address various issues in USER-MDI.cmake for downloaded MDI library

cmake/Modules/Packages/USER-MDI.cmake

@@ -12,37 +12,88 @@ if(DOWNLOAD_MDI)
   set(MDI_MD5 "ddfa46d6ee15b4e59cfd527ec7212184" CACHE STRING "MD5 checksum for MDI tarball")
   mark_as_advanced(MDI_URL)
   mark_as_advanced(MDI_MD5)
+  enable_language(C)
 
-  set(LAMMPS_LIB_MDI_BIN_DIR ${LAMMPS_LIB_BINARY_DIR}/mdi)
+  # only ON/OFF are allowed for "mpi" flag when building MDI library
+  # so translate boolean value of BUILD_MPI
+  # always disable MPI when cross-compiling to Windows.
+  if((BUILD_MPI) AND NOT((CMAKE_SYSTEM_NAME STREQUAL Windows) AND CMAKE_CROSSCOMPILING))
+    set(MDI_USE_MPI ON)
+  else()
+    set(MDI_USE_MPI OFF)
+  endif()
 
+  # detect if we have python development support and thus can enable python plugins
+  set(MDI_USE_PYTHON_PLUGINS OFF)
+  if(CMAKE_VERSION VERSION_LESS 3.12)
+    find_package(PythonLibs QUIET) # Deprecated since version 3.12
+    if (PYTHONLIBS_FOUND)
+      set(MDI_USE_PYTHON_PLUGINS ON)
+    endif()
+  else()
+    find_package(Python QUIET COMPONENTS Development)
+    if (Python_Development_FOUND)
+      set(MDI_USE_PYTHON_PLUGINS ON)
+    endif()
+  endif()
+
+  # download/ build MDI library
+  # always build static library with -fpic
+  # support cross-compilation and ninja-build
   include(ExternalProject)
-  message(STATUS "Building mdi.")
-  ExternalProject_Add(mdi_external
-      URL     ${MDI_URL}
-      URL_MD5 ${MDI_MD5}
-      UPDATE_COMMAND ""
-      CMAKE_ARGS ${CMAKE_REQUEST_PIC}
-                 -DCMAKE_INSTALL_PREFIX=${LAMMPS_LIB_MDI_BIN_DIR}
-                 -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
-                 -DCMAKE_INSTALL_LIBDIR=${CMAKE_INSTALL_LIBDIR}
-                 -DCMAKE_INSTALL_INCLUDEDIR=${CMAKE_INSTALL_INCLUDEDIR}
-                 -DBUILD_SHARED_LIBS=${BUILD_SHARED_LIBS}
-                 -Dlanguage=C
-      CMAKE_CACHE_ARGS -DCMAKE_C_FLAGS:STRING=${CMAKE_C_FLAGS}
-                       -DCMAKE_CXX_FLAGS:STRING=${CMAKE_CXX_FLAGS}
-                       -DTargetOpenMP_FIND_COMPONENTS:STRING=C;CXX)
+  ExternalProject_Add(mdi_build
+    URL     ${MDI_URL}
+    URL_MD5 ${MDI_MD5}
+    CMAKE_ARGS ${CMAKE_REQUEST_PIC}
+    -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
+    -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+    -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+    -DCMAKE_MAKE_PROGRAM=${CMAKE_MAKE_PROGRAM}
+    -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE}
+    -Dlanguage=C
+    -Dlibtype=STATIC
+    -Dmpi=${MDI_USE_MPI}
+    -Dpython_plugins=${MDI_USE_PYTHON_PLUGINS}
+    UPDATE_COMMAND ""
+    INSTALL_COMMAND ""
+    BUILD_BYPRODUCTS "<BINARY_DIR>/MDI_Library/libmdi.a"
+    )
 
-  # Link the lammps library against MDI
-  target_include_directories(lammps PRIVATE ${LAMMPS_LIB_MDI_BIN_DIR}/${CMAKE_INSTALL_INCLUDEDIR}/mdi)
-  target_link_directories(lammps PRIVATE ${LAMMPS_LIB_MDI_BIN_DIR}/${CMAKE_INSTALL_LIBDIR}/mdi)
-  target_link_libraries(lammps PRIVATE mdi)
-  add_dependencies(lammps mdi_external)
+  # where is the compiled library?
+  ExternalProject_get_property(mdi_build BINARY_DIR)
+  # workaround for older CMake versions
+  file(MAKE_DIRECTORY "${BINARY_DIR}/MDI_Library")
 
-  # Link the lammps executable against MDI
-  target_include_directories(lmp PRIVATE ${LAMMPS_LIB_MDI_BIN_DIR}/${CMAKE_INSTALL_INCLUDEDIR}/mdi)
-  target_link_directories(lmp PRIVATE ${LAMMPS_LIB_MDI_BIN_DIR}/${CMAKE_INSTALL_LIBDIR}/mdi)
-  target_link_libraries(lmp PRIVATE mdi)
-  add_dependencies(lmp mdi_external)
+  # create imported target for the MDI library
+  add_library(LAMMPS::MDI UNKNOWN IMPORTED)
+  add_dependencies(LAMMPS::MDI mdi_build)
+  set_target_properties(LAMMPS::MDI PROPERTIES
+    IMPORTED_LOCATION "${BINARY_DIR}/MDI_Library/libmdi.a"
+    INTERFACE_INCLUDE_DIRECTORIES "${BINARY_DIR}/MDI_Library"
+    )
+
+  # need to add support for dlopen/dlsym, except when compiling for Windows.
+  set(MDI_DL_LIBS "")
+  if(NOT ${CMAKE_SYSTEM_NAME} STREQUAL "Windows")
+    set(MDI_DL_LIBS "${CMAKE_DL_LIBS}")
+  endif()
+
+  # if compiling with python plugins we need to add python libraries as dependency.
+  if(MDI_USE_PYTHON_PLUGINS)
+    if(CMAKE_VERSION VERSION_LESS 3.12)
+      set_target_properties(LAMMPS::MDI PROPERTIES
+        IMPORTED_LINK_INTERFACE_LIBRARIES "${PYTHON_LIBRARIES};${MDI_DL_LIBS}")
+    else()
+      set_target_properties(LAMMPS::MDI PROPERTIES
+        IMPORTED_LINK_INTERFACE_LIBRARIES "Python::Python;${MDI_DL_LIBS}")
+    endif()
+  else()
+    set_target_properties(LAMMPS::MDI PROPERTIES
+      IMPORTED_LINK_INTERFACE_LIBRARIES ${MDI_DL_LIBS})
+  endif()
+
+  target_link_libraries(lammps PRIVATE LAMMPS::MDI)
+  target_link_libraries(lmp PRIVATE LAMMPS::MDI)
 
 else()