From 62ff23abe7c202b2ff82bd337b2d484145cf5fe8 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Thu, 27 Jan 2022 15:59:48 -0500
Subject: [PATCH] simplify building serial executables by incorporating the
 STUBS/mpi.o object in LAMMPS library

---
 cmake/CMakeLists.txt                 | 23 +++--------------------
 cmake/Modules/Packages/GPU.cmake     |  4 ++--
 unittest/force-styles/CMakeLists.txt |  2 --
 unittest/fortran/mpi_stubs.f90       |  2 +-
 4 files changed, 6 insertions(+), 25 deletions(-)

diff --git a/cmake/CMakeLists.txt b/cmake/CMakeLists.txt
index 408528f6dd..62507dd29a 100644
--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@@ -290,25 +290,8 @@ if(BUILD_MPI)
     endif()
   endif()
 else()
-  file(GLOB MPI_SOURCES ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
-  add_library(mpi_stubs STATIC ${MPI_SOURCES})
-  set_target_properties(mpi_stubs PROPERTIES OUTPUT_NAME lammps_mpi_stubs${LAMMPS_MACHINE})
-  target_include_directories(mpi_stubs PUBLIC $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
-  if(BUILD_SHARED_LIBS)
-    target_link_libraries(lammps PRIVATE mpi_stubs)
-    if(MSVC)
-      target_link_libraries(lmp PRIVATE mpi_stubs)
-      target_include_directories(lmp INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
-      target_compile_definitions(lmp INTERFACE $<INSTALL_INTERFACE:LAMMPS_LIB_NO_MPI>)
-    endif()
-    target_include_directories(lammps INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
-    target_compile_definitions(lammps INTERFACE $<INSTALL_INTERFACE:LAMMPS_LIB_NO_MPI>)
-  else()
-    target_include_directories(lammps INTERFACE $<BUILD_INTERFACE:${LAMMPS_SOURCE_DIR}/STUBS>)
-    target_compile_definitions(lammps INTERFACE $<INSTALL_INTERFACE:LAMMPS_LIB_NO_MPI>)
-    target_link_libraries(lammps PUBLIC mpi_stubs)
-  endif()
-  add_library(MPI::MPI_CXX ALIAS mpi_stubs)
+  target_sources(lammps PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS/mpi.cpp)
+  target_include_directories(lammps PUBLIC ${LAMMPS_SOURCE_DIR}/STUBS)
 endif()
 
 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)")
@@ -594,7 +577,7 @@ if(PKG_ATC)
   if(BUILD_MPI)
     target_link_libraries(atc PRIVATE MPI::MPI_CXX)
   else()
-    target_link_libraries(atc PRIVATE mpi_stubs)
+    target_include_directories(atc PRIVATE ${LAMMPS_SOURCE_DIR}/STUBS)
   endif()
   target_include_directories(atc PRIVATE ${LAMMPS_SOURCE_DIR})
   target_compile_definitions(atc PRIVATE -DLAMMPS_${LAMMPS_SIZES})
diff --git a/cmake/Modules/Packages/GPU.cmake b/cmake/Modules/Packages/GPU.cmake
index 048c0ed473..863265250d 100644
--- a/cmake/Modules/Packages/GPU.cmake
+++ b/cmake/Modules/Packages/GPU.cmake
@@ -424,8 +424,8 @@ RegisterFixStyle(${GPU_SOURCES_DIR}/fix_gpu.h)
 get_property(GPU_SOURCES GLOBAL PROPERTY GPU_SOURCES)
 
 if(NOT BUILD_MPI)
-  # mpistubs is aliased to MPI::MPI_CXX, but older versions of cmake won't work forward the include path
-  target_link_libraries(gpu PRIVATE mpi_stubs)
+  # 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()
diff --git a/unittest/force-styles/CMakeLists.txt b/unittest/force-styles/CMakeLists.txt
index 464cd9426a..fd794bd8d7 100644
--- a/unittest/force-styles/CMakeLists.txt
+++ b/unittest/force-styles/CMakeLists.txt
@@ -48,8 +48,6 @@ 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)
-else()
-  target_link_libraries(style_tests PUBLIC mpi_stubs)
 endif()
 # propagate sanitizer options to test tools
 if(ENABLE_SANITIZER AND (NOT (ENABLE_SANITIZER STREQUAL "none")))
diff --git a/unittest/fortran/mpi_stubs.f90 b/unittest/fortran/mpi_stubs.f90
index 3f87fc38f7..8601f436d2 100644
--- a/unittest/fortran/mpi_stubs.f90
+++ b/unittest/fortran/mpi_stubs.f90
@@ -9,7 +9,7 @@ MODULE MPI
       mpi_comm_split
 
 CONTAINS
-  
+
   SUBROUTINE mpi_comm_split(comm,color,key,newcomm,ierr)
     INTEGER, INTENT(in)  :: comm,color,key
     INTEGER, INTENT(out) :: newcomm,ierr