Fix MPI support

Signed-off-by: Cristian Le <[email protected]>

CMakeLists.txt

@@ -76,7 +76,10 @@ set(Wannier90_MPI ${WANNIER90_WITH_MPI})
 find_package(BLAS REQUIRED)
 find_package(LAPACK REQUIRED)
 if (WANNIER90_MPI)
-	find_package(MPI REQUIRED)
+	find_package(MPI REQUIRED COMPONENTS Fortran)
+	if (NOT MPI_Fortran_HAVE_F08_MODULE)
+		message(SEND_ERROR "mpi_f08 module is required for building Wannier90 with MPI")
+	endif ()
 endif ()
 
 #[=============================================================================[

cmake/Wannier90Config.cmake.in

@@ -4,5 +4,21 @@
 ## Define basic variables
 set(Wannier90_MPI @WANNIER90_MPI@)
 
+## Include dependencies
+include(CMakeFindDependencyMacro)
+if (Wannier90_MPI)
+	# Note: In the future the MPI support can be converted to an (optional) package component.
+	# This would however require a breaking change in the library definition
+	find_dependency(MPI COMPONENTS Fortran)
+	if (NOT MPI_Fortran_FOUND OR NOT MPI_Fortran_HAVE_F08_MODULE)
+		message(WARNING
+				"Wannier90 was built and packaged with MPI, but the system does not have compatible MPI support.\n"
+				"This is an issue with the packager of Wannier90."
+		)
+		set(${CMAKE_FIND_PACKAGE_NAME}_FOUND FALSE)
+		return()
+	endif ()
+endif ()
+
 ## Parse find_package request
 include(${CMAKE_CURRENT_LIST_DIR}/Wannier90Targets.cmake)

src/CMakeLists.txt

@@ -44,7 +44,10 @@ target_sources(Wannier90_lib
 		${CMAKE_Fortran_MODULE_DIRECTORY}/w90_library.mod
 )
 if (WANNIER90_MPI)
-	target_link_libraries(Wannier90_lib PRIVATE MPI::MPI_Fortran)
+	target_link_libraries(Wannier90_lib PUBLIC MPI::MPI_Fortran)
+	target_compile_definitions(Wannier90_lib PRIVATE
+			MPI08 MPI
+	)
 endif ()
 
 add_subdirectory(postw90)