Don't delete items we didn't create

Up until this patch, we've always deleted "old" items when a new one is
assigned. For example, the style's implementation of contentItem will
be destroyed here as it is not accessible by the user and is no longer
used:

    Button {
        contentItem: Item { /* ... */ }
    }

This was especially important before the introduction of deferred
execution, as the "default" items would always be created, regardless
of whether the user had overridden it with one of their own items.
By deleting the old items, we free unused resources that would
otherwise persist until application shutdown (calling gc() does not
result in the items being garbage-collected, from my testing).

Although this has largely worked without issues, deleting objects
that weren't created by us in C++ is not supported. User-assigned items
can be created in QML (with JavaScriptOwnership) or C++ (with
CppOwnership), and it is up to the user and/or the QML engine to
manage the lifetime of these items.

After the introduction of deferred execution, it became possible to
skip creation of the default items altogether, meaning that there was
nothing to delete when assigning a new, user-specified item. This
requires that no ids are used in these items, as doing so prevents
deferred execution. Assuming that users avoid using ids in their items,
there should be no unused items that live unnecessarily until
application shutdown. The remaining cases where items do not get
destroyed when they should result from the following:

- Imperative assignments (e.g. assigning an item to a Button's
  contentItem in Component.onCompleted). We already encourage
  declarative bindings rather than imperative assignments.
- Using ids in items.

Given that these are use cases that we will advise against in the
documentation, it's an acceptable compromise.

[ChangeLog][Important Behavior Changes] Old delegate items (background,
contentItem, etc.) are no longer destroyed, as they are technically
owned by user code. Instead, they are hidden, unparented from the
control (QQuickItem parent, not QObject), and Accessible.ignored is
set to true. This prevents them from being unintentionally visible and
interfering with the accessibility tree when a new delegate item is
set.

Change-Id: I56c39a73dfee989dbe8f8b8bb33aaa187750fdb7
Task-number: QTBUG-72085
Fixes: QTBUG-70144
Fixes: QTBUG-75605
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

22 files changed, 235 insertions, 49 deletions

diff --git a/src/imports/controls/doc/src/includes/customize-button-background.qdocinc b/src/imports/controls/doc/src/includes/customize-button-background.qdocinc
new file mode 100644
index 00000000..59df7d8e
--- /dev/null
+++ b/src/imports/controls/doc/src/includes/customize-button-background.qdocinc
@@ -0,0 +1,25 @@
+//! [file]
+\qml \QtMinorVersion
+import QtQuick 2.\1
+import QtQuick.Controls 2.\1
+
+ApplicationWindow {
+    width: 400
+    height: 400
+    visible: true
+
+    Button {
+        id: button
+        text: "A Special Button"
+        background: Rectangle {
+            implicitWidth: 100
+            implicitHeight: 40
+            color: button.down ? "#d6d6d6" : "#f6f6f6"
+            border.color: "#26282a"
+            border.width: 1
+            radius: 4
+        }
+    }
+}
+\endqml
+//! [file]
diff --git a/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc b/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
index cd06a456..857e4e70 100644
--- a/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
+++ b/src/imports/controls/doc/src/qtquickcontrols2-customize.qdoc
@@ -48,29 +48,7 @@
     can override the \l {Control::}{background} item and set the radius
     property of Rectangle:
 
-    \qml \QtMinorVersion
-    import QtQuick 2.\1
-    import QtQuick.Controls 2.\1
-
-    ApplicationWindow {
-        width: 400
-        height: 400
-        visible: true
-
-        Button {
-            id: button
-            text: "A Special Button"
-            background: Rectangle {
-                implicitWidth: 100
-                implicitHeight: 40
-                color: button.down ? "#d6d6d6" : "#f6f6f6"
-                border.color: "#26282a"
-                border.width: 1
-                radius: 4
-            }
-        }
-    }
-    \endqml
+    \include customize-button-background.qdocinc file
 
     The second way to create the button is good if you plan to use your rounded
     button in several places. It involves moving the code into its own QML file
@@ -213,6 +191,102 @@
         files.
     \endlist
 
