[libc++] Implement file_clock::{to,from}_sys
This is part of https://wg21.link/P0355R7. I am adding these methods
to provide an alternative for the {from,to}_time_t methods that were
removed in https://llvm.org/D113027.
Differential Revision: https://reviews.llvm.org/D113430
GitOrigin-RevId: dce5fc56b6191ec63fd1d2bed7d3c815bacc49b7
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index 9ccb211..62e5a0c 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -80,7 +80,9 @@
- Removed the nonstandard methods ``std::chrono::file_clock::to_time_t`` and
``std::chrono::file_clock::from_time_t``; neither libstdc++ nor MSVC STL
- had such methods.
+ had such methods. Instead, in C++20, you can use ``std::chrono::file_clock::from_sys``
+ and ``std::chrono::file_clock::to_sys``, which are specified in the Standard.
+ If you are not using C++20, you should move to it.
- The declarations of functions ``declare_reachable``, ``undeclare_reachable``, ``declare_no_pointers``,
``undeclare_no_pointers``, and ``get_pointer_safety`` have been removed not only from C++2b but
diff --git a/include/chrono b/include/chrono
index ec510a9..f703d6c 100644
--- a/include/chrono
+++ b/include/chrono
@@ -276,7 +276,23 @@
using sys_seconds = sys_time<seconds>; // C++20
using sys_days = sys_time<days>; // C++20
-class file_clock; // C++20
+class file_clock // C++20
+{
+public:
+ typedef see-below rep;
+ typedef nano period;
+ typedef chrono::duration<rep, period> duration;
+ typedef chrono::time_point<file_clock> time_point;
+ static constexpr bool is_steady = false;
+
+ static time_point now() noexcept;
+
+ template<class Duration>
+ static sys_time<see-below> to_sys(const file_time<Duration>&);
+
+ template<class Duration>
+ static file_time<see-below> from_sys(const sys_time<Duration>&);
+};
template<class Duration>
using file_time = time_point<file_clock, Duration>; // C++20
@@ -2798,6 +2814,20 @@
static _LIBCPP_CONSTEXPR_AFTER_CXX11 const bool is_steady = false;
_LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_FUNC_VIS static time_point now() noexcept;
+
+#if _LIBCPP_STD_VER > 17
+ template <class _Duration>
+ _LIBCPP_HIDE_FROM_ABI
+ static chrono::sys_time<_Duration> to_sys(const chrono::file_time<_Duration>& __t) {
+ return chrono::sys_time<_Duration>(__t.time_since_epoch());
+ }
+
+ template <class _Duration>
+ _LIBCPP_HIDE_FROM_ABI
+ static chrono::file_time<_Duration> from_sys(const chrono::sys_time<_Duration>& __t) {
+ return chrono::file_time<_Duration>(__t.time_since_epoch());
+ }
+#endif // _LIBCPP_STD_VER > 17
};
_LIBCPP_END_NAMESPACE_FILESYSTEM
#endif // !_LIBCPP_CXX03_LANG
diff --git a/test/std/utilities/time/time.clock/time.clock.file/to_from_sys.pass.cpp b/test/std/utilities/time/time.clock/time.clock.file/to_from_sys.pass.cpp
new file mode 100644
index 0000000..d8fecd9
--- /dev/null
+++ b/test/std/utilities/time/time.clock/time.clock.file/to_from_sys.pass.cpp
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-has-no-filesystem-library
+
+// Filesystem is supported on Apple platforms starting with macosx10.15.
+// UNSUPPORTED: use_system_cxx_lib && target={{.+}}-apple-macosx10.{{9|10|11|12|13|14}}
+
+// TODO(ldionne): This test fails on Ubuntu Focal on our CI nodes (and only there), in 32 bit mode.
+// UNSUPPORTED: linux && 32bits-on-64bits
+
+// <chrono>
+//
+// file_clock
+//
+// template<class Duration>
+// static sys_time<see-below> to_sys(const file_time<Duration>&);
+//
+// template<class Duration>
+// static file_time<see-below> from_sys(const sys_time<Duration>&);
+
+#include <chrono>
+#include <cassert>
+
+int main(int, char**) {
+ // Test round-trip through the system clock, starting from file_clock::now()
+ {
+ std::chrono::file_clock::time_point const ft = std::chrono::file_clock::now();
+ auto st = std::chrono::file_clock::to_sys(ft);
+ assert(ft == std::chrono::file_clock::from_sys(st));
+ }
+
+ // Test round-trip through the system clock, starting from system_clock::now()
+ {
+ std::chrono::system_clock::time_point const st = std::chrono::system_clock::now();
+ auto ft = std::chrono::file_clock::from_sys(st);
+ assert(st == std::chrono::file_clock::to_sys(ft));
+ }
+
+ // Make sure the value we get is in the ballpark of something reasonable
+ {
+ std::chrono::file_clock::time_point const file_now = std::chrono::file_clock::now();
+ std::chrono::system_clock::time_point const sys_now = std::chrono::system_clock::now();
+ {
+ auto diff = sys_now - std::chrono::file_clock::to_sys(file_now);
+ assert(std::chrono::milliseconds(-500) < diff && diff < std::chrono::milliseconds(500));
+ }
+ {
+ auto diff = std::chrono::file_clock::from_sys(sys_now) - file_now;
+ assert(std::chrono::milliseconds(-500) < diff && diff < std::chrono::milliseconds(500));
+ }
+ }
+
+ // Make sure to_sys and from_sys are consistent with each other
+ {
+ std::chrono::file_clock::time_point const ft = std::chrono::file_clock::now();
+ std::chrono::system_clock::time_point const st = std::chrono::system_clock::now();
+ auto sys_diff = std::chrono::file_clock::to_sys(ft) - st;
+ auto file_diff = ft - std::chrono::file_clock::from_sys(st);
+ assert(sys_diff == file_diff);
+ }
+
+ return 0;
+}
