Allow partial creation of more than 10 QQmlComponent instances

The recursion detection in QQmlComponent erroneously triggered when
calling beginCreate() on >= 10 different instances. This may happen by
intention and is not necessarily a sign of recursion.

Since beginCreate() does never invoke a potentially nested
Qt.createComponent(), but completeCreate() does, it is better to
modify the creationDepth counter in completeCreate(). This also leads
to simpler code.

The test, however, can remain in beginCreate().

Task-number: QTBUG-47633
Change-Id: If413a8b08421d321d6a426ec16600996cb3f6ea1
Reviewed-by: Matthew Vogt <matthew.vogt@qinetic.com.au>
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

3 files changed, 27 insertions, 15 deletions

diff --git a/src/qml/qml/qqmlcomponent.cpp b/src/qml/qml/qqmlcomponent.cpp
index 1802932f45..22e20de8d7 100644
--- a/src/qml/qml/qqmlcomponent.cpp
+++ b/src/qml/qml/qqmlcomponent.cpp
@@ -845,13 +845,10 @@ QQmlComponentPrivate::beginCreate(QQmlContextData *context)
 
     // Do not create infinite recursion in object creation
     static const int maxCreationDepth = 10;
-    if (++creationDepth.localData() >= maxCreationDepth) {
+    if (creationDepth.localData() >= maxCreationDepth) {
         qWarning("QQmlComponent: Component creation is recursing - aborting");
-        --creationDepth.localData();
         return nullptr;
     }
-    Q_ASSERT(creationDepth.localData() >= 1);
-    depthIncreased = true;
 
     QQmlEnginePrivate *enginePriv = QQmlEnginePrivate::get(engine);
 
@@ -875,10 +872,6 @@ QQmlComponentPrivate::beginCreate(QQmlContextData *context)
         ddata->indestructible = true;
         ddata->explicitIndestructibleSet = true;
         ddata->rootObjectInCreation = false;
-    } else {
-        Q_ASSERT(creationDepth.localData() >= 1);
-        --creationDepth.localData();
-        depthIncreased = false;
     }
 
     return rv;
@@ -952,14 +945,10 @@ void QQmlComponent::completeCreate()
 void QQmlComponentPrivate::completeCreate()
 {
     if (state.completePending) {
+        ++creationDepth.localData();
         QQmlEnginePrivate *ep = QQmlEnginePrivate::get(engine);
         complete(ep, &state);
-    }
-
-    if (depthIncreased) {
-        Q_ASSERT(creationDepth.localData() >= 1);
         --creationDepth.localData();
-        depthIncreased = false;
     }
 }
 
diff --git a/src/qml/qml/qqmlcomponent_p.h b/src/qml/qml/qqmlcomponent_p.h
index 83af5074b8..9b2db4bccf 100644
--- a/src/qml/qml/qqmlcomponent_p.h
+++ b/src/qml/qml/qqmlcomponent_p.h
@@ -79,7 +79,7 @@ class Q_QML_PRIVATE_EXPORT QQmlComponentPrivate : public QObjectPrivate, public
 
 public:
     QQmlComponentPrivate()
-        : progress(0.), start(-1), engine(nullptr), creationContext(nullptr), depthIncreased(false) {}
+        : progress(0.), start(-1), engine(nullptr), creationContext(nullptr) {}
 
     void loadUrl(const QUrl &newUrl, QQmlComponent::CompilationMode mode = QQmlComponent::PreferSynchronous);
 
@@ -136,7 +136,6 @@ public:
 
     QQmlEngine *engine;
     QQmlGuardedContextData creationContext;
-    bool depthIncreased;
 
     void clear();
 
diff --git a/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp b/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
index 6a0dc28ca4..0263115db8 100644
--- a/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
+++ b/tests/auto/qml/qqmlcomponent/tst_qqmlcomponent.cpp
@@ -116,6 +116,7 @@ private slots:
     void onDestructionCount();
     void recursion();
     void recursionContinuation();
+    void partialComponentCreation();
     void callingContextForInitialProperties();
     void relativeUrl_data();
     void relativeUrl();
@@ -526,6 +527,29 @@ void tst_qqmlcomponent::recursionContinuation()
     QVERIFY(object->property("success").toBool());
 }
 
+void tst_qqmlcomponent::partialComponentCreation()
+{
+    const int maxCount = 17;
+    QQmlEngine engine;
+    QScopedPointer<QQmlComponent> components[maxCount];
+    QScopedPointer<QObject> objects[maxCount];
+    QQmlTestMessageHandler messageHandler;
+
+    QCOMPARE(engine.outputWarningsToStandardError(), true);
+
+    for (int i = 0; i < maxCount; i++) {
+        components[i].reset(new QQmlComponent(&engine, testFileUrl("QtObjectComponent.qml")));
+        objects[i].reset(components[i]->beginCreate(engine.rootContext()));
+        QVERIFY(objects[i].isNull() == false);
+    }
+    QVERIFY2(messageHandler.messages().isEmpty(), qPrintable(messageHandler.messageString()));
+
+    for (int i = 0; i < maxCount; i++) {
+        components[i]->completeCreate();
+    }
+    QVERIFY2(messageHandler.messages().isEmpty(), qPrintable(messageHandler.messageString()));
+}
+
 class CallingContextCheckingClass : public QObject
 {
     Q_OBJECT