Crash fix in QTreeView::sizeHintForColumn().

Vertical scrollbar may get out of sync. When this happens, the calculation of
firstVisibleItem will retrun "-1". This must be handled in ::sizeHintForColumn().
Added an auto-test for the crashes.

Task-number: QTBUG-34717

Change-Id: I867fd144ef3ce45e382337c5eafe345f573cd944
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
index 8d31fcdf13..ccdce1fe0c 100644
--- a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
+++ b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
@@ -259,6 +259,7 @@ private slots:
     void taskQTBUG_25333_adjustViewOptionsForIndex();
     void taskQTBUG_18539_emitLayoutChanged();
     void taskQTBUG_8176_emitOnExpandAll();
+    void taskQTBUG_34717_collapseAtBottom();
     void testInitialFocus();
 };
 
@@ -4240,6 +4241,35 @@ void tst_QTreeView::taskQTBUG_8176_emitOnExpandAll()
     QCOMPARE(spy2.size(), 1); // item2 is collapsed
 }
 
+// From QTBUG_34717 (QTreeWidget crashes when scrolling to the end
+// of an expanded tree, then collapse all)
+// The test passes simply if it doesn't crash.
+void tst_QTreeView::taskQTBUG_34717_collapseAtBottom()
+{
+    QTreeWidget treeWidget;
+    treeWidget.header()->setSectionResizeMode(QHeaderView::ResizeToContents);
+    treeWidget.setColumnCount(2);
+    QTreeWidgetItem *mainItem = new QTreeWidgetItem(&treeWidget, QStringList() << "Root");
+    for (int i = 0; i < 200; ++i) {
+        QTreeWidgetItem *item = new QTreeWidgetItem(mainItem, QStringList(QString("Item")));
+        new QTreeWidgetItem(item, QStringList() << "Child" << "1");
+        new QTreeWidgetItem(item, QStringList() << "Child" << "2");
+        new QTreeWidgetItem(item, QStringList() << "Child" << "3");
+    }
+    treeWidget.show();
+    treeWidget.expandAll();
+    treeWidget.scrollToBottom();
+    treeWidget.collapseAll();
+
+    treeWidget.setAnimated(true);
+    treeWidget.expandAll();
+    treeWidget.scrollToBottom();
+    mainItem->setExpanded(false);
+
+    PublicView *pview = (PublicView*) &treeWidget;
+    QVERIFY(pview->sizeHintForColumn(1) >= 0);
+}
+
 void tst_QTreeView::testInitialFocus()
 {
     QTreeWidget treeWidget;