QProperty: Handle eager binding calling setBinding

When an eager binding  triggers a setBinding call, we end up with a
special kind of binding loop:
setBinding() -> evaluate -> notifyObserver
      ^                           |
      |                           /
      ----------------------------
We now catch set condition, and set the binding status to BindingLoop
(with a distinct description).

Task-number: QTBUG-87153
Task-number: QTBUG-87733
Change-Id: I9f9915797d82eab820fc279baceaf89d7e5a3f4a
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit ddc585b7c773786045f3658d7da5425ed2f2f786)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/corelib/kernel/qproperty.cpp b/src/corelib/kernel/qproperty.cpp
index d2fd572b69..715e421295 100644
--- a/src/corelib/kernel/qproperty.cpp
+++ b/src/corelib/kernel/qproperty.cpp
@@ -246,6 +246,10 @@ QUntypedPropertyBinding QPropertyBindingData::setBinding(const QUntypedPropertyB
     if (auto *existingBinding = d.bindingPtr()) {
         if (existingBinding == newBinding.data())
             return QUntypedPropertyBinding(static_cast<QPropertyBindingPrivate *>(oldBinding.data()));
+        if (existingBinding->isEagerlyUpdating()) {
+            existingBinding->setError({QPropertyBindingError::BindingLoop, QStringLiteral("Binding set during binding evaluation!")});
+            return QUntypedPropertyBinding(static_cast<QPropertyBindingPrivate *>(oldBinding.data()));
+        }
         oldBinding = QPropertyBindingPrivatePtr(existingBinding);
         observer = static_cast<QPropertyBindingPrivate *>(oldBinding.data())->takeObservers();
         static_cast<QPropertyBindingPrivate *>(oldBinding.data())->unlinkAndDeref();
@@ -265,9 +269,11 @@ QUntypedPropertyBinding QPropertyBindingData::setBinding(const QUntypedPropertyB
             newBindingRaw->prependObserver(observer);
         newBindingRaw->setStaticObserver(staticObserverCallback, guardCallback);
         if (newBindingRaw->requiresEagerEvaluation()) {
+            newBindingRaw->setEagerlyUpdating(true);
             auto changed = newBindingRaw->evaluateIfDirtyAndReturnTrueIfValueChanged(propertyDataPtr);
             if (changed)
                 observer.notify(newBindingRaw, propertyDataPtr, /*alreadyKnownToHaveChanged=*/true);
+            newBindingRaw->setEagerlyUpdating(false);
         }
     } else if (observer) {
         d.setObservers(observer.ptr);