2 files changed, 79 insertions, 4 deletions

diff --git a/src/widgets/widgets/qtabbar.cpp b/src/widgets/widgets/qtabbar.cpp
index 0954a02d07..1ee28e4331 100644
--- a/src/widgets/widgets/qtabbar.cpp
+++ b/src/widgets/widgets/qtabbar.cpp
@@ -408,10 +408,12 @@ void QTabBarPrivate::init()
 {
     Q_Q(QTabBar);
     leftB = new QToolButton(q);
+    leftB->setObjectName(QStringLiteral("ScrollLeftButton"));
     leftB->setAutoRepeat(true);
     QObject::connect(leftB, SIGNAL(clicked()), q, SLOT(_q_scrollTabs()));
     leftB->hide();
     rightB = new QToolButton(q);
+    rightB->setObjectName(QStringLiteral("ScrollRightButton"));
     rightB->setAutoRepeat(true);
     QObject::connect(rightB, SIGNAL(clicked()), q, SLOT(_q_scrollTabs()));
     rightB->hide();
@@ -824,21 +826,24 @@ void QTabBarPrivate::_q_scrollTabs()
     Q_Q(QTabBar);
     const QObject *sender = q->sender();
     const bool horizontal = !verticalTabs(shape);
-    const QRect scrollRect = normalizedScrollRect();
+    const QRect scrollRect = normalizedScrollRect().translated(scrollOffset, 0);
+
     int i = -1;
 
     if (sender == leftB) {
         for (i = tabList.count() - 1; i >= 0; --i) {
             int start = horizontal ? tabList.at(i)->rect.left() : tabList.at(i)->rect.top();
-            if (start < scrollRect.left() + scrollOffset) {
+            if (start < scrollRect.left()) {
                 makeVisible(i);
                 return;
             }
         }
     } else if (sender == rightB) {
         for (i = 0; i < tabList.count(); ++i) {
-            int end = horizontal ? tabList.at(i)->rect.right() : tabList.at(i)->rect.bottom();
-            if (end > scrollRect.right() + scrollOffset) {
+            const auto tabRect = tabList.at(i)->rect;
+            int start = horizontal ? tabRect.left() : tabRect.top();
+            int end = horizontal ? tabRect.right() : tabRect.bottom();
+            if (end > scrollRect.right() && start > scrollOffset) {
                 makeVisible(i);
                 return;
             }
diff --git a/tests/auto/widgets/widgets/qtabbar/tst_qtabbar.cpp b/tests/auto/widgets/widgets/qtabbar/tst_qtabbar.cpp
index 7f713ebe6d..68f416a6c1 100644
--- a/tests/auto/widgets/widgets/qtabbar/tst_qtabbar.cpp
+++ b/tests/auto/widgets/widgets/qtabbar/tst_qtabbar.cpp
@@ -31,6 +31,7 @@
 #include <QApplication>
 #include <QTabBar>
 #include <QPushButton>
+#include <QLabel>
 #include <QStyle>
 #include <QStyleOptionTab>
 #include <QProxyStyle>
@@ -101,6 +102,9 @@ private slots:
 
     void mouseWheel();
 
+    void scrollButtons_data();
+    void scrollButtons();
+
 private:
     void checkPositions(const TabBar &tabbar, const QList<int> &positions);
 };
@@ -927,6 +931,72 @@ void tst_QTabBar::mouseWheel()
     QVERIFY(tabbar.currentIndex() != startIndex);
 }
 
+void tst_QTabBar::scrollButtons_data()
+{
+    QTest::addColumn<QTabWidget::TabPosition>("tabPosition");
+    QTest::addColumn<Qt::LayoutDirection>("layoutDirection");
+
+    for (auto ld : {Qt::LeftToRight, Qt::RightToLeft}) {
+        const char *ldStr = ld == Qt::LeftToRight ? "LTR" : "RTL";
+        QTest::addRow("North, %s", ldStr) << QTabWidget::North << ld;
+        QTest::addRow("South, %s", ldStr) << QTabWidget::South << ld;
+        QTest::addRow("West, %s", ldStr) << QTabWidget::West << ld;
+        QTest::addRow("East, %s", ldStr) << QTabWidget::East << ld;
+    }
+}
+
+void tst_QTabBar::scrollButtons()
+{
+    QFETCH(QTabWidget::TabPosition, tabPosition);
+    QFETCH(Qt::LayoutDirection, layoutDirection);
+
+    QWidget window;
+    QTabWidget tabWidget(&window);
+    tabWidget.setLayoutDirection(layoutDirection);
+    tabWidget.setTabPosition(tabPosition);
+    tabWidget.setElideMode(Qt::ElideNone);
+    tabWidget.setUsesScrollButtons(true);
+
+    const int tabCount = 5;
+    for (int i = 0; i < tabCount; ++i)
+    {
+        const QString num = QString::number(i);
+        tabWidget.addTab(new QLabel(num), num + " - Really long tab name to force arrows");
+    }
+    tabWidget.move(0, 0);
+    tabWidget.resize(tabWidget.minimumSizeHint());
+    window.show();
+    QVERIFY(QTest::qWaitForWindowActive(&window));
+
+    auto *leftB = tabWidget.tabBar()->findChild<QAbstractButton*>(QStringLiteral("ScrollLeftButton"));
+    auto *rightB = tabWidget.tabBar()->findChild<QAbstractButton*>(QStringLiteral("ScrollRightButton"));
+
+    QVERIFY(leftB->isVisible());
+    QVERIFY(!leftB->isEnabled());
+    QVERIFY(rightB->isVisible());
+    QVERIFY(rightB->isEnabled());
+    QVERIFY(!tabWidget.tabBar()->tabRect(1).intersects(tabWidget.tabBar()->rect()));
+
+    int index = 0;
+    for (; index < tabWidget.count(); ++index) {
+        QCOMPARE(leftB->isEnabled(), index > 0);
+        QCOMPARE(rightB->isEnabled(), index < tabWidget.count() - 1);
+        QVERIFY(tabWidget.tabBar()->tabRect(index).intersects(tabWidget.tabBar()->rect()));
+        QCOMPARE(tabWidget.tabBar()->tabAt(tabWidget.tabBar()->rect().center()), index);
+        if (rightB->isEnabled())
+            rightB->click();
+    }
+    for (--index; index >= 0; --index) {
+        QCOMPARE(leftB->isEnabled(), index >= 0);
+        QCOMPARE(rightB->isEnabled(), index < tabWidget.count() - 1);
+
+        QVERIFY(tabWidget.tabBar()->tabRect(index).intersects(tabWidget.tabBar()->rect()));
+        if (leftB->isEnabled())
+            leftB->click();
+    }
+    QVERIFY(!leftB->isEnabled());
+}
+
 #endif // QT_CONFIG(wheelevent)
 
 QTEST_MAIN(tst_QTabBar)