# SwiftLint A tool to enforce Swift style and conventions, loosely based on the now archived [GitHub Swift Style Guide](https://github.com/github/swift-style-guide). SwiftLint enforces the style guide rules that are generally accepted by the Swift community. These rules are well described in popular style guides like [Kodeco's Swift Style Guide](https://github.com/kodecocodes/swift-style-guide). SwiftLint hooks into [Clang](http://clang.llvm.org) and [SourceKit](http://www.jpsim.com/uncovering-sourcekit) to use the [AST](http://clang.llvm.org/docs/IntroductionToTheClangAST.html) representation of your source files for more accurate results. [](https://dev.azure.com/jpsim/SwiftLint/_build/latest?definitionId=4?branchName=main) [](https://buildkite.com/swiftlint/swiftlint)  This project adheres to the [Contributor Covenant Code of Conduct](https://realm.io/conduct). By participating, you are expected to uphold this code. Please report unacceptable behavior to [[email protected]](mailto:[email protected]). > Switch Language: > [中文](https://github.com/realm/SwiftLint/blob/main/README_CN.md) > [한국어](https://github.com/realm/SwiftLint/blob/main/README_KR.md) ## Video Introduction To get a high-level overview of SwiftLint, we encourage you to watch this presentation recorded January 9th, 2017 by JP Simard (transcript provided): [](https://youtu.be/9Z1nTMTejqU) ## Installation ### [Swift Package Manager](https://github.com/apple/swift-package-manager) SwiftLint can be used as a [command plugin](#swift-package-command-plugin) or a [build tool plugin](#build-tool-plugins). Add ```swift .package(url: "https://github.com/SimplyDanny/SwiftLintPlugins", from: "") ``` to your `Package.swift` file to consume the latest release of SwiftLint automatically or pin the dependency to a specific version: ```swift .package(url: "https://github.com/SimplyDanny/SwiftLintPlugins", exact: "") ``` Therein, replace `` with the desired minimum or exact version. > [!NOTE] > Consuming the plugins directly from the SwiftLint repository comes > with several drawbacks. To avoid them and reduce the overhead imposed, it's > highly recommended to consume the plugins from the dedicated > [SwiftLintPlugins repository](https://github.com/SimplyDanny/SwiftLintPlugins), > even though plugins from the SwiftLint repository are also absolutely > functional. If the plugins from SwiftLint are preferred, just use the URL > `https://github.com/realm/SwiftLint` in the package declarations above. > > However, [SwiftLintPlugins](https://github.com/SimplyDanny/SwiftLintPlugins) > facilitates plugin adoption massively. It lists some of the reasons that > drive the plugins as provided by SwiftLint itself very troublesome. Since > the plugin code and the releases are kept in sync, there is no difference > in functionality between the two, but you spare yourself a lot of time and > trouble using the dedicated plugins repository. > > This document assumes you're relying on SwiftLintPlugins. ### [Xcode Package Dependency](https://developer.apple.com/documentation/xcode/adding-package-dependencies-to-your-app) Use the following link to add SwiftLint as a Package Dependency to an Xcode project: ```bash https://github.com/SimplyDanny/SwiftLintPlugins ``` ### [Homebrew](http://brew.sh) ```bash brew install swiftlint ``` ### [CocoaPods](https://cocoapods.org) Add the following to your `Podfile`: ```ruby 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. Installing via Cocoapods also enables pinning to a specific version of SwiftLint rather than simply the latest (which is the case with [Homebrew](#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. ### [Mint](https://github.com/yonaskolb/mint) ```bash mint install realm/SwiftLint ``` ### [Bazel](https://bazel.build) Put this in your `MODULE.bazel`: ```bzl bazel_dep(name = "swiftlint", version = "0.52.4", repo_name = "SwiftLint") ``` Or put this in your `WORKSPACE`:

OPTIONS: --version Show the version. -h, --help Show help information. SUBCOMMANDS: analyze Run analysis rules docs Open SwiftLint documentation website in the default web browser generate-docs Generates markdown documentation for selected group of rules lint (default) Print lint warnings and errors baseline Operations on existing baselines reporters Display the list of reporters and their identifiers rules Display the list of rules and their identifiers version Display the current version of SwiftLint See 'swiftlint help ' for detailed help. ``` 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 `analyze` (like the list of files modified by Xcode specified by the [`ExtraBuildPhase`](https://github.com/norio-nomura/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 - 1}`. Similarly, files can be read from file lists by passing the option `--use-script-input-file-lists` and setting the following instance variables: `SCRIPT_INPUT_FILE_LIST_COUNT` and `SCRIPT_INPUT_FILE_LIST_0`, `SCRIPT_INPUT_FILE_LIST_1`, ..., `SCRIPT_INPUT_FILE_LIST_{SCRIPT_INPUT_FILE_LIST_COUNT - 1}`. These are same environment variables set for input files to [custom Xcode script phases](http://indiestack.com/2014/12/speeding-up-custom-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: ```shell TOOLCHAINS=com.apple.dt.toolchain.Swift_2_3 swiftlint --fix ``` On Linux, SourceKit is expected to be located in `/usr/lib/libsourcekitdInProc.so` or specified by the `LINUX_SOURCEKIT_LIB_PATH` environment variable. ## Git `pre-commit` Hook SwiftLint can be run as a [pre-commit](https://pre-commit.com/) hook. Once [installed](https://pre-commit.com/#install), add this to the `.pre-commit-config.yaml` in the root of your repository: ```yaml repos: - repo: https://github.com/realm/SwiftLint rev: 0.50.3 hooks: - id: swiftlint ``` Adjust `rev` to the SwiftLint version of your choice. `pre-commit autoupdate` can be used to update to the current version. SwiftLint can be configured using `entry` to apply fixes and fail on errors: ```yaml - repo: https://github.com/realm/SwiftLint rev: 0.50.3 hooks: - id: swiftlint entry: swiftlint --fix --strict ``` ## Rules Over 200 rules are included in SwiftLint and the Swift community (that's you!) continues to contribute more over time. [Pull requests](https://github.com/realm/SwiftLint/blob/main/CONTRIBUTING.md) are encouraged. You can find an updated list of rules and more information about them [here](https://realm.github.io/SwiftLint/rule-directory.html). You can also check the [Source/SwiftLintBuiltInRules/Rules](https://github.com/realm/SwiftLint/tree/main/Source/SwiftLintBuiltInRules/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 [ ...]