PyCMethod_New not defined in python3.lib

[barry-scott]

BPO	43155
Nosy	@barry-scott, @vstinner, @encukou, @ZackerySpytz
PRs	bpo-43155: Add PyCMethod_New to PC/python3dll.c #24500 [3.9] bpo-43155: Add PyCMethod_New to PC/python3dll.c (GH-24500) #24554

^{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 = None
closed_at = <Date 2021-02-17.10:57:38.946>
created_at = <Date 2021-02-07.18:05:58.745>
labels = ['3.9', '3.10']
title = 'PyCMethod_New not defined in python3.lib'
updated_at = <Date 2021-02-17.10:57:38.945>
user = 'https://github.com/barry-scott'

bugs.python.org fields:

activity = <Date 2021-02-17.10:57:38.945>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2021-02-17.10:57:38.946>
closer = 'vstinner'
components = []
creation = <Date 2021-02-07.18:05:58.745>
creator = 'barry-scott'
dependencies = []
files = []
hgrepos = []
issue_num = 43155
keywords = ['patch']
message_count = 9.0
messages = ['386595', '386800', '386870', '386923', '387074', '387075', '387076', '387141', '387143']
nosy_count = 4.0
nosy_names = ['barry-scott', 'vstinner', 'petr.viktorin', 'ZackerySpytz']
pr_nums = ['24500', '24554']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue43155'
versions = ['Python 3.9', 'Python 3.10']

[barry-scott]

When using the limited API PyCMethod_New is not defined in python3.lib.
This leads to a link error.

This error is in 3.9 and 3.10a5

Discovered when I improved the PyCXX test suite.

Example output:

Link obj\simple.pyd
cl /nologo /W4 /LD /Zi /MT /EHsc /Zi /MT /EHsc -I. -ISrc -IC:\Python310.win64\include -D_CRT_NONSTDC_NO_DEPRECATE -U_DEBUG -DNDEBUG -DPy_LIMITED_API=0x3090000 /Feobj\simple.pyd /Fdobj\simple.pdf obj\simple.obj obj\cxxsupport.obj obj\cxx_extensions.obj obj\cxx_exceptions.obj obj\cxxextensions.obj obj\IndirectPythonInterface.obj C:\Python310.win64\libs\python3.lib
Creating library obj\simple.lib and object obj\simple.exp
simple.obj : error LNK2019: unresolved external symbol __imp_PyCMethod_New referenced in function "protected: virtual class Py::Object __cdecl Py::PythonExtension<class old_style_class>::getattr_methods(char const *)" (?getattr_methods@?$PythonExtension@Vold_style_class@@@py@@Meaa?AVObject@2@PEBD@Z)
obj\simple.pyd : fatal error LNK1120: 1 unresolved externals
NMAKE : fatal error U1077: '"c:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Tools\MSVC\14.16.27023\bin\HostX64\x64\cl.EXE"' : return code '0x2'
Stop.

[barry-scott]

Is there a test suite that checks that the limited API functions can all be linked against?

[encukou]

Is there a test suite that checks that the limited API functions can all be linked against?

Not yet. There's not even consensus about exactly what functions are part of the limited API.
I plan to address both issues in PEP-652 (currently in Draft status).

[barry-scott]

Thanks Petr, I'll watch for the PEP.

FYI: I work on the assumption that if I use Py_LIMITED_API and the header
files provide an API guarded by an #if then its "offical".

[vstinner]

Is there a test suite that checks that the limited API functions can all be linked against?

Pablo Galindo wrote a new Tools/scripts/stable_abi.py for Unix, but this tool doesn't check PC/python3dll.c yet. The tool uses Doc/data/stable_abi.dat which *does* include PyCMethod_New symbol.

I created bpo-43235 "Tools/scripts/stable_abi.py should also check PC/python3dll.c (Windows stable ABI)".

[vstinner]

New changeset 8a8b5df by Zackery Spytz in branch 'master':
bpo-43155: Add PyCMethod_New to PC/python3dll.c (GH-24500)
8a8b5df

[vstinner]

The symbol was exported on Unix since Python 3.9.0, but not on Windows. Is it ok to export it starting with Python 3.9.2? (backport the fix). IMO yes, it's ok.

[vstinner]

New changeset ebe20d9 by Zackery Spytz in branch '3.9':
bpo-43155: Add PyCMethod_New to PC/python3.def (GH-24500) (GH-24554)
ebe20d9

[vstinner]

Thanks Barry for the bug report and thanks Zackery for the fix! It's now fixed.

See bpo-43235 and bpo-43239 follow-up issues.