Fix calling Qt.binding() on bound functions

Calling Qt.binding() on a bound function object is a valid use
case and used to work until Qt 5.8.

The problem was that we optimized the code in QQmlBinding and
QQmlJavascriptExpression to directly work on a QV4::Function,
so this wouldn't work anymore.

To fix this make sure recursive calls to Function.bind() are
unrolled (so that the BoundFunction's target is never a bound
function itself), then add the bound function as an optional
member to the QQmlBinding and use it's bound arguments if
present.

Task-number: QTBUG-61927
Change-Id: I472214ddd82fc2a1212efd9b769861fc43d2ddaf
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/qml/jsruntime/qv4qobjectwrapper.cpp b/src/qml/jsruntime/qv4qobjectwrapper.cpp
index c1bbe2a330..816c259b9b 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper.cpp
+++ b/src/qml/jsruntime/qv4qobjectwrapper.cpp
@@ -460,9 +460,12 @@ void QObjectWrapper::setProperty(ExecutionEngine *engine, QObject *object, QQmlP
 
             QV4::Scoped<QQmlBindingFunction> bindingFunction(scope, (const Value &)f);
 
+            QV4::ScopedFunctionObject f(scope, bindingFunction->bindingFunction());
             QV4::ScopedContext ctx(scope, bindingFunction->scope());
-            newBinding = QQmlBinding::create(property, bindingFunction->function(), object, callingQmlContext, ctx);
+            newBinding = QQmlBinding::create(property, f->function(), object, callingQmlContext, ctx);
             newBinding->setSourceLocation(bindingFunction->currentLocation());
+            if (f->isBoundFunction())
+                newBinding->setBoundFunction(static_cast<QV4::BoundFunction *>(f.getPointer()));
             newBinding->setTarget(object, *property, nullptr);
         }
     }