QPropertyBinding: Add sticky mode

A sticky QPropertyBinding is a binding that does not get removed when a
write occurs. This is used in the QML engine to implement support for
the QQmlPropertyData::DontRemoveBinding flag.

Task-number: QTBUG-91689
Change-Id: Ib575b49abe634215318ccc7ba46212cc21eb4dad
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

1 files changed, 25 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index 0b05353bf0..c403276464 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -56,6 +56,7 @@ private slots:
     void avoidDependencyAllocationAfterFirstEval();
     void boolProperty();
     void takeBinding();
+    void stickyBinding();
     void replaceBinding();
     void changeHandler();
     void propertyChangeHandlerApi();
@@ -307,6 +308,30 @@ void tst_QProperty::takeBinding()
     QVERIFY(!existingBinding.isNull());
 }
 
+void tst_QProperty::stickyBinding()
+{
+    QProperty<int> prop;
+    QProperty<int> prop2 {2};
+    prop.setBinding([&](){ return prop2.value(); });
+    QCOMPARE(prop.value(), 2);
+    auto privBinding = QPropertyBindingPrivate::get(prop.binding());
+    // If we make a binding sticky,
+    privBinding->setSticky();
+    // then writing to the property does not remove it
+    prop = 1;
+    QVERIFY(prop.hasBinding());
+    // but the value still changes.
+    QCOMPARE(prop.value(), 1);
+    // The binding continues to work normally.
+    prop2 = 3;
+    QCOMPARE(prop.value(), 3);
+    // If we remove the stickiness
+    privBinding->setSticky(false);
+    // the binding goes away on the next write
+    prop = 42;
+    QVERIFY(!prop.hasBinding());
+}
+
 void tst_QProperty::replaceBinding()
 {
     QProperty<int> first(100);