+    \section3 Considerations for custom styles
+
+    When implementing your own style and customizing controls, there are some
+    points to keep in mind to ensure that your application is as performant as
+    possible.
+
+    \section4 Avoid assigning an id to styles' implementations of item delegates
+
+    As explained in \l {Definition of a Style}, when you implement your
+    own style for a control, you start off with the relevant template for
+    that control. For example, a style's \c Button.qml will be structured
+    similarly to this:
+
+    \qml
+    T.Button {
+        // ...
+
+        background: Rectangle {
+            // ...
+        }
+
+        contentItem: Text {
+            // ...
+        }
+
+        // ...
+    }
+    \endqml
+
+    When you use a Button in your application, the \c background and
+    \c contentItem items will be created and parented to the root \c Button
+    item:
+
+    \qml
+    // Creates the Button root item, the Rectangle background,
+    // and the Text contentItem.
+    Button {
+        text: qsTr("Confirm")
+    }
+    \endqml
+
+    Suppose you then needed to do a one-off customization of the Button (as
+    explained in \l {Customizing a Control}):
+
+    \include customize-button-background.qdocinc file
+
+    In QML, this would normally result in both the default \c background
+    implementation and the one-off, custom \c background items being created.
+    Qt Quick Controls uses a technique that avoids creating both items, and
+    instead only creates the custom \c background, greatly improving the
+    creation performance of controls.
+
+    This technique relies on the absence of an \l {The id Attribute}{id} in the
+    style's implementation of that item. If an id is assigned, the technique
+    cannot work, and both items will be created. For example, it can be
+    tempting to assign an id to the \c background or \c contentItem so that
+    other objects within the file can refer to those items:
+
+    \qml
+    T.Button {
+        // ...
+
+        background: Rectangle {
+            id: backgroundRect
+            // ...
+        }
+
+        contentItem: Text {
+            // Use backgroundRect in some way...
+        }
+
+        // ...
+    }
+    \endqml
+
+    With this code, every time a Button instance with a customized background
+    is created, both backgrounds will be created, resulting in sub-optimal
+    creation performance.
+
+    Prior to Qt 5.15, the old, unused background would be deleted to release
+    the resources associated with it. However, as the control does not own the
+    items, it should not delete them. As of Qt 5.15, old items are no longer
+    deleted, and so the \c backgroundRect item will live longer than it needs
+    to—typically until the application exits. Although the old item will be
+    hidden, visually unparented from the control, and removed from the
+    accessibility tree, it is important to keep the creation time and memory
+    usage of these unused items in mind when assigning an id in this context.
+
+    \section4 Avoid imperative assignments of custom items
+
+    The technique mentioned in the section above only works when an item is
+    \l {Prefer Declarative Bindings Over Imperative Assignments}{declaratively}
+    assigned for the first time, and so imperative assignments will result in
+    orphaned items. Always use declarative bindings to assign custom items
+    when possible.
+
     \section3 Attached properties
 
     It is common for a style to have certain properties or attributes that
diff --git a/src/quicktemplates2/qquickabstractbutton.cpp b/src/quicktemplates2/qquickabstractbutton.cpp
index bb07d13e..eb592032 100644
--- a/src/quicktemplates2/qquickabstractbutton.cpp
+++ b/src/quicktemplates2/qquickabstractbutton.cpp
@@ -712,7 +712,7 @@ void QQuickAbstractButton::setIndicator(QQuickItem *indicator)
     const qreal oldImplicitIndicatorHeight = implicitIndicatorHeight();
 
     d->removeImplicitSizeListener(d->indicator);
-    delete d->indicator;
+    QQuickControlPrivate::hideOldItem(d->indicator);
     d->indicator = indicator;
 
     if (indicator) {
diff --git a/src/quicktemplates2/qquickapplicationwindow.cpp b/src/quicktemplates2/qquickapplicationwindow.cpp
index 19f6f82b..9739650e 100644
--- a/src/quicktemplates2/qquickapplicationwindow.cpp
+++ b/src/quicktemplates2/qquickapplicationwindow.cpp
@@ -407,7 +407,7 @@ void QQuickApplicationWindow::setBackground(QQuickItem *background)
     if (!d->background.isExecuting())
         d->cancelBackground();
 
