libstdc++: Implement P1872R0 and P1394R0 for std::span

This also fixes a bug in the implementation of LWG 3255, which causes:
FAIL: 23_containers/span/lwg3255.cc (test for excess errors)
That's because the test was wrong and verified the buggy behaviour. That
will be fixed in the following commit.

2019-12-05  JeanHeyd "ThePhD" Meneide  <phdofthehouse@gmail.com>

	Implement P1872R0 and P1394R0 for std::span
	* include/bits/range_access.h (__adl_begin, __adl_end): Remove.
	(sentinel_t, range_value_t, range_reference_t)
	(range_rvalue_reference_t, __forwarding_range, disable_sized_range)
	(output_range, input_range, forward_range, bidirectional_range)
	(random_access_range, contiguous_range, common_range): Move here from
	<ranges>, to make this the "ranges lite" internal header.
	* include/std/ranges: Move basic aliases and concepts to
	<bits/range_access.h>.
	* include/std/span: Use concepts and ranges:: calls instead of
	enable_if and friends.
	* include/std/type_traits: Add __is_array_convertible trait.

From-SVN: r279000

libstdc++-v3/ChangeLog

+2019-12-05  JeanHeyd "ThePhD" Meneide  <phdofthehouse@gmail.com>
+
+	Implement P1872R0 and P1394R0 for std::span
+	* include/bits/range_access.h (__adl_begin, __adl_end): Remove.
+	(sentinel_t, range_value_t, range_reference_t)
+	(range_rvalue_reference_t, __forwarding_range, disable_sized_range)
+	(output_range, input_range, forward_range, bidirectional_range)
+	(random_access_range, contiguous_range, common_range): Move here from
+	<ranges>, to make this the "ranges lite" internal header.
+	* include/std/ranges: Move basic aliases and concepts to
+	<bits/range_access.h>.
+	* include/std/span: Use concepts and ranges:: calls instead of
+	enable_if and friends.
+	* include/std/type_traits: Add __is_array_convertible trait.
+
 2019-12-05  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/bits/stl_algobase.h (lexicographical_compare_three_way):

libstdc++-v3/include/bits/range_access.h

@@ -336,19 +336,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ssize(const _Tp (&)[_Num]) noexcept
     { return _Num; }
 
-  // "why are these in namespace std:: and not __gnu_cxx:: ?"
-  // because if we don't put them here it's impossible to
-  // have implicit ADL with "using std::begin/end/size/data;".
-  template <typename _Container>
-    constexpr auto
-    __adl_begin(_Container& __cont) noexcept(noexcept(begin(__cont)))
-    { return begin(__cont); }
-
-  template <typename _Container>
-    constexpr auto
-    __adl_data(_Container& __cont) noexcept(noexcept(data(__cont)))
-    { return data(__cont); }
-
 #ifdef __cpp_lib_concepts
 namespace ranges
 {
@@ -869,11 +856,71 @@ namespace ranges
   template<typename _Tp>
     concept range = __detail::__range_impl<_Tp&>;
 
+  template<range _Range>
+    using sentinel_t = decltype(ranges::end(std::declval<_Range&>()));
+
+  template<range _Range>
+    using iterator_t = decltype(ranges::begin(std::declval<_Range&>()));
+
+  template<range _Range>
+    using range_value_t = iter_value_t<iterator_t<_Range>>;
+
+  template<range _Range>
+    using range_reference_t = iter_reference_t<iterator_t<_Range>>;
+
+  template<range _Range>
+    using range_rvalue_reference_t
+      = iter_rvalue_reference_t<iterator_t<_Range>>;
+
+  template<range _Range>
+    using range_difference_t = iter_difference_t<iterator_t<_Range>>;
+
+  namespace __detail
+  {
+    template<typename _Tp>
+      concept __forwarding_range = range<_Tp> && __range_impl<_Tp>;
+  } // namespace __detail
+
   /// [range.sized] The sized_range concept.
   template<typename _Tp>
     concept sized_range = range<_Tp>
       && requires(_Tp& __t) { ranges::size(__t); };
 
