feat: gazelle_test test rule

[hunshcn]

What type of PR is this?

Feature

What package or component does this PR mostly affect?

bazel test

What does this PR do? Why is it needed?
Now we can use gazelle_test to verify generated content. It would be useful as a presubmit.

Which issues(s) does this PR fix?

Fixes #15

Other notes for review

[fmeum]

@linzhp @tyler-french Do you happen to have a solution for this at Uber?

[linzhp]

We used the diff mode on CI and post the patch back to Phabricator when the check fails.

I have mixed feelings of running Gazelle as a test. I understand that it's easy to set up because we don't need a separate CI job to run Gazelle, and can rely on bazel test //... to include the Gazelle check. However, for large repos, running Gazelle for the whole repo is very slow. So @tyler-french designed an algorithm to detect whether we should run Gazelle at all and if so, what part of repo we need to run Gazelle with. So the CI avoided running Gazelle from the root for majority of diffs.

With the generated patch posted from CI jobs to Phabricator, users only need to run Gazelle from relevant directories to fix the issue, or even simply apply the patch to the diff.

With Git sparse checkout that many users have, running Gazelle from root is not even possible

[hunshcn]

We used the diff mode on CI and post the patch back to Phabricator the check fails.

I have mixed feelings of running Gazelle as a test. I understand that it's easy to set up because we don't need a separate CI job to run Gazelle, and can rely on bazel test //... to include the Gazelle check. However, for large repos, running Gazelle for the whole repo is very slow. So @tyler-french designed an algorithm to detect whether we should run Gazelle at all and if so, what part of repo we need to run Gazelle with. So the CI avoided running Gazelle from the root for majority of diffs.

With the generated patch posted from CI jobs to Phabricator, users only need to run Gazelle from relevant directories to fix the issue, or even simply apply the patch to the diff.

With Git sparse checkout that many users have, running Gazelle from root is not even possible

There is such a problem, but I think the reason for this problem is that it is difficult to run gazelle from root, not just gazelle_test.

gazelle_test is only responsible for gazelle's results. If gazelle rule exists, then gazelle_test is feasible.

@linzhp @fmeum WDYT

[linzhp]

No objection for adding the rule. Just to point out it's not as useful as people thought in presubmit of large repos

[hunshcn]

could we continue?

[hunshcn]

@fmeum ping

[fmeum]

I haven't forgotten about this PR and will probably get to it early next week. Sorry for the delay, there's plenty of stuff going on for the next Bazel release.

[hunshcn]

ping @fmeum no rush, just a reminder.

[fmeum]

Thanks for the ping and sorry for the wait, 7.2.0 taking more time than expected.