Make C++ feature checks extensible

Turn the feature check for cxx11_unordered_map into a function such that
we can use it for other features as well.  Drop the 11 suffix, as we may
want to check features from other standards.

1 files changed, 36 insertions, 0 deletions

diff --git a/Source/Checks/cm_cxx_features.cmake b/Source/Checks/cm_cxx_features.cmake
new file mode 100644
index 0000000..b0ecc4c
--- /dev/null
+++ b/Source/Checks/cm_cxx_features.cmake
@@ -0,0 +1,36 @@
+
+function(cm_check_cxx_feature name)
+  string(TOUPPER ${name} FEATURE)
+  if(NOT DEFINED CMake_HAVE_CXX_${FEATURE})
+    message(STATUS "Checking if compiler supports C++ ${name}")
+    try_compile(CMake_HAVE_CXX_${FEATURE}
+      ${CMAKE_CURRENT_BINARY_DIR}
+      ${CMAKE_CURRENT_LIST_DIR}/cm_cxx_${name}.cxx
+      CMAKE_FLAGS -DCMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD}
+      OUTPUT_VARIABLE OUTPUT
+      )
+    # If using the feature causes warnings, treat it as broken/unavailable.
+    if(OUTPUT MATCHES "warning")
+      set(CMake_HAVE_CXX_${FEATURE} OFF CACHE INTERNAL "TRY_COMPILE" FORCE)
+    endif()
+    if(CMake_HAVE_CXX_${FEATURE})
+      message(STATUS "Checking if compiler supports C++ ${name} - yes")
+      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
+        "Determining if compiler supports C++ ${name} passed with the following output:\n"
+        "${OUTPUT}\n"
+        "\n"
+        )
+    else()
+      message(STATUS "Checking if compiler supports C++ ${name} - no")
+      file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
+        "Determining if compiler supports C++ ${name} failed with the following output:\n"
+        "${OUTPUT}\n"
+        "\n"
+        )
+    endif()
+  endif()
+endfunction()
+
+if(CMAKE_CXX_STANDARD)
+  cm_check_cxx_feature(unordered_map)
+endif()