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.

Build 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 info@realm.io.

Language Switch: 中文, 한국어.

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 Mint:

$ mint install realm/SwiftLint

Using a pre-built package:

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

Installing from source:

You can also build and install from source by cloning this project and running make install (Xcode 11.4 or later).

Known Installation Issues On MacOS Before 10.14.4

Starting with SwiftLint 0.32.0, if you get an error similar to dyld: Symbol not found: _$s11SubSequenceSlTl when running SwiftLint, you’ll need to install the Swift 5 Runtime Support for Command Line Tools.

Alternatively, you can:

  • Update to macOS 10.14.4 or later
  • Install Xcode 11.4 or later at /Applications/Xcode.app
  • Rebuild SwiftLint from source using Xcode 11.4 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 your Xcode project to get warnings and errors displayed in the issue navigator.

To do this click the Project in the file navigator, then click the primary app target, and go to Build Phases. Click the + and select “New Run Script Phase”. Insert the following as the script:

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

You might want to move your SwiftLint phase directly before ‘Compile Sources’ step, to detect errors quickly before compiling. However, SwiftLint is designed to run on valid Swift code that cleanly completes the compiler’s parsing stage. So running SwiftLint before ‘Compile Sources’ might yield some incorrect results.

If you wish to autocorrect violations as well, your script could run swiftlint autocorrect && swiftlint instead of just swiftlint. This will mean that all correctable violations are fixed, while ensuring warnings show up in your project for remaining violations.

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 or later without disabling 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.

fastlane

You can use the official swiftlint fastlane action to run SwiftLint as part of your fastlane process.

swiftlint(
    mode: :lint,                            # SwiftLint mode: :lint (default) or :autocorrect
    executable: "Pods/SwiftLint/swiftlint", # The SwiftLint binary path (optional). Important if you've installed it via CocoaPods
    path: "/path/to/lint",                  # Specify path to lint (optional)
    output_file: "swiftlint.result.json",   # The path of the output file (optional)
    reporter: "json",                       # The custom reporter to use (optional)
    config_file: ".swiftlint-ci.yml",       # The path of the configuration file (optional)
    files: [                                # List of files to process (optional)
        "AppDelegate.swift",
        "path/to/project/Model.swift"
    ],
    ignore_exit_status: true,               # Allow fastlane to continue even if SwiftLint returns a non-zero exit status (Default: false)
    quiet: true,                            # Don't print status logs like 'Linting ' & 'Done linting' (Default: false)
    strict: true                            # Fail on warnings? (Default: false)
)

Command Line

$ swiftlint help
Available commands:

   analyze         [Experimental] Run analysis rules
   autocorrect     Automatically correct warnings and errors
   generate-docs   Generates markdown documentation for all rules
   help            Display general or command-specific help
   lint            Print lint warnings and errors (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, autocorrect or analyze (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_1SCRIPT_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.

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.

Swift Version Support

Here’s a reference of which SwiftLint version to use for a given Swift version.

Swift version Last supported SwiftLint release
Swift 1.x SwiftLint 0.1.2
Swift 2.x SwiftLint 0.18.1
Swift 3.x SwiftLint 0.25.1
Swift 4.0-4.1.x SwiftLint 0.28.2
Swift 4.2.x SwiftLint 0.35.0
Swift 5.x Latest

Rules

Over 100 rules are included in SwiftLint and the Swift community (that’s you!) continues to contribute more over time. Pull requests are encouraged.

You can find an updated list of rules and more information about them here.

You can also check Source/SwiftLintFramework/Rules directory to see their implementation.

Opt-In Rules

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

Guidelines on when to mark 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)

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

Including the all keyword will disable all rules until the linter sees a matching enable comment:

// swiftlint:disable all // swiftlint:enable all

For example:

// swiftlint:disable all
let noWarning :String = "" // No warning about colons immediately after variable names!
let i = "" // Also no warning about short identifier names
// swiftlint:enable all
let hasWarning :String = "" // Warning generated about colons immediately after variable names
let y = "" // Warning generated about short identifier 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.
  • only_rules: Only the rules specified in this list will be enabled. Cannot be specified alongside disabled_rules or opt_in_rules.
  • analyzer_rules: This is an entirely separate list of rules that are only run by the analyze command. All analyzer rules are opt-in, so this is the only configurable rule list, there are no equivalents for disabled_rules only_rules.
# By default, SwiftLint uses a set of sensible default rules you can adjust:
disabled_rules: # rule identifiers turned on by default to exclude from running
  - colon
  - comma
  - control_statement
opt_in_rules: # some rules are turned off by default, so you need to opt-in
  - empty_count # Find all the available rules by running: `swiftlint rules`

# Alternatively, specify all rules explicitly by uncommenting this option:
# only_rules: # delete `disabled_rules` & `opt_in_rules` if using this
#   - empty_parameters
#   - vertical_whitespace

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
  - Source/*/ExcludedFile.swift # Exclude files with a wildcard
analyzer_rules: # Rules run by `swiftlint analyze` (experimental)
  - explicit_self

# 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
  allowed_symbols: ["_"] # these are allowed in type names
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, codeclimate, junit, html, emoji, sonarqube, markdown, github-actions-logging)

You can also use environment variables in your configuration file, by using ${SOME_VARIABLE} in a string.

