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, 2 insertions, 0 deletions

diff --git a/src/qml/jsruntime/qv4functionobject_p.h b/src/qml/jsruntime/qv4functionobject_p.h
index d6066ec648..32e71a175b 100644
--- a/src/qml/jsruntime/qv4functionobject_p.h
+++ b/src/qml/jsruntime/qv4functionobject_p.h
@@ -90,6 +90,8 @@ DECLARE_HEAP_OBJECT(FunctionObject, Object) {
     void init();
     void destroy();
 
+    void setFunction(Function *f);
+
     unsigned int formalParameterCount() { return function ? function->nFormals : 0; }
     unsigned int varCount() { return function ? function->compiledFunction->nLocals : 0; }