Parallel HDF5 requests MPI_Fortran even if unneeded if language Fortran enabled.

[cjosey]

Describe the bug
I work on a program that uses a mixture of C and Fortran. Only the C side of the code interacts with HDF5 or MPI. As a result, we typically don't enable Fortran support in our MPI and HDF5 builds.

If I build our code with parallel HDF5 2.1.0 or 2.1.1, however, the call to find_dependency(MPI QUIET REQUIRED), [here] will see that we have the Fortran language enabled, and attempt to load MPI::MPI_Fortran.

Here is a minimum working example that shows this behavior. To trigger a failure requires a build of MPI without Fortran enabled, such as OpenMPI with the --enable-mpi-fortran=no configure option.

CMakeLists.txt:

cmake_minimum_required(VERSION 3.27)

project(TestProject LANGUAGES C Fortran)

find_package(HDF5 NAMES hdf5 REQUIRED COMPONENTS C)

add_executable(test
    test.c
    test.f90
)

set_target_properties(test PROPERTIES LINKER_LANGUAGE C)

target_link_libraries(test PRIVATE hdf5-shared)

test.c:

#include "hdf5.h"

extern double return_1();

int main(void) {
    double fortran_value = return_1();
    printf("Fortran function returned: %f\n", fortran_value);

    // Create HDF5 file
    hid_t file_id = H5Fcreate("test.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT);

    H5Fclose(file_id);
}

test.f90:

function return_1() result(val) bind(C, name="return_1")
    use iso_c_binding
    implicit none
    real(c_double) :: val

    val = 1.0d0
end function return_1

On my machine, I get the output:

CMake Error at ${BUILDSYSTEM}/cmake/cmake-4.3.1/share/cmake-4.3/Modules/FindPackageHandleStandardArgs.cmake:290 (message):
  Could NOT find MPI (missing: MPI_Fortran_FOUND) (found version "3.1")
Call Stack (most recent call first):
  ${BUILDSYSTEM}/cmake/cmake-4.3.1/share/cmake-4.3/Modules/FindPackageHandleStandardArgs.cmake:654 (_FPHSA_FAILURE_MESSAGE)
  ${BUILDSYSTEM}/cmake/cmake-4.3.1/share/cmake-4.3/Modules/FindMPI.cmake:2006 (find_package_handle_standard_args)
  ${BUILDSYSTEM}/cmake/cmake-4.3.1/share/cmake-4.3/Modules/CMakeFindDependencyMacro.cmake:93 (find_package)
  ${BUILDSYSTEM}/cmake/cmake-4.3.1/share/cmake-4.3/Modules/CMakeFindDependencyMacro.cmake:125 (__find_dependency_common)
  ${HOME}/HDF5/cmake/hdf5-config.cmake:124 (find_dependency)
  CMakeLists.txt:5 (find_package)

Replacing find_dependency(MPI QUIET REQUIRED) with find_dependency(MPI QUIET REQUIRED COMPONENTS C) in hdf5-config.cmake.in appears to fix it, but I don't know enough of HDF5's architecture to know if this will cause problems.

Expected behavior
I expect a non-Fortran build of HDF5 to not need MPI_Fortran.

Platform

• HDF5 commit f010df9
• Linux, RHEL 8
• Intel 2024.2.1 (icx + ifort)
• CMake 4.3.1 + Ninja 1.13.2
• Built with cmake .. -G Ninja -DHDF5_ENABLE_PARALLEL=ON -DHDF5_BUILD_FORTRAN=OFF
• OpenMPI 5.0.10 with --enable-mpi-fortran=no

We have also tested 2.1.1 and 2.1.0 on various other systems, such as Windows with MS-MPI, which does not provide Fortran bindings, and have had similar issues.