-    delete d->background;
+    QQuickControlPrivate::hideOldItem(d->background);
     d->background = background;
     if (background) {
         background->setParentItem(QQuickWindow::contentItem());
diff --git a/src/quicktemplates2/qquickcombobox.cpp b/src/quicktemplates2/qquickcombobox.cpp
index 6b03bbf2..dcd427f3 100644
--- a/src/quicktemplates2/qquickcombobox.cpp
+++ b/src/quicktemplates2/qquickcombobox.cpp
@@ -51,6 +51,7 @@
 #include <QtQml/qqmlcontext.h>
 #include <QtQml/private/qlazilyallocated_p.h>
 #include <private/qqmldelegatemodel_p.h>
+#include <QtQuick/private/qquickaccessibleattached_p.h>
 #include <QtQuick/private/qquickevents_p_p.h>
 #include <QtQuick/private/qquicktextinput_p.h>
 #include <QtQuick/private/qquickitemview_p.h>
@@ -264,6 +265,8 @@ public:
     void itemImplicitWidthChanged(QQuickItem *item) override;
     void itemImplicitHeightChanged(QQuickItem *item) override;
 
+    static void hideOldPopup(QQuickPopup *popup);
+
     bool flat = false;
     bool down = false;
     bool hasDown = false;
@@ -774,6 +777,21 @@ void QQuickComboBoxPrivate::itemImplicitHeightChanged(QQuickItem *item)
         emit q->implicitIndicatorHeightChanged();
 }
 
+void QQuickComboBoxPrivate::hideOldPopup(QQuickPopup *popup)
+{
+    if (!popup)
+        return;
+
+    qCDebug(lcItemManagement) << "hiding old popup" << popup;
+
+    popup->setVisible(false);
+    popup->setParentItem(nullptr);
+    // Remove the item from the accessibility tree.
+    QQuickAccessibleAttached *accessible = accessibleAttached(popup);
+    if (accessible)
+        accessible->setIgnored(true);
+}
+
 QQuickComboBox::QQuickComboBox(QQuickItem *parent)
     : QQuickControl(*(new QQuickComboBoxPrivate), parent)
 {
@@ -794,7 +812,7 @@ QQuickComboBox::~QQuickComboBox()
         // Disconnect visibleChanged() to avoid a spurious highlightedIndexChanged() signal
         // emission during the destruction of the (visible) popup. (QTBUG-57650)
         QObjectPrivate::disconnect(d->popup.data(), &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
-        delete d->popup;
+        QQuickComboBoxPrivate::hideOldPopup(d->popup);
         d->popup = nullptr;
     }
 }
@@ -1136,7 +1154,7 @@ void QQuickComboBox::setIndicator(QQuickItem *indicator)
     const qreal oldImplicitIndicatorHeight = implicitIndicatorHeight();
 
     d->removeImplicitSizeListener(d->indicator);
-    delete d->indicator;
+    QQuickControlPrivate::hideOldItem(d->indicator);
     d->indicator = indicator;
     if (indicator) {
         if (!indicator->parentItem())
@@ -1184,7 +1202,7 @@ void QQuickComboBox::setPopup(QQuickPopup *popup)
 
     if (d->popup) {
         QObjectPrivate::disconnect(d->popup.data(), &QQuickPopup::visibleChanged, d, &QQuickComboBoxPrivate::popupVisibleChanged);
-        delete d->popup;
+        QQuickComboBoxPrivate::hideOldPopup(d->popup);
     }
     if (popup) {
         QQuickPopupPrivate::get(popup)->allowVerticalFlip = true;
diff --git a/src/quicktemplates2/qquickcombobox_p.h b/src/quicktemplates2/qquickcombobox_p.h
index c9063d6a..00bc1242 100644
--- a/src/quicktemplates2/qquickcombobox_p.h
+++ b/src/quicktemplates2/qquickcombobox_p.h
@@ -48,10 +48,13 @@
 // We mean it.
 //
 
+#include <QtCore/qloggingcategory.h>
 #include <QtQuickTemplates2/private/qquickcontrol_p.h>
 
