The presence of a template-head on this constructor is a copy & paste
error from the primary template.

libstdc++-v3/ChangeLog:

	PR libstdc++/109182
	* include/std/expected (expected<void>::expected(in_place_t)):
	Remove template-head.

libstdc++-v3/ChangeLog:

	PR libstdc++/108413
	* include/c_compatibility/stdatomic.h: Change copyright line to
	be consistent with other headers contributed under DCO terms.
	* include/std/expected: Add full stop to copyright line.
	* src/c++20/tzdb.cc: Likewise.

This was approved for C++23 last month in Kona.

libstdc++-v3/ChangeLog:

	* include/std/expected (expected): Add monadic operations.
	(expected<void, E>): Likewise.
	* include/std/version (__cpp_lib_expected): Bump value.
	* testsuite/20_util/expected/synopsis.cc: Adjust expected macro
	value.
	* testsuite/20_util/expected/version.cc: Likewise.
	* testsuite/20_util/expected/illformed_neg.cc: Prune additional
	errors from ill-formed monadic operations.
	* testsuite/20_util/expected/observers.cc: Check error_or.
	* testsuite/20_util/expected/monadic.cc: New test.

This fixes some bugs in the swap functions for std::expected.

It also disables the noexcept-specifiers for equality operators, because
those are problematic when querying whether a std::expected is equality
comparable. The operator==(const expected<T,E>&, const U&) function is
not constrained, so is viable for comparing expected<T,E> with
expected<void,G>, but then we get an error from the noexcept-specifier.

libstdc++-v3/ChangeLog:

	* include/std/expected (expected::_M_swap_val_unex): Guard the
	correct object.
	(expected::swap): Move is_swappable
	requirement from static_assert to constraint.
	(swap): Likewise.
	(operator==): Remove noexcept-specifier.
	* testsuite/20_util/expected/swap.cc: Check swapping of
	types without non-throwing move constructor. Check constraints
	on swap.
	* testsuite/20_util/expected/unexpected.cc: Check constraints on
	swap.
	* testsuite/20_util/expected/equality.cc: New test.

Hui Xie pointed out that we don't need a dummy member in the union,
because all constructors always initialize either _M_val or _M_unex.

We still need the _M_void member of the expected<void, E>
specialization, because the constructor has to initialize something when
not using the _M_unex member.

libstdc++-v3/ChangeLog:

	* include/std/expected (expected::_M_invalid): Remove.

The P2549R1 paper was accepted for C++23. I already implemented it for
our <expected>, but I didn't rename the private daata members, only the
public member functions. This renames the data members for consistency
with the working draft.

libstdc++-v3/ChangeLog:

	* include/std/expected (unexpected::_M_val): Rename to _M_unex.
	(bad_expected_access::_M_val): Likewise.

libstdc++-v3/ChangeLog:

	PR libstdc++/105153
	* include/std/expected
	(expected<void,E>::expected(expected<U,G>&&)): Fix constraints.
	* testsuite/20_util/expected/cons.cc: Check constructor.

libstdc++-v3/ChangeLog:

	PR libstdc++/105154
	* include/std/expected (expected<void, E>::swap): Set
	_M_has_value to false for objects that previously had a value.
	* testsuite/20_util/expected/swap.cc: Fix test to check void
	specialization.

libstdc++-v3/ChangeLog:

	PR libstdc++/105146
	* include/std/expected (bad_expected_access): Move constructor
	parameter.
	* testsuite/20_util/expected/bad.cc: New test.

Because this adds a new class template called std::unexpected, we have
to stop declaring the std::unexpected() function (which was deprecated
in C++11 and removed in C++17).

libstdc++-v3/ChangeLog:

	* doc/doxygen/user.cfg.in: Add new header.
	* include/Makefile.am: Likewise.
	* include/Makefile.in: Regenerate.
	* include/precompiled/stdc++.h: Add new header.
	* include/std/version (__cpp_lib_expected): Define.
	* libsupc++/exception [__cplusplus > 202002] (unexpected)
	(unexpected_handler, set_unexpected): Do not declare for C++23.
	* include/std/expected: New file.
	* testsuite/20_util/expected/assign.cc: New test.
	* testsuite/20_util/expected/cons.cc: New test.
	* testsuite/20_util/expected/illformed_neg.cc: New test.
	* testsuite/20_util/expected/observers.cc: New test.
	* testsuite/20_util/expected/requirements.cc: New test.
	* testsuite/20_util/expected/swap.cc: New test.
	* testsuite/20_util/expected/synopsis.cc: New test.
	* testsuite/20_util/expected/unexpected.cc: New test.
	* testsuite/20_util/expected/version.cc: New test.