StackLayout: Do not set size of children to (-1, -1)

The item-size-hint-cache in StackLayout was not always valid when
QQuickStackLayout::rearrange() was entered, so it would end up setting
the size of the item to (-1, -1)

Fixes: QTBUG-105899
Change-Id: I632aa18bb10b84d59af35cd3c7cb0c675d8d1692
Reviewed-by: Oliver Eftevaag <oliver.eftevaag@qt.io>
(cherry picked from commit 9a4874ab7f18a54b2497f689dfd7f7a2ee0516b8)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 63 insertions, 4 deletions

diff --git a/src/quicklayouts/qquickstacklayout.cpp b/src/quicklayouts/qquickstacklayout.cpp
index 5b2b0dcbcd..c81b0b5acc 100644
--- a/src/quicklayouts/qquickstacklayout.cpp
+++ b/src/quicklayouts/qquickstacklayout.cpp
@@ -190,10 +190,8 @@ QSizeF QQuickStackLayout::sizeHint(Qt::SizeHint whichSizeHint) const
         maxS = QSizeF(std::numeric_limits<qreal>::infinity(), std::numeric_limits<qreal>::infinity());
 
         const int count = itemCount();
-        m_cachedItemSizeHints.resize(count);
         for (int i = 0; i < count; ++i) {
-            SizeHints &hints = m_cachedItemSizeHints[i];
-            QQuickStackLayout::collectItemSizeHints(itemAt(i), hints.array);
+            SizeHints &hints = cachedItemSizeHints(i);
             minS = minS.expandedTo(hints.min());
             prefS = prefS.expandedTo(hints.pref());
             //maxS = maxS.boundedTo(hints.max());       // Can be resized to be larger than any of its items.
@@ -287,6 +285,7 @@ void QQuickStackLayout::childItemsChanged()
     if (count != d->count) {
         d->count = count;
         emit countChanged();
+        m_cachedItemSizeHints.resize(count);
     }
     for (int i = 0; i < count; ++i) {
         QQuickItem *child = itemAt(i);
@@ -302,6 +301,14 @@ void QQuickStackLayout::childItemsChanged()
     }
 }
 
+QQuickStackLayout::SizeHints &QQuickStackLayout::cachedItemSizeHints(int index) const {
+    SizeHints &hints = m_cachedItemSizeHints[index];
+    if (!hints.min().isValid())
+        QQuickStackLayout::collectItemSizeHints(itemAt(index), hints.array);
+    return hints;
+}
+
+
 void QQuickStackLayout::rearrange(const QSizeF &newSize)
 {
     Q_D(QQuickStackLayout);
@@ -312,7 +319,7 @@ void QQuickStackLayout::rearrange(const QSizeF &newSize)
 
     if (d->currentIndex == -1 || d->currentIndex >= m_cachedItemSizeHints.count())
         return;
-    QQuickStackLayout::SizeHints &hints = m_cachedItemSizeHints[d->currentIndex];
+    QQuickStackLayout::SizeHints &hints = cachedItemSizeHints(d->currentIndex);
     QQuickItem *item = itemAt(d->currentIndex);
     Q_ASSERT(item);
     item->setPosition(QPointF(0,0));    // ### respect alignment?
diff --git a/src/quicklayouts/qquickstacklayout_p.h b/src/quicklayouts/qquickstacklayout_p.h
index c7c174450e..bf52e83e73 100644
--- a/src/quicklayouts/qquickstacklayout_p.h
+++ b/src/quicklayouts/qquickstacklayout_p.h
@@ -76,6 +76,7 @@ private:
 
     mutable QVector<SizeHints> m_cachedItemSizeHints;
     mutable QSizeF m_cachedSizeHints[Qt::NSizeHints];
+    SizeHints &cachedItemSizeHints(int index) const;
 };
 
 class QQuickStackLayoutPrivate : public QQuickLayoutPrivate
diff --git a/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml b/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml
index a04e7a9dd7..3455dd5cc1 100644
--- a/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml
+++ b/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml
@@ -263,5 +263,56 @@ Item {
             compare(layout.implicitWidth, 20)
             compare(layout.implicitHeight, 20)
         }
+
+        Component {
+            id: layout_setCurrentIndex_Component
+
+            StackLayout {
+                width: 200
+                height: 200
+
+                property alias firstItem : rect
+                property alias secondItem: rowLayout
+
+                Rectangle {
+                    id: rect
+                    color: "red"
+                    implicitWidth: 10
+                    implicitHeight: 10
+                }
+                RowLayout {
+                    id: rowLayout
+                    spacing: 0
+                    Rectangle {
+                        color: "green"
+                        implicitWidth: 10
+                        implicitHeight: 10
+                        Layout.fillWidth: true
+                        Layout.fillHeight: true
+                    }
+                    Rectangle {
+                        color: "blue"
+                        implicitWidth: 10
+                        implicitHeight: 10
+                        Layout.fillWidth: true
+                        Layout.fillHeight: true
+                    }
+                }
+            }
+        }
+
+        function test_setCurrentIndex()
+        {
+            var layout = layout_setCurrentIndex_Component.createObject(container)
+            compare(layout.firstItem.width, 200)
+
+            // Invalidate the StackLayout (and its cached size hints)
+            layout.firstItem.implicitWidth = 42
+
+            layout.currentIndex = 1
+            compare(layout.secondItem.width, 200)   // width should not be -1
+            layout.destroy()
+        }
+
     }
 }