Prevent endless markDirtyAndNotifyObservers <-> notify loop

Before we had the option of eager evaluation, we were able to use the
dirty flag to detect whether we are recursing. However, eager properties
will lead to a evaluateIfDirtyAndReturnTrueIfValueChanged call, and that
in turn will clear the dirty flag.
Introduce a new member to detect that situation, and set the bindings
error state to BindingLoop if we detect that kind of loop.

Change-Id: If40b93221848bd9e9422502318d992fad95b0b74
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

2 files changed, 17 insertions, 2 deletions

diff --git a/src/corelib/kernel/qproperty.cpp b/src/corelib/kernel/qproperty.cpp
index 72f74ac1e8..81871587e8 100644
--- a/src/corelib/kernel/qproperty.cpp
+++ b/src/corelib/kernel/qproperty.cpp
@@ -41,6 +41,7 @@
 #include "qproperty_p.h"
 
 #include <qscopedvaluerollback.h>
+#include <QScopeGuard>
 
 QT_BEGIN_NAMESPACE
 
@@ -82,6 +83,13 @@ void QPropertyBindingPrivate::markDirtyAndNotifyObservers()
     if (dirty)
         return;
     dirty = true;
+    if (eagerlyUpdating) {
+        error = QPropertyBindingError(QPropertyBindingError::BindingLoop);
+        return;
+    }
+
+    eagerlyUpdating = true;
+    QScopeGuard guard([&](){eagerlyUpdating = false;});
     if (requiresEagerEvaluation()) {
         // these are compat properties that we will need to evaluate eagerly
         evaluateIfDirtyAndReturnTrueIfValueChanged(propertyDataPtr);
diff --git a/src/corelib/kernel/qproperty_p.h b/src/corelib/kernel/qproperty_p.h
index c5c74147c1..999760ec86 100644
--- a/src/corelib/kernel/qproperty_p.h
+++ b/src/corelib/kernel/qproperty_p.h
@@ -163,10 +163,15 @@ private:
     using ObserverArray = std::array<QPropertyObserver, 4>;
 
     // QSharedData is 4 bytes. Use the padding for the bools as we need 8 byte alignment below.
+
+    // a dependent property has changed, and the binding needs to be reevaluated on access
     bool dirty = false;
+    // used to detect binding loops for lazy evaluated properties
     bool updating = false;
     bool hasStaticObserver = false;
-    bool hasBindingWrapper = false;
+    bool hasBindingWrapper:1;
+    // used to detect binding loops for eagerly evaluated properties
+    bool eagerlyUpdating:1;
 
     QUntypedPropertyBinding::BindingEvaluationFunction evaluationFunction;
 
@@ -192,7 +197,9 @@ public:
 
     QPropertyBindingPrivate(QMetaType metaType, QUntypedPropertyBinding::BindingEvaluationFunction evaluationFunction,
                             const QPropertyBindingSourceLocation &location)
-        : evaluationFunction(std::move(evaluationFunction))
+        : hasBindingWrapper(false)
+        , eagerlyUpdating(false)
+        , evaluationFunction(std::move(evaluationFunction))
         , inlineDependencyObservers() // Explicit initialization required because of union
         , location(location)
         , metaType(metaType)