Add macros cmake_push/pop_check_state() as discussed on the list.

This patch adds two macros cmake_push_check_state() and
cmake_pop_check_state(), which can be used to save and restore
the contents of the CMAKE_REQUIRED_xxx variables.

Alex

Modules/CMakePushCheckState.cmake

@@ -0,0 +1,52 @@
+# This module defines two macros:
+# CMAKE_PUSH_CHECK_STATE()
+# and
+# CMAKE_POP_CHECK_STATE()
+# These two macros can be used to save and restore the state of the variables
+# CMAKE_REQUIRED_FLAGS, CMAKE_REQUIRED_DEFINITIONS, CMAKE_REQUIRED_LIBRARIES
+# and CMAKE_REQUIRED_INCLUDES used by the various Check-files coming with CMake,
+# like e.g. check_function_exists() etc.
+# The variable contents are pushed on a stack, pushing multiple times is supported.
+# This is useful e.g. when executing such tests in a Find-module, where they have to be set,
+# but after the Find-module has been executed they should have the same value
+# as they had before.
+#
+# Usage:
+#   cmake_push_check_state()
+#   set(CMAKE_REQUIRED_DEFINITIONS ${CMAKE_REQUIRED_DEFINITIONS} -DSOME_MORE_DEF)
+#   check_function_exists(...)
+#   cmake_pop_check_state()
+
+# Copyright (c) 2006-2011, Alexander Neundorf, <neundorf@kde.org>
+#
+# Redistribution and use is allowed according to the terms of the BSD license.
+# For details see the accompanying COPYING-CMAKE-SCRIPTS file.
+
+MACRO(CMAKE_PUSH_CHECK_STATE)
+
+   IF(NOT DEFINED _CMAKE_PUSH_CHECK_STATE_COUNTER)
+      SET(_CMAKE_PUSH_CHECK_STATE_COUNTER 0)
+   ENDIF()
+
+   MATH(EXPR _CMAKE_PUSH_CHECK_STATE_COUNTER "${_CMAKE_PUSH_CHECK_STATE_COUNTER}+1")
+
+   SET(_CMAKE_REQUIRED_INCLUDES_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}    ${CMAKE_REQUIRED_INCLUDES})
+   SET(_CMAKE_REQUIRED_DEFINITIONS_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER} ${CMAKE_REQUIRED_DEFINITIONS})
+   SET(_CMAKE_REQUIRED_LIBRARIES_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}   ${CMAKE_REQUIRED_LIBRARIES})
+   SET(_CMAKE_REQUIRED_FLAGS_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}       ${CMAKE_REQUIRED_FLAGS})
+ENDMACRO(CMAKE_PUSH_CHECK_STATE)
+
+MACRO(CMAKE_POP_CHECK_STATE)
+
+# don't pop more than we pushed
+   IF("${_CMAKE_PUSH_CHECK_STATE_COUNTER}" GREATER "0")
+
+      SET(CMAKE_REQUIRED_INCLUDES    ${_CMAKE_REQUIRED_INCLUDES_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}})
+      SET(CMAKE_REQUIRED_DEFINITIONS ${_CMAKE_REQUIRED_DEFINITIONS_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}})
+      SET(CMAKE_REQUIRED_LIBRARIES   ${_CMAKE_REQUIRED_LIBRARIES_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}})
+      SET(CMAKE_REQUIRED_FLAGS       ${_CMAKE_REQUIRED_FLAGS_SAVE_${_CMAKE_PUSH_CHECK_STATE_COUNTER}})
+
+      MATH(EXPR _CMAKE_PUSH_CHECK_STATE_COUNTER "${_CMAKE_PUSH_CHECK_STATE_COUNTER}-1")
+   ENDIF()
+
+ENDMACRO(CMAKE_POP_CHECK_STATE)

Tests/CMakeTests/CMakeLists.txt

@@ -28,6 +28,7 @@ AddCMakeTest(Math "")
 AddCMakeTest(CMakeMinimumRequired "")
 AddCMakeTest(CompilerIdVendor "")
 AddCMakeTest(ProcessorCount "")
+AddCMakeTest(PushCheckState "")
 
 AddCMakeTest(FileDownload "")
 set_property(TEST CMake.FileDownload PROPERTY

Tests/CMakeTests/PushCheckStateTest.cmake.in

@@ -0,0 +1,30 @@
+include(CMakePushCheckState)
+
+set(CMAKE_REQUIRED_DEFINITIONS defs1 )
+
+cmake_push_check_state()
+
+set(CMAKE_REQUIRED_DEFINITIONS defs2)
+
+cmake_push_check_state()
+
+set(CMAKE_REQUIRED_DEFINITIONS defs3)
+
+cmake_pop_check_state()
+
+if (NOT "${CMAKE_REQUIRED_DEFINITIONS}" STREQUAL "defs2")
+  set(fatal TRUE)
+  message("ERROR: "CMAKE_REQUIRED_DEFINITIONS is \"${CMAKE_REQUIRED_DEFINITIONS}\" (expected \"defs2\")" )
+endif()
+
+cmake_pop_check_state()
+
+if (NOT "${CMAKE_REQUIRED_DEFINITIONS}" STREQUAL "defs1")
+  set(fatal TRUE)
+  message("ERROR: "CMAKE_REQUIRED_DEFINITIONS is \"${CMAKE_REQUIRED_DEFINITIONS}\" (expected \"defs1\")" )
+endif()
+
+
+if(fatal)
+  message(FATAL_ERROR "cmake_push_check_state() test failed")
+endif()