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>

12 files changed, 37 insertions, 34 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);
diff --git a/src/qml/types/qqmldelegatemodel_p.h b/src/qml/types/qqmldelegatemodel_p.h
index 186144d107..5ae2d48969 100644
--- a/src/qml/types/qqmldelegatemodel_p.h
+++ b/src/qml/types/qqmldelegatemodel_p.h
@@ -54,6 +54,7 @@
 #include <private/qtqmlglobal_p.h>
 #include <private/qqmllistcompositor_p.h>
 #include <private/qqmlobjectmodel_p.h>
+#include <private/qqmlincubator_p.h>
 
 #include <QtCore/qabstractitemmodel.h>
 #include <QtCore/qstringlist.h>
@@ -109,7 +110,7 @@ public:
 
     int count() const override;
     bool isValid() const override { return delegate() != 0; }
-    QObject *object(int index, bool asynchronous = false) override;
+    QObject *object(int index, QQmlIncubator::IncubationMode incubationMode = QQmlIncubator::AsynchronousIfNested) override;
     ReleaseFlags release(QObject *object) override;
     void cancel(int index) override;
     QString stringValue(int index, const QString &role) override;
diff --git a/src/qml/types/qqmldelegatemodel_p_p.h b/src/qml/types/qqmldelegatemodel_p_p.h
index 0f8438870a..a6a7853116 100644
--- a/src/qml/types/qqmldelegatemodel_p_p.h
+++ b/src/qml/types/qqmldelegatemodel_p_p.h
@@ -261,7 +261,7 @@ public:
     void connectModel(QQmlAdaptorModel *model);
 
     void requestMoreIfNecessary();
-    QObject *object(Compositor::Group group, int index, bool asynchronous);
+    QObject *object(Compositor::Group group, int index, QQmlIncubator::IncubationMode incubationMode);
     QQmlDelegateModel::ReleaseFlags release(QObject *object);
     QString stringValue(Compositor::Group group, int index, const QString &name);
     void emitCreatedPackage(QQDMIncubationTask *incubationTask, QQuickPackage *package);
@@ -357,7 +357,7 @@ public:
 
     int count() const override;
     bool isValid() const override;
-    QObject *object(int index, bool asynchronous = false) override;
+    QObject *object(int index, QQmlIncubator::IncubationMode incubationMode = QQmlIncubator::AsynchronousIfNested) override;
     ReleaseFlags release(QObject *item) override;
     QString stringValue(int index, const QString &role) override;
     QList<QByteArray> watchedRoles() const { return m_watchedRoles; }
diff --git a/src/qml/types/qqmlinstantiator.cpp b/src/qml/types/qqmlinstantiator.cpp
index 2de5875deb..6e2b66aea7 100644
--- a/src/qml/types/qqmlinstantiator.cpp
+++ b/src/qml/types/qqmlinstantiator.cpp
@@ -85,7 +85,7 @@ void QQmlInstantiatorPrivate::clear()
 QObject *QQmlInstantiatorPrivate::modelObject(int index, bool async)
 {
     requestedIndex = index;
-    QObject *o = instanceModel->object(index, async);
+    QObject *o = instanceModel->object(index, async ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested);
     requestedIndex = -1;
     return o;
 }
@@ -123,7 +123,7 @@ void QQmlInstantiatorPrivate::_q_createdItem(int idx, QObject* item)
     if (objects.contains(item)) //Case when it was created synchronously in regenerate
         return;
     if (requestedIndex != idx) // Asynchronous creation, reference the object
-        (void)instanceModel->object(idx, false);
+        (void)instanceModel->object(idx);
     item->setParent(q);
     if (objects.size() < idx + 1) {
         int modelCount = instanceModel->count();
diff --git a/src/qml/types/qqmlobjectmodel.cpp b/src/qml/types/qqmlobjectmodel.cpp
index dcd0360199..dcb41469ba 100644
--- a/src/qml/types/qqmlobjectmodel.cpp
+++ b/src/qml/types/qqmlobjectmodel.cpp
@@ -267,7 +267,7 @@ bool QQmlObjectModel::isValid() const
     return true;
 }
 
-QObject *QQmlObjectModel::object(int index, bool)
+QObject *QQmlObjectModel::object(int index, QQmlIncubator::IncubationMode)
 {
     Q_D(QQmlObjectModel);
     QQmlObjectModelPrivate::Item &item = d->children[index];
diff --git a/src/qml/types/qqmlobjectmodel_p.h b/src/qml/types/qqmlobjectmodel_p.h
index fc4c03874f..5e4a9c686f 100644
--- a/src/qml/types/qqmlobjectmodel_p.h
+++ b/src/qml/types/qqmlobjectmodel_p.h
@@ -52,6 +52,7 @@
 //
 
 #include <private/qtqmlglobal_p.h>
+#include <private/qqmlincubator_p.h>
 #include <QtQml/qqml.h>
 #include <QtCore/qobject.h>
 
