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, 5 insertions, 4 deletions

diff --git a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
index 1371f1f041..9e7c84011b 100644
--- a/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
+++ b/src/qml/qml/v8/qqmlbuiltinfunctions.cpp
@@ -1344,11 +1344,12 @@ ReturnedValue QtObject::method_locale(const FunctionObject *b, const Value *, co
     return QQmlLocale::locale(scope.engine, code);
 }
 
-void Heap::QQmlBindingFunction::init(const QV4::FunctionObject *originalFunction)
+void Heap::QQmlBindingFunction::init(const QV4::FunctionObject *bindingFunction)
 {
-    Scope scope(originalFunction->engine());
-    ScopedContext context(scope, originalFunction->scope());
-    FunctionObject::init(context, originalFunction->function());
+    Scope scope(bindingFunction->engine());
+    ScopedContext context(scope, bindingFunction->scope());
+    FunctionObject::init(context, bindingFunction->function());
+    this->bindingFunction.set(internalClass->engine, bindingFunction->d());
 }
 
 QQmlSourceLocation QQmlBindingFunction::currentLocation() const