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>

3 files changed, 59 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()
diff --git a/tests/auto/qml/qqmlecmascript/data/bindingBoundFunctions.qml b/tests/auto/qml/qqmlecmascript/data/bindingBoundFunctions.qml
new file mode 100644
index 0000000000..8dbd2fd3d9
--- /dev/null
+++ b/tests/auto/qml/qqmlecmascript/data/bindingBoundFunctions.qml
@@ -0,0 +1,34 @@
+import QtQuick 2.6
+
+QtObject {
+    property bool success: false
+    property var num: 100
+    property var simple: 0
+    property var complex: 0
+
+
+    Component.onCompleted: {
+        function s(x) {
+            return x
+        }
+        function c(x) {
+            return x + num
+        }
+
+        var bound = s.bind(undefined, 100)
+        simple = Qt.binding(bound)
+        if (simple != 100)
+            return;
+        var bound = c.bind(undefined, 100)
+        complex = Qt.binding(bound);
+
+        if (complex != 200)
+            return;
+        num = 0;
+        if (complex != 100)
+            return;
+
+        print("success!!!");
+        success = true;
+    }
+}
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index c0cf123243..f40a9758f7 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -289,6 +289,7 @@ private slots:
     void withStatement();
     void tryStatement();
     void replaceBinding();
+    void bindingBoundFunctions();
     void deleteRootObjectInCreation();
     void onDestruction();
     void onDestructionViaGC();
@@ -7247,6 +7248,17 @@ void tst_qqmlecmascript::replaceBinding()
     delete obj;
 }
 
+void tst_qqmlecmascript::bindingBoundFunctions()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("bindingBoundFunctions.qml"));
+    QObject *obj = c.create();
+    QVERIFY(obj != nullptr);
+
+    QVERIFY(obj->property("success").toBool());
+    delete obj;
+}
+
 void tst_qqmlecmascript::deleteRootObjectInCreation()
 {
     {