ escaped spaces, or paths in quotes
• Removed extra space added inside @objc selectors
• Fixed incorrect spacing for tuple bindings
• Fixed space before enum case inside closure

Version 0.6

• Refactored how switch/case is handled, and fixed a bunch of bugs
• Better indenting logic, now handles multiple closure arguments in a single function call

Version 0.5.1

• Fixed critical bug where double unwrap (e.g. foo??.bar()) was not handled correctly
• Fixed bug where case let .SomeEnum was not handled correctly

Version 0.5

• swiftformat command-line tool now supports reading from stdin/writing to stdout
• Added new linebreaks rule for normalizing linebreak characters (defaults to LF)
• More robust handling of linebreaks and whitespace within comments
• Trailing whitespace within comments is now stripped, as it was for other lines

Version 0.4

• Added new semicolons rule, which removes semicolons wherever it's safe to do so
• Added --semicolons command-line argument for enabling inline semicolon stripping
• The todos rule now corrects MARK : to MARK: instead of MARK: :
• Paths containing ~ are now handled correctly by the command line tool
• Fixed some bugs in generics and custom operator parsing, and added more tests
• Removed trailing whitespace on blank lines caused by the indent rule

Version 0.3

• Fixed several cases where generics were misidentified as operators
• Fixed a bug where a comment on a line before a brace broke K&R indenting
• Fixed a bug where a comment on a previous line caused incorrect indenting for wrapped lines
• Added new todos rule, for ensuring TODO:, MARK:, and FIXME: comments are formatted correctly
• Whitespace at the start of comments is now handled differently, but it shouldn't affect output

Version 0.2

• Fixed formatting of generic function types
• Fixed indenting of if case statements
• Fixed indenting of else when separated from if statement by a comment
• Changed private(set) spacing to match Apple standard
• Added swiftformat as a build phase to SwiftFormat, so I'm eating my own dogfood

Version 0.1

• First release