Ask the compiler what libcxx should be (conan-io#118)

* Ask the compiler what libcxx should be

* fix typo

* merge libc++ and libstdc++ detection functions

conan.cmake

@@ -122,7 +122,7 @@ function(conan_cmake_settings result)
         set(_CONAN_SETTING_COMPILER gcc)
         set(_CONAN_SETTING_COMPILER_VERSION ${COMPILER_VERSION})
         if (USING_CXX)
-            conan_cmake_detect_gnu_libcxx(_LIBCXX)
+            conan_cmake_detect_unix_libcxx(_LIBCXX)
             set(_CONAN_SETTING_COMPILER_LIBCXX ${_LIBCXX})
         endif ()
     elseif (${CMAKE_${LANGUAGE}_COMPILER_ID} STREQUAL AppleClang)
@@ -133,37 +133,29 @@ function(conan_cmake_settings result)
         set(_CONAN_SETTING_COMPILER apple-clang)
         set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR}.${MINOR})
         if (USING_CXX)
-            set(_CONAN_SETTING_COMPILER_LIBCXX libc++)
+            conan_cmake_detect_unix_libcxx(_LIBCXX)
+            set(_CONAN_SETTING_COMPILER_LIBCXX ${_LIBCXX})
         endif ()
     elseif (${CMAKE_${LANGUAGE}_COMPILER_ID} STREQUAL Clang)
         string(REPLACE "." ";" VERSION_LIST ${CMAKE_${LANGUAGE}_COMPILER_VERSION})
         list(GET VERSION_LIST 0 MAJOR)
         list(GET VERSION_LIST 1 MINOR)
+        set(_CONAN_SETTING_COMPILER clang)
+        set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR}.${MINOR})
         if(APPLE)
             cmake_policy(GET CMP0025 APPLE_CLANG_POLICY_ENABLED)
             if(NOT APPLE_CLANG_POLICY_ENABLED)
                 message(STATUS "Conan: APPLE and Clang detected. Assuming apple-clang compiler. Set CMP0025 to avoid it")
                 set(_CONAN_SETTING_COMPILER apple-clang)
-                set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR}.${MINOR})
-            else()
-                set(_CONAN_SETTING_COMPILER clang)
-                set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR}.${MINOR})
-            endif()
-            if (USING_CXX)
-                set(_CONAN_SETTING_COMPILER_LIBCXX libc++)
-            endif ()
-        else()
-            set(_CONAN_SETTING_COMPILER clang)
-            if(${MAJOR} GREATER 7)
-                set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR})
-            else()
-                set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR}.${MINOR})
             endif()
-            if (USING_CXX)
-                conan_cmake_detect_gnu_libcxx(_LIBCXX)
-                set(_CONAN_SETTING_COMPILER_LIBCXX ${_LIBCXX})
-            endif ()
         endif()
+        if(${_CONAN_SETTING_COMPILER} STREQUAL clang AND ${MAJOR} GREATER 7)
+            set(_CONAN_SETTING_COMPILER_VERSION ${MAJOR})
+        endif()
+        if (USING_CXX)
+            conan_cmake_detect_unix_libcxx(_LIBCXX)
+            set(_CONAN_SETTING_COMPILER_LIBCXX ${_LIBCXX})
+        endif ()
     elseif(${CMAKE_${LANGUAGE}_COMPILER_ID} STREQUAL MSVC)
         set(_VISUAL "Visual Studio")
         _get_msvc_ide_version(_VISUAL_VERSION)
@@ -237,36 +229,53 @@ function(conan_cmake_settings result)
 endfunction()
 
 
-function(conan_cmake_detect_gnu_libcxx result)
-    # Allow -D_GLIBCXX_USE_CXX11_ABI=ON/OFF as argument to cmake
-    if(DEFINED _GLIBCXX_USE_CXX11_ABI)
-        if(_GLIBCXX_USE_CXX11_ABI)
-            set(${result} libstdc++11 PARENT_SCOPE)
-            return()
-        else()
-            set(${result} libstdc++ PARENT_SCOPE)
-            return()
-        endif()
-    endif()
+function(conan_cmake_detect_unix_libcxx result)
+    # Take into account any -stdlib in compile options
+    get_directory_property(compile_options DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} COMPILE_OPTIONS)
 
-    # Check if there's any add_definitions(-D_GLIBCXX_USE_CXX11_ABI=0)
+    # Take into account any _GLIBCXX_USE_CXX11_ABI in compile definitions
     get_directory_property(defines DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} COMPILE_DEFINITIONS)
     foreach(define ${defines})
-        if(define STREQUAL "_GLIBCXX_USE_CXX11_ABI=0")
-            set(${result} libstdc++ PARENT_SCOPE)
-            return()
+        if(define MATCHES "_GLIBCXX_USE_CXX11_ABI")
+            if(define MATCHES "^-D")
+                set(compile_options ${compile_options} "${define}")
+            else()
+                set(compile_options ${compile_options} "-D${define}")
+            endif()
         endif()
     endforeach()
 
-    # Use C++11 stdlib as default if gcc is 5.1+
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS "5.1")
-      set(${result} libstdc++ PARENT_SCOPE)
+    execute_process(
+        COMMAND ${CMAKE_COMMAND} -E echo "#include <string>"
+        COMMAND ${CMAKE_CXX_COMPILER} -x c++ ${compile_options} -E -dM -
+        OUTPUT_VARIABLE string_defines
+    )
+
+    if(string_defines MATCHES "#define __GLIBCXX__")
+        # Allow -D_GLIBCXX_USE_CXX11_ABI=ON/OFF as argument to cmake
+        if(DEFINED _GLIBCXX_USE_CXX11_ABI)
+            if(_GLIBCXX_USE_CXX11_ABI)
+                set(${result} libstdc++11 PARENT_SCOPE)
+                return()
+            else()
+                set(${result} libstdc++ PARENT_SCOPE)
+                return()
+            endif()
+        endif()
+
+        if(string_defines MATCHES "#define _GLIBCXX_USE_CXX11_ABI 1\n")
+            set(${result} libstdc++11 PARENT_SCOPE)
+        else()
+            # Either the compiler is missing the define because it is old, and so
+            # it can't use the new abi, or the compiler was configured to use the
+            # old abi by the user or distro (e.g. devtoolset on RHEL/CentOS)
+            set(${result} libstdc++ PARENT_SCOPE)
+        endif()
     else()
-      set(${result} libstdc++11 PARENT_SCOPE)
+        set(${result} libc++ PARENT_SCOPE)
     endif()
 endfunction()
 
-
 function(conan_cmake_detect_vs_runtime result)
     string(TOUPPER ${CMAKE_BUILD_TYPE} build_type)
     set(variables CMAKE_CXX_FLAGS_${build_type} CMAKE_C_FLAGS_${build_type} CMAKE_CXX_FLAGS CMAKE_C_FLAGS)
@@ -516,4 +525,3 @@ macro(conan_add_remote)
     execute_process(COMMAND ${CONAN_CMD} remote add ${CONAN_NAME} ${CONAN_URL}
       ${CONAN_INDEX_ARG} -f)
 endmacro()
-