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, 13 insertions, 0 deletions

diff --git a/tests/auto/qml/qjsengine/tst_qjsengine.cpp b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
index e62e4a0980..f862cdb048 100644
--- a/tests/auto/qml/qjsengine/tst_qjsengine.cpp
+++ b/tests/auto/qml/qjsengine/tst_qjsengine.cpp
@@ -129,6 +129,7 @@ private slots:
     void arraySort();
     void lookupOnDisappearingProperty();
     void arrayConcat();
+    void recursiveBoundFunctions();
 
     void qRegExpInport_data();
     void qRegExpInport();
@@ -3022,6 +3023,18 @@ void tst_QJSEngine::arrayConcat()
     QCOMPARE(v.toString(), QString::fromLatin1("6,10,11,12"));
 }
 
+void tst_QJSEngine::recursiveBoundFunctions()
+{
+
+    QJSEngine eng;
+    QJSValue v = eng.evaluate("function foo(x, y, z)"
+                              "{ return this + x + y + z; }"
+                              "var bar = foo.bind(-1, 10);"
+                              "var baz = bar.bind(-2, 20);"
+                              "baz(30)");
+    QCOMPARE(v.toInt(), 59);
+}
+
 static QRegExp minimal(QRegExp r) { r.setMinimal(true); return r; }
 
 void tst_QJSEngine::qRegExpInport_data()