QFormLayout: Fix assert when showing with hidden rows

Amends a74cdf778c0c72fa22d9354207d729b2cbf88128, after which the
initialization of items in invisible rows is skipped. Since data members
in QFormLayoutItem were lazily initialized, this resulted in out-of-bounds
access of QList entries.

Use member initialization for all QFormLayoutItem fields, and check that
vLayoutIndex is valid before using it to access the list entry. Skip
labels and fields for which it is not initialized.

Add test case. As a drive-by, silence the test's provoked warning
messages via ignoreMessage.

Change-Id: I374b414a51df20b9af3087a2676061fc6b7f23e2
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 14 insertions, 14 deletions

diff --git a/src/widgets/kernel/qformlayout.cpp b/src/widgets/kernel/qformlayout.cpp
index e043ca243f..8fc473ee5c 100644
--- a/src/widgets/kernel/qformlayout.cpp
+++ b/src/widgets/kernel/qformlayout.cpp
@@ -110,7 +110,7 @@ enum { ColumnCount = 2 };
 // This owns the QLayoutItem
 struct QFormLayoutItem
 {
-    QFormLayoutItem(QLayoutItem* i) : item(i), fullRow(false), isHfw(false) { }
+    QFormLayoutItem(QLayoutItem* i) : item(i) { }
     ~QFormLayoutItem() { delete item; }
 
     // Wrappers
@@ -133,27 +133,27 @@ struct QFormLayoutItem
     // For use with FixedColumnMatrix
     bool operator==(const QFormLayoutItem& other) { return item == other.item; }
 
-    QLayoutItem *item;
-    bool fullRow;
+    QLayoutItem *item = nullptr;
+    bool fullRow = false;
     bool isVisible = true;
 
     // set by updateSizes
-    bool isHfw;
+    bool isHfw = false;
     QSize minSize;
     QSize sizeHint;
     QSize maxSize;
 
     // also set by updateSizes
-    int sbsHSpace; // only used for side by side, for the field item only (not label)
-    int vSpace; // This is the spacing to the item in the row above
+    int sbsHSpace = -1; // only used for side by side, for the field item only (not label)
+    int vSpace = -1; // This is the spacing to the item in the row above
 
     // set by setupVerticalLayoutData
-    bool sideBySide;
-    int vLayoutIndex;
+    bool sideBySide = false;
+    int vLayoutIndex = -1;
 
     // set by setupHorizontalLayoutData
-    int layoutPos;
-    int layoutWidth;
+    int layoutPos = -1;
+    int layoutWidth = -1;
 };
 
 static void hideOrShowWidgetsInLayout(QLayout *layout, bool on)
@@ -540,7 +540,7 @@ void QFormLayoutPrivate::setupHfwLayoutData()
         QFormLayoutItem *label = m_matrix(i, 0);
         QFormLayoutItem *field = m_matrix(i, 1);
 
-        if (label) {
+        if (label && label->vLayoutIndex > -1) {
             if (label->isHfw) {
                 // We don't check sideBySide here, since a label is only
                 // ever side by side with its field
@@ -555,7 +555,7 @@ void QFormLayoutPrivate::setupHfwLayoutData()
             }
         }
 
-        if (field) {
+        if (field && field->vLayoutIndex > -1) {
             int hfw = field->isHfw ? field->heightForWidth(field->layoutWidth) : 0;
             int h = field->isHfw ? hfw : field->sizeHint.height();
             int mh = field->isHfw ? hfw : field->minSize.height();
@@ -2226,7 +2226,7 @@ void QFormLayoutPrivate::arrangeWidgets(const QList<QLayoutStruct> &layouts, QRe
         QFormLayoutItem *label = m_matrix(i, 0);
         QFormLayoutItem *field = m_matrix(i, 1);
 
-        if (label) {
+        if (label && label->vLayoutIndex > -1) {
             int height = layouts.at(label->vLayoutIndex).size;
             if ((label->expandingDirections() & Qt::Vertical) == 0) {
                 /*
@@ -2253,7 +2253,7 @@ void QFormLayoutPrivate::arrangeWidgets(const QList<QLayoutStruct> &layouts, QRe
             label->setGeometry(QStyle::visualRect(layoutDirection, rect, QRect(p, sz)));
         }
 
-        if (field) {
+        if (field && field->vLayoutIndex > -1) {
             QSize sz(field->layoutWidth, layouts.at(field->vLayoutIndex).size);
             QPoint p(field->layoutPos + leftOffset + rect.x(), layouts.at(field->vLayoutIndex).pos);
 /*