initial support for rules_python

[junyer]

See bazelbuild/bazel#8674 (comment) for background.

For historical reasons, this logic enforces that python_version is "2", "3" or "". My current thinking is to extend that to permit "3.<minor>" and "DEFAULT" and "resolve" such versions to Labels via INTERPRETER_LABELS (and DEFAULT_PYTHON_VERSION) as provided by @pythons_hub//:interpreters.bzl.

Ping (again), @rickeylev and @rwgk. :)

[mutongx]

Thanks @junyer! I was previously unsure about where to ask for help so I ended up with that workaround in my company internal repo. Very happy to see that pybind11_bazel is initiating support for rules_python, and please let me know if you need any testers. I will be here to help.

[junyer]

Glad to hear that you are keen, @mutongx. #65 isn't going to fly, unfortunately, but I do want to solve this problem in the not too distant future, so... back to the drawing board. :)

[rickeylev]

I just wanted to drop a couple sketches of how I see this likely working. This is based on how Google makes pybind work internally, where the C++ integration is better with the Python rules.

Fundamentally, what we want to to is define a cc_library that depends on targets that provide the headers, copts, and linkopts we need. Where do we get that information? From "the toolchain", specifically, the @rules_python//python/cc:toolchain_type toolchain.

The end result would look something like this...

def pybind11_library(name, ...):
  py_library(name=name, deps=[name + "_cc"], ...)
  cc_library(
    name = name + "_cc",
    deps = [
      "@rules_python//python/cc:current_py_cc_headers",
      "@rules_python//python/cc:current_py_dsos",
      "@rules_python//python/cc:current_py_linkopts",
      "@rules_python//python/cc:current_py_copts",
    ]
)

I broke out separate current_py_* targets just for illustrative purposes. I'm not entirely sure the granularity that is needed. In any case, think of those targets "magic" cc_library targets that rules_python defines that know how to get the right values. e.g., they conceptually look like this:

# rules_python/python/cc/BUILD
cc_library(name = "current_py_cc_headers", srcs=["Python.h"])
cc_library(name = "current_py_dsos", srcs="libpython310.so"])
cc_library(name = "current_py_linkopts", linkopts=["-lm", ...], ...)

(except they use toolchain stuff to fill the values in).

[junyer]

SGTM. Thanks! :D

[junyer]

Closing this issue in favour of issue #71 (and PR #72).