From db4e69bf38ed57695145445565eb9dc1a9b6ec8c Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 27 Jan 2022 23:28:54 -0500
Subject: [PATCH] further simplification by making STUBS an interface and alias
 to MPI::MPI_CXX

---
 cmake/CMakeLists.txt                      | 14 +++++---------
 cmake/Modules/Packages/GPU.cmake          |  7 +------
 examples/plugins/LAMMPSInterfaceCXX.cmake |  4 +---
 unittest/force-styles/CMakeLists.txt      |  4 +---
 4 files changed, 8 insertions(+), 21 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 62507dd29a..49d3bfb845 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -280,10 +280,8 @@ if(BUILD_MPI)
   # We use a non-standard procedure to cross-compile with MPI on Windows
   if((CMAKE_SYSTEM_NAME STREQUAL "Windows") AND CMAKE_CROSSCOMPILING)
     include(MPI4WIN)
-    target_link_libraries(lammps PUBLIC MPI::MPI_CXX)
   else()
     find_package(MPI REQUIRED)
-    target_link_libraries(lammps PUBLIC MPI::MPI_CXX)
     option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
     if(LAMMPS_LONGLONG_TO_LONG)
       target_compile_definitions(lammps PRIVATE -DLAMMPS_LONGLONG_TO_LONG)
@@ -291,8 +289,11 @@ if(BUILD_MPI)
   endif()
 else()
   target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
-  target_include_directories(lammps PUBLIC ${LAMMPS_SOURCE_DIR}/STUBS)
+  add_library(mpi_stubs INTERFACE)
+  target_include_directories(mpi_stubs INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
+  add_library(MPI::MPI_CXX ALIAS mpi_stubs)
 endif()
+target_link_libraries(lammps PUBLIC MPI::MPI_CXX)
 
 set(LAMMPS_SIZES "smallbig" CACHE STRING "LAMMPS integer sizes (smallsmall: all 32-bit, smallbig: 64-bit #atoms #timesteps, bigbig: also 64-bit imageint, 64-bit atom ids)")
 set(LAMMPS_SIZES_VALUES smallbig bigbig smallsmall)
@@ -573,12 +574,7 @@ if(PKG_ATC)
   if(LAMMPS_SIZES STREQUAL "BIGBIG")
     message(FATAL_ERROR "The ATC Package is not compatible with -DLAMMPS_BIGBIG")
   endif()
-  target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES})
-  if(BUILD_MPI)
-    target_link_libraries(atc PRIVATE MPI::MPI_CXX)
-  else()
-    target_include_directories(atc PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS)
-  endif()
+  target_link_libraries(atc PRIVATE ${LAPACK_LIBRARIES} MPI::MPI_CXX)
   target_include_directories(atc PRIVATE ${LAMMPS_SOURCE_DIR})
   target_compile_definitions(atc PRIVATE -DLAMMPS_${LAMMPS_SIZES})
 endif()
diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index 863265250d..ee839e20e1 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -423,13 +423,8 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 
-if(NOT BUILD_MPI)
-  # add include include path to MPI STUBS for non-MPI build
-  target_include_directories(gpu PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS)
-else()
-  target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
-endif()
 target_compile_definitions(gpu PRIVATE -DLAMMPS_${LAMMPS_SIZES})
 set_target_properties(gpu PROPERTIES OUTPUT_NAME lammps_gpu${LAMMPS_MACHINE})
 target_sources(lammps PRIVATE ${GPU_SOURCES})
 target_include_directories(lammps PRIVATE ${GPU_SOURCES_DIR})
+target_link_libraries(gpu PRIVATE MPI::MPI_CXX)
diff --git a/examples/plugins/LAMMPSInterfaceCXX.cmake b/examples/plugins/LAMMPSInterfaceCXX.cmake
index d52cf8f4e5..e910ec2923 100644
--- a/examples/plugins/LAMMPSInterfaceCXX.cmake
+++ b/examples/plugins/LAMMPSInterfaceCXX.cmake
@@ -42,10 +42,8 @@ if(BUILD_MPI)
   if(LAMMPS_LONGLONG_TO_LONG)
     target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
   endif()
-  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
-else()
-  target_include_directories(lammps INTERFACE "${LAMMPS_SOURCE_DIR}/STUBS")
 endif()
+target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
 
 set(LAMMPS_SIZES "smallbig" CACHE STRING "LAMMPS integer sizes (smallsmall: all 32-bit, smallbig: 64-bit #atoms #timesteps, bigbig: also 64-bit imageint, 64-bit atom ids)")
 set(LAMMPS_SIZES_VALUES smallbig bigbig smallsmall)
diff --git a/unittest/force-styles/CMakeLists.txt b/unittest/force-styles/CMakeLists.txt
index fd794bd8d7..5fec488e22 100644
--- a/unittest/force-styles/CMakeLists.txt
+++ b/unittest/force-styles/CMakeLists.txt
@@ -46,9 +46,7 @@ else()
 endif()
 target_include_directories(style_tests PRIVATE ${LAMMPS_SOURCE_DIR})
 target_link_libraries(style_tests PUBLIC gmock Yaml::Yaml lammps)
-if(BUILD_MPI)
-  target_link_libraries(style_tests PUBLIC MPI::MPI_CXX)
-endif()
+
 # propagate sanitizer options to test tools
 if(ENABLE_SANITIZER AND (NOT (ENABLE_SANITIZER STREQUAL "none")))
   if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13)