[gcc r14-7219] libstdc++: Use C++23 deducing this in std::bind_front

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:3e1ffa7dd111374a5e277b71269f9b6e10b3ec57

commit r14-7219-g3e1ffa7dd111374a5e277b71269f9b6e10b3ec57
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jan 12 22:55:43 2024 -0500

    libstdc++: Use C++23 deducing this in std::bind_front
    
    This simplifies the operator() of _Bind_front using C++23 deducing
    this, allowing us to condense multiple operator() overloads into one.
    
    In passing I think we can remove _Bind_front's defaulted special member
    declarations and just let the compiler implicitly generate them for us.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/functional (_Bind_front): Remove =default special
            member function declarations.
            (_Bind_front::operator()): Implement using C++23 deducing this
            when available.
            * testsuite/20_util/function_objects/bind_front/111327.cc:
            Adjust testcase to expect better errors in C++23 mode.

Diff:
---
 libstdc++-v3/include/std/functional                   | 19 +++++++++++++------
 .../20_util/function_objects/bind_front/111327.cc     | 14 ++++++++------
 2 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index 8d50a730889..fcfd2df7957 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -934,12 +934,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  _M_bound_args(std::forward<_Args>(__args)...)
 	{ static_assert(sizeof...(_Args) == sizeof...(_BoundArgs)); }
 
-      _Bind_front(const _Bind_front&) = default;
-      _Bind_front(_Bind_front&&) = default;
-      _Bind_front& operator=(const _Bind_front&) = default;
-      _Bind_front& operator=(_Bind_front&&) = default;
-      ~_Bind_front() = default;
-
+#if __cpp_explicit_this_parameter
+      template<typename _Self, typename... _CallArgs>
+	constexpr
+	invoke_result_t<__like_t<_Self, _Fd>, __like_t<_Self, _BoundArgs>..., _CallArgs...>
+	operator()(this _Self&& __self, _CallArgs&&... __call_args)
+	noexcept(is_nothrow_invocable_v<__like_t<_Self, _Fd>,
+					__like_t<_Self, _BoundArgs>..., _CallArgs...>)
+	{
+	  return _S_call(std::forward<_Self>(__self), _BoundIndices(),
+			 std::forward<_CallArgs>(__call_args)...);
+	}
+#else
       template<typename... _CallArgs>
 	requires true
 	constexpr
@@ -997,6 +1003,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename... _CallArgs>
 	void operator()(_CallArgs&&...) const && = delete;
+#endif
 
     private:
       using _BoundIndices = index_sequence_for<_BoundArgs...>;
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
index 43b56ca4378..5fe0a83baec 100644
--- a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
+++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/111327.cc
@@ -17,24 +17,26 @@ struct G {
 
 int main() {
   auto f0 = std::bind_front(F{});
-  f0(); // { dg-error "deleted" }
+  f0(); // { dg-error "deleted|no match" }
   std::move(f0)();
   std::as_const(f0)();
   std::move(std::as_const(f0))();
 
   auto g0 = std::bind_front(G{});
-  g0(); // { dg-error "deleted" }
-  std::move(g0)(); // { dg-error "deleted" }
+  g0(); // { dg-error "deleted|no match" }
+  std::move(g0)(); // { dg-error "deleted|no match" }
   std::move(std::as_const(g0))();
 
   auto f1 = std::bind_front(F{}, 42);
-  f1(); // { dg-error "deleted" }
+  f1(); // { dg-error "deleted|no match" }
   std::move(f1)();
   std::as_const(f1)();
   std::move(std::as_const(f1))();
 
   auto g1 = std::bind_front(G{}, 42);
-  g1(); // { dg-error "deleted" }
-  std::move(g1)(); // { dg-error "deleted" }
+  g1(); // { dg-error "deleted|no match" }
+  std::move(g1)(); // { dg-error "deleted|no match" }
   std::move(std::as_const(g1))();
 }
+
+// { dg-error "no type named 'type' in 'struct std::invoke_result" "" { target c++23 } 0 }