QQuickAttachedPropertyPropagator: fix child window propagation

After the recent changes to window code, a child window's transient
parent is not available as early as it used to be. Account for this
by listening to changes in the window's parent as we do for items.

Fixes: QTBUG-122008
Change-Id: I2cd93e3c487e7ce4567e740886ef65a756c1350f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 5f7b25a694eb46cc520b6dd2651f1e3f99e310f0)
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 9ca9468ffd464c9b131dfe2f7170c34a2d1413c7)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

2 files changed, 66 insertions, 21 deletions

diff --git a/src/quickcontrols/qquickattachedpropertypropagator.cpp b/src/quickcontrols/qquickattachedpropertypropagator.cpp
index 855f48ad0a..251e81b164 100644
--- a/src/quickcontrols/qquickattachedpropertypropagator.cpp
+++ b/src/quickcontrols/qquickattachedpropertypropagator.cpp
@@ -227,6 +227,7 @@ public:
     void setAttachedParent(QQuickAttachedPropertyPropagator *parent);
 
     void itemWindowChanged(QQuickWindow *window);
+    void transientParentWindowChanged(QWindow *newTransientParent);
     void itemParentChanged(QQuickItem *item, QQuickItem *parent) override;
 
     QList<QQuickAttachedPropertyPropagator *> attachedChildren;
@@ -235,22 +236,37 @@ public:
 
 void QQuickAttachedPropertyPropagatorPrivate::attachTo(QObject *object)
 {
-    QQuickItem *item = findAttachedItem(object);
-    if (item) {
+    if (QQuickItem *item = findAttachedItem(object)) {
         connect(item, &QQuickItem::windowChanged, this, &QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged);
         QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::Parent);
+    } else if (auto *window = qobject_cast<QQuickWindow *>(object)) {
+        QObjectPrivate::connect(window, &QWindow::transientParentChanged, this,
+            &QQuickAttachedPropertyPropagatorPrivate::transientParentWindowChanged);
     }
 }
 
 void QQuickAttachedPropertyPropagatorPrivate::detachFrom(QObject *object)
 {
-    QQuickItem *item = findAttachedItem(object);
-    if (item) {
+    if (QQuickItem *item = findAttachedItem(object)) {
         disconnect(item, &QQuickItem::windowChanged, this, &QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged);
         QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::Parent);
+    } else if (auto *window = qobject_cast<QQuickWindow *>(object)) {
+        QObjectPrivate::disconnect(window, &QWindow::transientParentChanged,
+            this, &QQuickAttachedPropertyPropagatorPrivate::transientParentWindowChanged);
     }
 }
 
+static QString debugName(QQuickAttachedPropertyPropagator *attached)
+{
+    QString string;
+    QDebug stream(&string);
+    if (!attached)
+        stream << "(null)";
+    else
+        stream.nospace().noquote() << attached << " (which is attached to " << attached->parent() << ')';
+    return string;
+}
+
 /*!
     \internal
 
@@ -276,14 +292,14 @@ void QQuickAttachedPropertyPropagatorPrivate::setAttachedParent(QQuickAttachedPr
         return;
 
     QQuickAttachedPropertyPropagator *oldParent = attachedParent;
-    qCDebug(lcAttached) << "setAttachedParent called on" << q->parent();
+    qCDebug(lcAttached).noquote() << "setAttachedParent called on" << debugName(q) << "with parent" << debugName(parent);
     if (attachedParent) {
-        qCDebug(lcAttached) << "- removing ourselves as an attached child of" << attachedParent->parent() << attachedParent;
+        qCDebug(lcAttached).noquote() << "- removing ourselves as an attached child of" << debugName(attachedParent);
         QQuickAttachedPropertyPropagatorPrivate::get(attachedParent)->attachedChildren.removeOne(q);
     }
     attachedParent = parent;
     if (parent) {
-        qCDebug(lcAttached) << "- adding ourselves as an attached child of" << parent->parent() << parent;
+        qCDebug(lcAttached).noquote() << "- adding ourselves as an attached child of" << debugName(parent);
         QQuickAttachedPropertyPropagatorPrivate::get(parent)->attachedChildren.append(q);
     }
     q->attachedParentChange(parent, oldParent);
@@ -293,13 +309,24 @@ void QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged(QQuickWindow *wi
 {
     Q_Q(QQuickAttachedPropertyPropagator);
     QQuickAttachedPropertyPropagator *attachedParent = nullptr;
-    qCDebug(lcAttached) << "window of" << q->parent() << "changed to" << window;
+    qCDebug(lcAttached).noquote() << "window of" << debugName(q) << "changed to" << window;
     attachedParent = findAttachedParent(q->metaObject(), q->parent());
     if (!attachedParent)
         attachedParent = attachedObject(q->metaObject(), window);
     setAttachedParent(attachedParent);
 }
 