 QT_BEGIN_NAMESPACE
 
+Q_DECLARE_LOGGING_CATEGORY(lcItemManagement)
+
 class QValidator;
 class QQuickPopup;
 class QQmlInstanceModel;
diff --git a/src/quicktemplates2/qquickcontainer.cpp b/src/quicktemplates2/qquickcontainer.cpp
index 5f38c5b9..08129866 100644
--- a/src/quicktemplates2/qquickcontainer.cpp
+++ b/src/quicktemplates2/qquickcontainer.cpp
@@ -219,7 +219,7 @@ void QQuickContainerPrivate::cleanup()
             QQuickWindowPrivate::get(window)->clearFocusInScope(contentItem, focusItem, Qt::OtherFocusReason);
 
         q->contentItemChange(nullptr, contentItem);
-        delete contentItem;
+        QQuickControlPrivate::hideOldItem(contentItem);
     }
 
     QObject::disconnect(contentModel, &QQmlObjectModel::countChanged, q, &QQuickContainer::countChanged);
diff --git a/src/quicktemplates2/qquickcontrol.cpp b/src/quicktemplates2/qquickcontrol.cpp
index 0ebaf9a3..3306ff09 100644
--- a/src/quicktemplates2/qquickcontrol.cpp
+++ b/src/quicktemplates2/qquickcontrol.cpp
@@ -56,6 +56,8 @@
 
 QT_BEGIN_NAMESPACE
 
+Q_LOGGING_CATEGORY(lcItemManagement, "qt.quick.controls.control.itemmanagement")
+
 /*!
     \qmltype Control
     \inherits Item
@@ -420,7 +422,7 @@ void QQuickControlPrivate::setContentItem_helper(QQuickItem *item, bool notify)
 
     contentItem = item;
     q->contentItemChange(item, oldContentItem);
-    delete oldContentItem;
+    QQuickControlPrivate::hideOldItem(oldContentItem);
 
     if (item) {
         connect(contentItem.data(), &QQuickItem::baselineOffsetChanged, this, &QQuickControlPrivate::updateBaselineOffset);
@@ -838,6 +840,22 @@ void QQuickControlPrivate::executeBackground(bool complete)
         quickCompleteDeferred(q, backgroundName(), background);
 }
 
+void QQuickControlPrivate::hideOldItem(QQuickItem *item)
+{
+    if (!item)
+        return;
+
+    qCDebug(lcItemManagement) << "hiding old item" << item;
+
+    item->setVisible(false);
+    item->setParentItem(nullptr);
+
+    // Remove the item from the accessibility tree.
+    QQuickAccessibleAttached *accessible = accessibleAttached(item);
+    if (accessible)
+        accessible->setIgnored(true);
+}
+
 void QQuickControlPrivate::updateBaselineOffset()
 {
     Q_Q(QQuickControl);
@@ -1590,7 +1608,7 @@ void QQuickControl::setBackground(QQuickItem *background)
     }
 
     d->removeImplicitSizeListener(d->background, QQuickControlPrivate::ImplicitSizeChanges | QQuickItemPrivate::Geometry);
-    delete d->background;
+    QQuickControlPrivate::hideOldItem(d->background);
     d->background = background;
 
     if (background) {
diff --git a/src/quicktemplates2/qquickcontrol_p_p.h b/src/quicktemplates2/qquickcontrol_p_p.h
index a657307b..b649db0a 100644
--- a/src/quicktemplates2/qquickcontrol_p_p.h
+++ b/src/quicktemplates2/qquickcontrol_p_p.h
@@ -60,8 +60,12 @@
 #include <QtGui/qaccessible.h>
 #endif
 
+#include <QtCore/qloggingcategory.h>
+
 QT_BEGIN_NAMESPACE
 
+Q_DECLARE_LOGGING_CATEGORY(lcItemManagement)
+
 class QQuickAccessibleAttached;
 
 class Q_QUICKTEMPLATES2_PRIVATE_EXPORT QQuickControlPrivate : public QQuickItemPrivate, public QQuickItemChangeListener
@@ -168,6 +172,8 @@ public:
     virtual void cancelBackground();
     virtual void executeBackground(bool complete = false);
 
+    static void hideOldItem(QQuickItem *item);
+
     void updateBaselineOffset();
 
     static const ChangeTypes ImplicitSizeChanges;
diff --git a/src/quicktemplates2/qquickdial.cpp b/src/quicktemplates2/qquickdial.cpp
index 431b25a8..65fed91c 100644
--- a/src/quicktemplates2/qquickdial.cpp
+++ b/src/quicktemplates2/qquickdial.cpp
@@ -620,7 +620,7 @@ void QQuickDial::setHandle(QQuickItem *handle)
     if (!d->handle.isExecuting())
         d->cancelHandle();
 
