Implement LWG#2761: 'basic_string should require that charT match traits::char_type'. Tests for string_view, too

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@297872 91177308-0d34-0410-b5e6-96231b3b80d8

include/string

@@ -637,7 +637,7 @@ public:
     typedef basic_string                                 __self;
     typedef basic_string_view<_CharT, _Traits>           __self_view;
     typedef _Traits                                      traits_type;
-    typedef typename traits_type::char_type              value_type;
+    typedef _CharT                                       value_type;
     typedef _Allocator                                   allocator_type;
     typedef allocator_traits<allocator_type>             __alloc_traits;
     typedef typename __alloc_traits::size_type           size_type;
@@ -648,7 +648,7 @@ public:
     typedef typename __alloc_traits::const_pointer       const_pointer;
 
     static_assert(is_pod<value_type>::value, "Character type of basic_string must be a POD");
-    static_assert((is_same<_CharT, value_type>::value),
+    static_assert((is_same<_CharT, typename traits_type::char_type>::value),
                   "traits_type::char_type must be the same type as CharT");
     static_assert((is_same<typename allocator_type::value_type, value_type>::value),
                   "Allocator::value_type must be same type as value_type");

include/string_view

@@ -199,6 +199,10 @@ public:
 	typedef ptrdiff_t                                  difference_type;
 	static _LIBCPP_CONSTEXPR const size_type npos = -1; // size_type(-1);
 
+    static_assert(is_pod<value_type>::value, "Character type of basic_string_view must be a POD");
+    static_assert((is_same<_CharT, typename traits_type::char_type>::value),
+                  "traits_type::char_type must be the same type as CharT");
+
 	// [string.view.cons], construct/copy
 	_LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
 	basic_string_view() _NOEXCEPT : __data (nullptr), __size(0) {}

test/std/strings/basic.string/traits_mismatch.fail.cpp

@@ -0,0 +1,18 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <string>
+//   The strings's value type must be the same as the traits's char_type
+
+#include <string>
+
+int main()
+{
+    std::basic_string<char, std::char_traits<wchar_t>> s;
+}

test/std/strings/string.view/nothing_to_do.pass.cpp → test/std/strings/string.view/traits_mismatch.fail.cpp

@@ -7,6 +7,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+// <string_view>
+//   The string_views's value type must be the same as the traits's char_type
+
 #include <string_view>
 
-int main () {}
+int main()
+{
+    std::basic_string_view<char, std::char_traits<wchar_t>> s;
+}

www/cxx1z_status.html

@@ -463,7 +463,7 @@
 	<tr><td><a href="http://wg21.link/LWG2853">2853</a></td><td>Possible inconsistency in specification of erase in [vector.modifiers]</td><td>Kona</td><td></td></tr>
 	<tr><td><a href="http://wg21.link/LWG2855">2855</a></td><td>std::throw_with_nested("string_literal")</td><td>Kona</td><td></td></tr>
 	<tr><td><a href="http://wg21.link/LWG2857">2857</a></td><td>{variant,optional,any}::emplace should return the constructed value</td><td>Kona</td><td></td></tr>
-	<tr><td><a href="http://wg21.link/LWG2861">2861</a></td><td>basic_string should require that charT match traits::char_type</td><td>Kona</td><td></td></tr>
+	<tr><td><a href="http://wg21.link/LWG2861">2861</a></td><td>basic_string should require that charT match traits::char_type</td><td>Kona</td><td>Clow</td></tr>
 	<tr><td><a href="http://wg21.link/LWG2866">2866</a></td><td>Incorrect derived classes constraints</td><td>Kona</td><td></td></tr>
 	<tr><td><a href="http://wg21.link/LWG2868">2868</a></td><td>Missing specification of bad_any_cast::what()</td><td>Kona</td><td>Complete</td></tr>
 	<tr><td><a href="http://wg21.link/LWG2872">2872</a></td><td>Add definition for direct-non-list-initialization</td><td>Kona</td><td>Complete</td></tr>