Fix issue #10155 - default value of CMAKE_OSX_DEPLOYMENT_TARGET should always be the empty string. When the value of CMAKE_OSX_DEPLOYMENT_TARGET is the empty string, the -mmacosx-version-min flag should not show up on the compiler command line. The logic for selecting default value of CMAKE_OSX_SYSROOT is orthogonal to and independent of the value of the deployment target. The default value for CMAKE_OSX_SYSROOT is the SDK that corresponds to the current version of Mac OSX on which cmake is running.

Modules/CMakeCCompiler.cmake.in

@@ -38,6 +38,7 @@ IF(CMAKE_C_COMPILER_ABI)
 ENDIF(CMAKE_C_COMPILER_ABI)
 
 SET(CMAKE_C_HAS_ISYSROOT "@CMAKE_C_HAS_ISYSROOT@")
+@CMAKE_C_OSX_DEPLOYMENT_TARGET_FLAG_CODE@
 
 SET(CMAKE_C_IMPLICIT_LINK_LIBRARIES "@CMAKE_C_IMPLICIT_LINK_LIBRARIES@")
 SET(CMAKE_C_IMPLICIT_LINK_DIRECTORIES "@CMAKE_C_IMPLICIT_LINK_DIRECTORIES@")

Modules/CMakeCXXCompiler.cmake.in

@@ -39,6 +39,7 @@ IF(CMAKE_CXX_COMPILER_ABI)
 ENDIF(CMAKE_CXX_COMPILER_ABI)
 
 SET(CMAKE_CXX_HAS_ISYSROOT "@CMAKE_CXX_HAS_ISYSROOT@")
+@CMAKE_CXX_OSX_DEPLOYMENT_TARGET_FLAG_CODE@
 
 SET(CMAKE_CXX_IMPLICIT_LINK_LIBRARIES "@CMAKE_CXX_IMPLICIT_LINK_LIBRARIES@")
 SET(CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES "@CMAKE_CXX_IMPLICIT_LINK_DIRECTORIES@")

Modules/Platform/Darwin-GNU-C.cmake

@@ -1,3 +1,4 @@
 include(Platform/Darwin-GNU)
 __darwin_compiler_gnu(C)
 cmake_gnu_has_isysroot(C)
+cmake_gnu_set_osx_deployment_target_flag(C)

Modules/Platform/Darwin-GNU-CXX.cmake

@@ -1,3 +1,4 @@
 include(Platform/Darwin-GNU)
 __darwin_compiler_gnu(CXX)
 cmake_gnu_has_isysroot(CXX)
+cmake_gnu_set_osx_deployment_target_flag(CXX)

Modules/Platform/Darwin-GNU.cmake

@@ -42,3 +42,23 @@ macro(cmake_gnu_has_isysroot lang)
     endif()
   endif()
 endmacro()
+
+macro(cmake_gnu_set_osx_deployment_target_flag lang)
+  if(NOT DEFINED CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG)
+    set(_doc "${lang} compiler supports OSX deployment target flag")
+    message(STATUS "Checking whether ${_doc}")
+    execute_process(
+      COMMAND ${CMAKE_${lang}_COMPILER} "-v" "--help"
+      OUTPUT_VARIABLE _gcc_help
+      ERROR_VARIABLE _gcc_help
+      )
+    if("${_gcc_help}" MATCHES "macosx-version-min")
+      message(STATUS "Checking whether ${_doc} - yes")
+      set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mmacosx-version-min=")
+    else()
+      message(STATUS "Checking whether ${_doc} - no")
+      set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "")
+    endif()
+    set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG_CODE "SET(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG \"${CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG}\")")
+  endif()
+endmacro()

Modules/Platform/Darwin.cmake

@@ -77,35 +77,20 @@ EXECUTE_PROCESS(COMMAND sw_vers -productVersion
   OUTPUT_VARIABLE CURRENT_OSX_VERSION
   OUTPUT_STRIP_TRAILING_WHITESPACE)
 
+#----------------------------------------------------------------------------
+# _CURRENT_OSX_VERSION - as a two-component string: 10.5, 10.6, ...
+#
+STRING(REGEX REPLACE "^([0-9]+\\.[0-9]+).*$" "\\1"
+  _CURRENT_OSX_VERSION "${CURRENT_OSX_VERSION}")
+
 #----------------------------------------------------------------------------
 # CMAKE_OSX_DEPLOYMENT_TARGET
 
-# Environment variable set by the user overrides our default.
-# Use the same environment variable that Xcode uses.
-SET(ENV_MACOSX_DEPLOYMENT_TARGET "$ENV{MACOSX_DEPLOYMENT_TARGET}")
-
-# Set CMAKE_OSX_DEPLOYMENT_TARGET_DEFAULT - if user has already specified an SDK
-# with CMAKE_OSX_SYSROOT, then deployment target should default to "", otherwise,
-# default it to the current OSX version.
-IF(CMAKE_OSX_SYSROOT)
-  SET(CMAKE_OSX_DEPLOYMENT_TARGET_DEFAULT "")
-ELSE(CMAKE_OSX_SYSROOT)
-  STRING(REGEX REPLACE "^.*(10)\\.([0-9]+)\\.*([0-9]+)*.*$" "\\1.\\2"
-    CMAKE_OSX_DEPLOYMENT_TARGET_DEFAULT ${CURRENT_OSX_VERSION})
-ENDIF(CMAKE_OSX_SYSROOT)
-
-# Use environment or default as initial cache value:
-IF(NOT ENV_MACOSX_DEPLOYMENT_TARGET STREQUAL "")
-  SET(CMAKE_OSX_DEPLOYMENT_TARGET_VALUE ${ENV_MACOSX_DEPLOYMENT_TARGET})
-ELSE(NOT ENV_MACOSX_DEPLOYMENT_TARGET STREQUAL "")
-  SET(CMAKE_OSX_DEPLOYMENT_TARGET_VALUE ${CMAKE_OSX_DEPLOYMENT_TARGET_DEFAULT})
-ENDIF(NOT ENV_MACOSX_DEPLOYMENT_TARGET STREQUAL "")
-
 # Set cache variable - end user may change this during ccmake or cmake-gui configure.
-IF(CURRENT_OSX_VERSION GREATER 10.3)
+IF(_CURRENT_OSX_VERSION VERSION_GREATER 10.3)
-  SET(CMAKE_OSX_DEPLOYMENT_TARGET ${CMAKE_OSX_DEPLOYMENT_TARGET_VALUE} CACHE STRING
+  SET(CMAKE_OSX_DEPLOYMENT_TARGET "$ENV{MACOSX_DEPLOYMENT_TARGET}" CACHE STRING
     "Minimum OS X version to target for deployment (at runtime); newer APIs weak linked. Set to empty string for default value.")
-ENDIF(CURRENT_OSX_VERSION GREATER 10.3)
+ENDIF(_CURRENT_OSX_VERSION VERSION_GREATER 10.3)
 
