LibJS: Always keep a reference to the global object in Shape

We need to move towards supporting multiple global objects, which will
be a large refactoring. To keep it manageable, let's do it in steps,
starting with giving Object a way to find the GlobalObject it lives
inside by asking its Shape for it.

Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -70,7 +70,7 @@ GlobalObject::GlobalObject()
 void GlobalObject::initialize()
 {
     // These are done first since other prototypes depend on their presence.
-    m_empty_object_shape = heap().allocate<Shape>();
+    m_empty_object_shape = heap().allocate<Shape>(*this);
     m_object_prototype = heap().allocate<ObjectPrototype>();
     m_function_prototype = heap().allocate<FunctionPrototype>();
 

Libraries/LibJS/Runtime/Object.cpp

@@ -91,7 +91,7 @@ Object::Object(Object* prototype)
         m_shape = interpreter().global_object().empty_object_shape();
         set_prototype(prototype);
     } else {
-        m_shape = interpreter().heap().allocate<Shape>();
+        m_shape = interpreter().heap().allocate<Shape>(interpreter().global_object());
     }
 }
 

Libraries/LibJS/Runtime/Object.h

@@ -73,6 +73,8 @@ public:
     Shape& shape() { return *m_shape; }
     const Shape& shape() const { return *m_shape; }
 
+    GlobalObject& global_object() const { return shape().global_object(); }
+
     virtual Value get(PropertyName) const;
 
     virtual bool has_property(PropertyName) const;

Libraries/LibJS/Runtime/Shape.cpp

@@ -25,13 +25,14 @@
  */
 
 #include <LibJS/Interpreter.h>
+#include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Shape.h>
 
 namespace JS {
 
 Shape* Shape::create_unique_clone() const
 {
-    auto* new_shape = heap().allocate<Shape>();
+    auto* new_shape = heap().allocate<Shape>(m_global_object);
     new_shape->m_unique = true;
     new_shape->m_prototype = m_prototype;
     ensure_property_table();
@@ -45,7 +46,7 @@ Shape* Shape::create_put_transition(const FlyString& property_name, PropertyAttr
     TransitionKey key { property_name, attributes };
     if (auto* existing_shape = m_forward_transitions.get(key).value_or(nullptr))
         return existing_shape;
-    auto* new_shape = heap().allocate<Shape>(this, property_name, attributes, TransitionType::Put);
+    auto* new_shape = heap().allocate<Shape>(*this, property_name, attributes, TransitionType::Put);
     m_forward_transitions.set(key, new_shape);
     return new_shape;
 }
@@ -55,31 +56,34 @@ Shape* Shape::create_configure_transition(const FlyString& property_name, Proper
     TransitionKey key { property_name, attributes };
     if (auto* existing_shape = m_forward_transitions.get(key).value_or(nullptr))
         return existing_shape;
-    auto* new_shape = heap().allocate<Shape>(this, property_name, attributes, TransitionType::Configure);
+    auto* new_shape = heap().allocate<Shape>(*this, property_name, attributes, TransitionType::Configure);
     m_forward_transitions.set(key, new_shape);
     return new_shape;
 }
 
 Shape* Shape::create_prototype_transition(Object* new_prototype)
 {
-    return heap().allocate<Shape>(this, new_prototype);
+    return heap().allocate<Shape>(*this, new_prototype);
 }
 
-Shape::Shape()
+Shape::Shape(GlobalObject& global_object)
+    : m_global_object(global_object)
 {
 }
 
-Shape::Shape(Shape* previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType transition_type)
+Shape::Shape(Shape& previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType transition_type)
-    : m_previous(previous_shape)
+    : m_global_object(previous_shape.m_global_object)
+    , m_previous(&previous_shape)
     , m_property_name(property_name)
     , m_attributes(attributes)
-    , m_prototype(previous_shape->m_prototype)
+    , m_prototype(previous_shape.m_prototype)
     , m_transition_type(transition_type)
 {
 }
 
-Shape::Shape(Shape* previous_shape, Object* new_prototype)
+Shape::Shape(Shape& previous_shape, Object* new_prototype)
-    : m_previous(previous_shape)
+    : m_global_object(previous_shape.m_global_object)
+    , m_previous(&previous_shape)
     , m_prototype(new_prototype)
     , m_transition_type(TransitionType::Prototype)
 {
@@ -92,6 +96,7 @@ Shape::~Shape()
 void Shape::visit_children(Cell::Visitor& visitor)
 {
     Cell::visit_children(visitor);
+    visitor.visit(&m_global_object);
     visitor.visit(m_prototype);
     visitor.visit(m_previous);
     for (auto& it : m_forward_transitions)

Libraries/LibJS/Runtime/Shape.h

@@ -62,9 +62,9 @@ public:
         Prototype,
     };
 
-    Shape();
+    explicit Shape(GlobalObject&);
-    Shape(Shape* previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType);
+    Shape(Shape& previous_shape, const FlyString& property_name, PropertyAttributes attributes, TransitionType);
-    Shape(Shape* previous_shape, Object* new_prototype);
+    Shape(Shape& previous_shape, Object* new_prototype);
 
     Shape* create_put_transition(const FlyString& name, PropertyAttributes attributes);
     Shape* create_configure_transition(const FlyString& name, PropertyAttributes attributes);
@@ -73,6 +73,8 @@ public:
     bool is_unique() const { return m_unique; }
     Shape* create_unique_clone() const;
 
+    GlobalObject& global_object() const { return m_global_object; }
+
     Object* prototype() { return m_prototype; }
     const Object* prototype() const { return m_prototype; }
 
@@ -99,6 +101,8 @@ private:
 
     void ensure_property_table() const;
 
+    GlobalObject& m_global_object;
+
     mutable OwnPtr<HashMap<FlyString, PropertyMetadata>> m_property_table;
 
     HashMap<TransitionKey, Shape*> m_forward_transitions;