Allow composing rule implementations

[lberki]

Description of the feature request:

It would be nice of the implementation of a Starlark rule could call the implementation of another rule.

There are two current answers to this functionality:

• Macros (but they are much less powerful than rules and show up in bazel query, which is not ideal
• Calling the implementation function of another rule (it may or may not be exported, doesn't work for native rules and requires the attributes of the calling rule to be set up just right including their names, types, applied aspects, toolchains and implicit dependencies)

I am not very certain if this is the right approach: this came up within the context of writing custom C++ rules and it could very well be that a better cc_common API would make this request superfluous. On the surface, however, I think it's useful to at least discuss it.

What underlying problem are you trying to solve with this feature?

No response

Which operating system are you running Bazel on?

No response

What is the output of bazel info release?

No response

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[lberki]

cc @comius @brandjon @lizkammer

[brandjon]

I'd like to look into this in 2023 as part of a larger effort to understand the best path for making macros and rules play nicer together.