QStyleSheet: never treat styled scrollbars as transient

If a style sheet is applied to a scrollbar, then we cannot treat it as
transient, as the QStyleSheetStyle doesn't implement any fade-in/out
animation logic. And we also need to set the overlap to 0 (in both
the style sheet and the macOS style) if the scrollbars are not
transient; otherwise the opaque scrollbar will be placed on top of the
content.

Since a style sheet might only apply to a scrollbar based on its
orientation, we also have to pass the style option through to all calls
of the styleHint function.

And since that function is also called from other QStyle implementations
in the macOS style, we have to make sure that we call styleHint() on the
widget's style to get the correct value based on the style sheet.

Fixes: QTBUG-63381
Change-Id: Ic67ce3a7cb5089f885dabfd5a1951e3029915446
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit f5105ea89a76d6051f058834d99385582cc61f85)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

4 files changed, 42 insertions, 20 deletions

diff --git a/src/plugins/styles/mac/qmacstyle_mac.mm b/src/plugins/styles/mac/qmacstyle_mac.mm
index af28ff5f98..7bce1e3454 100644
--- a/src/plugins/styles/mac/qmacstyle_mac.mm
+++ b/src/plugins/styles/mac/qmacstyle_mac.mm
@@ -2589,10 +2589,13 @@ int QMacStyle::pixelMetric(PixelMetric metric, const QStyleOption *opt, const QW
     case PM_ToolBarFrameWidth:
         ret = 1;
         break;
-    case PM_ScrollView_ScrollBarOverlap:
-        ret = [NSScroller preferredScrollerStyle] == NSScrollerStyleOverlay ?
-               pixelMetric(PM_ScrollBarExtent, opt, widget) : 0;
+    case PM_ScrollView_ScrollBarOverlap: {
+        const QStyle *realStyle = widget ? widget->style() : proxy();
+        ret = realStyle->styleHint(SH_ScrollBar_Transient, opt, widget)
+            ? realStyle->pixelMetric(PM_ScrollBarExtent, opt, widget)
+            : 0;
         break;
+    }
     default:
         ret = QCommonStyle::pixelMetric(metric, opt, widget);
         break;
@@ -5256,7 +5259,8 @@ void QMacStyle::drawComplexControl(ComplexControl cc, const QStyleOptionComplex
             const auto cocoaSize = d->effectiveAquaSizeConstrain(opt, widget);
             const CGFloat maxExpandScale = expandedKnobWidths[cocoaSize] / knobWidths[cocoaSize];
 
-            const bool isTransient = proxy()->styleHint(SH_ScrollBar_Transient, opt, widget);
+            const QStyle *realStyle = widget ? widget->style() : proxy();
+            const bool isTransient = realStyle->styleHint(SH_ScrollBar_Transient, opt, widget);
             if (!isTransient)
                 d->stopAnimation(opt->styleObject);
             bool wasActive = false;
diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index a2730d3817..97b4f0d5f9 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -5111,7 +5111,7 @@ int QStyleSheetStyle::pixelMetric(PixelMetric m, const QStyleOption *opt, const
         break;
 
     case PM_ScrollView_ScrollBarOverlap:
-        if (!rule.hasNativeBorder() || rule.hasBox())
+        if (!proxy()->styleHint(SH_ScrollBar_Transient, opt, w))
             return 0;
         break;
 #endif // QT_CONFIG(scrollbar)
@@ -5722,7 +5722,7 @@ int QStyleSheetStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWi
         case SH_TitleBar_ShowToolTipsOnButtons: s = QLatin1String("titlebar-show-tooltips-on-buttons"); break;
         case SH_Widget_Animation_Duration: s = QLatin1String("widget-animation-duration"); break;
         case SH_ScrollBar_Transient:
-            if (!rule.hasNativeBorder() || rule.hasBox())
+            if (!rule.hasNativeBorder() || rule.hasBox() || rule.hasDrawable())
                 return 0;
             break;
         default: break;
diff --git a/src/widgets/widgets/qabstractscrollarea.cpp b/src/widgets/widgets/qabstractscrollarea.cpp
index 842a94d194..932c15435d 100644
--- a/src/widgets/widgets/qabstractscrollarea.cpp
+++ b/src/widgets/widgets/qabstractscrollarea.cpp
@@ -329,22 +329,25 @@ void QAbstractScrollAreaPrivate::layoutChildren()
 void QAbstractScrollAreaPrivate::layoutChildren_helper(bool *needHorizontalScrollbar, bool *needVerticalScrollbar)
 {
     Q_Q(QAbstractScrollArea);
-    bool htransient = hbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, hbar);
+    QStyleOptionSlider barOpt;
+
+    hbar->initStyleOption(&barOpt);
+    bool htransient = hbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, &barOpt, hbar);
     bool needh = *needHorizontalScrollbar || ((hbarpolicy != Qt::ScrollBarAlwaysOff) && ((hbarpolicy == Qt::ScrollBarAlwaysOn && !htransient)
                             || ((hbarpolicy == Qt::ScrollBarAsNeeded || htransient)
                             && hbar->minimum() < hbar->maximum() && !hbar->sizeHint().isEmpty())));
+    const int hscrollOverlap = hbar->style()->pixelMetric(QStyle::PM_ScrollView_ScrollBarOverlap, &barOpt, hbar);
 
