details about module search path on failure

cmake/MakePythonWheel.cmake

@@ -9,7 +9,19 @@ function( MakeWheel python_module)
     cmake_parse_arguments(MAKEWHEEL "PRINT_HELP" "MODULE;VERSION;SUMMARY;DESCRIPTION;HOMEPAGE;AUTHOR;EMAIL;LICENCE" "REQUIRES" ${ARGN} )
     set(version ${MAKEWHEEL_VERSION})
 
-    execute_process(COMMAND ${Python3_EXECUTABLE} -c "import setuptools" ERROR_QUIET RESULT_VARIABLE has_setuptools)
+    execute_process(
+        COMMAND ${Python3_EXECUTABLE} -c "
+import sys
+try:
+    import setuptools
+    sys.exit(0)
+except ImportError as e:
+    print(f'{e}. Search paths:', file=sys.stderr)
+    for p in sys.path: print(f'  {p}', file=sys.stderr)
+    sys.exit(1)
+"
+    RESULT_VARIABLE has_setuptools)
+
     if(has_setuptools EQUAL "1")
         message(FATAL_ERROR "Python module `setuptools` required for correct wheel filename generation.")
     endif()