-    delete d->handle;
+    QQuickControlPrivate::hideOldItem(d->handle);
     d->handle = handle;
     if (d->handle && !d->handle->parentItem())
         d->handle->setParentItem(this);
diff --git a/src/quicktemplates2/qquickgroupbox.cpp b/src/quicktemplates2/qquickgroupbox.cpp
index 7f3c7a2d..8f6f8bc4 100644
--- a/src/quicktemplates2/qquickgroupbox.cpp
+++ b/src/quicktemplates2/qquickgroupbox.cpp
@@ -199,7 +199,7 @@ void QQuickGroupBox::setLabel(QQuickItem *label)
     const qreal oldImplicitLabelHeight = implicitLabelHeight();
 
     d->removeImplicitSizeListener(d->label);
-    delete d->label;
+    QQuickControlPrivate::hideOldItem(d->label);
     d->label = label;
 
     if (label) {
diff --git a/src/quicktemplates2/qquicklabel.cpp b/src/quicktemplates2/qquicklabel.cpp
index f3e0d512..da9b6985 100644
--- a/src/quicktemplates2/qquicklabel.cpp
+++ b/src/quicktemplates2/qquicklabel.cpp
@@ -396,7 +396,7 @@ void QQuickLabel::setBackground(QQuickItem *background)
     }
 
     QQuickControlPrivate::removeImplicitSizeListener(d->background, d, QQuickControlPrivate::ImplicitSizeChanges | QQuickItemPrivate::Geometry);
-    delete d->background;
+    QQuickControlPrivate::hideOldItem(d->background);
     d->background = background;
 
     if (background) {
diff --git a/src/quicktemplates2/qquickmenuitem.cpp b/src/quicktemplates2/qquickmenuitem.cpp
index a7fc63e8..118db822 100644
--- a/src/quicktemplates2/qquickmenuitem.cpp
+++ b/src/quicktemplates2/qquickmenuitem.cpp
@@ -216,7 +216,7 @@ void QQuickMenuItem::setArrow(QQuickItem *arrow)
     if (!d->arrow.isExecuting())
         d->cancelArrow();
 
-    delete d->arrow;
+    QQuickControlPrivate::hideOldItem(d->arrow);
     d->arrow = arrow;
     if (arrow && !arrow->parentItem())
         arrow->setParentItem(this);
diff --git a/src/quicktemplates2/qquickoverlay.cpp b/src/quicktemplates2/qquickoverlay.cpp
index 73a31c84..bf2fc192 100644
--- a/src/quicktemplates2/qquickoverlay.cpp
+++ b/src/quicktemplates2/qquickoverlay.cpp
@@ -34,6 +34,7 @@
 **
 ****************************************************************************/
 
+#include "qquickcontrol_p_p.h"
 #include "qquickoverlay_p.h"
 #include "qquickoverlay_p_p.h"
 #include "qquickpopupitem_p_p.h"
@@ -342,7 +343,6 @@ void QQuickOverlay::setModal(QQmlComponent *modal)
     if (d->modal == modal)
         return;
 
-    delete d->modal;
     d->modal = modal;
     emit modalChanged();
 }
@@ -359,7 +359,6 @@ void QQuickOverlay::setModeless(QQmlComponent *modeless)
     if (d->modeless == modeless)
         return;
 
-    delete d->modeless;
     d->modeless = modeless;
     emit modelessChanged();
 }
@@ -671,7 +670,6 @@ void QQuickOverlayAttached::setModal(QQmlComponent *modal)
     if (d->modal == modal)
         return;
 
-    delete d->modal;
     d->modal = modal;
     emit modalChanged();
 }
@@ -704,7 +702,6 @@ void QQuickOverlayAttached::setModeless(QQmlComponent *modeless)
     if (d->modeless == modeless)
         return;
 
