libstdc++: Fix ref_view branch of views::as_const [PR119135]

Unlike for span<X> and empty_view<X>, the range_reference_t of
ref_view<X> doesn't correspond to X.  This patch fixes the ref_view
branch of views::as_const to correctly query its underlying range
type X.

	PR libstdc++/119135

libstdc++-v3/ChangeLog:

	* include/std/ranges: Include <utility>.
	(views::__detail::__is_ref_view): Replace with ...
	(views::__detail::__is_constable_ref_view): ... this.
	(views::_AsConst::operator()): Replace bogus use of element_type
	in the ref_view branch.
	* testsuite/std/ranges/adaptors/as_const/1.cc (test03): Extend
	test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index c2a2d6f4e05e8da3e70e2566b50cdb7f082b2862..ef277b81bd3c10344d1c74dbd36ecc23272c34b0 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -48,6 +48,7 @@
 #include <string_view>
 #include <tuple>
 #if __cplusplus > 202002L
+#include <utility>
 #include <variant>
 #endif
 #include <bits/ranges_util.h>
@@ -9324,10 +9325,11 @@ namespace views::__adaptor
     namespace __detail
     {
       template<typename _Tp>
-       inline constexpr bool __is_ref_view = false;
+       inline constexpr bool __is_constable_ref_view = false;
 
       template<typename _Range>
-       inline constexpr bool __is_ref_view<ref_view<_Range>> = true;
+       inline constexpr bool __is_constable_ref_view<ref_view<_Range>>
+         = constant_range<const _Range>;
 
       template<typename _Range>
        concept __can_as_const_view = requires { as_const_view(std::declval<_Range>()); };
@@ -9349,10 +9351,8 @@ namespace views::__adaptor
          return views::empty<const element_type>;
        else if constexpr (std::__detail::__is_span<_Tp>)
          return span<const element_type, _Tp::extent>(std::forward<_Range>(__r));
-       else if constexpr (__detail::__is_ref_view<_Tp>
-                          && constant_range<const element_type>)
-         return ref_view(static_cast<const element_type&>
-                         (std::forward<_Range>(__r).base()));
+       else if constexpr (__detail::__is_constable_ref_view<_Tp>)
+         return ref_view(std::as_const(std::forward<_Range>(__r).base()));
        else if constexpr (is_lvalue_reference_v<_Range>
                           && constant_range<const _Tp>
                           && !view<_Tp>)

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/as_const/1.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/as_const/1.cc
index c36786a8c5facdc8076e864f0214e819315a9e37..3f1f8eb17726cba9d09113630005cded671c72c0 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/as_const/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/as_const/1.cc
@@ -63,6 +63,10 @@ test03()
   std::vector<int> v;
   std::same_as<ranges::ref_view<const std::vector<int>>>
     auto r = views::as_const(v);
+
+  // PR libstdc++/119135
+  std::same_as<ranges::ref_view<const std::vector<int>>>
+    auto r2 = views::as_const(views::all(v));
 }
 
 int