q20: add C++20 chrono days/weeks/months/years

Change-Id: Ie2a167cbe6672694e15b7810daf7fad3fe0656a1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/CMakeLists.txt

@@ -99,6 +99,7 @@ qt_internal_add_module(Core
         ${core_version_tagging_files}
         global/qvolatile_p.h
         global/q20algorithm.h
+        global/q20chrono.h
         global/q20functional.h
         global/q20iterator.h
         global/q20memory.h

src/corelib/global/q20chrono.h

@@ -0,0 +1,62 @@
+// Copyright (C) 2023 Ahmad Samir <a.samirh78@gmail.com>
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef Q20CHRONO_H
+#define Q20CHRONO_H
+
+#include <QtCore/qtconfigmacros.h>
+
+#include <chrono>
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. Types and functions defined in this
+// file can reliably be replaced by their std counterparts, once available.
+// You may use these definitions in your own code, but be aware that we
+// will remove them once Qt depends on the C++ version that supports
+// them in namespace std. There will be NO deprecation warning, the
+// definitions will JUST go away.
+//
+// If you can't agree to these terms, don't use these definitions!
+//
+// We mean it.
+//
+
+QT_BEGIN_NAMESPACE
+
+namespace q20 {
+namespace chrono {
+
+#if defined(__GLIBCXX__)
+// https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=libstdc%2B%2B-v3/include/bits/chrono.h
+using IntRep = int64_t;
+#else
+// https://github.com/llvm/llvm-project/blob/main/libcxx/include/__chrono/duration.h
+// https://github.com/microsoft/STL/blob/main/stl/inc/__msvc_chrono.hpp
+using IntRep = int;
+#endif
+
+#if __cpp_lib_chrono >= 201611L && __cplusplus > 201703L
+using std::chrono::days;
+using std::chrono::weeks;
+using std::chrono::years;
+using std::chrono::months;
+
+static_assert(std::is_same_v<days::rep, IntRep>);
+static_assert(std::is_same_v<weeks::rep, IntRep>);
+static_assert(std::is_same_v<years::rep, IntRep>);
+static_assert(std::is_same_v<months::rep, IntRep>);
+#else // __cpp_lib_chrono >= 201907L
+using days = std::chrono::duration<IntRep, std::ratio<86400>>;
+using weeks = std::chrono::duration<IntRep, std::ratio_multiply<std::ratio<7>, days::period>>;
+using years = std::chrono::duration<IntRep, std::ratio_multiply<std::ratio<146097, 400>, days::period>>;
+using months = std::chrono::duration<IntRep, std::ratio_divide<years::period, std::ratio<12>>>;
+#endif // __cpp_lib_chrono >= 201611L
+} // namespace chrono
+} // namespace q20
+
+QT_END_NAMESPACE
+
+#endif /* Q20CHRONO_H */