Add stamping support to go_binary

[ian-h-chamberlain]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

Adds a stamp attribute to go_binary which can be used to override --[no]stamp behavior for a specific binary target.

Semantics match those of cc_binary, and are limited to just go_binary for now.

Which issues(s) does this PR fix?

Closes #2154

Other notes for review

Open questions / tasks:

• [ ] I am not 100% sure if there's additional documentation that needs to be updated, if someone can point me in the right direction I'm happy to add that.
• [ ] Should go_test have this attribute as well? I didn't think it made sense for libraries have it, since conflicts between dependencies would need to be resolved, but I could probably add it for _test without needing to address those.

[ian-h-chamberlain]

Sure, the use case we have in my organization is for iterating while manually testing one of our apps. We basically have two main use cases:

• Building for production via CI (we use --stamp in the build)
• Developer build for local testing (requires remembering --stamp every time to get a stamped build)

We don't want to stamp everything (non-Go, unit tests, etc.) all of the time, to maximize cache hits, so we don't have --stamp in our .bazelrc. However, we would ideally like to use stamping for developer builds to embed e.g. git data, build timestamp just for the final go_binary.

As it stands without this change (or equivalent), users have to remember to pass --stamp every time they build this particular target to get the embedded metadata, but with this change we could set stamp = 1 and forget it. For our purposes we would also be fine with stamp = True to force-stamp a particular target (where the default behavior for False would be to just follow --[no]stamp).

I mainly kept the ternary in case there would ever be users that want to forcefully disable stamping for certain targets, but I'm not sure if is particularly common. A quick search on GitHub shows some usage like this, but it seems fairly limited (mostly forks of llvm-bazel, I guess): https://github.com/search?q=%2F%5Cbstamp+%3D+0%2F+path%3A%2FBUILD%28%5C.bazel%29%3F%24%2F&type=code

[gpanders]

I was surprised to learn today that go_binary does not already have a stamp attribute, and found this PR after trying to figure out why.

Our use case is similar to the one described above. Having this attribute would be helpful to us as well.