Fix #4507: LWG-4053 Unary call to std::views::repeat does not decay the argument (#4685)

Author: Andor233

stl/inc/ranges

@@ -1708,8 +1708,8 @@ namespace ranges {
         }
     };
 
-    template <class _Ty, class _Bo>
-    repeat_view(_Ty, _Bo) -> repeat_view<_Ty, _Bo>;
+    template <class _Ty, class _Bo = unreachable_sentinel_t>
+    repeat_view(_Ty, _Bo = _Bo()) -> repeat_view<_Ty, _Bo>;
 
     namespace views {
         struct _Repeat_fn {

tests/std/tests/P2474R2_views_repeat/test.cpp

@@ -360,6 +360,16 @@ constexpr bool test() {
     test_iterator_arithmetic<wchar_t>();
     test_iterator_arithmetic<_Signed128>();
 
+    // GH-4507: LWG-4053 Unary call to std::views::repeat does not decay the argument
+    {
+        using RPV = ranges::repeat_view<const char*>;
+
+        static_assert(same_as<decltype(views::repeat("foo", unreachable_sentinel)), RPV>);
+        static_assert(same_as<decltype(views::repeat(+"foo", unreachable_sentinel)), RPV>);
+        static_assert(same_as<decltype(views::repeat("foo")), RPV>);
+        static_assert(same_as<decltype(views::repeat(+"foo")), RPV>);
+    }
+
     return true;
 }