-    bool vtransient = vbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, vbar);
+    vbar->initStyleOption(&barOpt);
+    bool vtransient = vbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, &barOpt, vbar);
     bool needv = *needVerticalScrollbar || ((vbarpolicy != Qt::ScrollBarAlwaysOff) && ((vbarpolicy == Qt::ScrollBarAlwaysOn && !vtransient)
                             || ((vbarpolicy == Qt::ScrollBarAsNeeded || vtransient)
                             && vbar->minimum() < vbar->maximum() && !vbar->sizeHint().isEmpty())));
+    const int vscrollOverlap = vbar->style()->pixelMetric(QStyle::PM_ScrollView_ScrollBarOverlap, &barOpt, vbar);
 
     QStyleOption opt(0);
     opt.initFrom(q);
 
-    const int hscrollOverlap = hbar->style()->pixelMetric(QStyle::PM_ScrollView_ScrollBarOverlap, &opt, hbar);
-    const int vscrollOverlap = vbar->style()->pixelMetric(QStyle::PM_ScrollView_ScrollBarOverlap, &opt, vbar);
-
     const int hsbExt = hbar->sizeHint().height();
     const int vsbExt = vbar->sizeHint().width();
     const QPoint extPoint(vsbExt, hsbExt);
@@ -1376,10 +1379,14 @@ bool QAbstractScrollAreaPrivate::canStartScrollingAt(const QPoint &startPos) con
 
 void QAbstractScrollAreaPrivate::flashScrollBars()
 {
-    bool htransient = hbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, hbar);
+    QStyleOptionSlider opt;
+    hbar->initStyleOption(&opt);
+
+    bool htransient = hbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, hbar);
     if ((hbarpolicy != Qt::ScrollBarAlwaysOff) && (hbarpolicy == Qt::ScrollBarAsNeeded || htransient))
         hbar->d_func()->flash();
-    bool vtransient = vbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, vbar);
+    vbar->initStyleOption(&opt);
+    bool vtransient = vbar->style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, vbar);
     if ((vbarpolicy != Qt::ScrollBarAlwaysOff) && (vbarpolicy == Qt::ScrollBarAsNeeded || vtransient))
         vbar->d_func()->flash();
 }
diff --git a/src/widgets/widgets/qscrollbar.cpp b/src/widgets/widgets/qscrollbar.cpp
index 17099177aa..ff4f45b2b2 100644
--- a/src/widgets/widgets/qscrollbar.cpp
+++ b/src/widgets/widgets/qscrollbar.cpp
@@ -224,7 +224,9 @@ void QScrollBarPrivate::setTransient(bool value)
     if (transient != value) {
         transient = value;
         if (q->isVisible()) {
-            if (q->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, q))
+            QStyleOptionSlider opt;
+            q->initStyleOption(&opt);
+            if (q->style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, q))
                 q->update();
         } else if (!transient) {
             q->show();
@@ -235,7 +237,9 @@ void QScrollBarPrivate::setTransient(bool value)
 void QScrollBarPrivate::flash()
 {
     Q_Q(QScrollBar);
-    if (!flashed && q->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, q)) {
+    QStyleOptionSlider opt;
+    q->initStyleOption(&opt);
+    if (!flashed && q->style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, q)) {
         flashed = true;
         if (!q->isVisible())
             q->show();
@@ -319,7 +323,7 @@ void QScrollBar::initStyleOption(QStyleOptionSlider *option) const
     option->upsideDown = d->invertedAppearance;
     if (d->orientation == Qt::Horizontal)
         option->state |= QStyle::State_Horizontal;
-    if ((d->flashed || !d->transient) && style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, this))
+    if ((d->flashed || !d->transient) && style()->styleHint(QStyle::SH_ScrollBar_Transient, option, this))
         option->state |= QStyle::State_On;
 }
 
@@ -376,7 +380,9 @@ void QScrollBarPrivate::init()
     invertedControls = true;
     pressedControl = hoverControl = QStyle::SC_None;
     pointerOutsidePressedControl = false;
-    transient = q->style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, q);
+    QStyleOption opt;
+    opt.initFrom(q);
+    transient = q->style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, q);
     flashed = false;
     flashTimer = 0;
     q->setFocusPolicy(Qt::NoFocus);
@@ -470,12 +476,17 @@ bool QScrollBar::event(QEvent *event)
         if (const QHoverEvent *he = static_cast<const QHoverEvent *>(event))
             d_func()->updateHoverControl(he->position().toPoint());
         break;
-    case QEvent::StyleChange:
-        d_func()->setTransient(style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, this));
+    case QEvent::StyleChange: {
+        QStyleOptionSlider opt;
+        initStyleOption(&opt);
+        d_func()->setTransient(style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, this));
         break;
+    }
     case QEvent::Timer:
         if (static_cast<QTimerEvent *>(event)->timerId() == d->flashTimer) {
-            if (d->flashed && style()->styleHint(QStyle::SH_ScrollBar_Transient, nullptr, this)) {
+            QStyleOptionSlider opt;
+            initStyleOption(&opt);
+            if (d->flashed && style()->styleHint(QStyle::SH_ScrollBar_Transient, &opt, this)) {
                 d->flashed = false;
                 update();
             }