tree 16bde246b8e6e39a11619c4ad6bc6355f45506f4
parent 4082693e23ec9615f3e9b2ed9fae542e2b3bed12
author Richard Levasseur <rlevasseur@google.com> 1688835492 -0700
committer GitHub <noreply@github.com> 1688835492 +0000
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feat: Expose Python C headers through the toolchain. (#1287)

This allows getting a build's `cc_library` of Python headers through
toolchain resolution instead of having to use the underlying toolchain's
repository `:python_headers` target directly.

Without this feature, it's not possible to reliably and correctly get
the C information about the runtime a build is going to use. Existing
solutions require carefully setting up repo names, external state,
and/or using specific build rules. In comparison, with this feature,
consumers are able to simply ask for the current headers via a helper
target or manually lookup the toolchain and pull the relevant
information; toolchain resolution handles finding the correct headers.

The basic way this works is by registering a second toolchain to carry
C/C++ related information; as such, it is named `py_cc_toolchain`. The
py cc toolchain has the same constraint settings as the regular py
toolchain; an expected invariant is that there is a 1:1 correspondence
between the two. This base functionality allows a consuming rule
implementation to use toolchain resolution to find the Python C
toolchain information.

Usually what downstream consumers need are the headers to feed into
another `cc_library` (or equivalent) target, so, rather than have every
project re-implement the same "lookup and forward cc_library info"
logic,
this is provided by the `//python/cc:current_py_cc_headers` target.
Targets that need the headers can then depend on that target as if it
was a `cc_library` target.

Work towards https://github.com/bazelbuild/rules_python/issues/824