Documentation issue: ctx.version_file is undocumented

[adam-azarchs]

Description of the problem / feature request:

A starlark rule can support stamping by looking at the ctx.version_file or ctx.info_file field. However, this field does not appear in the documentation for ctx. Same goes for ctx.info_file.

Feature requests: what underlying problem are you trying to solve with this feature?

The semantics of version stamping in starlark rules are far from clear. How can they use stamp information if and only if building with --stamp? How can they specify stamping be on by default? And so on. I needed to read through the implementation of go_binary to figure out what I did.

It seems a little bit strange that the documentation is missing, because there does appear to be documentation attached to the field in the java definition of the starlark API:

bazel/src/main/java/com/google/devtools/build/lib/skylarkbuildapi/StarlarkRuleContextApi.java

Line 516 in 656cc06

doc =

though I am not familiar with the process by which that documentation gets bubbled up to the documentation on the web. That would be a good start, although as I said it would be nice to also document the conditions under which that field is or is not populated.

What's the output of bazel info release?

release 3.3.0

Have you found anything relevant by searching the web?

There's uses of ctx.version_file in various rules repos including rules_go, rules_nodejs and so on. That suggests to me that the API is expected to remain stable.

Related: #4942

[laurentlb]

Duplicate with #9363