Features: Add cxx_decltype_incomplete_return_types.

Help/variable/CMAKE_CXX_KNOWN_FEATURES.rst

@@ -42,6 +42,11 @@ 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_incomplete_return_types``
+  Decltype on incomplete return types, as defined in N3276_.
+
+  .. _N3276 : http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3276.pdf
+
 ``cxx_decltype``
   Decltype, as defined in N2343_.
 

Modules/Compiler/GNU-CXX-FeatureTests.cmake

@@ -3,8 +3,9 @@
 
 set(_oldestSupported "(__GNUC__ * 100 + __GNUC_MINOR__) >= 408")
 # Introduced in GCC 4.8.1
-set(_cmake_feature_test_cxx_reference_qualified_functions
+set(GNU481_CXX11 "((__GNUC__ * 100 + __GNUC_MINOR__) > 408 || __GNUC_PATCHLEVEL__ >= 1) && __cplusplus >= 201103L")
-  "((__GNUC__ * 100 + __GNUC_MINOR__) > 408 || __GNUC_PATCHLEVEL__ >= 1) && __cplusplus >= 201103L")
+set(_cmake_feature_test_cxx_decltype_incomplete_return_types "${GNU481_CXX11}")
+set(_cmake_feature_test_cxx_reference_qualified_functions "${GNU481_CXX11}")
 set(GNU48_CXX11 "(__GNUC__ * 100 + __GNUC_MINOR__) >= 408 && __cplusplus >= 201103L")
 set(_cmake_feature_test_cxx_alignas "${GNU48_CXX11}")
 set(_cmake_feature_test_cxx_alignof "${GNU48_CXX11}")

Source/cmMakefile.cxx

@@ -49,6 +49,7 @@
   F(cxx_auto_type) \
   F(cxx_constexpr) \
   F(cxx_decltype) \
+  F(cxx_decltype_incomplete_return_types) \
   F(cxx_defaulted_functions) \
   F(cxx_delegating_constructors) \
   F(cxx_deleted_functions) \

Tests/CompileFeatures/cxx_decltype_incomplete_return_types.cpp

@@ -0,0 +1,14 @@
+
+template<class T>
+struct A
+{
+  ~A() = delete;
+};
+
+template<class T> auto h() -> A<T>;
+template<class T> auto i(T) -> T;
+template<class T> auto f(T) -> decltype(i(h<T>()));
+template<class T> auto f(T) -> void;
+auto g() -> void {
+  f(42);
+}