Defining Custom Rules

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

custom_rules:
  pirates_beat_ninjas: # rule identifier
    included: ".*\\.swift" # regex that defines paths to include during linting. optional.
    excluded: ".*Test\\.swift" # regex that defines paths to exclude during linting. optional
    name: "Pirates Beat Ninjas" # rule name. optional.
    regex: "([nN]inja)" # matching pattern
    capture_group: 0 # number of regex capture group to highlight the rule violation at. optional.
    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: "([nN]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

keyword
  • number
  • objectliteral
  • placeholder
  • string
  • string_interpolation_anchor
  • typeidentifier

If using custom rules in combination with only_rules, make sure to add custom_rules as an item under only_rules.

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.

Analyze (experimental)

The experimental swiftlint analyze command can lint Swift files using the full type-checked AST. The compiler log path containing the clean swiftc build command invocation (incremental builds will fail) must be passed to analyze via the --compiler-log-path flag. e.g. --compiler-log-path /path/to/xcodebuild.log

This can be obtained by running xcodebuild -workspace {WORKSPACE}.xcworkspace -scheme {SCHEME} > xcodebuild.log with a clean DerivedData folder.

This command and related code in SwiftLint is subject to substantial changes at any time while this feature is marked as experimental. Analyzer rules also tend to be considerably slower than lint rules.

Using Multiple Configuration Files

SwiftLint offers a variety of ways to include multiple configuration files. Multiple configuration files get merged into one single configuration that is then applied just as a single configuration file would get applied.

There are quite a lot of use cases where using multiple configuration files could be helpful:

For instance, one could use a team-wide shared SwiftLint configuration while allowing overrrides in each project via a child configuration file.

Team-Wide Configuration:

disabled_rules:
- force_cast

Project-Specific Configuration:

opt_in_rules:
- force_cast

Child / Parent Configs (Locally)

You can specify a child_config and / or a parent_config reference within a configuration file. These references should be local paths relative to the folder of the configuration file they are specified in. This even works recursively, as long as there are no cycles and no ambiguities.

A child config is treated as a refinement and therefore has a higher priority, while a parent config is considered a base with lower priority in case of conflicts.

Here’s an example, assuming you have the following file structure:

ProjectRoot
    |_ .swiftlint.yml
    |_ .swiftlint_refinement.yml
    |_ Base
        |_ .swiftlint_base.yml

To include both the refinement and the base file, your .swiftlint.yml should look like this:

child_config: .swiftlint_refinement.yml
parent_config: Base/.swiftlint_base.yml

When merging parent and child configs, included and excluded configurations are processed carefully to account for differences in the directory location of the containing configuration files.

Child / Parent Configs (Remote)

Just as you can provide local child_config / parent_config references, instead of referencing local paths, you can just put urls that lead to configuration files. In order for SwiftLint to detect these remote references, they must start with http:// or https://.

The referenced remote configuration files may even recursively reference other remote configuration files, but aren’t allowed to include local references.

Using a remote reference, your .swiftlint.yml could look like this:

parent_config: https://myteamserver.com/our-base-swiftlint-config.yml

Every time you run SwiftLint and have an Internet connection, SwiftLint tries to get a new version of every remote configuration that is referenced. If this request times out, a cached version is used if available. If there is no cached version available, SwiftLint fails – but no worries, a cached version should be there once SwiftLint has run successfully at least once.

If needed, the timeouts for the remote configuration fetching can be specified manually via the configuration file(s) using the remote_timeout / remote_timeout_if_cached specifiers. These values default to 2 / 1 second(s).

Command Line

Instead of just providing one configuration file when running SwiftLint via the command line, you can also pass a hierarchy, where the first configuration is treated as a parent, while the last one is treated as the highest-priority child.

A simple example including just two configuration files looks like this:

swiftlint --config ".swiftlint.yml .swiftlint_child.yml"

Nested Configurations

In addition to a main configuration (the .swiftlint.yml file in the root folder), you can put other configuration files named .swiftlint.yml into the directory structure that then get merged as a child config, but only with an effect for those files that are within the same directory as the config or in a deeper directory where there isn’t another configuration file. In other words: Nested configurations don’t work recursively – there’s a maximum number of one nested configuration per file that may be applied in addition to the main configuration.

.swiftlint.yml files are only considered as a nested configuration if they have not been used to build the main configuration already (e. g. by having been referenced via something like child_config: Folder/.swiftlint.yml). Also, parent_config / child_config specifications of nested configurations are getting ignored because there’s no sense to that.

If one (or more) SwiftLint file(s) are explicitly specified via the --config parameter, that configuration will be treated as an override, no matter whether there exist other .swiftlint.yml files somewhere within the directory. So if you want to use use nested configurations, you can’t use the -- config parameter.

License

MIT licensed.

About

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

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

Our thanks to MacStadium for providing a Mac Mini to run our performance tests.