gazelle:default_visibility directive does not work properly about bazel-gazelle

[sluongng]

cc: @dnathe4th

The BUILD file must have already existed for package() to be generated. If there is no existing BUILD file, only the go language extension would pick up *.go files and generate targets with public visibility.

Then on the 2nd run, the actual package() is generated on the newly created BUILD file.

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I think the fix here is as follows:

1. Add a doc to ensure that language/bazel/visibility should always be run last, and when it runs, it should consider/detect newly generated BUILD files by language extensions that run prior.

2. Apply "corrective" visibility over existing targets (unless # keep is used).

WDYT?

[dnathe4th]

Yeah I think (1) is the answer. Let me dig in a bit to see why it isn't detecting the newly created BUILD file (since the example repo does have the extension running after the go extension. It is unfortunate there isn't a good way to articulate a dependency between extensions.

(2) brings up a good point I went back and forth with in consulting another engineer when I originally authored the extension. There was a reasonable argument to be made that the package level default construct was not needed at all; the directive could just write to all rules' visibility attributes directly. The argument against this approach was that package(default_visibility) was a construct that already existed and was not going away, so better to have gazelle lean in on existing bazel rather than layering on an independent path to achieve the same goal. I think the same argument can also be made against overwriting any visibility directly: there's already a bazel pattern of the default and the rule specific attribute co-existing, let's not violate that by making a guess as to whether this extension should rewrite.