Improved how cmake sets up clang and cuda. This is basically to work around

partial C++11 support and funny cmake behavior of clang on OS X.

dlib/CMakeLists.txt

@@ -506,11 +506,20 @@ if (NOT TARGET dlib)
 
          if (CUDA_FOUND AND COMPILER_CAN_DO_CPP_11)
 
+            # There is some bug in cmake that causes it to mess up the
+            # -std=c++11 option if you let it propagate it to nvcc in some
+            # cases.  So instead we disable this and manually include
+            # things from CMAKE_CXX_FLAGS in the CUDA_NVCC_FLAGS list below.
+            set(CUDA_PROPAGATE_HOST_FLAGS OFF)
+            # Grab all the -D flags from CMAKE_CXX_FLAGS so we can pass them
+            # to nvcc.
+            string(REGEX MATCHALL "-D[^ ]*" FLAGS_FOR_NVCC ${CMAKE_CXX_FLAGS})
+
             set(CUDA_HOST_COMPILATION_CPP ON)
             # Note that we add __STRICT_ANSI__ to avoid freaking out nvcc with gcc specific
             # magic in the standard C++ header files (since nvcc uses gcc headers on
             # linux).
-            list(APPEND CUDA_NVCC_FLAGS "-arch=sm_30;-std=c++11;-D__STRICT_ANSI__;-D_MWAITXINTRIN_H_INCLUDED;-D_FORCE_INLINES")
+            list(APPEND CUDA_NVCC_FLAGS "-arch=sm_30;-std=c++11;-D__STRICT_ANSI__;-D_MWAITXINTRIN_H_INCLUDED;-D_FORCE_INLINES;${FLAGS_FOR_NVCC}")
 
             include(cmake_utils/test_for_cudnn/find_cudnn.txt)
 

dlib/cmake_utils/use_cpp_11.cmake

@@ -22,6 +22,19 @@ if(MSVC AND MSVC_VERSION VERSION_LESS 1900)
    message(FATAL_ERROR "C++11 is required to use dlib, but the version of Visual Studio you are using is too old and doesn't support C++11.  You need Visual Studio 2015 or newer. ")
 endif()
 
+macro(test_compiler_for_cpp11)
+   message(STATUS "Building a C++11 test project to see if your compiler supports C++11")
+   try_compile(test_for_cpp11_worked ${PROJECT_BINARY_DIR}/cpp11_test_build 
+      ${CMAKE_CURRENT_LIST_DIR}/test_for_cpp11 cpp11_test)
+   if (test_for_cpp11_worked)
+      message(STATUS "C++11 activated.")
+      set(COMPILER_CAN_DO_CPP_11 1)
+   else()
+      set(COMPILER_CAN_DO_CPP_11 0)
+      message(STATUS "********** Your compiler failed to build a C++11 project.  C++11 is required to use all parts of dlib! **********")
+   endif()
+endmacro()
+
 # Now turn on the appropriate compiler switch to enable C++11 if you have a
 # C++11 compiler.  In CMake 3.1 there is a simple flag you can set, but earlier
 # verions of CMake are not so convenient.
@@ -43,15 +56,7 @@ if (CMAKE_VERSION VERSION_LESS "3.1.2")
       endif()
    else()
       # Since we don't know what compiler this is just try to build a c++11 project and see if it compiles.
-      message(STATUS "Building a C++11 test project to see if your compiler supports C++11")
+      test_compiler_for_cpp11()
-      try_compile(test_for_cpp11_worked ${PROJECT_BINARY_DIR}/cpp11_test_build 
-         ${CMAKE_CURRENT_LIST_DIR}/test_for_cpp11 cpp11_test)
-      if (test_for_cpp11_worked)
-         message(STATUS "C++11 activated.")
-         set(COMPILER_CAN_DO_CPP_11 1)
-      else()
-         message(FATAL_ERROR "*** Your compiler failed to build a C++11 project, so dlib won't use C++11 features.***")
-      endif()
    endif()
 elseif(MSVC AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.0.24215.1 ) 
    message(STATUS "NOTE: Visual Studio didn't have good enough C++11 support until Visual Studio 2015 update 3 (v19.0.24215.1)")
@@ -79,10 +84,14 @@ else()
       if (NOT CMAKE_CXX_STANDARD OR CMAKE_CXX_STANDARD LESS 11)
          set(CMAKE_CXX_STANDARD 11)
          set(CMAKE_CXX_STANDARD_REQUIRED YES)
-         if (APPLE AND "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+         if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
+            # Sometimes clang will lie and report that it supports C++11 when
+            # really it doesn't support thread_local.  So check for that.
+            test_compiler_for_cpp11()
             add_global_compiler_switch("-std=c++11")
+         else()
+            message(STATUS "C++11 activated.")
          endif()
-         message(STATUS "C++11 activated.")
       endif()
    endif()
 endif()