-    delete d->modeless;
     d->modeless = modeless;
     emit modelessChanged();
 }
diff --git a/src/quicktemplates2/qquickrangeslider.cpp b/src/quicktemplates2/qquickrangeslider.cpp
index 378ece50..17948987 100644
--- a/src/quicktemplates2/qquickrangeslider.cpp
+++ b/src/quicktemplates2/qquickrangeslider.cpp
@@ -267,7 +267,7 @@ void QQuickRangeSliderNode::setHandle(QQuickItem *handle)
     const qreal oldImplicitHandleHeight = implicitHandleHeight();
 
     QQuickControlPrivate::get(d->slider)->removeImplicitSizeListener(d->handle);
-    delete d->handle;
+    QQuickControlPrivate::hideOldItem(d->handle);
     d->handle = handle;
 
     if (handle) {
diff --git a/src/quicktemplates2/qquickslider.cpp b/src/quicktemplates2/qquickslider.cpp
index 054ea502..c7f8a025 100644
--- a/src/quicktemplates2/qquickslider.cpp
+++ b/src/quicktemplates2/qquickslider.cpp
@@ -579,7 +579,7 @@ void QQuickSlider::setHandle(QQuickItem *handle)
     const qreal oldImplicitHandleHeight = implicitHandleHeight();
 
     d->removeImplicitSizeListener(d->handle);
-    delete d->handle;
+    QQuickControlPrivate::hideOldItem(d->handle);
     d->handle = handle;
 
     if (handle) {
diff --git a/src/quicktemplates2/qquickspinbox.cpp b/src/quicktemplates2/qquickspinbox.cpp
index 389e5c54..bc8ec809 100644
--- a/src/quicktemplates2/qquickspinbox.cpp
+++ b/src/quicktemplates2/qquickspinbox.cpp
@@ -1126,7 +1126,7 @@ void QQuickSpinButton::setIndicator(QQuickItem *indicator)
 
     QQuickSpinBox *spinBox = static_cast<QQuickSpinBox *>(parent());
     QQuickSpinBoxPrivate::get(spinBox)->removeImplicitSizeListener(d->indicator);
-    delete d->indicator;
+    QQuickControlPrivate::hideOldItem(d->indicator);
     d->indicator = indicator;
 
     if (indicator) {
diff --git a/src/quicktemplates2/qquicktextarea.cpp b/src/quicktemplates2/qquicktextarea.cpp
index ef59bd93..ef452fd0 100644
--- a/src/quicktemplates2/qquicktextarea.cpp
+++ b/src/quicktemplates2/qquicktextarea.cpp
@@ -633,7 +633,7 @@ void QQuickTextArea::setBackground(QQuickItem *background)
     }
 
     QQuickControlPrivate::removeImplicitSizeListener(d->background, d, QQuickControlPrivate::ImplicitSizeChanges | QQuickItemPrivate::Geometry);
-    delete d->background;
+    QQuickControlPrivate::hideOldItem(d->background);
     d->background = background;
 
     if (background) {
diff --git a/src/quicktemplates2/qquicktextfield.cpp b/src/quicktemplates2/qquicktextfield.cpp
index 740edff0..c03b05da 100644
--- a/src/quicktemplates2/qquicktextfield.cpp
+++ b/src/quicktemplates2/qquicktextfield.cpp
@@ -501,7 +501,7 @@ void QQuickTextField::setBackground(QQuickItem *background)
     }
 
     QQuickControlPrivate::removeImplicitSizeListener(d->background, d, QQuickControlPrivate::ImplicitSizeChanges | QQuickItemPrivate::Geometry);
-    delete d->background;
+    QQuickControlPrivate::hideOldItem(d->background);
     d->background = background;
 
     if (background) {
diff --git a/tests/auto/controls/data/tst_spinbox.qml b/tests/auto/controls/data/tst_spinbox.qml
index d3a0d8bb..22dbb352 100644
--- a/tests/auto/controls/data/tst_spinbox.qml
+++ b/tests/auto/controls/data/tst_spinbox.qml
@@ -658,4 +658,20 @@ TestCase {
             compare(control.displayText, data.displayTexts[i])
         }
     }
+
+    Component {
+        id: overriddenSpinBox
+        SpinBox {
+            value: 50
+            up.indicator: Rectangle {
+                property string s: "this is the one"
+            }
+        }
+    }
+
+    function test_indicatorOverridden() {
+        var control = createTemporaryObject(overriddenSpinBox, testCase)
+        verify(control)
+        compare(control.up.indicator.s, "this is the one");
+    }
 }
diff --git a/tests/auto/customization/data/styles/identified/AbstractButton.qml b/tests/auto/customization/data/styles/identified/AbstractButton.qml
index b9656f7a..cd2b5bdc 100644
--- a/tests/auto/customization/data/styles/identified/AbstractButton.qml
+++ b/tests/auto/customization/data/styles/identified/AbstractButton.qml
@@ -58,15 +58,18 @@ T.AbstractButton {
     indicator: Item {
         id: indicator
         objectName: "abstractbutton-indicator-identified"
+        Accessible.name: objectName
     }
 
