Updates MPI setup in Axom export to optionally depend on Fortran

RELEASE-NOTES.md

@@ -24,6 +24,8 @@ The Axom project release numbers follow [Semantic Versioning](http://semver.org/
 - Primal: Axom's polygon clipping was modified to handle some corner cases.
 
 ### Fixed
+- MPI setup in exported Axom config only requires Fortran when Axom's MPI was set up with Fortran.
+  This is in support of configs that require Fortran and MPI, but not an MPI wrapper for Fortran.
 
 ### Removed
 

src/cmake/AxomConfig.cmake

@@ -28,6 +28,24 @@ if(AXOM_ENABLE_MPI AND ENABLE_FORTRAN)
   endif()
 endif()
 
+# Allow user to selectively enable which languages have MPI targets
+# based on enabled languages and whether they've supplied MPI_<lang>_COMPILER
+if(AXOM_ENABLE_MPI)
+  set(_axom_required_mpi_components)
+  get_property(_axom_enabled_languages GLOBAL PROPERTY ENABLED_LANGUAGES)
+
+  if("C" IN_LIST _axom_enabled_languages AND MPI_C_COMPILER)
+    list(APPEND _axom_required_mpi_components C)
+  endif()
+  if("CXX" IN_LIST _axom_enabled_languages AND MPI_CXX_COMPILER)
+    list(APPEND _axom_required_mpi_components CXX)
+  endif()
+  if("Fortran" IN_LIST _axom_enabled_languages AND MPI_Fortran_COMPILER)
+    list(APPEND _axom_required_mpi_components Fortran)
+  endif()
+  set(AXOM_REQUIRED_MPI_COMPONENTS "${_axom_required_mpi_components}")
+endif()
+
 
 ## Add a configuration define for each enabled axom component
 foreach(comp ${AXOM_COMPONENTS_ENABLED})

src/cmake/axom-config.cmake.in

@@ -157,7 +157,16 @@ if(NOT AXOM_FOUND)
 
     # Load mpi targets because we require the optional Conduit mpi targets
     if(AXOM_USE_MPI)
-      find_package(MPI REQUIRED)
+      set(_axom_required_mpi_components "@AXOM_REQUIRED_MPI_COMPONENTS@")
+      if(NOT CMAKE_Fortran_COMPILER_LOADED)
+        list(REMOVE_ITEM _axom_required_mpi_components Fortran)
+      endif()
+
+      if(_axom_required_mpi_components)
+        find_package(MPI REQUIRED COMPONENTS ${_axom_required_mpi_components})
+      else()
+        find_package(MPI REQUIRED)
+      endif()
     endif()
 
     find_dependency(Conduit REQUIRED