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SwiftLint

A tool to enforce Swift style and conventions, loosely based on GitHub's Swift Style Guide.

SwiftLint hooks into Clang and SourceKit to use the AST representation of your source files for more accurate results.

Test Status codecov.io

This project adheres to the Contributor Covenant Code of Conduct. By participating, you are expected to uphold this code. Please report unacceptable behavior to [email protected].

Installation

Using Homebrew:

brew install swiftlint

Using CocoaPods:

Simply add the following line to your Podfile:

pod 'SwiftLint'

This will download the SwiftLint binaries and dependencies in Pods/ during your next pod install execution and will allow you to invoke it via ${PODS_ROOT}/SwiftLint/swiftlint in your Script Build Phases.

This is the recommended way to install a specific version of SwiftLint since it supports installing a pinned version rather than simply the latest (which is the case with Homebrew).

Note that this will add the SwiftLint binaries, its dependencies' binaries and the Swift binary library distribution to the Pods/ directory, so checking in this directory to SCM such as git is discouraged.

Using a pre-built package:

You can also install SwiftLint by downloading SwiftLint.pkg from the latest GitHub release and running it.

Compiling from source:

You can also build from source by cloning this project and running git submodule update --init --recursive; make install (Xcode 8.0 or later).

Usage

Presentation

To get a high-level overview of recommended ways to integrate SwiftLint into your project, we encourage you to watch this presentation or read the transcript:

Presentation

Xcode

Integrate SwiftLint into an Xcode scheme to get warnings and errors displayed in the IDE. Just add a new "Run Script Phase" with:

if which swiftlint >/dev/null; then
  swiftlint
else
  echo "warning: SwiftLint not installed, download from https://github.com/realm/SwiftLint"
fi

Alternatively, if you've installed SwiftLint via CocoaPods the script should look like this:

"${PODS_ROOT}/SwiftLint/swiftlint"

Format on Save Xcode Plugin

To run swiftlint autocorrect on save in Xcode, install the SwiftLintXcode plugin from Alcatraz.

⚠ ️This plugin will not work with Xcode 8 without diabling SIP. This is not recommended.

AppCode

To integrate SwiftLint with AppCode, install this plugin and configure SwiftLint's installed path in the plugin's preferences. The autocorrect action is available via ⌥⏎.

Atom

To integrate SwiftLint with Atom, install the linter-swiftlint package from APM.

Command Line

$ swiftlint help
Available commands:

   autocorrect  Automatically correct warnings and errors
   help         Display general or command-specific help
   lint         Print lint warnings and errors for the Swift files in the current directory (default command)
   rules        Display the list of rules and their identifiers
   version      Display the current version of SwiftLint

Run swiftlint in the directory containing the Swift files to lint. Directories will be searched recursively.

To specify a list of files when using lint or autocorrect (like the list of files modified by Xcode specified by the ExtraBuildPhase Xcode plugin, or modified files in the working tree based on git ls-files -m), you can do so by passing the option --use-script-input-files and setting the following instance variables: SCRIPT_INPUT_FILE_COUNT and SCRIPT_INPUT_FILE_0, SCRIPT_INPUT_FILE_1...SCRIPT_INPUT_FILE_{SCRIPT_INPUT_FILE_COUNT}.

These are same environment variables set for input files to custom Xcode script phases.

Working With Multiple Swift Versions

SwiftLint hooks into SourceKit so it continues working even as Swift evolves!

This also keeps SwiftLint lean, as it doesn't need to ship with a full Swift compiler, it just communicates with the official one you already have installed on your machine.

You should always run SwiftLint with the same toolchain you use to compile your code.

You may want to override SwiftLint's default Swift toolchain if you have multiple toolchains or Xcodes installed, or if you're using legacy Swift versions (e.g. Swift 2.3 with Xcode 8).

Here's the order in which SwiftLint determines which Swift toolchain to use:

  • $XCODE_DEFAULT_TOOLCHAIN_OVERRIDE
  • $TOOLCHAIN_DIR or $TOOLCHAINS
  • xcrun -find swift
  • /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain
  • /Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain
  • ~/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain
  • ~/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain

sourcekitd.framework is expected to be found in the usr/lib/ subdirectory of the value passed in the paths above.

You may also set the TOOLCHAINS environment variable to the reverse-DNS notation that identifies a Swift toolchain version:

$ TOOLCHAINS=com.apple.dt.toolchain.Swift_2_3 swiftlint autocorrect

On Linux, SourceKit is expected to be located in /usr/lib/libsourcekitdInProc.so or specified by the LINUX_SOURCEKIT_LIB_PATH environment variable.

Rules

Over 75 rules are included in SwiftLint and the Swift community (that's you!) continues to contribute more over time. Pull requests are encouraged.

See the Source/SwiftLintFramework/Rules directory to see the currently implemented rules.

opt_in_rules are disabled by default (i.e., you have to explicitly enable them in your configuration file).

