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, 16 insertions, 5 deletions

diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index 5ae92e8981..ca2de478cf 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -462,6 +462,7 @@ class BindingLoopTester : public QObject
         eagerData2.setBinding(Qt::makePropertyBinding([&](){ return eagerData.value() + 1; }  ) );
         i->setValue(42);
     }
+    BindingLoopTester() {}
 
     int eagerProp() {return eagerData.value();}
     void setEagerProp(int i) { eagerData = i; }
@@ -495,11 +496,21 @@ void tst_QProperty::bindingLoop()
     QCOMPARE(secondProp.binding().error().type(), QPropertyBindingError::BindingLoop);
 
 
-    QProperty<int> i;
-    BindingLoopTester tester(&i);
-    QCOMPARE(tester.bindableEagerProp().binding().error().type(), QPropertyBindingError::BindingLoop);
-    QEXPECT_FAIL("", "Only the first property in a dependency cycle is set to the error state", Continue);
-    QCOMPARE(tester.bindableEagerProp2().binding().error().type(), QPropertyBindingError::BindingLoop);
+    {
+        QProperty<int> i;
+        BindingLoopTester tester(&i);
+        QCOMPARE(tester.bindableEagerProp().binding().error().type(), QPropertyBindingError::BindingLoop);
+        QCOMPARE(tester.bindableEagerProp2().binding().error().type(), QPropertyBindingError::BindingLoop);
+    }
+    {
+        BindingLoopTester tester;
+        auto handler = tester.bindableEagerProp().onValueChanged([&]() {
+            tester.bindableEagerProp().setBinding([](){return 42;});
+        });
+        tester.bindableEagerProp().setBinding([]() {return 42;});
+        QCOMPARE(tester.bindableEagerProp().binding().error().type(), QPropertyBindingError::BindingLoop);
+        QCOMPARE(tester.bindableEagerProp().binding().error().description(), "Binding set during binding evaluation!");
+    }
 }
 
 class ReallocTester : public QObject