[BUG]: Not detecting the SUFFIX and DEBUG_POSTFIX for cmake correctly

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What version (or hash if on master) of pybind11 are you using?

2.10.4

Problem description

pybind11 uses this to figure out the SUFFIX (extension) for cmake.

Lines 100 to 102 in 0e43fcc

    
           COMMAND 
        
             "${${_Python}_EXECUTABLE}" "-c" 
        
             "import sys, importlib; s = importlib.import_module('distutils.sysconfig' if sys.version_info < (3, 10) else 'sysconfig'); print(s.get_config_var('EXT_SUFFIX') or s.get_config_var('SO'))"

This is problematic because this can also contain the debug postfix ("_d" on Windows in debug mode) because of this:

https://github.com/python/cpython/blob/a8d69fe92c65d636fc454cfb1825c357eb2e6325/Python/dynload_win.c#L18

What should be done instead is splitting the result into SUFFIX and DEBUG_POSTFIX.

At the moment, we are trying to use pybind11 with a Python that sets the DEBUG_POSTFIX _d when it needs. This is great for all python libraries.

However, cmake combines DEBUG_POSTFIX and SUFFIX, so we end up with double _d, so we _d_d which then crashes since Windows in debug mode is looking for a single _d.

At the moment, as a consumer of pybind11, we have no easy solution to fix this, only to avoid using pybind11_add_module, but then we would need to reinvent quite a bit of boilerplate, which does not look sustainable.

So, the issue is that our Python package sets the DEBUG_POSTFIX and pybind11 sets the SUFFIX. These two get combined in debug mode. They do not overwrite each other.

pybind11_extension sets SUFFIX to _d.something and we set DEBUG_POSTFIX to _d.

_d + _d.something = _d_d.something

Reproducible example code

Call pybind11_add_module() from a consumer cmake extension module in the CMakeLists.txt file on Windows in debug mode.

Is this a regression? Put the last known working version here if it is.

Not a regression

pybind11 should instead use this code to derive the extension:

import sys
import importlib

s = importlib.import_module('distutils.sysconfig' if sys.version_info < (3, 10) else 'sysconfig')

print((s.get_config_var('EXT_SUFFIX') or s.get_config_var('SO')).replace('.', ';.', 1))

This will for example output _d;.cp311-win_amd64.pyd, which is a suitable CMake list with 2 elements: the value for DEBUG_POSTFIX and SUFFIX:

function(pybind11_extension name)
  list(GET PYTHON_MODULE_EXTENSION 0 debug_postfix)
  list(GET PYTHON_MODULE_EXTENSION 1 suffix)
  set_target_properties(${name} PROPERTIES PREFIX "" SUFFIX "${suffix}" DEBUG_POSTFIX "${debug_postfix}")
endfunction()

cmake: split extension

fix(cmake): support DEBUG_POSTFIX correctly (#4761)

Are you sure that the fix also works for multi-config generators like Visual Studio? As far as I can tell from the code change, both PYTHON_MODULE_DEBUG_POSTFIX and PYTHON_MODULE_EXTENSION are being generated from the same single python.exe.

But in a multi-config generator, one would need to consider a single build with both python.exe and python_d.exe on Windows. And I don't see this reflected in the logic?

FindPython does not find an interpreter with the python_d basename.

git merge smart_holder (#30066)

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[BUG]: Not detecting the SUFFIX and DEBUG_POSTFIX for cmake correctly #4699

Required prerequisites

What version (or hash if on master) of pybind11 are you using?

Problem description

Reproducible example code

Is this a regression? Put the last known working version here if it is.

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	COMMAND
	"${${_Python}_EXECUTABLE}" "-c"
	"import sys, importlib; s = importlib.import_module('distutils.sysconfig' if sys.version_info < (3, 10) else 'sysconfig'); print(s.get_config_var('EXT_SUFFIX') or s.get_config_var('SO'))"

[BUG]: Not detecting the SUFFIX and DEBUG_POSTFIX for cmake correctly #4699

Description

Required prerequisites

What version (or hash if on master) of pybind11 are you using?

Problem description

Reproducible example code

Is this a regression? Put the last known working version here if it is.

Activity

friendlyanon commented on Jun 12, 2023

macdew commented on Oct 2, 2023

friendlyanon commented on Oct 2, 2023

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