Avoid needless notifications when destroying layouts

When deleting a layout with children, it ends up in ~QQuickItem(), which in
turn will call setParentItem(0).  setParentItem(0) will in turn call
setEffectiveVisibleRecur(), which will recurse down all its descendants.
Therefore, deleting a top level layout might trigger item change listeners
for *all* its descendants, not only its direct children.

This behavior might even cause crashes: The visibility changes will then
trigger an invalidation of the layout, which will propagate up the parent
hierarchy, and potentially call invalidate() on a partially-destroyed
layout, which then might crash.

Change-Id: I48e11d57f69e9011ced6c3a0b51e3d89b24ad5c1
Task-number: QTBUG-55103
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml b/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
index 2d4e227a9e..97860458fe 100644
--- a/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
+++ b/tests/auto/quick/qquicklayouts/data/tst_rowlayout.qml
@@ -802,6 +802,27 @@ Item {
             layout.destroy()    // Do not crash
         }
 
+        Component {
+            id: rectangle_Component
+            Rectangle {
+                width: 100
+                height: 50
+            }
+        }
+
+        function test_destroyImplicitInvisibleLayout()
+        {
+            var root = rectangle_Component.createObject(container)
+            root.visible = false
+            var layout = layout_deleteLayout.createObject(root)
+            layout.visible = true
+            // at this point the layout is still invisible because root is invisible
+            layout.destroy()
+            // Do not crash when destructing the layout
+            waitForRendering(container)      // should ideally call gc(), but does not work
+            root.destroy()
+        }
+
         function test_sizeHintWithHiddenChildren(data) {
             var layout = layout_sizeHint_Component.createObject(container)
             var grid = layout.children[0]