QHeaderView: Simplify and fix layoutChange handling

A layoutChange indicates that anything can have moved to anywhere else,
including as a result purely of new items being added. It can also
indicate that items are removed.

The old code here incorrectly assumed that the section count remained
constant over this operation by setting the size of the oldSectionHidden
QBitArray - whose size is the size before the layoutChange operation -
and then calling setBit with model rows numbered after the layoutChange
operation.  As the two are not necessarily the same dimensions, this can
result in asserts from the setBit call.

Simplify the handling of layoutChanged entirely by clearing section
information, and using the QPersistentIndexes which indicate hidden
state to restore that state after re-population.

Task-number: QTBUG-53221
Change-Id: I3cda13e86b51b3029b37b647a48748fb604db252
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>

1 files changed, 10 insertions, 24 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index 298270a785..4e4c9572a3 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -2086,40 +2086,26 @@ void QHeaderViewPrivate::_q_layoutChanged()
 {
     Q_Q(QHeaderView);
     viewport->update();
-    if (persistentHiddenSections.isEmpty() || modelIsEmpty()) {
-        if (modelSectionCount() != sectionCount())
-            q->initializeSections();
-        persistentHiddenSections.clear();
+
+    const auto hiddenSections = persistentHiddenSections;
+    persistentHiddenSections.clear();
+
+    clear();
+    q->initializeSections();
+    invalidateCachedSizeHint();
+
+    if (modelIsEmpty()) {
         return;
     }
 
-    QBitArray oldSectionHidden = sectionsHiddenToBitVector();
-    oldSectionHidden.resize(sectionItems.size());
-    bool sectionCountChanged = false;
-
-    for (int i = 0; i < persistentHiddenSections.count(); ++i) {
-        QModelIndex index = persistentHiddenSections.at(i);
+    for (const auto &index : hiddenSections) {
         if (index.isValid()) {
             const int logical = (orientation == Qt::Horizontal
                                  ? index.column()
                                  : index.row());
             q->setSectionHidden(logical, true);
-            oldSectionHidden.setBit(logical, false);
-        } else if (!sectionCountChanged && (modelSectionCount() != sectionCount())) {
-            sectionCountChanged = true;
-            break;
         }
     }
-    persistentHiddenSections.clear();
-
-    for (int i = 0; i < oldSectionHidden.count(); ++i) {
-        if (oldSectionHidden.testBit(i))
-            q->setSectionHidden(i, false);
-    }
-
-    // the number of sections changed; we need to reread the state of the model
-    if (sectionCountChanged)
-        q->initializeSections();
 }
 
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