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)

3 files changed, 61 insertions, 4 deletions

diff --git a/src/imports/layouts/qquickstacklayout.cpp b/src/imports/layouts/qquickstacklayout.cpp
index 443fa0d266..bd2f93c630 100644
--- a/src/imports/layouts/qquickstacklayout.cpp
+++ b/src/imports/layouts/qquickstacklayout.cpp
@@ -192,10 +192,8 @@ 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.
@@ -286,6 +284,7 @@ void QQuickStackLayout::updateLayoutItems()
     if (count != d->count) {
         d->count = count;
         emit countChanged();
+        m_cachedItemSizeHints.resize(count);
     }
     for (int i = 0; i < count; ++i) {
         QQuickItem *child = itemAt(i);
@@ -294,6 +293,13 @@ void QQuickStackLayout::updateLayoutItems()
     }
 }
 
+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);
@@ -305,7 +311,7 @@ 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/imports/layouts/qquickstacklayout_p.h b/src/imports/layouts/qquickstacklayout_p.h
index e1bd84eb3c..e46c608926 100644
--- a/src/imports/layouts/qquickstacklayout_p.h
+++ b/src/imports/layouts/qquickstacklayout_p.h
@@ -97,6 +97,7 @@ 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 3a41bdb3e0..de335386cf 100644
--- a/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml
+++ b/tests/auto/quick/qquicklayouts/data/tst_stacklayout.qml
@@ -103,5 +103,55 @@ Item {
 
             layout.destroy()
         }
+
+        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()
+        }
     }
 }