On my Ubuntu setup, compilation failes when using med.h, since

libmedc is built with openMPI, while freeCAD selects hdf5-serial.

libmed declares functions prototypes which has MPI parameters if
built for openMPI, causing compilation errors. Doing some online
searches reveals that some users manually changes the include-paths
to hdf5-openmpi if this error happens.

This patch tries to autodetect this situation.

CMakeLists.txt

@@ -703,12 +703,21 @@ endif()
         list(REMOVE_ITEM VTK_LIBRARIES "optimized" "debug")
 
         if(NOT FREECAD_USE_EXTERNAL_SMESH)
+            find_package(MEDFile REQUIRED)
             # See https://www.hdfgroup.org/HDF5/release/cmakebuild.html
             if (WIN32)
                 find_package(HDF5 COMPONENTS NO_MODULE REQUIRED static)
             else()
                 find_package(PkgConfig)
-                pkg_search_module(HDF5 hdf5-serial)
+		FILE(READ ${meddotH} TMPTXT)
+		STRING(FIND "${TMPTXT}" "#define MED_HAVE_MPI" matchres)
+		if(${matchres} EQUAL -1)
+			message(STATUS "We guess that libmed was built using hdf5-serial version")
+			pkg_search_module(HDF5 hdf5-serial)
+		else()
+			message(STATUS "We guess that libmed was built using hdf5-openmpi version")
+	                pkg_search_module(HDF5 hdf5-openmpi)
+		endif()
                 if(NOT HDF5_FOUND)
                     find_package(HDF5 REQUIRED)
                 else()
@@ -735,7 +744,6 @@ endif()
                     message( WARNING "mpi.h was not found. Check for error above.")
                 endif()
             endif()
-            find_package(MEDFile REQUIRED)
             set(SMESH_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/src/3rdParty/salomesmesh/inc)
 
         else(NOT FREECAD_USE_EXTERNAL_SMESH)

cMake/FindMEDFile.cmake

@@ -41,6 +41,10 @@ IF(MEDFILE_ROOT_DIR)
 ENDIF(MEDFILE_ROOT_DIR)
 
 FIND_PATH(MEDFILE_INCLUDE_DIRS med.h PATH_SUFFIXES med)
+find_file(meddotH med.h PATHS ${MEDFILE_INCLUDE_DIRS} NO_DEFAULT_PATH)
+if(NOT meddotH)
+  message( FATAL_ERROR "med.h not found in an error message above.")
+endif()
 #FIND_PROGRAM(MDUMP mdump)
 FIND_LIBRARY(MEDFILE_C_LIBRARIES NAMES medC)
 FIND_LIBRARY(MEDFILE_F_LIBRARIES NAMES med)