Respect .bazelignore

[Whoaa512]

What type of PR is this?

Feature

What package or component does this PR mostly affect?

walk/config

What does this PR do? Why is it needed?

The code for this re-purposes the original PR #1022 but makes a few
modifications for performance and correctness.

First we only load the .bazelignore once when rel == "" since that means
we're in the root; the previous implementation seemed to do the same load
for every directory visited. Next we only match files relative to repo
root to have parity with how Bazel itself parses the ignore file.

Which issues(s) does this PR fix?

Fixes #318

Other notes for review

[sluongng]

I reviewed this without knowing that this was a recreation of a previously merged+reverted PR so some questions might have been answered in the past unknowningly to me.

Overall this looks good to me but need some more work to take it over the finish line.

[Whoaa512]

@sluongng Updated to resolve comments and add the glob ignore test case

[sluongng]

Thanks for the update. Latest version looks very clean to me. 👍

My current concern of this PR is that I am not clear on whether .bazelignore would still be loaded if gazelle was invoked in a working directory that is different from root of the workspace/repository.

I.e. given a project like this

> tree project
.
├── BUILD.bazel
├── README.md
├── WORKSPACE
├── .bazelignore
├── foo
│   ├── BUILD.bazel
│   └── a.go
└── bar
    ├── BUILD.bazel
    └── b.go

Would .bazelignore still get loaded when somebody were to run cd foo && gazelle?

Imo try explore using sync.Once to load .bazelignore regardless of the current value of rel would be clearer and help avoid this situation regardless? WDYT?

[Whoaa512]

@sluongng Yea using sync.Once seems cleaner than relying on rel. Updated tho I don't know how to test this case that you mentioned as we usually run gazelle via bazel and always from the root

[sluongng]

LGTM

Pinging @blico @achew22 for additional reviews

[Whoaa512]

friendly ping @blico @achew22

[achew22]

LGTM

@linzhp and @blico, could I have you give this a once over in your more complex repo? Since you detected the rollback from the last time we tried this I'd like to be a bit cautious.

Thanks!

[linzhp]

It works in Uber