Add an executable target to generate the CODEOWNERS file in the workspace

[sudoforge]

Output Path

codeowners_register() should take a filepath parameter that defaults to .github/CODEOWNERS (or another one of the valid GitHub CODEOWNERS paths). This will be consumed at build time.

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Building

In an ideal world, we'd be able to bazel build ..., and the codeowners() rules would be picked up and compiled into a file that's output to filepath. Unfortunately, we can't do that. What we can do is provide a target that is runnable and does the same work; we'd only need to provide the name -- this would be similar to other rules such as bazelbuild/bazel-gazelle and bazelbuild/buildtools, and would be invoked as such:

$ cat BUILD.bazel
load("@rules_codeowners//:foo.bzl", "generate_codeowners")
generate_codeowners(name = "codeowners")


$ bazel run //:codeowners

This would parse all of the codeowners() rules and create the generated file at the specified output path (from codeowners_register(), above).

I think following the pattern of established tool integrations like bazel-gazelle and buildifier (via buildtools) is a great way forward.

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Depends-On: #25
Sourced from: #13 (comment)