Add a QJSManagedValue

A QJSManagedValue is a view on a QJSValue which always knows the engine
the value belongs to. This allows us to implement the JavaScript
semantics of the various QJSValue methods in a much more rigorous way.

[ChangeLog][QtQml] The new QJSManagedValue should be used instead of
QJSValue for manipulating properties and prototypes of JavaScript
values, as well as for calling JavaScript functions.

Change-Id: I9d445ffcf68dfa72dba9bae0818e83c80665ad66
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 26 insertions, 3 deletions

diff --git a/src/qml/jsapi/qjsvalue_p.h b/src/qml/jsapi/qjsvalue_p.h
index 9e371118cc..cea48fd9e2 100644
--- a/src/qml/jsapi/qjsvalue_p.h
+++ b/src/qml/jsapi/qjsvalue_p.h
@@ -83,6 +83,12 @@ class Q_AUTOTEST_EXPORT QJSValuePrivate
         return (m & IsString) ? nullptr : reinterpret_cast<QV4::Value *>(m);
     }
 
+    static QV4::Value *managedValue(QV4::Value &v)
+    {
+        quintptr m = quintptr(v.m());
+        return (m & IsString) ? nullptr : reinterpret_cast<QV4::Value *>(m);
+    }
+
     static const QString *qstring(const QV4::Value &v)
     {
         const quintptr m = quintptr(v.m());
@@ -108,14 +114,13 @@ class Q_AUTOTEST_EXPORT QJSValuePrivate
         return QV4::Value::fromHeapObject(reinterpret_cast<QV4::Heap::Base *>(m)).asReturnedValue();
     }
 
-protected:
-    // Only for the test. You're not supposed to subclass QJSValuePrivate otherwise.
+public:
+
     static void setRawValue(QJSValue *jsval, QV4::Value *m)
     {
         jsval->d = encodeRawValue(quintptr(m));
     }
 
-public:
     static QJSValue fromReturnedValue(QV4::ReturnedValue d)
     {
         QJSValue result;
@@ -134,6 +139,19 @@ public:
         return nullptr;
     }
 
+    // This is a move operation and transfers ownership.
+    static QV4::Value *takeManagedValue(QJSValue *jsval)
+    {
+        QV4::Value v = QV4::Value::fromReturnedValue(jsval->d);
+        if (!v.isManaged())
+            return nullptr;
+        if (QV4::Value *value = managedValue(v)) {
+            setValue(jsval, QV4::Encode::undefined());
+            return value;
+        }
+        return nullptr;
+    }
+
     static QV4::ReturnedValue asPrimitiveType(const QJSValue *jsval)
     {
         const QV4::Value v = QV4::Value::fromReturnedValue(jsval->d);
@@ -170,6 +188,11 @@ public:
         jsval->d = v.isManaged() ? encode(v) : v.asReturnedValue();
     }
 
+    static void adoptValue(QJSValue *jsval, QV4::Value *v)
+    {
+        jsval->d = v->isManaged() ? encodeRawValue(quintptr(v)) : v->asReturnedValue();
+    }
+
     // Moves any QString onto the V4 heap, changing the value to reflect that.
     static void manageStringOnV4Heap(QV4::ExecutionEngine *e, QJSValue *jsval)
     {