Fix deferred execution

If the QML engine refuses to defer execution of a delegate (it contains
an ID), we must make sure to cancel any pending deferred execution for
the same delegate. Otherwise, we may end up overriding a custom (non-
deferred) delegate with a default (deferred) delegate.

This patch adds a new test style "identified" to tst_customization.
This style contains delegates with IDs so we can test the behavior with
IDs in base styles. Furthermore, overriding delegates is now tested
in various ways (with and without IDs in the base and custom styles) in
a separate test method. This is done by generating QML code to override
delegates with dummy Item instances with appropriate IDs and names.

Task-number: QTBUG-65341
Change-Id: Ie6dca287cb74672004d9d8f599760b9d32c3a380
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 24 insertions, 8 deletions

diff --git a/src/quicktemplates2/qquickdeferredexecute.cpp b/src/quicktemplates2/qquickdeferredexecute.cpp
index 802ed3d0..ca6953bc 100644
--- a/src/quicktemplates2/qquickdeferredexecute.cpp
+++ b/src/quicktemplates2/qquickdeferredexecute.cpp
@@ -55,13 +55,24 @@ static inline uint qHash(QObject *object, const QString &propertyName)
 
 Q_GLOBAL_STATIC(DeferredStates, deferredStates)
 
-static void beginDeferred(QQmlEnginePrivate *enginePriv, const QQmlProperty &property, QQmlComponentPrivate::DeferredState *deferredState)
+static void cancelDeferred(QObject *object, int propertyIndex)
+{
+    QQmlData *ddata = QQmlData::get(object);
+    auto dit = ddata->deferredData.rbegin();
+    while (dit != ddata->deferredData.rend()) {
+        (*dit)->bindings.remove(propertyIndex);
+        ++dit;
+    }
+}
+
+static bool beginDeferred(QQmlEnginePrivate *enginePriv, const QQmlProperty &property, QQmlComponentPrivate::DeferredState *deferredState)
 {
     QObject *object = property.object();
     QQmlData *ddata = QQmlData::get(object);
     Q_ASSERT(!ddata->deferredData.isEmpty());
 
     int propertyIndex = property.index();
+    int wasInProgress = enginePriv->inProgressCreations;
 
     for (auto dit = ddata->deferredData.rbegin(); dit != ddata->deferredData.rend(); ++dit) {
         QQmlData::DeferredData *deferData = *dit;
@@ -91,12 +102,11 @@ static void beginDeferred(QQmlEnginePrivate *enginePriv, const QQmlProperty &pro
 
         // Cleanup any remaining deferred bindings for this property, also in inner contexts,
         // to avoid executing them later and overriding the property that was just populated.
-        while (dit != ddata->deferredData.rend()) {
-            (*dit)->bindings.remove(propertyIndex);
-            ++dit;
-        }
+        cancelDeferred(object, propertyIndex);
         break;
     }
+
+    return enginePriv->inProgressCreations > wasInProgress;
 }
 
 void beginDeferred(QObject *object, const QString &property)
@@ -106,15 +116,21 @@ void beginDeferred(QObject *object, const QString &property)
         QQmlEnginePrivate *ep = QQmlEnginePrivate::get(data->context->engine);
 
         QQmlComponentPrivate::DeferredState *state = new QQmlComponentPrivate::DeferredState;
-        beginDeferred(ep, QQmlProperty(object, property), state);
+        if (beginDeferred(ep, QQmlProperty(object, property), state))
+            deferredStates()->insert(qHash(object, property), state);
+        else
+            delete state;
 
         // Release deferred data for those compilation units that no longer have deferred bindings
         data->releaseDeferredData();
-
-        deferredStates()->insert(qHash(object, property), state);
     }
 }
 
+void cancelDeferred(QObject *object, const QString &property)
+{
+    cancelDeferred(object, QQmlProperty(object, property).index());
+}
+
 void completeDeferred(QObject *object, const QString &property)
 {
     QQmlData *data = QQmlData::get(object);