` The rules will be disabled until the end of the file or until the linter sees a matching enable comment: `// swiftlint:enable [ ...]` For example: ```swift // 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: ```swift // 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: ```swift // 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 that are not part of the default set. The special `all` identifier will enable all opt in linter rules, except the ones listed in `disabled_rules`. * `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` and `only_rules`. The special `all` identifier can also be used here to enable all analyzer rules, except the ones listed in `disabled_rules`. ```yaml # 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 analyzer_rules: # rules run by `swiftlint analyze` - explicit_self # Case-sensitive paths to include during linting. Directory paths supplied on the # command line will be ignored. included: - Sources excluded: # case-sensitive paths to ignore during linting. Takes precedence over `included` - Carthage - Pods - Sources/ExcludedFolder - Sources/ExcludedFile.swift - Sources/*/ExcludedFile.swift # exclude files with a wildcard # If true, SwiftLint will not fail if no lintable files are found. allow_zero_lintable_files: false # If true, SwiftLint will treat all warnings as errors. strict: false # If true, SwiftLint will treat all errors as warnings. lenient: false # The path to a baseline file, which will be used to filter out detected violations. baseline: Baseline.json # The path to save detected violations to as a new baseline. write_baseline: Baseline.json # If true, SwiftLint will check for updates after linting or analyzing. check_for_updates: true # 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, summary) ``` You can also use environment variables in your configuration file, by using `${SOME_VARIABLE}` in a string. ### Defining Custom Rules In addition to the rules that the main SwiftLint project ships with, SwiftLint can also run two types of custom rules that you can define yourself in your own projects: #### 1. Swift Custom Rules These rules are written the same way as the Swift-based rules that ship with SwiftLint so they're fast, accurate, can leverage SwiftSyntax, can be unit tested, and more. Using these requires building SwiftLint with Bazel as described in [this video](https://vimeo.com/820572803) or its associated code in [github.com/jpsim/swiftlint-bazel-example](https://github.com/jpsim/swiftlint-bazel-example). #### 2. Regex Custom Rules You can define custom regex-based rules in your configuration file using the following syntax: ```yaml 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:  It is important to note that the regular expression pattern is used with the flags `s` and `m` enabled, that is `.` [matches newlines](https://developer.apple.com/documentation/foundation/nsregularexpression/options/1412529-dotmatcheslineseparators) and `^`/`$` [match the start and end of lines](https://developer.apple.com/documentation/foundation/nsregularexpression/options/1408263-anchorsmatchlines), respectively. If you do not want to have `.` match newlines, for example, the regex can be prepended by `(?-s)`. 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` All syntax kinds used in a snippet of Swift code can be extracted asking [SourceKitten](https://github.com/jpsim/SourceKitten). For example, `sourcekitten syntax --text "struct S {}"` delivers * `source.lang.swift.syntaxtype.keyword` for the `struct` keyword and * `source.lang.swift.syntaxtype.identifier` for its name `S` which match to `keyword` and `identifier` in the above list. If using custom rules in combination with `only_rules`, you must include the literal string `custom_rules` in the `only_rules` list: ```yaml only_rules: - custom_rules custom_rules: no_hiding_in_strings: regex: "([nN]inja)" match_kinds: string ``` Unlike Swift custom rules, you can use official SwiftLint builds (e.g. from Homebrew) to run regex custom 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 --fix`, 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 The `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 1. Cleaning DerivedData (incremental builds won't work with analyze) 2. Running `xcodebuild -workspace {WORKSPACE}.xcworkspace -scheme {SCHEME} > xcodebuild.log` 3. Running `swiftlint analyze --compiler-log-path xcodebuild.log` Analyzer rules 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 overrides in each project via a child configuration file. Team-Wide Configuration: ```yaml disabled_rules: - force_cast ``` Project-Specific Configuration: ```yaml 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 thus 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: ```txt 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: ```yaml 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: ```yaml 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 seconds or 1 second, respectively. ### 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 --config .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 nested configurations, you can't use the `--config` parameter.** ## License [MIT licensed.](https://github.com/realm/SwiftLint/blob/main/LICENSE) ## 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](https://github.com/realm), read [our blog](https://realm.io/news), or say hi on twitter ([@realm](https://twitter.com/realm)). Our thanks to MacStadium for providing a Mac Mini to run our performance tests.