Features: Add cxx_decltype.

Help/variable/CMAKE_CXX_KNOWN_FEATURES.rst

@@ -22,6 +22,11 @@ The features known to this version of CMake are:
 
   .. _N2235: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf
 
+``cxx_decltype``
+  Decltype, as defined in N2343_.
+
+  .. _N2343: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2343.pdf
+
 ``cxx_delegating_constructors``
   Delegating constructors, as defined in N1986_.
 

Modules/Compiler/GNU-CXX-FeatureTests.cmake

@@ -30,5 +30,6 @@ set(_cmake_feature_test_cxx_variadic_templates "${GNU44_CXX11}")
 # http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2555.pdf
 # TODO: Should be supported by GNU 4.3
 set(GNU43_CXX11 "${_oldestSupported} && __cplusplus >= 201103L")
+set(_cmake_feature_test_cxx_decltype "${GNU43_CXX11}")
 set(_cmake_feature_test_cxx_static_assert "${GNU43_CXX11}")
 set(_oldestSupported)

Source/cmMakefile.cxx

@@ -44,6 +44,7 @@
 #define FOR_EACH_CXX_FEATURE(F) \
   F(cxx_auto_type) \
   F(cxx_constexpr) \
+  F(cxx_decltype) \
   F(cxx_delegating_constructors) \
   F(cxx_final) \
   F(cxx_override) \

Tests/CompileFeatures/cxx_decltype.cpp

@@ -0,0 +1,7 @@
+
+int someFunc()
+{
+  int i = 0;
+  decltype(i) other = 0;
+  return other;
+}