QDate(Time): add a addDuration method

To complement the existing addSecs / MSecs / etc., add a function
that takes any compatible std::chrono::duration.

QTime also features similar functions, but it's also "unique" in that
it uses modular arithmetic (it wraps around in case of "overflow").
I'm not so sure that adding durations to a QTime object therefore
makes sense, and I'm not doing it in this patch.

[ChangeLog][QtCore][QDate] Added addDuration().
[ChangeLog][QtCore][QDateTime] Added addDuration().

Change-Id: I02aa37ff024d7f56fa976dc8f4f73523bdba8d94
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/time/qdatetime.cpp

@@ -1284,6 +1284,28 @@ QDate QDate::addDays(qint64 ndays) const
         return fromJulianDay(r);
 }
 
+/*!
+    \fn QDate QDate::addDuration(std::chrono::days ndays) const
+
+    \since 6.4
+
+    Returns a QDate object containing a date \a ndays later than the
+    date of this object (or earlier if \a ndays is negative).
+
+    Returns a null date if the current date is invalid or the new date is
+    out of range.
+
+    \note Adding durations expressed in \c{std::chrono::months} or
+    \c{std::chrono::years} does not yield the same result obtained by using
+    addMonths() or addYears(). The former are fixed durations, calculated in
+    relation to the solar year; the latter use the Gregorian calendar definitions
+    of months/years.
+
+    \note This function requires C++20.
+
+    \sa addMonths(), addYears(), daysTo()
+*/
+
 /*!
     Returns a QDate object containing a date \a nmonths later than the
     date of this object (or earlier if \a nmonths is negative).
@@ -4605,6 +4627,26 @@ QDateTime QDateTime::addMSecs(qint64 msecs) const
     return dt;
 }
 
+/*!
+    \fn QDateTime QDateTime::addDuration(std::chrono::milliseconds msecs) const
+
+    \since 6.4
+
+    Returns a QDateTime object containing a datetime \a msecs milliseconds
+    later than the datetime of this object (or earlier if \a msecs is
+    negative).
+
+    If this datetime is invalid, an invalid datetime will be returned.
+
+    \note Adding durations expressed in \c{std::chrono::months} or
+    \c{std::chrono::years} does not yield the same result obtained by using
+    addMonths() or addYears(). The former are fixed durations, calculated in
+    relation to the solar year; the latter use the Gregorian calendar definitions
+    of months/years.
+
+    \sa addMSecs(), msecsTo(), addDays(), addMonths(), addYears()
+*/
+
 /*!
     Returns the number of days from this datetime to the \a other
     datetime. The number of days is counted as the number of times

src/corelib/time/qdatetime.h

@@ -162,6 +162,13 @@ public:
     void getDate(int *year, int *month, int *day) const;
 
     [[nodiscard]] QDate addDays(qint64 days) const;
+#if __cpp_lib_chrono >= 201907L || defined(Q_QDOC)
+    QT_POST_CXX17_API_IN_EXPORTED_CLASS
+    [[nodiscard]] QDate addDuration(std::chrono::days days) const
+    {
+        return addDays(days.count());
+    }
+#endif
     // Gregorian-optimized:
     [[nodiscard]] QDate addMonths(int months) const;
     [[nodiscard]] QDate addYears(int years) const;
@@ -387,6 +394,10 @@ public:
     [[nodiscard]] QDateTime addYears(int years) const;
     [[nodiscard]] QDateTime addSecs(qint64 secs) const;
     [[nodiscard]] QDateTime addMSecs(qint64 msecs) const;
+    [[nodiscard]] QDateTime addDuration(std::chrono::milliseconds msecs) const
+    {
+        return addMSecs(msecs.count());
+    }
 
     QDateTime toTimeSpec(Qt::TimeSpec spec) const;
     inline QDateTime toLocalTime() const { return toTimeSpec(Qt::LocalTime); }

tests/auto/corelib/time/qdate/tst_qdate.cpp

@@ -767,11 +767,19 @@ void tst_QDate::addDays()
     QFETCH( int, expectedDay );
 
     QDate dt( year, month, day );
-    dt = dt.addDays( amountToAdd );
+    QDate dt2 = dt.addDays( amountToAdd );
 
-    QCOMPARE( dt.year(), expectedYear );
-    QCOMPARE( dt.month(), expectedMonth );
-    QCOMPARE( dt.day(), expectedDay );
+    QCOMPARE( dt2.year(), expectedYear );
+    QCOMPARE( dt2.month(), expectedMonth );
+    QCOMPARE( dt2.day(), expectedDay );
+
+#if __cpp_lib_chrono >= 201907L
+    QDate dt3 = dt.addDuration( std::chrono::days( amountToAdd ) );
+
+    QCOMPARE( dt3.year(), expectedYear );
+    QCOMPARE( dt3.month(), expectedMonth );
+    QCOMPARE( dt3.day(), expectedDay );
+#endif
 }
 
 void tst_QDate::addDays_data()

tests/auto/corelib/time/qdatetime/tst_qdatetime.cpp

@@ -1524,16 +1524,21 @@ void tst_QDateTime::addMSecs()
     QFETCH(const qint64, nsecs);
     QFETCH(const QDateTime, result);
 
-    QDateTime test = dt.addMSecs(qint64(nsecs) * 1000);
-    if (!result.isValid()) {
-        QVERIFY(!test.isValid());
-    } else {
-        QCOMPARE(test, result);
-        QCOMPARE(test.timeSpec(), dt.timeSpec());
-        if (test.timeSpec() == Qt::OffsetFromUTC)
-            QCOMPARE(test.offsetFromUtc(), dt.offsetFromUtc());
-        QCOMPARE(result.addMSecs(qint64(-nsecs) * 1000), dt);
-    }
+    const auto verify = [&](const QDateTime &test) {
+        if (!result.isValid()) {
+            QVERIFY(!test.isValid());
+        } else {
+            QCOMPARE(test, result);
+            QCOMPARE(test.timeSpec(), dt.timeSpec());
+            if (test.timeSpec() == Qt::OffsetFromUTC)
+                QCOMPARE(test.offsetFromUtc(), dt.offsetFromUtc());
+            QCOMPARE(result.addMSecs(qint64(-nsecs) * 1000), dt);
+        }
+    };
+
+    verify(dt.addMSecs(qint64(nsecs) * 1000));
+    verify(dt.addDuration(std::chrono::seconds(nsecs)));
+    verify(dt.addDuration(std::chrono::milliseconds(nsecs * 1000)));
 }
 
 void tst_QDateTime::toTimeSpec_data()