From faeddf64f21b592a5663803ca8accdf9f4b73c29 Mon Sep 17 00:00:00 2001
From: Stephen Kelly <steveire@gmail.com>
Date: Thu, 17 Oct 2013 11:47:29 +0200
Subject: project: Add infrastructure for recording CXX compiler features

Add a feature test using the compiler macros and the preprocessor to
determine available features.

Add a CMAKE_CXX_COMPILE_FEATURES variable which contains all features
known to the loaded compiler, and a CMAKE_CXX_KNOWN_FEATURES variable
containing all features known to CMake.  Add language standard specific
variables for internal use to determine the standard-specific compile
flags to use.

This will be extended to other languages in the future.  Follow-up
commits will add features which will be recorded by the feature test.
---
 Modules/Internal/FeatureTesting.cmake | 57 +++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 Modules/Internal/FeatureTesting.cmake

(limited to 'Modules/Internal/FeatureTesting.cmake')

diff --git a/Modules/Internal/FeatureTesting.cmake b/Modules/Internal/FeatureTesting.cmake
new file mode 100644
index 0000000000..92d262cad7
--- /dev/null
+++ b/Modules/Internal/FeatureTesting.cmake
@@ -0,0 +1,57 @@
+
+macro(record_compiler_features lang compile_flags feature_list)
+  include("${CMAKE_ROOT}/Modules/Compiler/${CMAKE_${lang}_COMPILER_ID}-${lang}-FeatureTests.cmake" OPTIONAL)
+
+  string(TOLOWER ${lang} lang_lc)
+  file(REMOVE "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.bin")
+  file(WRITE "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.${lang_lc}" "
+  extern const char features[] = {\"\"\n")
+  foreach(feature ${CMAKE_${lang}_KNOWN_FEATURES})
+    if (_cmake_feature_test_${feature})
+      if (${_cmake_feature_test_${feature}} STREQUAL 1)
+        set(_feature_condition "\"1\" ")
+      else()
+        set(_feature_condition "#if ${_cmake_feature_test_${feature}}\n\"1\"\n#else\n\"0\"\n#endif\n")
+      endif()
+      file(APPEND "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.${lang_lc}" "\"${lang}_FEATURE:\"\n${_feature_condition}\"${feature}\\n\"\n")
+    endif()
+  endforeach()
+  file(APPEND "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.${lang_lc}"
+    "\n};\n\nint main(int, char **) { return 0; }\n")
+
+  try_compile(CMAKE_${lang}_FEATURE_TEST
+    ${CMAKE_BINARY_DIR} "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.${lang_lc}"
+    COMPILE_DEFINITIONS "${compile_flags}"
+    OUTPUT_VARIABLE _output
+    COPY_FILE "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.bin"
+    COPY_FILE_ERROR _copy_error
+    )
+  if(CMAKE_${lang}_FEATURE_TEST AND NOT _copy_error)
+    set(_result 0)
+  else()
+    set(_result 255)
+  endif()
+  unset(CMAKE_${lang}_FEATURE_TEST CACHE)
+
+  if (_result EQUAL 0)
+    file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
+      "\n\nDetecting ${lang} [${compile_flags}] compiler features compiled with the following output:\n${_output}\n\n")
+    if(EXISTS "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.bin")
+      file(STRINGS "${CMAKE_BINARY_DIR}/CMakeFiles/feature_tests.bin"
+        features REGEX "${lang}_FEATURE:.*")
+      foreach(info ${features})
+        file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
+          "    Feature record: ${info}\n")
+        string(REPLACE "${lang}_FEATURE:" "" info ${info})
+        string(SUBSTRING ${info} 0 1 has_feature)
+        if(has_feature)
+          string(REGEX REPLACE "^1" "" feature ${info})
+          list(APPEND ${feature_list} ${feature})
+        endif()
+      endforeach()
+    endif()
+  else()
+    file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
+      "Detecting ${lang} [${compile_flags}] compiler features failed to compile with the following output:\n${_output}\n${_copy_error}\n\n")
+  endif()
+endmacro()
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