 #----------------------------------------------------------------------------
 # CMAKE_OSX_SYSROOT
@@ -114,20 +99,20 @@ ENDIF(CURRENT_OSX_VERSION GREATER 10.3)
 # Use the same environment variable that Xcode uses.
 SET(ENV_SDKROOT "$ENV{SDKROOT}")
 
-# Set CMAKE_OSX_SYSROOT_DEFAULT based on CMAKE_OSX_DEPLOYMENT_TARGET,
+# Set CMAKE_OSX_SYSROOT_DEFAULT based on _CURRENT_OSX_VERSION,
 # accounting for the known specially named SDKs.
 SET(CMAKE_OSX_SYSROOT_DEFAULT
-  "${OSX_DEVELOPER_ROOT}/SDKs/MacOSX${CMAKE_OSX_DEPLOYMENT_TARGET}.sdk")
+  "${OSX_DEVELOPER_ROOT}/SDKs/MacOSX${_CURRENT_OSX_VERSION}.sdk")
 
-IF(CMAKE_OSX_DEPLOYMENT_TARGET EQUAL "10.4")
+IF(_CURRENT_OSX_VERSION STREQUAL "10.4")
   SET(CMAKE_OSX_SYSROOT_DEFAULT
     "${OSX_DEVELOPER_ROOT}/SDKs/MacOSX10.4u.sdk")
-ENDIF(CMAKE_OSX_DEPLOYMENT_TARGET EQUAL "10.4")
+ENDIF(_CURRENT_OSX_VERSION STREQUAL "10.4")
 
-IF(CMAKE_OSX_DEPLOYMENT_TARGET EQUAL "10.3")
+IF(_CURRENT_OSX_VERSION STREQUAL "10.3")
   SET(CMAKE_OSX_SYSROOT_DEFAULT
     "${OSX_DEVELOPER_ROOT}/SDKs/MacOSX10.3.9.sdk")
-ENDIF(CMAKE_OSX_DEPLOYMENT_TARGET EQUAL "10.3")
+ENDIF(_CURRENT_OSX_VERSION STREQUAL "10.3")
 
 # Use environment or default as initial cache value:
 IF(NOT ENV_SDKROOT STREQUAL "")
@@ -152,7 +137,7 @@ function(SanityCheckSDKAndDeployTarget _sdk_path _deploy)
 
   string(REGEX REPLACE "(.*MacOSX*)(....)(.*\\.sdk)" "\\2" SDK "${_sdk_path}")
   if(_deploy GREATER "${SDK}")
-    message(FATAL_ERROR "CMAKE_OSX_DEPLOYMENT_TARGET (${_deploy}) is greater than CMAKE_OSX_SYSROOT SDK (${_sdk_path}). Please set CMAKE_OSX_DEPLOYMENT_TARGET to ${SDK}")
+    message(FATAL_ERROR "CMAKE_OSX_DEPLOYMENT_TARGET (${_deploy}) is greater than CMAKE_OSX_SYSROOT SDK (${_sdk_path}). Please set CMAKE_OSX_DEPLOYMENT_TARGET to ${SDK} or lower")
   endif()
 endfunction(SanityCheckSDKAndDeployTarget)
 #----------------------------------------------------------------------------

Source/cmLocalGenerator.cxx

@@ -1784,6 +1784,9 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
       this->Makefile->GetDefinition("CMAKE_OSX_DEPLOYMENT_TARGET");
     std::string isysrootVar = std::string("CMAKE_") + lang + "_HAS_ISYSROOT";
     bool hasIsysroot = this->Makefile->IsOn(isysrootVar.c_str());
+    std::string deploymentTargetFlagVar = std::string("CMAKE_") + lang + "_OSX_DEPLOYMENT_TARGET_FLAG";
+    const char* deploymentTargetFlag =
+      this->Makefile->GetDefinition(deploymentTargetFlagVar.c_str());
     bool flagsUsed = false;
     if(!archs.empty() && sysroot && lang && (lang[0] =='C' || lang[0] == 'F'))
       {
@@ -1815,10 +1818,11 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
       flags += sysroot;
       }
 
-    if (deploymentTarget && *deploymentTarget &&
+    if (deploymentTargetFlag && *deploymentTargetFlag &&
-        lang && (lang[0] =='C' || lang[0] == 'F'))
+        deploymentTarget && *deploymentTarget)
       {
-      flags += " -mmacosx-version-min=";
+      flags += " ";
+      flags += deploymentTargetFlag;
       flags += deploymentTarget;
       }
     }