add CMake build environment demo for plugins

examples/plugins/CMakeLists.txt

@@ -0,0 +1,56 @@
+##########################################
+# CMake build system for plugin examples.
+# The is meant to be used as a template for plugins that are
+# distributed independent from the LAMMPS package.
+##########################################
+
+cmake_minimum_required(VERSION 3.10)
+
+# enforce out-of-source build
+if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_BINARY_DIR})
+  message(FATAL_ERROR "In-source builds are not allowed. You must create and use a build directory. "
+    "Please remove CMakeCache.txt and CMakeFiles first.")
+endif()
+
+project(plugins VERSION 1.0 LANGUAGES CXX)
+
+# NOTE: the next line should be commented out when used outside of the LAMMPS package
+get_filename_component(LAMMPS_SOURCE_DIR ${PROJECT_SOURCE_DIR}/../../src ABSOLUTE)
+set(LAMMPS_HEADER_DIR ${LAMMPS_SOURCE_DIR} CACHE PATH "Location of LAMMPS headers")
+if(NOT LAMMPS_HEADER_DIR)
+  message(FATAL_ERROR "Must set LAMMPS_HEADER_DIR")
+endif()
+
+# by default, install into $HOME/.local (not /usr/local),
+# so that no root access (and sudo) is needed
+if(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+  set(CMAKE_INSTALL_PREFIX "$ENV{HOME}/.local" CACHE PATH "Default install path" FORCE)
+endif()
+
+# C++11 is required
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+# bail out on windows
+if(CMAKE_SYSTEM_NAME STREQUAL Windows)
+  message(FATAL_ERROR "LAMMPS plugins are currently not supported on Windows")
+endif()
+
+set(CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR})
+include(CheckIncludeFileCXX)
+include(LAMMPSInterfaceCXX)
+
+##########################
+# building the plugins
+
+add_library(morse2plugin MODULE morse2plugin.cpp pair_morse2.cpp pair_morse2_omp.cpp)
+target_include_directories(morse2plugin PRIVATE "${LAMMPS_HEADER_DIR}/USER-OMP")
+target_link_libraries(morse2plugin PRIVATE lammps)
+
+add_library(nve2plugin MODULE nve2plugin.cpp fix_nve2.cpp)
+target_link_libraries(nve2plugin PRIVATE lammps)
+
+add_library(helloplugin MODULE helloplugin.cpp)
+target_link_libraries(helloplugin PRIVATE lammps)
+
+set_target_properties(morse2plugin nve2plugin helloplugin PROPERTIES PREFIX "")

examples/plugins/LAMMPSInterfaceCXX.cmake

@@ -0,0 +1,86 @@
+# Cmake script code to define the LAMMPS C++ interface
+# settings required for building LAMMPS plugins
+
+################################################################################
+# helper function
+function(validate_option name values)
+  string(TOLOWER ${${name}} needle_lower)
+  string(TOUPPER ${${name}} needle_upper)
+  list(FIND ${values} ${needle_lower} IDX_LOWER)
+  list(FIND ${values} ${needle_upper} IDX_UPPER)
+  if(${IDX_LOWER} LESS 0 AND ${IDX_UPPER} LESS 0)
+    list_to_bulletpoints(POSSIBLE_VALUE_LIST ${${values}})
+    message(FATAL_ERROR "\n########################################################################\n"
+      "Invalid value '${${name}}' for option ${name}\n"
+      "\n"
+      "Possible values are:\n"
+      "${POSSIBLE_VALUE_LIST}"
+      "########################################################################")
+  endif()
+endfunction(validate_option)
+
+#################################################################################
+# LAMMPS C++ interface. We only need the header related parts.
+add_library(lammps INTERFACE)
+target_include_directories(lammps INTERFACE ${LAMMPS_HEADER_DIR})
+
+################################################################################
+# MPI configuration
+if(NOT CMAKE_CROSSCOMPILING)
+  set(MPI_CXX_SKIP_MPICXX TRUE)
+  find_package(MPI QUIET)
+  option(BUILD_MPI "Build MPI version" ${MPI_FOUND})
+else()
+  option(BUILD_MPI "Build MPI version" OFF)
+endif()
+
+if(BUILD_MPI)
+  find_package(MPI REQUIRED)
+  option(LAMMPS_LONGLONG_TO_LONG "Workaround if your system or MPI version does not recognize 'long long' data types" OFF)
+  if(LAMMPS_LONGLONG_TO_LONG)
+    target_compile_definitions(lammps INTERFACE -DLAMMPS_LONGLONG_TO_LONG)
+  endif()
+  target_link_libraries(lammps INTERFACE MPI::MPI_CXX)
+else()
+  target_include_directories(lammps INTERFACE "${LAMMPS_SOURCE_DIR}/STUBS")
+endif()
+
+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)
+set_property(CACHE LAMMPS_SIZES PROPERTY STRINGS ${LAMMPS_SIZES_VALUES})
+validate_option(LAMMPS_SIZES LAMMPS_SIZES_VALUES)
+string(TOUPPER ${LAMMPS_SIZES} LAMMPS_SIZES)
+target_compile_definitions(lammps INTERFACE -DLAMMPS_${LAMMPS_SIZES})
+
+################################################################################
+# detect if we may enable OpenMP support by default
+set(BUILD_OMP_DEFAULT OFF)
+find_package(OpenMP QUIET)
+if(OpenMP_FOUND)
+  check_include_file_cxx(omp.h HAVE_OMP_H_INCLUDE)
+  if(HAVE_OMP_H_INCLUDE)
+    set(BUILD_OMP_DEFAULT ON)
+  endif()
+endif()
+
+option(BUILD_OMP "Build with OpenMP support" ${BUILD_OMP_DEFAULT})
+
+if(BUILD_OMP)
+  find_package(OpenMP REQUIRED)
+  check_include_file_cxx(omp.h HAVE_OMP_H_INCLUDE)
+  if(NOT HAVE_OMP_H_INCLUDE)
+    message(FATAL_ERROR "Cannot find the 'omp.h' header file required for full OpenMP support")
+  endif()
+
+  if (((CMAKE_CXX_COMPILER_ID STREQUAL "GNU") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 9.0)) OR
+      (CMAKE_CXX_COMPILER_ID STREQUAL "PGI") OR
+      ((CMAKE_CXX_COMPILER_ID STREQUAL "Clang") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 10.0)) OR
+      ((CMAKE_CXX_COMPILER_ID STREQUAL "Intel") AND (CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 19.0)))
+    # GCC 9.x and later plus Clang 10.x and later implement strict OpenMP 4.0 semantics for consts.
+    # Intel 18.0 was tested to support both, so we switch to OpenMP 4+ from 19.x onward to be safe.
+    target_compile_definitions(lammps INTERFACE -DLAMMPS_OMP_COMPAT=4)
+  else()
+    target_compile_definitions(lammps INTERFACE -DLAMMPS_OMP_COMPAT=3)
+  endif()
+  target_link_libraries(lammps INTERFACE OpenMP::OpenMP_CXX)
+endif()