Building issue with mpi not found by the CMakeLists.txt

[lhy11009]

Description

I am experiencing an issue with MPI detection after the recent changes to CMakeLists.txt. The build works fine in build_0, but build_1 fails to find mpi.h when I try to configure with CMake.

Steps to Reproduce

1. Clone the repository.
2. Build in the build_0 directory using an older version of CMakeLists.txt (this works).
3. Build in the build_1 directory using the newer version of CMakeLists.txt.

Observed Behavior

• The line CMAKE_CXX_COMPILER in CMakeCache.txt for build_1 is set to /usr/bin/c++ instead of the expected /usr/bin/mpicxx.
• MPI_C_COMPILER and MPI_CXX_COMPILER remain UNINITIALIZED.

Differences in CMakeLists.txt

Here are the key differences between the two versions of CMakeLists.txt:

• [List any specific lines or sections that changed and may impact MPI detection]

Environment

• CMake version: 3.18.4
• OS: Ubuntu 21.10
• MPI version: 4.1.0

Additional Information

• I have verified that both mpicc and mpicxx are available in /usr/bin/.
• I have tried various configurations without success.

Any insights or guidance would be appreciated!

[lhy11009]

Additional information: on the other system with these environments, it works:

CMake version: 3.20.5
OS: Ubuntu 22.04.4 LTS
MPI version: 4.1.5

[tjhei]

Recent CMakeLists.txt changes were done by @bangerth, so he might have an idea.

[lhy11009]

Thanks @tjhei. I tested building inside the dealii 9.5 docker today and it produces no error. So I am looking at the differences between these environments. I have an idea the environment setup might be the triggering instead of the compiler versions. Anyway, I'll let you know how that goes.