[PATCH] libstdc++/ranges: Define _S_has_simple_call_op on newer adaptors

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

-- >8 --

This compile-time and diagnostic improvement[1] is less important in
C++23 mode where deducing this is available and used in _Pipe, but for
benefit of C++20 mode and for consistency let's set the flag on the most
recently added range adaptors which lack it.

[1]: Defining _S_has_simple_call_op=true for a range adaptor closure
object signals that the adaptor has an operator() that's not overloaded
according to the constness/value category of the object, which in turn
allows us to implement the operator() of the composition of such adaptors
in a simpler way.

libstdc++-v3/ChangeLog:

        * include/std/ranges (views::_Adjacent::_S_has_simple_call_op):
        Define to true.
        (views::_AsRvalue::_S_has_simple_call_op): Likewise.
        (views::_Enumerate::_S_has_simple_call_op): Likewise.
        (views::_AsConst::_S_has_simple_call_op): Likewise.
---
 libstdc++-v3/include/std/ranges | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 7ef835f486a..66502cc1da4 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -5669,6 +5669,8 @@ namespace views::__adaptor
            else
              return adjacent_view<all_t<_Range>, 
_Nm>(std::forward<_Range>(__r));
          }
+
+       static constexpr bool _S_has_simple_call_op = true;
       };
 
     template<size_t _Nm>
@@ -8844,6 +8846,8 @@ namespace views::__adaptor
          else
            return as_rvalue_view(std::forward<_Range>(__r));
        }
+
+      static constexpr bool _S_has_simple_call_op = true;
     };
 
     inline constexpr _AsRvalue as_rvalue;
@@ -9147,6 +9151,8 @@ namespace views::__adaptor
        constexpr auto
        operator() [[nodiscard]] (_Range&& __r) const
        { return enumerate_view<all_t<_Range>>(std::forward<_Range>(__r)); }
+
+      static constexpr bool _S_has_simple_call_op = true;
     };
 
     inline constexpr _Enumerate enumerate;
@@ -9253,6 +9259,8 @@ namespace views::__adaptor
        else
          return as_const_view(std::forward<_Range>(__r));
       }
+
+      static constexpr bool _S_has_simple_call_op = true;
     };
 
     inline constexpr _AsConst as_const;
-- 
2.43.0.367.g186b115d30