@@ -74,7 +75,7 @@ public:
 
     virtual int count() const = 0;
     virtual bool isValid() const = 0;
-    virtual QObject *object(int index, bool asynchronous=false) = 0;
+    virtual QObject *object(int index, QQmlIncubator::IncubationMode incubationMode = QQmlIncubator::AsynchronousIfNested) = 0;
     virtual ReleaseFlags release(QObject *object) = 0;
     virtual void cancel(int) {}
     virtual QString stringValue(int, const QString &) = 0;
@@ -113,7 +114,7 @@ public:
 
     int count() const override;
     bool isValid() const override;
-    QObject *object(int index, bool asynchronous = false) override;
+    QObject *object(int index, QQmlIncubator::IncubationMode incubationMode = QQmlIncubator::AsynchronousIfNested) override;
     ReleaseFlags release(QObject *object) override;
     QString stringValue(int index, const QString &role) override;
     void setWatchedRoles(const QList<QByteArray> &) override {}
diff --git a/src/quick/items/qquickgridview.cpp b/src/quick/items/qquickgridview.cpp
index c570b95a21..e59c579790 100644
--- a/src/quick/items/qquickgridview.cpp
+++ b/src/quick/items/qquickgridview.cpp
@@ -511,9 +511,11 @@ bool QQuickGridViewPrivate::addVisibleItems(qreal fillFrom, qreal fillTo, qreal
     FxGridItemSG *item = 0;
     bool changed = false;
 
+    QQmlIncubator::IncubationMode incubationMode = doBuffer ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested;
+
     while (modelIndex < model->count() && rowPos <= fillTo + rowSize()*(columns - colNum)/(columns+1)) {
         qCDebug(lcItemViewDelegateLifecycle) << "refill: append item" << modelIndex << colPos << rowPos;
-        if (!(item = static_cast<FxGridItemSG*>(createItem(modelIndex, doBuffer))))
+        if (!(item = static_cast<FxGridItemSG*>(createItem(modelIndex, incubationMode))))
             break;
         if (!transitioner || !transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) // pos will be set by layoutVisibleItems()
             item->setPosition(colPos, rowPos, true);
@@ -548,7 +550,7 @@ bool QQuickGridViewPrivate::addVisibleItems(qreal fillFrom, qreal fillTo, qreal
     colPos = colNum * colSize();
     while (visibleIndex > 0 && rowPos + rowSize() - 1 >= fillFrom - rowSize()*(colNum+1)/(columns+1)){
         qCDebug(lcItemViewDelegateLifecycle) << "refill: prepend item" << visibleIndex-1 << "top pos" << rowPos << colPos;
-        if (!(item = static_cast<FxGridItemSG*>(createItem(visibleIndex-1, doBuffer))))
+        if (!(item = static_cast<FxGridItemSG*>(createItem(visibleIndex-1, incubationMode))))
             break;
         --visibleIndex;
         if (!transitioner || !transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) // pos will be set by layoutVisibleItems()
diff --git a/src/quick/items/qquickitemview.cpp b/src/quick/items/qquickitemview.cpp
index c203f389ae..82dbf04090 100644
--- a/src/quick/items/qquickitemview.cpp
+++ b/src/quick/items/qquickitemview.cpp
@@ -1729,7 +1729,7 @@ void QQuickItemViewPrivate::updateCurrent(int modelIndex)
     FxViewItem *oldCurrentItem = currentItem;
     int oldCurrentIndex = currentIndex;
     currentIndex = modelIndex;
-    currentItem = createItem(modelIndex, false);
+    currentItem = createItem(modelIndex, QQmlIncubator::AsynchronousIfNested);
     if (oldCurrentItem && oldCurrentItem->attached && (!currentItem || oldCurrentItem->item != currentItem->item))
         oldCurrentItem->attached->setIsCurrentItem(false);
     if (currentItem) {
@@ -2325,11 +2325,11 @@ void QQuickItemViewPrivate::viewItemTransitionFinished(QQuickItemViewTransitiona
   When the item becomes available, refill() will be called and the item
   will be returned on the next call to createItem().
 */
-FxViewItem *QQuickItemViewPrivate::createItem(int modelIndex, bool asynchronous)
+FxViewItem *QQuickItemViewPrivate::createItem(int modelIndex, QQmlIncubator::IncubationMode incubationMode)
 {
     Q_Q(QQuickItemView);
 
-    if (requestedIndex == modelIndex && asynchronous)
+    if (requestedIndex == modelIndex && incubationMode == QQmlIncubator::Asynchronous)
         return 0;
 
     for (int i=0; i<releasePendingTransition.count(); i++) {
@@ -2340,11 +2340,11 @@ FxViewItem *QQuickItemViewPrivate::createItem(int modelIndex, bool asynchronous)
         }
     }
 
-    if (asynchronous)
+    if (incubationMode == QQmlIncubator::Asynchronous)
         requestedIndex = modelIndex;
     inRequest = true;
 
