QQmlIntanceModel: use QQmlIncubator::IncubationMode instead of bool to specify incubation mode

The current implementation would pass a boolean to signal if asynchronous
or synchronous incubation should be used to create an item. The problem with this approach
is that passing 'synchronous" would translate to QQmlIncubation::AsynchronousIfNested
later down the chain. This meant that even if the caller requested synchronous incubation, it
could end up with asynchronous incubation anyway, e.g if an async parent incubator was active at
the time of the call. And this can easily come as an unhandled supprise for the caller, and as
such, cause unforseen bugs.

This patch is a first of a set of patches that is done to fix the bug reported in the task below.
It will not change any behavior, it is written to preserve the logic exactly as it were, just
as a preparation for subsequent patches. It makes it explicit at the call location what
incubation mode will be used, and especially make it clear whenever the AsynchronousIfNested
flag is in play.

Task-number: QTBUG-61537
Change-Id: I8b3ba5438ebb2cd59983a098bd8ceeeb844da87b
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>

1 files changed, 9 insertions, 12 deletions

diff --git a/src/qml/types/qqmldelegatemodel.cpp b/src/qml/types/qqmldelegatemodel.cpp
index e3906f2a7e..4da7199d1e 100644
--- a/src/qml/types/qqmldelegatemodel.cpp
+++ b/src/qml/types/qqmldelegatemodel.cpp
@@ -931,7 +931,7 @@ void QQmlDelegateModelPrivate::setInitialState(QQDMIncubationTask *incubationTas
         emitInitItem(incubationTask, cacheItem->object);
 }
 
-QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bool asynchronous)
+QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, QQmlIncubator::IncubationMode incubationMode)
 {
     if (!m_delegate || index < 0 || index >= m_compositor.count(group)) {
         qWarning() << "DelegateModel::item: index out range" << index << m_compositor.count(group);
@@ -962,7 +962,8 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bo
     cacheItem->referenceObject();
 
     if (cacheItem->incubationTask) {
-        if (!asynchronous && cacheItem->incubationTask->incubationMode() == QQmlIncubator::Asynchronous) {
+        bool sync = (incubationMode == QQmlIncubator::Synchronous || incubationMode == QQmlIncubator::AsynchronousIfNested);
+        if (sync && cacheItem->incubationTask->incubationMode() == QQmlIncubator::Asynchronous) {
             // previously requested async - now needed immediately
             cacheItem->incubationTask->forceCompletion();
         }
@@ -971,7 +972,7 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bo
 
         cacheItem->scriptRef += 1;
 
-        cacheItem->incubationTask = new QQDMIncubationTask(this, asynchronous ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested);
+        cacheItem->incubationTask = new QQDMIncubationTask(this, incubationMode);
         cacheItem->incubationTask->incubating = cacheItem;
         cacheItem->incubationTask->clear();
 
@@ -1024,7 +1025,7 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, bo
   to ensure a reference is held.  Any call to item() which returns a valid item
   must be matched by a call to release() in order to destroy the item.
 */
-QObject *QQmlDelegateModel::object(int index, bool asynchronous)
+QObject *QQmlDelegateModel::object(int index, QQmlIncubator::IncubationMode incubationMode)
 {
     Q_D(QQmlDelegateModel);
     if (!d->m_delegate || index < 0 || index >= d->m_compositor.count(d->m_compositorGroup)) {
@@ -1032,11 +1033,7 @@ QObject *QQmlDelegateModel::object(int index, bool asynchronous)
         return 0;
     }
 
-    QObject *object = d->object(d->m_compositorGroup, index, asynchronous);
-    if (!object)
-        return 0;
-
-    return object;
+    return d->object(d->m_compositorGroup, index, incubationMode);
 }
 
 QString QQmlDelegateModelPrivate::stringValue(Compositor::Group group, int index, const QString &name)
@@ -2659,7 +2656,7 @@ void QQmlDelegateModelGroup::create(QQmlV4Function *args)
         return;
     }
 
-    QObject *object = model->object(group, index, false);
+    QObject *object = model->object(group, index, QQmlIncubator::AsynchronousIfNested);
     if (object) {
         QVector<Compositor::Insert> inserts;
         Compositor::iterator it = model->m_compositor.find(group, index);
@@ -3147,7 +3144,7 @@ bool QQmlPartsModel::isValid() const
     return m_model->isValid();
 }
 
-QObject *QQmlPartsModel::object(int index, bool asynchronous)
+QObject *QQmlPartsModel::object(int index, QQmlIncubator::IncubationMode incubationMode)
 {
     QQmlDelegateModelPrivate *model = QQmlDelegateModelPrivate::get(m_model);
 
@@ -3156,7 +3153,7 @@ QObject *QQmlPartsModel::object(int index, bool asynchronous)
         return 0;
     }
 
-    QObject *object = model->object(m_compositorGroup, index, asynchronous);
+    QObject *object = model->object(m_compositorGroup, index, incubationMode);
 
     if (QQuickPackage *package = qmlobject_cast<QQuickPackage *>(object)) {
         QObject *part = package->part(m_part);