libstdc++: Implement C++26 function_ref [PR119126]

This patch implements C++26 function_ref as specified in P0792R14,
with correction for constraints for constructor accepting nontype_t
parameter from LWG 4256.

As function_ref may store a pointer to the const object, __Ptrs::_M_obj is
changed to const void*, so again we do not cast away const from const
objects. To help with necessary casts, a __polyfunc::__cast_to helper is
added, that accepts reference to or target type direclty.

The _Invoker now defines additional call methods used by function_ref:
_S_ptrs() for invoking target passed by reference, and __S_nttp, _S_bind_ptr,
_S_bind_ref for handling constructors accepting nontype_t. The existing
_S_call_storage is changed to thin wrapper, that initialies _Ptrs, and forwards
to _S_call_ptrs.

This reduced the most uses of _Storage::_M_ptr and _Storage::_M_ref,
so this functions was removed, and _Manager uses were adjusted.

Finally we make function_ref available in freestanding mode, as
move_only_function and copyable_function are currently only available in hosted,
so we define _Manager and _Mo_base only if either __glibcxx_move_only_function
or __glibcxx_copyable_function is defined.

	PR libstdc++/119126

libstdc++-v3/ChangeLog:

	* doc/doxygen/stdheader.cc: Added funcref_impl.h file.
	* include/Makefile.am: Added funcref_impl.h file.
	* include/Makefile.in: Added funcref_impl.h file.
	* include/bits/funcref_impl.h: New file.
	* include/bits/funcwrap.h: (_Ptrs::_M_obj): Const-qualify.
	(_Storage::_M_ptr, _Storage::_M_ref): Remove.
	(__polyfunc::__cast_to) Define.
	(_Base_invoker::_S_ptrs, _Base_invoker::_S_nttp)
	(_Base_invoker::_S_bind_ptrs, _Base_invoker::_S_bind_ref)
	(_Base_invoker::_S_call_ptrs): Define.
	(_Base_invoker::_S_call_storage): Foward to _S_call_ptrs.
	(_Manager::_S_local, _Manager::_S_ptr): Adjust for _M_obj being
	const qualified.
	(__polyfunc::_Manager, __polyfunc::_Mo_base): Guard with
	__glibcxx_move_only_function || __glibcxx_copyable_function.
	(__polyfunc::__skip_first_arg, __polyfunc::__deduce_funcref)
	(std::function_ref) [__glibcxx_function_ref]: Define.
	* include/bits/utility.h (std::nontype_t, std::nontype)
	(__is_nontype_v) [__glibcxx_function_ref]: Define.
	* include/bits/version.def: Define function_ref.
	* include/bits/version.h: Regenerate.
	* include/std/functional: Define __cpp_lib_function_ref.
	* src/c++23/std.cc.in (std::nontype_t, std::nontype)
	(std::function_ref) [__cpp_lib_function_ref]: Export.
	* testsuite/20_util/function_ref/assign.cc: New test.
	* testsuite/20_util/function_ref/call.cc: New test.
	* testsuite/20_util/function_ref/cons.cc: New test.
	* testsuite/20_util/function_ref/cons_neg.cc: New test.
	* testsuite/20_util/function_ref/conv.cc: New test.
	* testsuite/20_util/function_ref/deduction.cc: New test.
	* testsuite/20_util/function_ref/mutation.cc: New test.

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

0 files changed, 0 insertions, 0 deletions