QBindable: Mark non-modifying methods as const

A few methods in QBindable which do not modify anything were not marked
as const so far. This adds the missing const, and a test to verify that
they work.

As all methods are fully inline, this does not cause any binary
compatibility issues.

Fixes: QTBUG-89508
Change-Id: If06d33bc405232887b8c371c268840ba34dbadf6
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
index 7ba5ba33b7..848226713c 100644
--- a/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
+++ b/tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp
@@ -80,6 +80,7 @@ private slots:
     void typeNoOperatorEqual();
     void bindingValueReplacement();
     void quntypedBindableApi();
+    void readonlyConstQBindable();
 
     void testNewStuff();
     void qobjectObservers();
@@ -1030,6 +1031,26 @@ void tst_QProperty::quntypedBindableApi()
     QVERIFY(propLess.takeBinding().isNull());
 }
 
+void tst_QProperty::readonlyConstQBindable()
+{
+    QProperty<int> i {42};
+    const QBindable<int> bindableI(const_cast<const QProperty<int> *>(&i));
+
+    // check that read-only operations work with a const QBindable
+    QVERIFY(bindableI.isReadOnly());
+    QVERIFY(!bindableI.hasBinding());
+    // we can still create a binding to a read only bindable through the interface
+    QProperty<int> j;
+    j.setBinding(bindableI.makeBinding());
+    QCOMPARE(j.value(), bindableI.value());
+    int counter = 0;
+    auto observer = bindableI.subscribe([&](){++counter;});
+    QCOMPARE(counter, 1);
+    auto observer2 = bindableI.onValueChanged([&](){++counter;});
+    i = 0;
+    QCOMPARE(counter, 3);
+}
+
 class MyQObject : public QObject
 {
     Q_OBJECT