QHeaderView: relayout on resetDefaultSectionSize

We now call setDefaultSectionSize with the new default section size.
This clamps the value to min/max section size and it will resize
affected sections.

Pick-to: 6.5
Fixes: QTBUG-116013
Change-Id: I39849aca8d0672629ce0b3ca244038c27e045d4b
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit a8df174369cecd90f14dac85bf162353b7cb25d1)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/itemviews/qheaderview.cpp

@@ -1560,13 +1560,14 @@ void QHeaderView::setDefaultSectionSize(int size)
     if (size < 0 || size > maxSizeSection)
         return;
     d->setDefaultSectionSize(size);
+    d->customDefaultSectionSize = true;
 }
 
 void QHeaderView::resetDefaultSectionSize()
 {
     Q_D(QHeaderView);
     if (d->customDefaultSectionSize) {
-        d->updateDefaultSectionSizeFromStyle();
+        d->setDefaultSectionSize(d->getDefaultSectionSizeFromStyle());
         d->customDefaultSectionSize = false;
     }
 }
@@ -2414,7 +2415,7 @@ bool QHeaderView::event(QEvent *e)
         break; }
     case QEvent::StyleChange:
         if (!d->customDefaultSectionSize)
-            d->updateDefaultSectionSizeFromStyle();
+            d->setDefaultSectionSize(d->getDefaultSectionSizeFromStyle());
         break;
     default:
         break;
@@ -3881,7 +3882,6 @@ void QHeaderViewPrivate::setDefaultSectionSize(int size)
     executePostedLayout();
     invalidateCachedSizeHint();
     defaultSectionSize = size;
-    customDefaultSectionSize = true;
     if (state == QHeaderViewPrivate::ResizeSection)
         preventCursorChangeInSetOffset = true;
     for (int i = 0; i < sectionItems.size(); ++i) {
@@ -3902,15 +3902,14 @@ void QHeaderViewPrivate::setDefaultSectionSize(int size)
     viewport->update();
 }
 
-void QHeaderViewPrivate::updateDefaultSectionSizeFromStyle()
+int QHeaderViewPrivate::getDefaultSectionSizeFromStyle() const
 {
-    Q_Q(QHeaderView);
+    Q_Q(const QHeaderView);
-    if (orientation == Qt::Horizontal) {
+    return orientation == Qt::Horizontal
-        defaultSectionSize = q->style()->pixelMetric(QStyle::PM_HeaderDefaultSectionSizeHorizontal, nullptr, q);
+            ? q->style()->pixelMetric(QStyle::PM_HeaderDefaultSectionSizeHorizontal, nullptr, q)
-    } else {
+            : qMax(q->minimumSectionSize(),
-        defaultSectionSize = qMax(q->minimumSectionSize(),
+                   q->style()->pixelMetric(QStyle::PM_HeaderDefaultSectionSizeVertical, nullptr,
-                                  q->style()->pixelMetric(QStyle::PM_HeaderDefaultSectionSizeVertical, nullptr, q));
+                                           q));
-    }
 }
 
 void QHeaderViewPrivate::recalcSectionStartPos() const // linear (but fast)
@@ -4219,7 +4218,7 @@ bool QHeaderViewPrivate::read(QDataStream &in)
     if (in.status() == QDataStream::Ok) {  // we haven't read past end
         customDefaultSectionSize = tmpbool;
         if (!customDefaultSectionSize)
-            updateDefaultSectionSizeFromStyle();
+            defaultSectionSize = getDefaultSectionSizeFromStyle();
     }
 
     lastSectionSize = -1;

src/widgets/itemviews/qheaderview_p.h

@@ -141,7 +141,7 @@ public:
 
     inline void setDefaultValues(Qt::Orientation o) {
         orientation = o;
-        updateDefaultSectionSizeFromStyle();
+        defaultSectionSize = getDefaultSectionSizeFromStyle();
         defaultAlignment = (o == Qt::Horizontal
                             ? Qt::Alignment(Qt::AlignCenter)
                             : Qt::AlignLeft|Qt::AlignVCenter);
@@ -309,7 +309,7 @@ public:
     void removeSectionsFromSectionItems(int start, int end);
     void resizeSectionItem(int visualIndex, int oldSize, int newSize);
     void setDefaultSectionSize(int size);
-    void updateDefaultSectionSizeFromStyle();
+    int getDefaultSectionSizeFromStyle() const;
     void recalcSectionStartPos() const; // not really const
 
     inline int headerLength() const { // for debugging

tests/auto/widgets/itemviews/qtableview/tst_qtableview.cpp

@@ -423,6 +423,7 @@ private slots:
     void selectColumnsAndCells();
     void selectWithHeader_data();
     void selectWithHeader();
+    void resetDefaultSectionSize();
 
 #if QT_CONFIG(wheelevent)
     void mouseWheel_data();
@@ -4909,6 +4910,21 @@ void tst_QTableView::selectWithHeader()
     QVERIFY(!isSelected());
 }
 
+void tst_QTableView::resetDefaultSectionSize()
+{
+    // Create a table and change its default section size and then reset it.
+    // This should be a no op so clicking on row 1 should select row 1 and not row
+    // 0 as previously. QTBUG-116013
+    QTableWidget view(10, 10);
+    view.resize(300, 300);
+    view.verticalHeader()->setSectionResizeMode(QHeaderView::Fixed);
+    view.verticalHeader()->setDefaultSectionSize(120);
+    view.verticalHeader()->resetDefaultSectionSize();
+    view.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&view));
+    QCOMPARE(view.verticalHeader()->logicalIndexAt(9, 45), 1);
+}
+
 // This has nothing to do with QTableView, but it's convenient to reuse the QtTestTableModel
 #if QT_CONFIG(textmarkdownwriter)