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SwiftLint Bazel Example

This is an example repo that integrates SwiftLint with Bazel.

Pre-Requisites

Install Bazel or Bazelisk (recommended): https://github.com/bazelbuild/bazelisk#installation
Install Xcode 15 or later: https://developer.apple.com/xcode/
You must be running macOS 13 or later

Basic Integration

Please see SwiftLint's bazel instructions if these instructions become out of date.

Make sure that you're using bzlmod by adding this line to your .bazelrc:

common --enable_bzlmod

Then put this in your MODULE.bazel:

bazel_dep(name = "swiftlint", version = "0.54.0", repo_name = "SwiftLint")

Then you can run SwiftLint with this command:

bazel run -c opt @SwiftLint//:swiftlint -- --help

Custom Rules

Setup

You can wire up SwiftLint to use some custom, private, native SwiftLint rules by adding this to your MODULE.bazel:

extra_rules = use_extension("@SwiftLint//bazel:extensions.bzl", "extra_rules")
extra_rules.setup(srcs = "@swiftlint-bazel-example//swiftlint_extra_rules:extra_rules")

Finally, you'll need to tell Bazel what source files you want to compile as part of SwiftLint by placing BUILD configuration into directory with custom rules sources.

During build, Bazel includes custom rules through func extraRules() -> [Rule.Type], which should exist in sources. Easiest way is to manually write this function in separate source file, but for example below this function is autogenerated.

:warning: Starting from SwiftLint 0.52.0 extra rules reside in separate module. This requires public keyword for func extraRules().

Example of swiftlint_extra_rules/BUILD configuration to include custom SwiftLint rules sources as well as autogenerated extra_rules.swift :

filegroup(
    name = "extra_rules",
    srcs = glob(["**/*.swift"]) + ["extra_rules.swift"],
    visibility = ["//visibility:public"],
)

genrule(
    name = "extra_rules_func",
    srcs = glob(["*.swift"]),
    outs = ["extra_rules.swift"],
    cmd = """
set -euo pipefail

echo "public func extraRules() -> [any Rule.Type] {" >> $(OUTS)
echo "  [" >> $(OUTS)
for file in $(SRCS); do
  filename=$$(basename -- "$$file")
  echo "    $${filename%.*}.self," >> $(OUTS)
done
echo "  ]" >> $(OUTS)
echo "}" >> $(OUTS)
    """,
)

Writing Rules

Then any Swift sources you add in the swiftlint_extra_rules directory will be compiled as part of the SwiftLintFramework module just as if those files had been in the official upstream SwiftLint git repository.

This means you have access to all the internal APIs in that module. These internal APIs can and will change over time, so you may need to adjust the custom code you write accordingly whenever you update the version of SwiftLint you target.

Then build and run SwiftLint and you should see your rule being applied:

$ bazel run -c opt @SwiftLint//:swiftlint
Linting Swift files in current working directory
Linting 'ForbiddenVarRule.swift' (2/3)
Linting 'file.swift' (1/3)
Linting 'ExtraRules.swift' (3/3)
file.swift:1:14: warning: Colon Spacing Violation: Colons should be next to the identifier when specifying a type and next to the key in dictionary literals. (colon)
file.swift:1:5: warning: Forbidden Var Violation: Can't name a variable 'forbidden' (forbidden_var)
Done linting! Found 2 violations, 0 serious in 3 files.

Testing Rules

You can validate the triggering, non-triggering and correction examples in your rule's description by running SwiftLint's "extra rules" tests:

bazel test --test_output=streamed @SwiftLint//Tests:ExtraRulesTests

Developing in Xcode

You can use the excellent rules_xcodeproj project to generate an Xcode project giving you Xcode's IDE functionality to help you develop your rules.

You can add it to the bottom of your MODULE.bazel file:

bazel_dep(name = "rules_xcodeproj", version = "1.4.0")

And define a BUILD file with this configuration:

load("@rules_xcodeproj//xcodeproj:defs.bzl", "xcodeproj")

xcodeproj(
    name = "swiftlint_xcodeproj",
    project_name = "SwiftLint",
    top_level_targets = [
        "@SwiftLint//:swiftlint",
        "@SwiftLint//Tests:ExtraRulesTests",
    ],
)

Generate and open the Xcode project with this command:

bazel run :swiftlint_xcodeproj && xed .

At which point you should have access to most Xcode features you'd want when developing.

Xcode