Include rctx.os.{name,arch} in the pre declared inputs hash

[fmeum]

Description

Motivation

Fixes bazel-contrib/rules_go#4581

Build API Changes

No

Checklist

• I have added tests for the new use cases (if any).
• I have updated the documentation (if applicable).

Release Notes

RELNOTES: The local and remote repo contents cache now include the host OS and CPU architecture in the cache key.

[fmeum]

@bazel-io fork 9.0.2

[fmeum]

@bazel-io fork 9.1.0

[fmeum]

@bazel-io fork 8.7.0

[meteorcloudy]

I guess there is no easy way to only add those when the repo rule inspects the value? Does http_archive actually do that?

[fmeum]

We could track access to these fields as recorded inputs. That is a bit more complicated, but it could get us this behavior. I can try that instead if you think it's worth it - I could see this go both ways.

[Wyverald]

We could track access to these fields as recorded inputs.

This is probably not very easy -- these are marked structField = true (code), which means that they don't get access to a StarlarkThread. So we'd have to make StarlarkOS a smart object (bleugh...).

I guess counting os.name/arch as predeclared inputs is the least harmful way to go about this. (in which case please add a small RELNOTES)

[fmeum]

Done. Always including these values in the key also avoids nasty surprises if the output implicitly depends on the OS. Since cross-platform testing is rare, such issues would be very difficult to find for ruleset authors.