Merge pull request #1915 from akohlmey/cpp-11-cmake-3.10

Require C++11 and CMake 3.10

cmake/CMakeLists.txt

@@ -2,7 +2,7 @@
 # CMake build system
 # This file is part of LAMMPS
 # Created by Christoph Junghans and Richard Berger
-cmake_minimum_required(VERSION 2.8.12)
+cmake_minimum_required(VERSION 3.10)
 
 project(lammps CXX)
 set(SOVERSION 0)
@@ -55,12 +55,9 @@ if(${CMAKE_CXX_COMPILER_ID} STREQUAL "Intel")
   set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -restrict -std=c++11")
 endif()
 
-option(DISABLE_CXX11_REQUIREMENT "Disable check that requires C++11 for compiling LAMMPS" OFF)
-if(DISABLE_CXX11_REQUIREMENT)
-  add_definitions(-DLAMMPS_CXX98)
-# else()
-#  set(CMAKE_CXX_STANDARD 11)
-endif()
+# we require C++11
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 # GNU compiler features
 if (${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
@@ -355,9 +352,6 @@ endforeach(HEADER)
 set(MATH_LIBRARIES "m" CACHE STRING "math library")
 mark_as_advanced( MATH_LIBRARIES )
 include(CheckLibraryExists)
-if (CMAKE_VERSION VERSION_LESS "3.4")
-  enable_language(C) # check_library_exists isn't supported without a C compiler before v3.4
-endif()
 # RB: disabled this check because it breaks with KOKKOS CUDA enabled
 #foreach(FUNC sin cos)
 #  check_library_exists(${MATH_LIBRARIES} ${FUNC} "" FOUND_${FUNC}_${MATH_LIBRARIES})

cmake/Modules/Packages/GPU.cmake

@@ -1,7 +1,4 @@
 if(PKG_GPU)
-    if (CMAKE_VERSION VERSION_LESS "3.1")
-      message(FATAL_ERROR "For the GPU package you need at least cmake-3.1")
-    endif()
     set(GPU_SOURCES_DIR ${LAMMPS_SOURCE_DIR}/GPU)
     set(GPU_SOURCES ${GPU_SOURCES_DIR}/gpu_extra.h
                     ${GPU_SOURCES_DIR}/fix_gpu.h

cmake/Modules/Packages/LATTE.cmake

@@ -8,9 +8,6 @@ if(PKG_LATTE)
   endif()
   option(DOWNLOAD_LATTE "Download the LATTE library instead of using an already installed one" ${DOWNLOAD_LATTE_DEFAULT})
   if(DOWNLOAD_LATTE)
-    if (CMAKE_VERSION VERSION_LESS "3.7") # due to SOURCE_SUBDIR
-      message(FATAL_ERROR "For downlading LATTE you need at least cmake-3.7")
-    endif()
     if(CMAKE_GENERATOR STREQUAL "Ninja")
       message(FATAL_ERROR "Cannot build downloaded LATTE library with Ninja build tool")
     endif()

cmake/Modules/Packages/MSCG.cmake

@@ -8,9 +8,6 @@ if(PKG_MSCG)
   endif()
   option(DOWNLOAD_MSCG "Download MSCG library instead of using an already installed one)" ${DOWNLOAD_MSCG_DEFAULT})
   if(DOWNLOAD_MSCG)
-    if (CMAKE_VERSION VERSION_LESS "3.7") # due to SOURCE_SUBDIR
-      message(FATAL_ERROR "For downlading MSCG you need at least cmake-3.7")
-    endif()
     if(CMAKE_GENERATOR STREQUAL "Ninja")
       message(FATAL_ERROR "Cannot build downloaded MSCG library with Ninja build tool")
     endif()

cmake/Modules/Packages/USER-MOLFILE.cmake

@@ -1,8 +1,4 @@
 if(PKG_USER-MOLFILE)
-  if (CMAKE_VERSION VERSION_LESS "3.10") # due to INTERFACE without a library
-    message(FATAL_ERROR "For configuring USER-MOLFILE you need CMake 3.10 or later")
-  endif()
-
   set(MOLFILE_INCLUDE_DIRS "${LAMMPS_LIB_SOURCE_DIR}/molfile" CACHE STRING "Path to VMD molfile plugin headers")
   add_library(molfile INTERFACE)
   target_include_directories(molfile INTERFACE ${MOLFILE_INCLUDE_DIRS})

doc/src/Build_cmake.rst

@@ -95,10 +95,8 @@ this directory or sub-directories within it that CMake creates.
    directory to un-install all packages.  The purge removes all the \*.h
    files auto-generated by make.
 
-You must have CMake version 2.8 or later on your system to build
-LAMMPS.  A handful of LAMMPS packages (KOKKOS, LATTE, MSCG) require a
-later version.  CMake will print a message telling you if a later
-version is required.  Installation instructions for CMake are below.
+You must have CMake version 3.10 or later on your system to build
+LAMMPS.  Installation instructions for CMake are below.
 
 After the initial build, if you edit LAMMPS source files, or add your
 own new files to the source directory, you can just re-type make from

doc/src/Build_settings.rst

@@ -23,11 +23,11 @@ explain how to do this for building both with CMake and make.
 C++11 standard compliance
 ------------------------------------------
 
-The LAMMPS developers plan to transition to make the C++11 standard the
-minimum requirement for compiling LAMMPS.  Currently this only applies to
-some packages like KOKKOS while the rest aims to be compatible with the C++98
-standard.  Most currently used compilers are compatible with C++11; some need
-to set extra flags to enable C++11 compliance.  Example for GNU c++:
+A C++11 standard compatible compiler is a requirement for compiling LAMMPS.
+LAMMPS version 3 March 2020 is the last version compatible with the previous
+C++98 standard for the core code and most packages. Most currently used
+C++ compilers are compatible with C++11, but some older ones may need extra
+flags to enable C++11 compliance.  Example for GNU c++ 4.8.x:
 
 .. code-block:: make
 

src/lmptype.h

@@ -28,6 +28,12 @@
 #ifndef LMP_LMPTYPE_H
 #define LMP_LMPTYPE_H
 
+// C++11 check
+
+#if __cplusplus < 201103L
+#error LAMMPS requires a C++11 (or later) compliant compiler. Enable C++11 compatibility or upgrade the compiler.
+#endif
+
 #ifndef __STDC_LIMIT_MACROS
 #define __STDC_LIMIT_MACROS
 #endif
@@ -38,8 +44,8 @@
 
 #include <climits>
 #include <cstdlib>
-#include <stdint.h>   // <cstdint> requires C++-11
-#include <inttypes.h> // <cinttypes> requires C++-11
+#include <cstdint>
+#include <cinttypes>
 
 // grrr - IBM Power6 does not provide this def in their system header files