scalafmt.md

Scalafmt

lucidsoftware/rules_scala contains copies of the default Scala rules with formatting capabilities, powered by Scalafmt. See the Stardoc on these rules for more information.

Toolchains are used to set the Scalafmt configuration file that's used by those targets that have formatting enabled. The default toolchain uses the .scalafmt.conf file at the root of this repository—the same configuration file that's used to format this repository's code. All you need to do to use the formatting rules is register the default toolchain with Bazel in your MODULE.bazel file:

register_toolchains("@rules_scala_annex//:annex_scalafmt")

That should be sufficient to get you started, but if you'd like to use your own .scalafmt.conf file, you'll need to declare your own toolchain and register it with Bazel:

/BUILD

load("@rules_scala_annex//rules/scalafmt:register_toolchain.bzl", "register_scalafmt_toolchain")

register_scalafmt_toolchain(
    name = "custom_scalafmt",
    config = ".scalafmt.conf",
)

/MODULE.bazel

register_toolchains(":custom_scalafmt")

Then, you can either:

• Use it for every target by default by adding the --@rules_scala_annex//rules/scalafmt:scalafmt-toolchain=custom_scalafmt flag to your .bazelrc file
• Use it for a specific target by setting the scalafmt_toolchain_name attribute:

  load("@rules_scala_annex//rules:scala_with_scalafmt.bzl", "scala_binary")
  
  scala_binary(
      ...,
      scalafmt_toolchain_name = "custom_scalafmt",
      ...,
  )

If you'd like to format all of the Scala files in your repository via a single target, you can use scala_format_test:

/BUILD

load("@rules_scala_annex//rules:scalafmt.bzl", "scala_format_test")
scala_format_test(
    name = "format",
    srcs = glob(["**/*.scala"]),
)

Then:

# check format, with diffs and non-zero exit in case of differences
$ bazel test :format

# format files in-place
$ bazel run :format

Note that like the Scala rules, scala_format_test too uses toolchains and accepts a scalafmt_toolchain_name attribute.