Stylesheet: Handle tabs with elide mode set correctly

In order for SE_TabBarTabText to correctly calculate the space available
for the text it needs to get the rectangle of the tab directly instead
of relying on the option's rectangle as this may have been modified
before this point. Therefore we introduce QStyleOptionTabV4 to be able
to store the index as part of the option so it can be queried directly.

[ChangeLog][QtWidgets] Added QStyleOptionTabV4 as a subclass of
QStyleOptionTab so that the tab's index information can be obtained.

Fixes: QTBUG-50637
Change-Id: If705f5069fdd14eeccf06bc63dba4e8d2e704359
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Christian Ehrlicher <ch.ehrlicher@gmx.de>

4 files changed, 43 insertions, 7 deletions

diff --git a/src/widgets/styles/qstyleoption.cpp b/src/widgets/styles/qstyleoption.cpp
index 5292d971ea..aca4eec0e7 100644
--- a/src/widgets/styles/qstyleoption.cpp
+++ b/src/widgets/styles/qstyleoption.cpp
@@ -1470,6 +1470,22 @@ QStyleOptionTab::QStyleOptionTab(int version)
     The default value is QSize(-1, -1), i.e. an invalid size;
 */
 
+/*!
+    Constructs a QStyleOptionTabV4 object, initializing the members
+    variables to their default values.
+ */
+
+QStyleOptionTabV4::QStyleOptionTabV4() : QStyleOptionTab(QStyleOptionTabV4::Version)
+{
+}
+
+/*!
+    \variable QStyleOptionTabV4::tabIndex
+    \brief the index for the tab being represented.
+
+    The default value is -1, i.e. a tab not on a tabbar;
+ */
+
 #endif // QT_CONFIG(tabbar)
 
 /*!
diff --git a/src/widgets/styles/qstyleoption.h b/src/widgets/styles/qstyleoption.h
index 7f5edf4279..a8ce3b465e 100644
--- a/src/widgets/styles/qstyleoption.h
+++ b/src/widgets/styles/qstyleoption.h
@@ -296,6 +296,14 @@ protected:
     QStyleOptionTab(int version);
 };
 
+class Q_WIDGETS_EXPORT QStyleOptionTabV4 : public QStyleOptionTab
+{
+public:
+    enum StyleOptionVersion { Version = 4 };
+    QStyleOptionTabV4();
+    int tabIndex = -1;
+};
+
 Q_DECLARE_OPERATORS_FOR_FLAGS(QStyleOptionTab::CornerWidgets)
 
 typedef Q_DECL_DEPRECATED QStyleOptionTab QStyleOptionTabV2;
diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 7e8c9a6050..7fe46e24b6 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -6009,6 +6009,16 @@ QRect QStyleSheetStyle::subElementRect(SubElement se, const QStyleOption *opt, c
     case SE_TabBarTabRightButton: {
         QRenderRule subRule = renderRule(w, opt, PseudoElement_TabBarTab);
         if (subRule.hasBox() || !subRule.hasNativeBorder()) {
+            if (se == SE_TabBarTabText) {
+                if (const QStyleOptionTabV4 *tab = qstyleoption_cast<const QStyleOptionTabV4 *>(opt)) {
+                    const QTabBar *bar = qobject_cast<const QTabBar *>(w);
+                    const QRect optRect = bar && tab->tabIndex != -1 ? bar->tabRect(tab->tabIndex) : opt->rect;
+                    const QRect r = positionRect(w, subRule, PseudoElement_TabBarTab, optRect, opt->direction);
+                    QStyleOptionTabV4 tabCopy(*tab);
+                    tabCopy.rect = subRule.contentsRect(r);
+                    return ParentStyle::subElementRect(se, &tabCopy, w);
+                }
+            }
             return ParentStyle::subElementRect(se, opt, w);
         }
         break;
diff --git a/src/widgets/widgets/qtabbar.cpp b/src/widgets/widgets/qtabbar.cpp
index aff95b0931..a7b115a1bc 100644
--- a/src/widgets/widgets/qtabbar.cpp
+++ b/src/widgets/widgets/qtabbar.cpp
@@ -229,6 +229,8 @@ void QTabBarPrivate::initBasicStyleOption(QStyleOptionTab *option, int tabIndex)
             option->cornerWidgets |= QStyleOptionTab::RightCornerWidget;
     }
 #endif
+    if (QStyleOptionTabV4 *optv4 = qstyleoption_cast<QStyleOptionTabV4 *>(option))
+        optv4->tabIndex = tabIndex;
 }
 
 /*!
@@ -628,7 +630,7 @@ QRect QTabBarPrivate::normalizedScrollRect(int index)
     // tab bar itself is in a different orientation.
 
     Q_Q(QTabBar);
-    QStyleOptionTab opt;
+    QStyleOptionTabV4 opt;
     q->initStyleOption(&opt, currentIndex);
     opt.rect = q->rect();
 
@@ -757,7 +759,7 @@ void QTabBarPrivate::layoutTab(int index)
     if (!(tab.leftWidget || tab.rightWidget))
         return;
 
-    QStyleOptionTab opt;
+    QStyleOptionTabV4 opt;
     q->initStyleOption(&opt, index);
     if (tab.leftWidget) {
         QRect rect = q->style()->subElementRect(QStyle::SE_TabBarTabLeftButton, &opt, q);
@@ -1003,7 +1005,7 @@ int QTabBar::insertTab(int index, const QIcon& icon, const QString &text)
     }
 
     if (d->closeButtonOnTabs) {
-        QStyleOptionTab opt;
+        QStyleOptionTabV4 opt;
         initStyleOption(&opt, index);
         ButtonPosition closeSide = (ButtonPosition)style()->styleHint(QStyle::SH_TabBar_CloseButtonPosition, nullptr, this);
         QAbstractButton *closeButton = new CloseButton(this);
@@ -1574,7 +1576,7 @@ QSize QTabBar::tabSizeHint(int index) const
     //Note: this must match with the computations in QCommonStylePrivate::tabLayout
     Q_D(const QTabBar);
     if (const QTabBarPrivate::Tab *tab = d->at(index)) {
-        QStyleOptionTab opt;
+        QStyleOptionTabV4 opt;
         d->initBasicStyleOption(&opt, index);
         opt.text = d->tabList.at(index).text;
         QSize iconSize = tab->icon.isNull() ? QSize(0, 0) : opt.iconSize;
@@ -1819,7 +1821,7 @@ void QTabBar::paintEvent(QPaintEvent *)
     for (int i = 0; i < d->tabList.count(); ++i) {
         if (!d->at(i)->visible)
             continue;
-        QStyleOptionTab tab;
+        QStyleOptionTabV4 tab;
         initStyleOption(&tab, i);
         if (d->paintWithOffsets && d->tabList[i].dragOffset != 0) {
             if (vertical) {
@@ -1859,7 +1861,7 @@ void QTabBar::paintEvent(QPaintEvent *)
 
     // Draw the selected tab last to get it "on top"
     if (selected >= 0) {
-        QStyleOptionTab tab;
+        QStyleOptionTabV4 tab;
         initStyleOption(&tab, selected);
         if (d->paintWithOffsets && d->tabList[selected].dragOffset != 0) {
             if (vertical)
@@ -2209,7 +2211,7 @@ void QTabBarPrivate::setupMovableTab()
     grabImage.fill(Qt::transparent);
     QStylePainter p(&grabImage, q);
 
-    QStyleOptionTab tab;
+    QStyleOptionTabV4 tab;
     q->initStyleOption(&tab, pressedIndex);
     tab.position = QStyleOptionTab::OnlyOneTab;
     if (verticalTabs(shape))