+void QQuickAttachedPropertyPropagatorPrivate::transientParentWindowChanged(QWindow *newTransientParent)
+{
+    Q_Q(QQuickAttachedPropertyPropagator);
+    QQuickAttachedPropertyPropagator *attachedParent = nullptr;
+    qCDebug(lcAttached).noquote() << "transient parent window of" << q << "changed to" << newTransientParent;
+    attachedParent = findAttachedParent(q->metaObject(), q->parent());
+    if (!attachedParent)
+        attachedParent = attachedObject(q->metaObject(), newTransientParent);
+    setAttachedParent(attachedParent);
+}
+
 void QQuickAttachedPropertyPropagatorPrivate::itemParentChanged(QQuickItem *item, QQuickItem *parent)
 {
     Q_Q(QQuickAttachedPropertyPropagator);
@@ -383,14 +410,15 @@ QQuickAttachedPropertyPropagator *QQuickAttachedPropertyPropagator::attachedPare
 void QQuickAttachedPropertyPropagator::initialize()
 {
     Q_D(QQuickAttachedPropertyPropagator);
+    qCDebug(lcAttached) << "initialize called for" << parent() << "- looking for attached parent...";
     QQuickAttachedPropertyPropagator *attachedParent = findAttachedParent(metaObject(), parent());
     if (attachedParent)
         d->setAttachedParent(attachedParent);
 
     const QList<QQuickAttachedPropertyPropagator *> attachedChildren = findAttachedChildren(metaObject(), parent());
-    qCDebug(lcAttached) << "initialize called for" << parent() << "- found" << attachedChildren.size() << "attached children";
+    qCDebug(lcAttached) << "- found" << attachedChildren.size() << "attached children:";
     for (QQuickAttachedPropertyPropagator *child : attachedChildren) {
-        qCDebug(lcAttached) << "-" << child->parent();
+        qCDebug(lcAttached) << "  -" << child->parent();
         QQuickAttachedPropertyPropagatorPrivate::get(child)->setAttachedParent(this);
     }
 }
diff --git a/tests/auto/quickcontrols/qquickmaterialstyle/data/tst_material.qml b/tests/auto/quickcontrols/qquickmaterialstyle/data/tst_material.qml
index 4fb19c7c0f..6d7fbffa64 100644
--- a/tests/auto/quickcontrols/qquickmaterialstyle/data/tst_material.qml
+++ b/tests/auto/quickcontrols/qquickmaterialstyle/data/tst_material.qml
@@ -51,17 +51,6 @@ TestCase {
     }
 
     Component {
-        id: styledWindowComponent
-        Window {
-            Material.theme: Material.Dark
-            Material.primary: Material.Brown
-            Material.accent: Material.Green
-            Material.background: Material.Yellow
-            Material.foreground: Material.Grey
-        }
-    }
-
-    Component {
         id: buttonLoaderComponent
         Loader {
             active: false
@@ -1277,4 +1266,32 @@ TestCase {
         // false => true => false.
         compare(buttonActiveFocusSpy.count, 2)
     }
+
+    Component {
+        id: childWindowComponent
+
+        ApplicationWindow {
+            objectName: "parentWindow"
+            property alias childWindow: childWindow
+
+            Material.theme: Material.Dark
+            Material.primary: Material.Brown
+            Material.accent: Material.Green
+            Material.background: Material.Yellow
+            Material.foreground: Material.Grey
+
+            ApplicationWindow {
+                id: childWindow
+                objectName: "childWindow"
+            }
+        }
+    }
+
+    function test_windowBackgroundColorPropagation() {
+        let parentWindow = createTemporaryObject(childWindowComponent, testCase)
+        verify(parentWindow)
+
+        let childWindow = parentWindow.childWindow
+        compare(childWindow.Material.theme, Material.Dark)
+    }
 }