First part of P0600 - '[[nodiscard] in the standard library'. Mark the 'empty()' methods of all the containers as nodiscard. If you're calling empty() w/o looking at the result, you probably meanto to call 'clear()'. c++2a only

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@318269 91177308-0d34-0410-b5e6-96231b3b80d8

include/queue

@@ -268,7 +268,7 @@ public:
 
 #endif  // _LIBCPP_CXX03_LANG
 
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY
     bool      empty() const {return c.empty();}
     _LIBCPP_INLINE_VISIBILITY
     size_type size() const  {return c.size();}
@@ -490,7 +490,7 @@ public:
                                                          _Alloc>::value>::type* = 0);
 #endif  // _LIBCPP_CXX03_LANG
 
-    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_NODISCARD_AFTER_CXX17 _LIBCPP_INLINE_VISIBILITY
     bool            empty() const {return c.empty();}
     _LIBCPP_INLINE_VISIBILITY
     size_type       size() const  {return c.size();}