Features: Add cxx_user_literals.

Help/variable/CMAKE_CXX_KNOWN_FEATURES.rst

@@ -122,6 +122,11 @@ The features known to this version of CMake are:
 
   .. _N2541: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2541.htm
 
+``cxx_user_literals``
+  User-defined literals, as defined in N2765_.
+
+  .. _N2765: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2765.pdf
+
 ``cxx_variadic_templates``
   Variadic templates, as defined in N2242_.
 

Modules/Compiler/GNU-CXX-FeatureTests.cmake

@@ -15,6 +15,7 @@ set(_cmake_feature_test_cxx_final "${GNU47_CXX11}")
 set(_cmake_feature_test_cxx_noexcept "${GNU47_CXX11}")
 set(_cmake_feature_test_cxx_nonstatic_member_init "${GNU47_CXX11}")
 set(_cmake_feature_test_cxx_override "${GNU47_CXX11}")
+set(_cmake_feature_test_cxx_user_literals "${GNU47_CXX11}")
 # NOTE: C++11 was ratified in September 2011. GNU 4.7 is the first minor
 # release following that (March 2012), and the first minor release to
 # support -std=c++11. Prior to that, support for C++11 features is technically

Source/cmMakefile.cxx

@@ -64,6 +64,7 @@
   F(cxx_static_assert) \
   F(cxx_strong_enums) \
   F(cxx_trailing_return_types) \
+  F(cxx_user_literals) \
   F(cxx_variadic_templates)
 
 class cmMakefile::Internals

Tests/CompileFeatures/cxx_user_literals.cpp

@@ -0,0 +1,7 @@
+
+long double operator "" _meters(long double);
+
+void someFunc()
+{
+  long double i = 1.2_meters;
+}