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

* cmake: split extension

Into suffix and debug postfix. Pybind11 is currently treating both as
suffix, which is problematic when something else defines the
DEBUG_POSTFIX because they will be concatenated.

pybind11_extension sets SUFFIX to _d.something and if DEBUG_POSTFIX is
set to _d.

    _d + _d.something = _d_d.something

The issue has been reported at:

https://github.com/pybind/pybind11/issues/4699

* style: pre-commit fixes

* fix(cmake): support postfix for old FindPythonInterp mode too

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

---------

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

tools/FindPythonLibsNew.cmake

@@ -188,13 +188,20 @@ _pybind11_get_if_undef(_PYTHON_VALUES 0 _PYTHON_VERSION_LIST)
 _pybind11_get_if_undef(_PYTHON_VALUES 1 PYTHON_PREFIX)
 _pybind11_get_if_undef(_PYTHON_VALUES 2 PYTHON_INCLUDE_DIR)
 _pybind11_get_if_undef(_PYTHON_VALUES 3 PYTHON_SITE_PACKAGES)
-_pybind11_get_if_undef(_PYTHON_VALUES 4 PYTHON_MODULE_EXTENSION)
 _pybind11_get_if_undef(_PYTHON_VALUES 5 PYTHON_IS_DEBUG)
 _pybind11_get_if_undef(_PYTHON_VALUES 6 PYTHON_SIZEOF_VOID_P)
 _pybind11_get_if_undef(_PYTHON_VALUES 7 PYTHON_LIBRARY_SUFFIX)
 _pybind11_get_if_undef(_PYTHON_VALUES 8 PYTHON_LIBDIR)
 _pybind11_get_if_undef(_PYTHON_VALUES 9 PYTHON_MULTIARCH)
 
+list(GET _PYTHON_VALUES 4 _PYTHON_MODULE_EXT_SUFFIX)
+if(PYBIND11_PYTHONLIBS_OVERWRITE OR NOT DEFINED PYTHON_MODULE_DEBUG_POSTFIX)
+  get_filename_component(PYTHON_MODULE_DEBUG_POSTFIX "${_PYTHON_MODULE_EXT_SUFFIX}" NAME_WE)
+endif()
+if(PYBIND11_PYTHONLIBS_OVERWRITE OR NOT DEFINED PYTHON_MODULE_EXTENSION)
+  get_filename_component(PYTHON_MODULE_EXTENSION "${_PYTHON_MODULE_EXT_SUFFIX}" EXT)
+endif()
+
 # Make sure the Python has the same pointer-size as the chosen compiler
 # Skip if CMAKE_SIZEOF_VOID_P is not defined
 # This should be skipped for (non-Apple) cross-compiles (like EMSCRIPTEN)

tools/pybind11NewTools.cmake

@@ -95,26 +95,37 @@ endif()
 
 # Get the suffix - SO is deprecated, should use EXT_SUFFIX, but this is
 # required for PyPy3 (as of 7.3.1)
-if(NOT DEFINED PYTHON_MODULE_EXTENSION)
+if(NOT DEFINED PYTHON_MODULE_EXTENSION OR NOT DEFINED PYTHON_MODULE_DEBUG_POSTFIX)
   execute_process(
     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'))"
-    OUTPUT_VARIABLE _PYTHON_MODULE_EXTENSION
-    ERROR_VARIABLE _PYTHON_MODULE_EXTENSION_ERR
+    OUTPUT_VARIABLE _PYTHON_MODULE_EXT_SUFFIX
+    ERROR_VARIABLE _PYTHON_MODULE_EXT_SUFFIX_ERR
     OUTPUT_STRIP_TRAILING_WHITESPACE)
 
-  if(_PYTHON_MODULE_EXTENSION STREQUAL "")
+  if(_PYTHON_MODULE_EXT_SUFFIX STREQUAL "")
     message(
       FATAL_ERROR "pybind11 could not query the module file extension, likely the 'distutils'"
-                  "package is not installed. Full error message:\n${_PYTHON_MODULE_EXTENSION_ERR}")
+                  "package is not installed. Full error message:\n${_PYTHON_MODULE_EXT_SUFFIX_ERR}"
+    )
   endif()
 
   # This needs to be available for the pybind11_extension function
+  if(NOT DEFINED PYTHON_MODULE_DEBUG_POSTFIX)
+    get_filename_component(_PYTHON_MODULE_DEBUG_POSTFIX "${_PYTHON_MODULE_EXT_SUFFIX}" NAME_WE)
+    set(PYTHON_MODULE_DEBUG_POSTFIX
+        "${_PYTHON_MODULE_DEBUG_POSTFIX}"
+        CACHE INTERNAL "")
+  endif()
+
+  if(NOT DEFINED PYTHON_MODULE_EXTENSION)
+    get_filename_component(_PYTHON_MODULE_EXTENSION "${_PYTHON_MODULE_EXT_SUFFIX}" EXT)
     set(PYTHON_MODULE_EXTENSION
         "${_PYTHON_MODULE_EXTENSION}"
         CACHE INTERNAL "")
   endif()
+endif()
 
 # Python debug libraries expose slightly different objects before 3.8
 # https://docs.python.org/3.6/c-api/intro.html#debugging-builds
@@ -253,6 +264,9 @@ endfunction()
 
 function(pybind11_extension name)
   # The extension is precomputed
-  set_target_properties(${name} PROPERTIES PREFIX "" SUFFIX "${PYTHON_MODULE_EXTENSION}")
-
+  set_target_properties(
+    ${name}
+    PROPERTIES PREFIX ""
+               DEBUG_POSTFIX "${PYTHON_MODULE_DEBUG_POSTFIX}"
+               SUFFIX "${PYTHON_MODULE_EXTENSION}")
 endfunction()

tools/pybind11Tools.cmake

@@ -65,6 +65,7 @@ _pybind11_promote_to_cache(PYTHON_INCLUDE_DIRS)
 _pybind11_promote_to_cache(PYTHON_LIBRARIES)
 _pybind11_promote_to_cache(PYTHON_MODULE_PREFIX)
 _pybind11_promote_to_cache(PYTHON_MODULE_EXTENSION)
+_pybind11_promote_to_cache(PYTHON_MODULE_DEBUG_POSTFIX)
 _pybind11_promote_to_cache(PYTHON_VERSION_MAJOR)
 _pybind11_promote_to_cache(PYTHON_VERSION_MINOR)
 _pybind11_promote_to_cache(PYTHON_VERSION)
@@ -148,7 +149,10 @@ endif()
 
 function(pybind11_extension name)
   # The prefix and extension are provided by FindPythonLibsNew.cmake
-  set_target_properties(${name} PROPERTIES PREFIX "${PYTHON_MODULE_PREFIX}"
+  set_target_properties(
+    ${name}
+    PROPERTIES PREFIX "${PYTHON_MODULE_PREFIX}"
+               DEBUG_POSTFIX "${PYTHON_MODULE_DEBUG_POSTFIX}"
                SUFFIX "${PYTHON_MODULE_EXTENSION}")
 endfunction()