+  template<typename>
+    inline constexpr bool disable_sized_range = false;
+
+  // [range.refinements]
+  template<typename _Range, typename _Tp>
+    concept output_range
+      = range<_Range> && output_iterator<iterator_t<_Range>, _Tp>;
+
+  template<typename _Tp>
+    concept input_range = range<_Tp> && input_iterator<iterator_t<_Tp>>;
+
+  template<typename _Tp>
+    concept forward_range
+      = input_range<_Tp> && forward_iterator<iterator_t<_Tp>>;
+
+  template<typename _Tp>
+    concept bidirectional_range
+      = forward_range<_Tp> && bidirectional_iterator<iterator_t<_Tp>>;
+
+  template<typename _Tp>
+    concept random_access_range
+      = bidirectional_range<_Tp> && random_access_iterator<iterator_t<_Tp>>;
+
+  template<typename _Tp>
+    concept contiguous_range
+      = random_access_range<_Tp> && contiguous_iterator<iterator_t<_Tp>>
+      && requires(_Tp& __t)
+      {
+	{ ranges::data(__t) } -> same_as<add_pointer_t<range_reference_t<_Tp>>>;
+      };
+
+  template<typename _Tp>
+    concept common_range
+      = range<_Tp> && same_as<iterator_t<_Tp>, sentinel_t<_Tp>>;
+
     // [range.iter.ops] range iterator operations
 
   template<input_or_output_iterator _It>
@@ -1009,12 +1056,6 @@ namespace ranges
     }
 
   template<range _Range>
-    using iterator_t = decltype(ranges::begin(std::declval<_Range&>()));
-
-  template<range _Range>
-    using range_difference_t = iter_difference_t<iterator_t<_Range>>;
-
-  template<range _Range>
     constexpr range_difference_t<_Range>
     distance(_Range&& __r)
     {

libstdc++-v3/include/std/ranges

@@ -56,64 +56,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 namespace ranges
 {
   // [range.range] The range concept.
-  // Defined in <bits/range_iterator.h>
-  // template<typename> concept range;
-
-  template<range _Range>
-    using sentinel_t = decltype(ranges::end(std::declval<_Range&>()));
-
-  template<range _Range>
-    using range_value_t = iter_value_t<iterator_t<_Range>>;
-
-  template<range _Range>
-    using range_reference_t = iter_reference_t<iterator_t<_Range>>;
-
-  template<range _Range>
-    using range_rvalue_reference_t
-      = iter_rvalue_reference_t<iterator_t<_Range>>;
-
-  namespace __detail
-  {
-    template<typename _Tp>
-      concept __forwarding_range = range<_Tp> && __range_impl<_Tp>;
-  } // namespace __detail
-
   // [range.sized] The sized_range concept.
-  // Defined in <bits/range_iterator.h>
-  // template<typename> concept sized_range;
+  // Defined in <bits/range_access.h>
 
   // [range.refinements]
-
-  template<typename _Range, typename _Tp>
-    concept output_range
-      = range<_Range> && output_iterator<iterator_t<_Range>, _Tp>;
-
-  template<typename _Tp>
-    concept input_range = range<_Tp> && input_iterator<iterator_t<_Tp>>;
-
-  template<typename _Tp>
-    concept forward_range
-      = input_range<_Tp> && forward_iterator<iterator_t<_Tp>>;
-
-  template<typename _Tp>
-    concept bidirectional_range
-      = forward_range<_Tp> && bidirectional_iterator<iterator_t<_Tp>>;
-
-  template<typename _Tp>
-    concept random_access_range
-      = bidirectional_range<_Tp> && random_access_iterator<iterator_t<_Tp>>;
-
-  template<typename _Tp>
-    concept contiguous_range
-      = random_access_range<_Tp> && contiguous_iterator<iterator_t<_Tp>>
-      && requires(_Tp& __t)
-      {
-	{ ranges::data(__t) } -> same_as<add_pointer_t<range_reference_t<_Tp>>>;
-      };
-
-  template<typename _Tp>
-    concept common_range
-      = range<_Tp> && same_as<iterator_t<_Tp>, sentinel_t<_Tp>>;
+  // Defined in <bits/range_access.h>
 
   struct view_base { };
 

libstdc++-v3/include/std/type_traits

@@ -1475,6 +1475,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 #pragma GCC diagnostic pop
 
+  // helper trait for unique_ptr<T[]>, shared_ptr<T[]>, and span<T, N>
+  template<typename _ToElementType, typename _FromElementType>
+    using __is_array_convertible
+      = is_convertible<_FromElementType(*)[], _ToElementType(*)[]>;
+
   // is_nothrow_convertible for C++11
   template<typename _From, typename _To>
     struct __is_nothrow_convertible