-    QObject* object = model->object(modelIndex, asynchronous);
+    QObject* object = model->object(modelIndex, incubationMode);
     QQuickItem *item = qmlobject_cast<QQuickItem*>(object);
     if (!item) {
         if (object) {
diff --git a/src/quick/items/qquickitemview_p_p.h b/src/quick/items/qquickitemview_p_p.h
index 2c04022cde..622ebb430f 100644
--- a/src/quick/items/qquickitemview_p_p.h
+++ b/src/quick/items/qquickitemview_p_p.h
@@ -206,7 +206,7 @@ public:
     void refill(qreal from, qreal to);
     void mirrorChange() override;
 
-    FxViewItem *createItem(int modelIndex, bool asynchronous = false);
+    FxViewItem *createItem(int modelIndex,QQmlIncubator::IncubationMode incubationMode = QQmlIncubator::AsynchronousIfNested);
     virtual bool releaseItem(FxViewItem *item);
 
     QQuickItem *createHighlightItem() const;
diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index a6236d9801..d924bc4460 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -669,11 +669,13 @@ bool QQuickListViewPrivate::addVisibleItems(qreal fillFrom, qreal fillTo, qreal
         }
     }
 
+    QQmlIncubator::IncubationMode incubationMode = doBuffer ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested;
+
     bool changed = false;
     FxListItemSG *item = 0;
     qreal pos = itemEnd;
     while (modelIndex < model->count() && pos <= fillTo) {
-        if (!(item = static_cast<FxListItemSG*>(createItem(modelIndex, doBuffer))))
+        if (!(item = static_cast<FxListItemSG*>(createItem(modelIndex, incubationMode))))
             break;
         qCDebug(lcItemViewDelegateLifecycle) << "refill: append item" << modelIndex << "pos" << pos << "buffer" << doBuffer << "item" << (QObject *)(item->item);
         if (!transitioner || !transitioner->canTransition(QQuickItemViewTransitioner::PopulateTransition, true)) // pos will be set by layoutVisibleItems()
@@ -690,7 +692,7 @@ bool QQuickListViewPrivate::addVisibleItems(qreal fillFrom, qreal fillTo, qreal
         return changed;
 
     while (visibleIndex > 0 && visibleIndex <= model->count() && visiblePos > fillFrom) {
-        if (!(item = static_cast<FxListItemSG*>(createItem(visibleIndex-1, doBuffer))))
+        if (!(item = static_cast<FxListItemSG*>(createItem(visibleIndex-1, incubationMode))))
             break;
         qCDebug(lcItemViewDelegateLifecycle) << "refill: prepend item" << visibleIndex-1 << "current top pos" << visiblePos << "buffer" << doBuffer << "item" << (QObject *)(item->item);
         --visibleIndex;
diff --git a/src/quick/items/qquickpathview.cpp b/src/quick/items/qquickpathview.cpp
index aac2b0296a..b9fea974ce 100644
--- a/src/quick/items/qquickpathview.cpp
+++ b/src/quick/items/qquickpathview.cpp
@@ -129,7 +129,7 @@ QQuickItem *QQuickPathViewPrivate::getItem(int modelIndex, qreal z, bool async)
     requestedIndex = modelIndex;
     requestedZ = z;
     inRequest = true;
-    QObject *object = model->object(modelIndex, async);
+    QObject *object = model->object(modelIndex, async ? QQmlIncubator::Asynchronous : QQmlIncubator::AsynchronousIfNested);
     QQuickItem *item = qmlobject_cast<QQuickItem*>(object);
     if (!item) {
         if (object) {
diff --git a/src/quick/items/qquickrepeater.cpp b/src/quick/items/qquickrepeater.cpp
index ebf6e9c5cb..658a7de3d4 100644
--- a/src/quick/items/qquickrepeater.cpp
+++ b/src/quick/items/qquickrepeater.cpp
@@ -401,7 +401,7 @@ void QQuickRepeater::regenerate()
 void QQuickRepeaterPrivate::requestItems()
 {
     for (int i = 0; i < itemCount; i++) {
-        QObject *object = model->object(i, false);
+        QObject *object = model->object(i, QQmlIncubator::AsynchronousIfNested);
         if (object)
             model->release(object);
     }
@@ -410,7 +410,7 @@ void QQuickRepeaterPrivate::requestItems()
 void QQuickRepeater::createdItem(int index, QObject *)
 {
     Q_D(QQuickRepeater);
-    QObject *object = d->model->object(index, false);
+    QObject *object = d->model->object(index, QQmlIncubator::AsynchronousIfNested);
     QQuickItem *item = qmlobject_cast<QQuickItem*>(object);
     emit itemAdded(index, item);
 }
@@ -508,7 +508,7 @@ void QQuickRepeater::modelUpdated(const QQmlChangeSet &changeSet, bool reset)
             int modelIndex = index + i;
             ++d->itemCount;
             d->deletables.insert(modelIndex, 0);
-            QObject *object = d->model->object(modelIndex, false);
+            QObject *object = d->model->object(modelIndex, QQmlIncubator::AsynchronousIfNested);
             if (object)
                 d->model->release(object);
         }