1 files changed, 44 insertions, 14 deletions

diff --git a/src/corelib/time/qdatetime.h b/src/corelib/time/qdatetime.h
index f8a9360fbb..77247dcd07 100644
--- a/src/corelib/time/qdatetime.h
+++ b/src/corelib/time/qdatetime.h
@@ -35,28 +35,28 @@ public:
 #if __cpp_lib_chrono >= 201907L || defined(Q_QDOC)
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     Q_IMPLICIT constexpr QDate(std::chrono::year_month_day date) noexcept
-        : jd(date.ok() ? stdSysDaysToJulianDay(date) : nullJd())
+        : jd(date.ok() ? stdSysDaysToJulianDay(date QT6_CALL_NEW_OVERLOAD_TAIL) : nullJd())
     {}
 
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     Q_IMPLICIT constexpr QDate(std::chrono::year_month_day_last date) noexcept
-        : jd(date.ok() ? stdSysDaysToJulianDay(date) : nullJd())
+        : jd(date.ok() ? stdSysDaysToJulianDay(date QT6_CALL_NEW_OVERLOAD_TAIL) : nullJd())
     {}
 
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     Q_IMPLICIT constexpr QDate(std::chrono::year_month_weekday date) noexcept
-        : jd(date.ok() ? stdSysDaysToJulianDay(date) : nullJd())
+        : jd(date.ok() ? stdSysDaysToJulianDay(date QT6_CALL_NEW_OVERLOAD_TAIL) : nullJd())
     {}
 
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     Q_IMPLICIT constexpr QDate(std::chrono::year_month_weekday_last date) noexcept
-        : jd(date.ok() ? stdSysDaysToJulianDay(date) : nullJd())
+        : jd(date.ok() ? stdSysDaysToJulianDay(date QT6_CALL_NEW_OVERLOAD_TAIL) : nullJd())
     {}
 
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     static constexpr QDate fromStdSysDays(const std::chrono::sys_days &days) noexcept
     {
-        return QDate(stdSysDaysToJulianDay(days));
+        return QDate(stdSysDaysToJulianDay(days QT6_CALL_NEW_OVERLOAD_TAIL));
     }
 
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
@@ -177,7 +177,9 @@ private:
     static constexpr inline qint64 unixEpochJd() { return Q_INT64_C(2440588); }
 
 #if __cpp_lib_chrono >= 201907L
-    static constexpr qint64 stdSysDaysToJulianDay(const std::chrono::sys_days &days) noexcept
+    QT_POST_CXX17_API_IN_EXPORTED_CLASS
+    static constexpr qint64
+    stdSysDaysToJulianDay(const std::chrono::sys_days &days QT6_DECL_NEW_OVERLOAD_TAIL) noexcept
     {
         const auto epochDays = days.time_since_epoch().count();
         // minJd() and maxJd() fit into 40 bits.
@@ -189,6 +191,13 @@ private:
         }
         return unixEpochJd() + epochDays;
     }
+
+#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
+    static constexpr qint64 stdSysDaysToJulianDay(const std::chrono::sys_days &days) noexcept
+    {
+        return stdSysDaysToJulianDay(days QT6_CALL_NEW_OVERLOAD_TAIL);
+    }
+#endif // QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
 #endif // __cpp_lib_chrono >= 201907L
 
     qint64 jd;
@@ -302,7 +311,7 @@ class Q_CORE_EXPORT QDateTime
         quintptr status : 8;
 #  endif
 #endif
-        friend constexpr bool operator==(const ShortData &lhs, const ShortData &rhs)
+        friend constexpr bool operator==(ShortData lhs, ShortData rhs)
         { return lhs.status == rhs.status && lhs.msecs == rhs.msecs; }
     };
 
@@ -499,8 +508,26 @@ public:
     NSDate *toNSDate() const Q_DECL_NS_RETURNS_AUTORELEASED;
 #endif
 
+    static QDateTime fromStdTimePoint(
+        std::chrono::time_point<
+            std::chrono::system_clock,
+            std::chrono::milliseconds
+        > time
+    );
+
 #if __cpp_lib_chrono >= 201907L || defined(Q_QDOC)
 #if __cpp_concepts >= 201907L || defined(Q_QDOC)
+private:
+    // The duration type of the result of a clock_cast<system_clock>.
+    // This duration may differ from the duration of the input.
+    template <typename Clock, typename Duration>
+    using system_clock_cast_duration = decltype(
+        std::chrono::clock_cast<std::chrono::system_clock>(
+            std::declval<const std::chrono::time_point<Clock, Duration> &>()
+        ).time_since_epoch()
+    );
+
+public:
     // Generic clock, as long as it's compatible with us (= system_clock)
     template <typename Clock, typename Duration>
     static QDateTime fromStdTimePoint(const std::chrono::time_point<Clock, Duration> &time)
@@ -508,14 +535,17 @@ public:
             requires(const std::chrono::time_point<Clock, Duration> &t) {
                 // the clock can be converted to system_clock
                 std::chrono::clock_cast<std::chrono::system_clock>(t);
-                // the duration can be converted to milliseconds
-                requires std::is_convertible_v<Duration, std::chrono::milliseconds>;
+                // after the conversion to system_clock, the duration type
+                // we get is convertible to milliseconds
+                requires std::is_convertible_v<
+                    system_clock_cast_duration<Clock, Duration>,
+                    std::chrono::milliseconds
+                >;
             }
     {
-        const auto sysTime = std::chrono::clock_cast<std::chrono::system_clock>(time);
-        // clock_cast can change the duration, so convert it again to milliseconds
-        const auto timeInMSec = std::chrono::time_point_cast<std::chrono::milliseconds>(sysTime);
-        return fromMSecsSinceEpoch(timeInMSec.time_since_epoch().count(), Qt::UTC);
+        using namespace std::chrono;
+        const sys_time<milliseconds> sysTime = clock_cast<system_clock>(time);
+        return fromStdTimePoint(sysTime);
     }
 #endif // __cpp_concepts
 
@@ -529,7 +559,7 @@ public:
     QT_POST_CXX17_API_IN_EXPORTED_CLASS
     static QDateTime fromStdLocalTime(const std::chrono::local_time<std::chrono::milliseconds> &time)
     {
-        QDateTime result(QDate(1970, 1, 1), QTime(0, 0, 0));
+        QDateTime result(QDate(1970, 1, 1), QTime(0, 0, 0), TransitionResolution::LegacyBehavior);
         return result.addMSecs(time.time_since_epoch().count());
     }