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https://github.com/jpsim/swiftlint-bazel-example

Example SwiftLint integration with custom native rules using Bazel
https://github.com/jpsim/swiftlint-bazel-example

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Example SwiftLint integration with custom native rules using Bazel

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# SwiftLint Bazel Example



This is an example repo that integrates [SwiftLint][SwiftLint] with

[Bazel][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][swiftlint-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if these instructions become out of date._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`:



```python

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

```



Then you can run SwiftLint with this command:



```console

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`:



```python

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` :



```python

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:



```console

$ 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:



```console

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

```



## Developing in Xcode



You can use the excellent [rules_xcodeproj][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:



```python

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

```



And define a `BUILD` file with this configuration:



```python

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:



```console

bazel run :swiftlint_xcodeproj && xed .

```



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

when developing.



![Xcode](xcode.png)



[SwiftLint]: https://github.com/realm/SwiftLint

[Bazel]: https://bazel.build

[swiftlint-bazel-instructions]: https://github.com/realm/SwiftLint#using-bazel

[rules_xcodeproj]: https://github.com/buildbuddy-io/rules_xcodeproj