Making pybind cmake version optional for CMake 3.8+

Author: henryiii

CMakeLists.txt

@@ -98,7 +98,11 @@ if(NOT (CMAKE_VERSION VERSION_LESS 3.0))  # CMake >= 3.0
   target_include_directories(pybind11 INTERFACE $<BUILD_INTERFACE:${PYBIND11_INCLUDE_DIR}>
                                                 $<BUILD_INTERFACE:${PYTHON_INCLUDE_DIRS}>
                                                 $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
-  target_compile_options(pybind11 INTERFACE $<BUILD_INTERFACE:${PYBIND11_CPP_STANDARD}>)
+  if(CMAKE_VERSION VERSION_LESS 3.8 OR PYBIND_CPP_STANDARD)
+    target_compile_options(pybind11 INTERFACE $<BUILD_INTERFACE:${PYBIND11_CPP_STANDARD}>)
+  else()
+    target_compile_features(pybind11 INTERFACE cxx_std_11)
+  endif()
 
   add_library(module INTERFACE)
   add_library(pybind11::module ALIAS module)

tools/pybind11Tools.cmake

@@ -18,26 +18,28 @@ find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} REQUIRED)
 include(CheckCXXCompilerFlag)
 include(CMakeParseArguments)
 
-if(NOT PYBIND11_CPP_STANDARD AND NOT CMAKE_CXX_STANDARD)
-  if(NOT MSVC)
-    check_cxx_compiler_flag("-std=c++14" HAS_CPP14_FLAG)
-
-    if (HAS_CPP14_FLAG)
-      set(PYBIND11_CPP_STANDARD -std=c++14)
-    else()
-      check_cxx_compiler_flag("-std=c++11" HAS_CPP11_FLAG)
-      if (HAS_CPP11_FLAG)
-        set(PYBIND11_CPP_STANDARD -std=c++11)
+if(NOT CMAKE_CXX_STANDARD)
+  if(NOT PYBIND11_CPP_STANDARD AND CMAKE_VERSION VERSION_LESS 3.8)
+    if(NOT MSVC)
+      check_cxx_compiler_flag("-std=c++14" HAS_CPP14_FLAG)
+   
+      if (HAS_CPP14_FLAG)
+        set(PYBIND11_CPP_STANDARD -std=c++14)
       else()
-        message(FATAL_ERROR "Unsupported compiler -- pybind11 requires C++11 support!")
+        check_cxx_compiler_flag("-std=c++11" HAS_CPP11_FLAG)
+        if (HAS_CPP11_FLAG)
+          set(PYBIND11_CPP_STANDARD -std=c++11)
+        else()
+          message(FATAL_ERROR "Unsupported compiler -- pybind11 requires C++11 support!")
+        endif()
       endif()
+    elseif(MSVC)
+      set(PYBIND11_CPP_STANDARD /std:c++14)
     endif()
-  elseif(MSVC)
-    set(PYBIND11_CPP_STANDARD /std:c++14)
+   
+    set(PYBIND11_CPP_STANDARD ${PYBIND11_CPP_STANDARD} CACHE STRING
+        "C++ standard flag, e.g. -std=c++11, -std=c++14, /std:c++14.  Defaults to C++14 mode." FORCE)
   endif()
-
-  set(PYBIND11_CPP_STANDARD ${PYBIND11_CPP_STANDARD} CACHE STRING
-      "C++ standard flag, e.g. -std=c++11, -std=c++14, /std:c++14.  Defaults to C++14 mode." FORCE)
 endif()
 
 # Checks whether the given CXX/linker flags can compile and link a cxx file.  cxxflags and
@@ -173,7 +175,11 @@ function(pybind11_add_module target_name)
   endif()
 
   # Make sure C++11/14 are enabled
-  target_compile_options(${target_name} PUBLIC ${PYBIND11_CPP_STANDARD})
+  if(PYBIND11_CPP_STANDARD OR ${CMAKE_VERSION} VERSION_LESS 3.8)
+      target_compile_options(${target_name} PUBLIC ${PYBIND11_CPP_STANDARD})
+  else()
+      target_compile_features(${target_name} PUBLIC cxx_std_11) # Will be 14 if parent project requests 14
+  endif()
 
   if(ARG_NO_EXTRAS)
     return()