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.

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

> 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).

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".

> 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)".

New changeset 8a8b5df93f379f561aab4f2fc5b2ad54f5009f7a by Zackery Spytz in branch 'master':
bpo-43155: Add PyCMethod_New to PC/python3dll.c (GH-24500)
https://github.com/python/cpython/commit/8a8b5df93f379f561aab4f2fc5b2ad54f5009f7a

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.

New changeset ebe20d9e7eb138c053958bc0a3058d34c6e1a679 by Zackery Spytz in branch '3.9':
bpo-43155: Add PyCMethod_New to PC/python3.def (GH-24500) (GH-24554)
https://github.com/python/cpython/commit/ebe20d9e7eb138c053958bc0a3058d34c6e1a679

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.