Update bazel to match only extension or whole name

[TheButlah]

The hook was originally matching all files in the repository as long as they had BUILD or BUILD.bazel in them. This commit ensures that, for example, BUILD.bazel and whatever/BUILD.bazel match, but not whateverBUILD.bazelasdf. It also adds support for whatever.BUILD files.

[TheButlah]

Duplicated from FelixSeptem/pre-commit-golang#3

[jlebar]

Thank you so much for the PR!

I agree the original code is broken (oops), but I'm not 100% sure the new code works as intended either. I may just be misunderstanding, though.

(^(BUILD\.bazel|BUILD)|/\2|\.BUILD)$

Deconstructed this is:

(
  ^(BUILD\.bazel|BUILD) |
  /\2 |
  \.BUILD
)$

I've only really used RE2, which doesn't support backreferences, so I may be misunderstanding how this is supposed to work. But AIUI /\2 will only match something if group 2 matches something first, but since there's an alternation (i.e. |), we can never match both group 2 and /\2.

WDYT, am I missing something?

[TheButlah]

Yep, I think you're right. Here's an updated regex: https://regex101.com/r/AYsCnu/1/
I can update the PR with the new version tomorrow

[jlebar]

I was confused what (|foo) was supposed to do, but now I realize it's the same as (foo)?.

WDYT of the following; maybe it's slightly easier to parse?

(?:^|.*/)(?:BUILD\.bazel|BUILD)$|\.BUILD$

https://regex101.com/r/f0fFhE/1

[TheButlah]

I agree, using (whatever)? instead of (|whatever) is better. That being said, why the non-capturing groups? pre-commit doesn't care about what the groups are, only whether a match is found so making them non-capturing just adds extra complexity to the expression.

How about this as the simplest version: https://regex101.com/r/f0fFhE/2

^(.*/)?(BUILD\.bazel|BUILD)$|\.BUILD$

[jlebar]

why the non-capturing groups?

Eh, you're right, it was a premature optimization. The whole purpose of noncapturing groups is to let the regex engine optimize things that it otherwise couldn't, but it doesn't matter in this case.

[jlebar]

LGTM, merging!

Thanks again for the PR.