     contentItem: Item {
         id: contentItem
         objectName: "abstractbutton-contentItem-identified"
+        Accessible.name: objectName
     }
 
     background: Item {
         id: background
         objectName: "abstractbutton-background-identified"
+        Accessible.name: objectName
     }
 }
diff --git a/tests/auto/customization/tst_customization.cpp b/tests/auto/customization/tst_customization.cpp
index 41efc2a6..cce74b41 100644
--- a/tests/auto/customization/tst_customization.cpp
+++ b/tests/auto/customization/tst_customization.cpp
@@ -42,6 +42,7 @@
 #include <QtQuick/qquickitem.h>
 #include <QtQuick/qquickwindow.h>
 #include <QtQuickControls2/qquickstyle.h>
+#include <QtQuickTemplates2/private/qquickcontrol_p_p.h>
 #include "../shared/visualtestutil.h"
 
 using namespace QQuickVisualTestUtil;
@@ -439,11 +440,36 @@ void tst_customization::override()
     QVERIFY2(qt_createdQObjects()->isEmpty(), qPrintable("unexpectedly created: " + qt_createdQObjects->join(", ")));
 
     if (!nonDeferred.isEmpty()) {
-        for (QString delegate : qAsConst(delegates)) {
-            if (!delegate.contains("-"))
-                delegate.append("-" + nonDeferred);
-            delegate.prepend(type.toLower() + "-");
-            QVERIFY2(qt_destroyedQObjects()->removeOne(delegate), qPrintable(delegate + " was not destroyed as expected"));
+        // There were items for which deferred execution was not possible.
+        for (QString delegateName : qAsConst(delegates)) {
+            if (!delegateName.contains("-"))
+                delegateName.append("-" + nonDeferred);
+            delegateName.prepend(type.toLower() + "-");
+
+            const int delegateIndex = qt_destroyedQObjects()->indexOf(delegateName);
+            QVERIFY2(delegateIndex == -1, qPrintable(delegateName + " was unexpectedly destroyed"));
+
+            const auto controlChildren = control->children();
+            const auto childIt = std::find_if(controlChildren.constBegin(), controlChildren.constEnd(), [delegateName](const QObject *child) {
+                return child->objectName() == delegateName;
+            });
+            // We test other delegates (like the background) here, so make sure we don't end up with XPASSes by using the wrong delegate.
+            if (delegateName.contains(QLatin1String("handle"))) {
+                QEXPECT_FAIL("identified:RangeSlider", "For some reason, items that are belong to grouped properties fail here", Abort);
+                QEXPECT_FAIL("overidentified:RangeSlider", "For some reason, items that are belong to grouped properties fail here", Abort);
+            }
+            if (delegateName.contains(QLatin1String("indicator"))) {
+                QEXPECT_FAIL("identified:SpinBox", "For some reason, items that are belong to grouped properties fail here", Abort);
+                QEXPECT_FAIL("overidentified:SpinBox", "For some reason, items that are belong to grouped properties fail here", Abort);
+            }
+            QVERIFY2(childIt != controlChildren.constEnd(), qPrintable(QString::fromLatin1(
+                "Expected delegate \"%1\" to still be a QObject child of \"%2\"").arg(delegateName).arg(controlName)));
+
+            const auto *delegate = qobject_cast<QQuickItem*>(*childIt);
+            // Ensure that the item is hidden, etc.
+            QVERIFY(delegate);
+            QCOMPARE(delegate->isVisible(), false);
+            QCOMPARE(delegate->parentItem(), nullptr);
         }
     }