Define Py_BUILD_CORE_MODULE in extensions instead of setup.py and Modules/Setup

[tiran]

BPO	43974
Nosy	@brettcannon, @tiran, @ericsnowcurrently, @pablogsal, @erlend-aasland
PRs	bpo-43974: Set Py_BUILD_CORE_MODULE for all core modules #25713 bpo-43974: Move Py_BUILD_CORE_MODULE into module code (GH-29157) #29157

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/tiran'
closed_at = <Date 2021-10-22.13:37:02.817>
created_at = <Date 2021-04-29.09:02:26.399>
labels = ['extension-modules', 'type-bug', 'build', '3.11']
title = 'Define Py_BUILD_CORE_MODULE in extensions instead of setup.py and Modules/Setup'
updated_at = <Date 2022-02-21.11:46:32.070>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2022-02-21.11:46:32.070>
actor = 'vstinner'
assignee = 'christian.heimes'
closed = True
closed_date = <Date 2021-10-22.13:37:02.817>
closer = 'christian.heimes'
components = ['Build', 'Extension Modules']
creation = <Date 2021-04-29.09:02:26.399>
creator = 'christian.heimes'
dependencies = []
files = []
hgrepos = []
issue_num = 43974
keywords = ['patch']
message_count = 8.0
messages = ['392293', '392295', '392332', '392333', '392587', '404755', '404757', '404768']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'christian.heimes', 'eric.snow', 'pablogsal', 'erlendaasland']
pr_nums = ['25713', '29157']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43974'
versions = ['Python 3.11']

[tiran]

CPython's setup.py contains lots of

 extra_compile_args = ['-DPy_BUILD_CORE_MODULE']

to mark modules as core module. Extra compiler args is the wrong option. It's also tedious and err-prone to define the macro in each and every Extension() class instance.

The compiler flag should be set automatically for all core extensions and it should use be set using the correct option define_macros.

[tiran]

Related to the change:

It looks like we can also cleanup Modules/Setup and remove -DPy_BUILD_CORE_BUILTIN and -DPy_BUILD_CORE_MODULE. Modules/makesetup adds $PY_BUILTIN_MODULE_CFLAGS in the compile step. The variable is defined as

PY_BUILTIN_MODULE_CFLAGS= $(PY_STDMODULE_CFLAGS) -DPy_BUILD_CORE_BUILTIN

[vstinner]

I would prefer to limit the usage of the internal C API in extension modules built as dynamic libraries. See bpo-41111: "[C API] Convert a few stdlib extensions to the limited C API (PEP-384)".

Also, this issue is motived by PR 25653 which requires to use the internal C API in many C extensions. But I proposed a different approach, PR 25710, which prevents that.

[vstinner]

It looks like we can also cleanup Modules/Setup and remove -DPy_BUILD_CORE_BUILTIN and -DPy_BUILD_CORE_MODULE. Modules/makesetup adds $PY_BUILTIN_MODULE_CFLAGS in the compile step.

Oh, I didn't notice.

[tiran]

I would prefer to limit the usage of the internal C API in extension modules built as dynamic libraries. See bpo-41111: "[C API] Convert a few stdlib extensions to the limited C API (PEP-384)".

Let's make this a coordinated effort in 3.11. I suggest that we slowly remove functions from Py_BUILD_CORE_MODULE. For now I'm interested to clean up and simplify setup.py.