libstdc++: Define and use chrono::is_clock for C++20

For C++20 the wait_until members of mutexes and condition variables are
required to be ill-formed if given a clock that doesn't meet the
requirements for a clock type. To implement that requirement this patch
adds static assertions using the chrono::is_clock trait, and defines
that trait.

To avoid expensive checks for the common cases, the trait (and
associated variable template) are explicitly specialized for the
standard clock types.

This also moves the filesystem::__file_clock type from <filesystem> to
<chrono>, so that chrono::file_clock and chrono::file_time can be
defined in <chrono> as required.

	* include/bits/fs_fwd.h (filesystem::__file_clock): Move to ...
	* include/std/chrono (filesystem::__file_clock): Here.
	(filesystem::__file_clock::from_sys, filesystem::__file_clock::to_sys):
	Define public member functions for C++20.
	(is_clock, is_clock_v): Define traits for C++20.
	* include/std/condition_variable (condition_variable::wait_until): Add
	check for valid clock.
	* include/std/future (_State_baseV2::wait_until): Likewise.
	* include/std/mutex (__timed_mutex_impl::_M_try_lock_until): Likewise.
	* include/std/shared_mutex (shared_timed_mutex::try_lock_shared_until):
	Likewise.
	* include/std/thread (this_thread::sleep_until): Likewise.
	* testsuite/30_threads/condition_variable/members/2.cc: Qualify
	slow_clock with new namespace.
	* testsuite/30_threads/condition_variable/members/clock_neg.cc: New
	test.
	* testsuite/30_threads/condition_variable_any/members/clock_neg.cc:
	New test.
	* testsuite/30_threads/future/members/clock_neg.cc: New test.
	* testsuite/30_threads/recursive_timed_mutex/try_lock_until/3.cc:
	Qualify slow_clock with new namespace.
	* testsuite/30_threads/recursive_timed_mutex/try_lock_until/
	clock_neg.cc: New test.
	* testsuite/30_threads/shared_future/members/clock_neg.cc: New
	test.
	* testsuite/30_threads/shared_lock/locking/clock_neg.cc: New test.
	* testsuite/30_threads/shared_timed_mutex/try_lock_until/clock_neg.cc:
	New test.
	* testsuite/30_threads/timed_mutex/try_lock_until/3.cc: Qualify
	slow_clock with new namespace.
	* testsuite/30_threads/timed_mutex/try_lock_until/4.cc: Likewise.
	* testsuite/30_threads/timed_mutex/try_lock_until/clock_neg.cc: New
	test.
	* testsuite/30_threads/unique_lock/locking/clock_neg.cc: New test.
	* testsuite/std/time/traits/is_clock.cc: New test.
	* testsuite/util/slow_clock.h (slow_clock): Move to __gnu_test
	namespace.

1 files changed, 3 insertions, 0 deletions

diff --git a/libstdc++-v3/include/std/condition_variable b/libstdc++-v3/include/std/condition_variable
index 5e98d1b..cc7f99f 100644
--- a/libstdc++-v3/include/std/condition_variable
+++ b/libstdc++-v3/include/std/condition_variable
@@ -131,6 +131,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       wait_until(unique_lock<mutex>& __lock,
 		 const chrono::time_point<_Clock, _Duration>& __atime)
       {
+#if __cplusplus > 201703L
+	static_assert(chrono::is_clock_v<_Clock>);
+#endif
 	const typename _Clock::time_point __c_entry = _Clock::now();
 	const __clock_t::time_point __s_entry = __clock_t::now();
 	const auto __delta = __atime - __c_entry;