Remove unnecessary QDateTime::detach() function

Last commit changed QDateTime::d to be a QSharedDataPointer that
implicitly detaches on non-const operator->() calls. That means we no
longer need to explicitly call detach().

More than that, we should not do it, so we avoid checking the ref count
and try to detach on every use. To do that, in functions where the d
pointer was accessed more than once, I detach at the top and shadow the
"d" variable with a local plain pointer. We don't compile our sources
with -Wshadow, so this should not be a problem.

Change-Id: Ic5d393bfd36e48a193fcffff13b969c281c36d0c
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

src/corelib/tools/qdatetime.cpp

@@ -3237,7 +3237,6 @@ bool QDateTime::isDaylightTime() const
 
 void QDateTime::setDate(const QDate &date)
 {
-    detach();
     d->setDateTime(date, time());
 }
 
@@ -3256,7 +3255,6 @@ void QDateTime::setDate(const QDate &date)
 
 void QDateTime::setTime(const QTime &time)
 {
-    detach();
     d->setDateTime(date(), time);
 }
 
@@ -3278,7 +3276,7 @@ void QDateTime::setTime(const QTime &time)
 
 void QDateTime::setTimeSpec(Qt::TimeSpec spec)
 {
-    detach();
+    QDateTimePrivate *d = this->d.data(); // detaches (and shadows d)
     d->setTimeSpec(spec, 0);
     d->checkValidDateTime();
 }
@@ -3300,7 +3298,7 @@ void QDateTime::setTimeSpec(Qt::TimeSpec spec)
 
 void QDateTime::setOffsetFromUtc(int offsetSeconds)
 {
-    detach();
+    QDateTimePrivate *d = this->d.data(); // detaches (and shadows d)
     d->setTimeSpec(Qt::OffsetFromUTC, offsetSeconds);
     d->checkValidDateTime();
 }
@@ -3319,7 +3317,7 @@ void QDateTime::setOffsetFromUtc(int offsetSeconds)
 
 void QDateTime::setTimeZone(const QTimeZone &toZone)
 {
-    detach();
+    QDateTimePrivate *d = this->d.data(); // detaches (and shadows d)
     d->m_spec = Qt::TimeZone;
     d->m_offsetFromUtc = 0;
     d->m_timeZone = toZone;
@@ -3395,7 +3393,7 @@ uint QDateTime::toTime_t() const
 */
 void QDateTime::setMSecsSinceEpoch(qint64 msecs)
 {
-    detach();
+    QDateTimePrivate *d = this->d.data(); // detaches (and shadows d)
 
     d->m_status = 0;
     switch (d->m_spec) {
@@ -3669,7 +3667,6 @@ QString QDateTime::toString(const QString& format) const
 QDateTime QDateTime::addDays(qint64 ndays) const
 {
     QDateTime dt(*this);
-    dt.detach();
     QPair<QDate, QTime> p = d->getDateTime();
     QDate &date = p.first;
     QTime &time = p.second;
@@ -3705,7 +3702,6 @@ QDateTime QDateTime::addDays(qint64 ndays) const
 QDateTime QDateTime::addMonths(int nmonths) const
 {
     QDateTime dt(*this);
-    dt.detach();
     QPair<QDate, QTime> p = d->getDateTime();
     QDate &date = p.first;
     QTime &time = p.second;
@@ -3741,7 +3737,6 @@ QDateTime QDateTime::addMonths(int nmonths) const
 QDateTime QDateTime::addYears(int nyears) const
 {
     QDateTime dt(*this);
-    dt.detach();
     QPair<QDate, QTime> p = d->getDateTime();
     QDate &date = p.first;
     QTime &time = p.second;
@@ -3790,7 +3785,6 @@ QDateTime QDateTime::addMSecs(qint64 msecs) const
         return QDateTime();
 
     QDateTime dt(*this);
-    dt.detach();
     if (d->m_spec == Qt::LocalTime || d->m_spec == Qt::TimeZone)
         // Convert to real UTC first in case crosses daylight transition
         dt.setMSecsSinceEpoch(d->toMSecsSinceEpoch() + msecs);
@@ -4267,7 +4261,6 @@ QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs)
 QDateTime QDateTime::fromMSecsSinceEpoch(qint64 msecs, Qt::TimeSpec spec, int offsetSeconds)
 {
     QDateTime dt;
-    dt.detach();
     dt.d->setTimeSpec(spec, offsetSeconds);
     dt.setMSecsSinceEpoch(msecs);
     return dt;
@@ -4687,14 +4680,6 @@ QDateTime QDateTime::fromString(const QString &string, const QString &format)
     \sa toTimeSpec()
 */
 
-/*!
-    \internal
- */
-void QDateTime::detach()
-{
-    d.detach();
-}
-
 /*****************************************************************************
   Date/time stream functions
  *****************************************************************************/
@@ -4846,8 +4831,6 @@ QDataStream &operator<<(QDataStream &out, const QDateTime &dateTime)
 
 QDataStream &operator>>(QDataStream &in, QDateTime &dateTime)
 {
-    dateTime.detach();
-
     QDate dt;
     QTime tm;
     qint8 ts = 0;

src/corelib/tools/qdatetime.h

@@ -321,7 +321,6 @@ public:
 
 private:
     friend class QDateTimePrivate;
-    void detach();
 
     // ### Qt6: Using a private here has high impact on runtime
     // on users such as QFileInfo. In Qt 6, the data members