Create "all_files" filegroup contains all rules_haskell sources

[k1nkreet]

#951: To be able to use buildifier_test target and integration test targets like go_bazel_build from https://github.com/bazelbuild/rules_go, this PR adds testonly filegroup contains all source files.

[aherrmann]

For the buildifer use-case we'll want to include all files under tests to make sure that they are format tested as well. But, for the go_bazel_test use-case perhaps not. Including them means that go_bazel_test type integration tests are re-run not only when rules_haskell's implementation changes, but also when any of its tests changes.
AFAIK rules_go does not include the tests tree in the all_files filegroups.
A simple option might be to omit //tests:all_files here and then add it to the buildifier test explicitly. What do you think?

[aherrmann]

A related instance is //vendor. It's needed for functionality, so will be needed for go_bazel_test, but it would be preferable to skip it for buildifier tests.

[k1nkreet]

Probably it makes sense to enumerate all necessary filegroups in buildifier_test srcs explicitly, because otherwise we'll inevitably end up with some kind of "sources for buildifer_test" filegroup. In this case name all_files is a bit odd for filegroup dedicated for integration_tests. rules_go for example doesn't include tests in all_files but use it both for integration tests and buildifier which is a bit kludgy imho. Some bazelbuild projects like bazel-skylib or rules_python uses name distribution for such filegroup, probably it makes sense to follow

[aherrmann]

Some bazelbuild projects like bazel-skylib or rules_python uses name distribution for such filegroup, probably it makes sense to follow

Nice find! Yes, that sounds like a good precedent to follow.

Probably it makes sense to enumerate all necessary filegroups in buildifier_test srcs explicitly, [...]

You mean at the top-level something like this?

buildifier_test(
    srcs = [
        "//haskell:all_files",
        "//nixpkgs:all_files",
        "//tests:all_files",
        ...
    ],

Yes, that sounds like a good solution to the problem.

[k1nkreet]

You mean at the top-level something like this?

Yes, that's exactly what I meant :)

[k1nkreet]

Some bazelbuild projects like bazel-skylib or rules_python uses name distribution for such filegroup, probably it makes sense to follow

Done

[aherrmann]

Thank you, looks good!