build issues with latest version 4.0.0 and openmc

[jon-proximafusion]

Hi

I'm just trying to get openmc building with NCRYSTAL and noticing this error.

Wondering if you might be able to help over here on this PR shimwell/openmc#67 (comment)

snippet from CI logs

  -- OPENMC_USE_MPI OFF
  -- OPENMC_USE_MCPL on
  -- OPENMC_USE_NCRYSTAL ON
  -- OPENMC_USE_UWUW OFF
  Traceback (most recent call last):
    File "/opt/hostedtoolcache/Python/3.11.11/x64/bin/ncrystal-config", line 5, in <module>
      from _ncrystal_core.info import _ncrystal_config_cli_wrapper
  ModuleNotFoundError: No module named '_ncrystal_core'
  CMake Error at CMakeLists.txt:135 (find_package):
    By not providing "FindNCrystal.cmake" in CMAKE_MODULE_PATH this project has
    asked CMake to find a package configuration file provided by "NCrystal",
    but CMake did not find one.

    Could not find a package configuration file provided by "NCrystal"
    (requested version 3.8.0) with any of the following names:

      NCrystalConfig.cmake
      ncrystal-config.cmake

    Add the installation prefix of "NCrystal" to CMAKE_PREFIX_PATH or set
    "NCrystal_DIR" to a directory containing one of the above files.  If
    "NCrystal" provides a separate development package or SDK, be sure it has
    been installed.


  -- Configuring incomplete, errors occurred!

  *** CMake configuration failed
  error: subprocess-exited-with-error

[tkittel]

Ok, I will comment on the PR.

[ahnaf-tahmid-chowdhury]

It seems that in the CMake configuration, NCrystal defines things as NCrystal_, but in the actual NCrystal CMakeLists.txt, these are set as NCRYSTAL_.

[ahnaf-tahmid-chowdhury]

I also suggest creating a method to retrieve the library path from the python side as well thus we may need to depend on subprocess. I think this might be helpful:
https://github.com/shimwell/openmc/blob/7b9eb0b74d06a7f6593763f9e94db7073c716b3d/openmc/__init__.py#L55