[CMake] Problem calling find_package(PythonLibs) consecutively on Windows with python debug

[Edison Gustavo Muenz]

Hi all,
The problem

I’m compiling a project in which I have:

   - python bindings for C++
   - VTK

When issuing a find_package(VTK) inside a FindMyLib.cmake I got this error:

CMake Error at D:/Work/Miniconda/envs/sci20/Library/share/cmake-3.4/Modules/FindPythonLibs.cmake:180
(get_filename_component):
  get_filename_component unknown component
  D:/Work/Miniconda/envs/sci20/libs/python27.lib
Call Stack (most recent call first):
  CMakeLists.txt:15 (find_package)

CMake Error at D:/Work/Miniconda/envs/sci20/Library/share/cmake-3.4/Modules/FindPythonLibs.cmake:181
(get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:15 (find_package)

I pinpointed the problem to:

find_package(PythonInterp)
find_package(PythonLibs)
find_package(PythonLibs)  # This call crashes

Minimum reproducible example

# CMakeLists.txt

cmake_minimum_required(VERSION 3.4.3)

project(my_project LANGUAGES CXX)

message("----------------------------------------------------------------------------")
message("1st Find Python
(${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE})")
message("-------")
find_package (PythonInterp REQUIRED)
find_package (PythonLibs REQUIRED)

message("----------------------------------------------------------------------------")
message("2nd Find Python
(${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE})")
message("-------")
find_package (PythonLibs REQUIRED)

Gives the output:

λ rm -rf * && cmake -G "Ninja" x:\etk\sci20
-- The CXX compiler identification is MSVC 16.0.40219.1
-- Check for working CXX compiler using: Ninja
-- Check for working CXX compiler using: Ninja -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
----------------------------------------------------------------------------1st
Find Python (X:/etk/sci20/CMakeLists.txt:6)
-------
-- Found PythonInterp: D:/Work/Miniconda/envs/sci20/python.exe (found
version "2.7.11")
-- Found PythonLibs:
optimized;D:/Work/Miniconda/envs/sci20/libs/python27.lib;debug;D:/Work/Miniconda/envs/sci20/libs/python27_d.lib
(found version "2.7.11")
----------------------------------------------------------------------------2nd
Find Python (X:/etk/sci20/CMakeLists.txt:12)
-------
CMake Error at D:/Work/Miniconda/envs/sci20/Library/share/cmake-3.4/Modules/FindPythonLibs.cmake:180
(get_filename_component):
  get_filename_component unknown component
  D:/Work/Miniconda/envs/sci20/libs/python27.lib
Call Stack (most recent call first):
  CMakeLists.txt:15 (find_package)

CMake Error at D:/Work/Miniconda/envs/sci20/Library/share/cmake-3.4/Modules/FindPythonLibs.cmake:181
(get_filename_component):
  get_filename_component called with incorrect number of arguments
Call Stack (most recent call first):
  CMakeLists.txt:15 (find_package)

-- Found PythonLibs:
optimized;optimized;optimized;D:/Work/Miniconda/envs/sci20/libs/python27.lib;optimized;debug;optimized;D:/Work/Miniconda/envs/sci20/libs/python27_d.lib;debug;D:/Work/Miniconda/envs/sci20/libs/python27_d.lib
(found version "2.7.11")
-- Configuring incomplete, errors occurred!
See also "X:/etk/sci20/build/ninja/CMakeFiles/CMakeOutput.log".

My environment:

   - Windows 7
   - CMake 3.4.3 and CMake 3.5 (both showed the problem)
   - Python 2.7 compiled in PYDEBUG
   <https://docs.python.org/devguide/setup.html#compiling-for-debugging>
   mode (python_d)

Diagnosis and workaround

The problem is that the PYTHON_LIBRARY variable at the 2nd call to
find_package(PythonLibs) is filled with:

optimized;D:/Work/Miniconda/envs/sci20/libs/python27.lib;debug;D:/Work/Miniconda/envs/sci20/libs/python27_d.lib

Which makes PythonBindings.cmake confused about what to do.
workaround

Call unset(PYTHON_LIBRARY) before any call to find_package(PythonLibs).
​
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