Enable C++11 by using CMake target_compile_features

CMake/VTKConfig.cmake.in

@@ -12,12 +12,6 @@ if (CMAKE_VERSION VERSION_LESS "3.3")
     message(FATAL_ERROR "VTK now requires CMake 3.3 or newer")
   endif()
 
-set(VTK_USE_CXX11_FEATURES @VTK_USE_CXX11_FEATURES@)
-if (VTK_USE_CXX11_FEATURES)
-  set(CMAKE_CXX_STANDARD 11)
-  set(CMAKE_CXX_STANDARD_REQUIRED 11)
-endif()
-
 # The C and C++ flags added by VTK to the cmake-configured flags.
 SET(VTK_REQUIRED_C_FLAGS "@VTK_REQUIRED_C_FLAGS@")
 SET(VTK_REQUIRED_CXX_FLAGS "@VTK_REQUIRED_CXX_FLAGS@")

CMake/vtkModuleMacros.cmake

@@ -536,6 +536,10 @@ endfunction()
 
 function(vtk_add_library name)
   add_library(${name} ${ARGN} ${headers})
+  # We use compile features to specify that VTK requires C++11
+  # But at the same time don't have to be concerned about
+  # polluting non-VTK targets with that requirement
+  target_compile_features(${name} PUBLIC cxx_nullptr)
   if(NOT ARGV1 STREQUAL OBJECT)
     vtk_target(${name})
   endif()

CMakeLists.txt

@@ -13,13 +13,12 @@ endif()
 
 project(VTK)
 
-option(VTK_USE_CXX11_FEATURES "Build VTK using C++11 features (if available)"
-       OFF)
-if (VTK_USE_CXX11_FEATURES)
-  set(CMAKE_CXX_STANDARD 11)
-  set(CMAKE_CXX_STANDARD_REQUIRED True)
-  set(CMAKE_CXX_EXTENSIONS False)
-endif()
+# Make sure we have C++11 enabled.
+# Needed to make sure libraries and executables not built
+# through the module system use C++11
+set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED True)
+set(CMAKE_CXX_EXTENSIONS False)
 
 # Objective-C++ compile flags.
 # CMake has no equivalent of CMAKE_CXX_FLAGS for Objective-C++ (bug #4756)