LibJS: Implement basic support for the "delete" operator

It turns out "delete" is actually a unary op :)
This patch implements deletion of object properties, it doesn't yet
work for casually deleting properties from the global object.

When deleting a property from an object, we switch that object to
having a unique shape, no longer sharing shapes with others.
Once an object has a unique shape, it no longer needs to care about
shape transitions.

1 files changed, 3 insertions, 0 deletions

diff --git a/Libraries/LibJS/Runtime/Object.h b/Libraries/LibJS/Runtime/Object.h
index 0b0ccc4fcc..5c945ea888 100644
--- a/Libraries/LibJS/Runtime/Object.h
+++ b/Libraries/LibJS/Runtime/Object.h
@@ -46,6 +46,8 @@ public:
     Shape& shape() { return *m_shape; }
     const Shape& shape() const { return *m_shape; }
 
+    Value delete_property(PropertyName);
+
     virtual Value get_by_index(i32 property_index) const;
     Value get(const FlyString& property_name) const;
     Value get(PropertyName) const;
@@ -102,6 +104,7 @@ public:
 
 private:
     void set_shape(Shape&);
+    void ensure_shape_is_unique();
 
     Shape* m_shape { nullptr };
     Vector<Value> m_storage;