Guidelines on when to implement a rule as opt-in:

  • A rule that can have many false positives (e.g. empty_count)
  • A rule that is too slow
  • A rule that is not general consensus or is only useful in some cases (e.g. force_unwrapping, missing_docs)

Disable rules in code

Rules can be disabled with a comment inside a source file with the following format:

// swiftlint:disable <rule1> [<rule2> <rule3>...]

The rules will be disabled until the end of the file or until the linter sees a matching enable comment:

// swiftlint:enable <rule1> [<rule2> <rule3>...]

For example:

// swiftlint:disable colon
let noWarning :String = "" // No warning about colons immediately after variable names!
// swiftlint:enable colon
let hasWarning :String = "" // Warning generated about colons immediately after variable names

It's also possible to modify a disable or enable command by appending :previous, :this or :next for only applying the command to the previous, this (current) or next line respectively.

For example:

// swiftlint:disable:next force_cast
let noWarning = NSNumber() as! Int
let hasWarning = NSNumber() as! Int
let noWarning2 = NSNumber() as! Int // swiftlint:disable:this force_cast
let noWarning3 = NSNumber() as! Int
// swiftlint:disable:previous force_cast

Run swiftlint rules to print a list of all available rules and their identifiers.

Configuration

Configure SwiftLint by adding a .swiftlint.yml file from the directory you'll run SwiftLint from. The following parameters can be configured:

Rule inclusion:

  • disabled_rules: Disable rules from the default enabled set.
  • opt_in_rules: Enable rules not from the default set.
  • whitelist_rules: Acts as a whitelist, only the rules specified in this list will be enabled. Can not be specified alongside disabled_rules or opt_in_rules.
disabled_rules: # rule identifiers to exclude from running
  - colon
  - comma
  - control_statement
opt_in_rules: # some rules are only opt-in
  - empty_count
  - missing_docs
  # Find all the available rules by running:
  # swiftlint rules
included: # paths to include during linting. `--path` is ignored if present.
  - Source
excluded: # paths to ignore during linting. Takes precedence over `included`.
  - Carthage
  - Pods
  - Source/ExcludedFolder
  - Source/ExcludedFile.swift

# configurable rules can be customized from this configuration file
# binary rules can set their severity level
force_cast: warning # implicitly
force_try:
  severity: warning # explicitly
# rules that have both warning and error levels, can set just the warning level
# implicitly
line_length: 110
# they can set both implicitly with an array
type_body_length:
  - 300 # warning
  - 400 # error
# or they can set both explicitly
file_length:
  warning: 500
  error: 1200
# naming rules can set warnings/errors for min_length and max_length
# additionally they can set excluded names
type_name:
  min_length: 4 # only warning
  max_length: # warning and error
    warning: 40
    error: 50
  excluded: iPhone # excluded via string
identifier_name:
  min_length: # only min_length
    error: 4 # only error
  excluded: # excluded via string array
    - id
    - URL
    - GlobalAPIKey
reporter: "xcode" # reporter type (xcode, json, csv, checkstyle, junit, html, emoji)

Defining Custom Rules

You can define custom regex-based rules in you configuration file using the following syntax:

custom_rules:
  pirates_beat_ninjas: # rule identifier
    included: ".*.swift" # regex that defines paths to include during linting. optional.
    name: "Pirates Beat Ninjas" # rule name. optional.
    regex: "([n,N]inja)" # matching pattern
    match_kinds: # SyntaxKinds to match. optional.
      - comment
      - identifier
    message: "Pirates are better than ninjas." # violation message. optional.
    severity: error # violation severity. optional.
  no_hiding_in_strings:
    regex: "([n,N]inja)"
    match_kinds: string

This is what the output would look like:

You can filter the matches by providing one or more match_kinds, which will reject matches that include syntax kinds that are not present in this list. Here are all the possible syntax kinds:

  • argument
  • attribute.builtin
  • attribute.id
  • buildconfig.id
  • buildconfig.keyword
  • comment
  • comment.mark
  • comment.url
  • doccomment
  • doccomment.field
  • identifier
  • keyword
  • number
  • objectliteral
  • parameter
  • placeholder
  • string
  • string_interpolation_anchor
  • typeidentifier

Nested Configurations

SwiftLint supports nesting configuration files for more granular control over the linting process.

  • Include additional .swiftlint.yml files where necessary in your directory structure.
  • Each file will be linted using the configuration file that is in its directory or at the deepest level of its parent directories. Otherwise the root configuration will be used.
  • excluded and included are ignored for nested configurations.

Auto-correct

SwiftLint can automatically correct certain violations. Files on disk are overwritten with a corrected version.

Please make sure to have backups of these files before running swiftlint autocorrect, otherwise important data may be lost.

Standard linting is disabled while correcting because of the high likelihood of violations (or their offsets) being incorrect after modifying a file while applying corrections.

License

MIT licensed.

About

SwiftLint is maintained and funded by Realm Inc. The names and logos for Realm are trademarks of Realm Inc.

We ❤️ open source software! See our other open source projects, read our blog, or say hi on twitter (@realm).