[libcxx] Implement C++20 std::chrono::is_clock, std::chrono::is_clock_v #160607
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@llvm/pr-subscribers-libcxx Author: Yuxuan Chen (yuxuanchen1997) ChangesImplemented [time.traits.is.clock] from P0355. Full diff: https://github.com/llvm/llvm-project/pull/160607.diff 5 Files Affected:
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index e050362abb658..210ea8be4a69d 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -261,6 +261,7 @@ set(files
__chrono/formatter.h
__chrono/gps_clock.h
__chrono/hh_mm_ss.h
+ __chrono/is_clock.h
__chrono/high_resolution_clock.h
__chrono/leap_second.h
__chrono/literals.h
diff --git a/libcxx/include/__chrono/is_clock.h b/libcxx/include/__chrono/is_clock.h
new file mode 100644
index 0000000000000..dc64c9eacd80b
--- /dev/null
+++ b/libcxx/include/__chrono/is_clock.h
@@ -0,0 +1,45 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___CHRONO_IS_CLOCK_H
+#define _LIBCPP___CHRONO_IS_CLOCK_H
+
+#include <__config>
+
+#if _LIBCPP_STD_VER >= 20
+
+# include <__type_traits/integral_constant.h>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace chrono {
+
+template <class>
+struct is_clock : std::false_type {};
+
+template <class _Tp>
+ requires requires {
+ typename _Tp::rep;
+ typename _Tp::period;
+ typename _Tp::duration;
+ typename _Tp::time_point;
+ _Tp::is_steady;
+ _Tp::now();
+ }
+struct is_clock<_Tp> : std::true_type {};
+
+template <class _Tp>
+_LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_clock_v = is_clock<_Tp>::value;
+
+} // namespace chrono
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER
+#endif // _LIBCPP___CHRONO_IS_CLOCK_H
diff --git a/libcxx/include/chrono b/libcxx/include/chrono
index 82e99a31bcc9f..f3bb08ef386c9 100644
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -1057,6 +1057,7 @@ constexpr chrono::year operator ""y(unsigned lo
# include <__chrono/day.h>
# include <__chrono/exception.h>
# include <__chrono/hh_mm_ss.h>
+# include <__chrono/is_clock.h>
# include <__chrono/literals.h>
# include <__chrono/local_info.h>
# include <__chrono/month.h>
diff --git a/libcxx/modules/std/chrono.inc b/libcxx/modules/std/chrono.inc
index 66eccd8d290ad..db405d482bf9e 100644
--- a/libcxx/modules/std/chrono.inc
+++ b/libcxx/modules/std/chrono.inc
@@ -25,8 +25,8 @@ export namespace std {
using std::chrono::duration_values;
- // using std::chrono::is_clock;
- // using std::chrono::is_clock_v;
+ using std::chrono::is_clock;
+ using std::chrono::is_clock_v;
// [time.duration.nonmember], duration arithmetic
using std::chrono::operator+;
diff --git a/libcxx/test/std/time/time.traits.is.clock/trait.is.clock.pass.cpp b/libcxx/test/std/time/time.traits.is.clock/trait.is.clock.pass.cpp
new file mode 100644
index 0000000000000..b15e91c48b0be
--- /dev/null
+++ b/libcxx/test/std/time/time.traits.is.clock/trait.is.clock.pass.cpp
@@ -0,0 +1,22 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++20
+
+#include <chrono>
+
+struct NotAClock {};
+
+int main(int, char**) {
+ static_assert(!std::chrono::is_clock_v<NotAClock>, "should not be treated as a clock");
+
+ static_assert(std::chrono::is_clock_v<std::chrono::system_clock>);
+ static_assert(std::chrono::is_clock_v<std::chrono::steady_clock>);
+ static_assert(std::chrono::is_clock_v<std::chrono::high_resolution_clock>);
+ return 0;
+}
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libcxx/test/std/time/time.traits.is.clock/trait.is.clock.compile.pass.cpp
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Would it make sense to create a sub-task to track this item in #99982? |
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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After some feedback, we decided to implement more checks based on the
The set of requirements for |
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frederick-vs-ja
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LGTM. CC @philnik777
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@H-G-Hristov I've just created the corresponding subtask. @yuxuanchen1997 I modified the PR description to associate this PR with the corresponding subtask. Please double-check. |
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libcxx/include/__chrono/is_clock.h
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| template <class _Tp> | ||
| _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_clock_v = requires { | ||
| typename _Tp::rep; | ||
| requires is_arithmetic_v<typename _Tp::rep>; |
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This seems wrong. Cpp17Clock requires the type to be "an arithmetic type or a class emulating an arithmetic type". I don't think "a class emulating an arithmetic type" is defined anywhere, but IMO we should rather be permissive here than strict.
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Can you clarify what a permissive outcome might be? Do we want to drop this requires? Or do we want a different check based on https://eel.is/c++draft/time.clock.req#:~:text=a%20class%20emulating%20an%20arithmetic%20type ?
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I guess at this moment we can use the following for simplicity. After all, we should submit an LWG issue for clarifying "class emulating an arithmetic type".
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| requires is_arithmetic_v<typename _Tp::rep>; | |
| requires is_arithmetic_v<typename _Tp::rep> || is_class_v<typename _Tp::rep> || is_union_v<typename _Tp::rep>; |
(Note that union types are also class types in the C++ core language.)
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I was informed by LWG that the issue has been long standing. I was advised, I quote, to "just write the code as though it's an arithmetic type, and if some program-defined class doesn't compile, then that class doesn't emulate an arithmetic type sufficiently closely."
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What do you mean by "informed by LWG"? Is there some issue about this?
libcxx/include/__chrono/is_clock.h
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| template <class _Rep, class _Period> | ||
| class duration; | ||
|
|
||
| template <class _Clock, class _Duration> | ||
| class time_point; |
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We shouldn't forward declare classes in random places. Either include the appropriate header or make a forward declaring header.
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I think we should introduce a forward declaring header here.
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Do you want them to be __fwd/duration.h or __fwd/__chrono/duration.h?
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@philnik777 @frederick-vs-ja I believe I have addressed all your comments. I am going to land this now. If anything doesn't work feel free to comment back. |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/186/builds/13770 Here is the relevant piece of the build log for the reference |
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@yuxuanchen1997 Please wait for approval next time, especially when changes have explicitly been requested. There is no need to rush patches in. |
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Sorry. There was an earlier acceptance and it was my oversight by treating your request to change as an earlier request. |
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…_v (llvm#160607) Implemented [[*time.traits.is.clock*]](https://eel.is/c++draft/time.traits.is.clock) from [P0355R7](https://wg21.link/p0355r7). This patch implements the C++20 feature `is_clock` and `is_clock_v` based on the documentation [on cppreference](https://en.cppreference.com/w/cpp/chrono/is_clock.html) Fixes llvm#166049.
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Implemented [time.traits.is.clock] from P0355R7.
This patch implements the C++20 feature
is_clockandis_clock_vbased on the documentation on cppreferenceFixes #166049.