QFormLayout: don't access out-of-bounds layout data

When rows are hidden (implicitly or explicitly), then their layout data
does not get fully updated. If rows get hidden after the layout data has
been calculated once, then we must make sure that their indices are
reset. Otherwise we might access array indices that are out of bounds
when the layout data structure gets resized to fit only visible rows.

For good measure, skip entirely over hidden rows when accessing the
layout data when arranging the widget.

Fixes: QTBUG-109237
Pick-to: 6.5 6.4
Change-Id: I4d6943b6a110edb61f60ce78d31f0fc64b5cc03d
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>

1 files changed, 44 insertions, 0 deletions

diff --git a/tests/auto/widgets/kernel/qformlayout/tst_qformlayout.cpp b/tests/auto/widgets/kernel/qformlayout/tst_qformlayout.cpp
index 33e6bd64db..44b716bb34 100644
--- a/tests/auto/widgets/kernel/qformlayout/tst_qformlayout.cpp
+++ b/tests/auto/widgets/kernel/qformlayout/tst_qformlayout.cpp
@@ -112,6 +112,7 @@ private slots:
     void setLayout();
     void hideShowRow();
     void showWithHiddenRow();
+    void hiddenRowAndStretch();
 
 /*
     QLayoutItem *itemAt(int row, ItemRole role) const;
@@ -1253,6 +1254,49 @@ void tst_QFormLayout::showWithHiddenRow()
     topLevel.show();
 }
 
+/*
+    Test that hiding rows does not leave outdated layout data behind
+    in hidden items that results in out-of-bounds array access. See
+    QTBUG-109237.
+*/
+void tst_QFormLayout::hiddenRowAndStretch()
+{
+    QWidget topLevel;
+    QFormLayout layout;
+    layout.setRowWrapPolicy(QFormLayout::WrapAllRows);
+
+    // We need our own stretcher item so that QFormLayout doesn't insert
+    // it's own, as that would grow the size of the layout data array again.
+    QSpacerItem *stretch = new QSpacerItem(100, 100, QSizePolicy::Expanding, QSizePolicy::Expanding);
+    layout.setItem(0, QFormLayout::FieldRole, stretch);
+
+    QLabel *lastLabel = nullptr;
+    QLineEdit *lastField = nullptr;
+    for (int row = 1; row < 4; ++row) {
+        QLabel *label = new QLabel(QString("Label %1").arg(row));
+        label->setWordWrap(true);
+        QLineEdit *field = new QLineEdit;
+        layout.setWidget(row, QFormLayout::LabelRole, label);
+        layout.setWidget(row, QFormLayout::FieldRole, field);
+        if (row == 3) {
+            lastLabel = label;
+            lastField = field;
+        }
+    }
+
+    Q_ASSERT(lastLabel);
+    Q_ASSERT(lastField);
+
+    topLevel.setLayout(&layout);
+    topLevel.sizeHint();
+
+    lastLabel->setVisible(false);
+    lastField->setVisible(false);
+
+    // should not assert here
+    topLevel.show();
+}
+
 void tst_QFormLayout::itemAt()
 {
     QWidget topLevel;