serenity/Userland/Libraries/LibJS/Runtime/Shape.h

/*
 * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/HashMap.h>
#include <AK/OwnPtr.h>
#include <AK/StringView.h>
#include <AK/WeakPtr.h>
#include <AK/Weakable.h>
#include <LibJS/Forward.h>
#include <LibJS/Heap/Cell.h>
#include <LibJS/Runtime/PropertyAttributes.h>
#include <LibJS/Runtime/StringOrSymbol.h>
#include <LibJS/Runtime/Value.h>

namespace JS {

struct PropertyMetadata {
    u32 offset { 0 };
    PropertyAttributes attributes { 0 };
};

struct TransitionKey {
    StringOrSymbol property_key;
    PropertyAttributes attributes { 0 };

    bool operator==(TransitionKey const& other) const
    {
        return property_key == other.property_key && attributes == other.attributes;
    }
};

class Shape final
    : public Cell
    , public Weakable<Shape> {
    JS_CELL(Shape, Cell);

public:
    virtual ~Shape() override = default;

    enum class TransitionType {
        Invalid,
        Put,
        Configure,
        Prototype,
    };

    Shape* create_put_transition(StringOrSymbol const&, PropertyAttributes attributes);
    Shape* create_configure_transition(StringOrSymbol const&, PropertyAttributes attributes);
    Shape* create_prototype_transition(Object* new_prototype);

    void add_property_without_transition(StringOrSymbol const&, PropertyAttributes);
    void add_property_without_transition(PropertyKey const&, PropertyAttributes);

    bool is_unique() const { return m_unique; }
    static FlatPtr is_unique_offset() { return OFFSET_OF(Shape, m_unique); }

    Shape* create_unique_clone() const;

    Realm& realm() const { return m_realm; }

    Object* prototype() { return m_prototype; }
    Object const* prototype() const { return m_prototype; }

    Optional<PropertyMetadata> lookup(StringOrSymbol const&) const;
    OrderedHashMap<StringOrSymbol, PropertyMetadata> const& property_table() const;
    u32 property_count() const { return m_property_count; }

    struct Property {
        StringOrSymbol key;
        PropertyMetadata value;
    };

    void set_prototype_without_transition(Object* new_prototype) { m_prototype = new_prototype; }

    void remove_property_from_unique_shape(StringOrSymbol const&, size_t offset);
    void add_property_to_unique_shape(StringOrSymbol const&, PropertyAttributes attributes);
    void reconfigure_property_in_unique_shape(StringOrSymbol const& property_key, PropertyAttributes attributes);

    [[nodiscard]] u64 unique_shape_serial_number() const { return m_unique_shape_serial_number; }
    static FlatPtr unique_shape_serial_number_offset() { return OFFSET_OF(Shape, m_unique_shape_serial_number); }

private:
    explicit Shape(Realm&);
    Shape(Shape& previous_shape, StringOrSymbol const& property_key, PropertyAttributes attributes, TransitionType);
    Shape(Shape& previous_shape, Object* new_prototype);

    virtual void visit_edges(Visitor&) override;

    Shape* get_or_prune_cached_forward_transition(TransitionKey const&);
    Shape* get_or_prune_cached_prototype_transition(Object* prototype);

    void ensure_property_table() const;

    NonnullGCPtr<Realm> m_realm;

    mutable OwnPtr<OrderedHashMap<StringOrSymbol, PropertyMetadata>> m_property_table;

    OwnPtr<HashMap<TransitionKey, WeakPtr<Shape>>> m_forward_transitions;
    OwnPtr<HashMap<GCPtr<Object>, WeakPtr<Shape>>> m_prototype_transitions;
    GCPtr<Shape> m_previous;
    StringOrSymbol m_property_key;
    GCPtr<Object> m_prototype;
    u32 m_property_count { 0 };

    PropertyAttributes m_attributes { 0 };
    TransitionType m_transition_type : 6 { TransitionType::Invalid };
    bool m_unique { false };

    // Since unique shapes never change identity, inline caches use this incrementing serial number
    // to know whether its property table has been modified since last time we checked.
    u64 m_unique_shape_serial_number { 0 };
};

}

template<>
struct AK::Traits<JS::TransitionKey> : public DefaultTraits<JS::TransitionKey> {
    static unsigned hash(const JS::TransitionKey& key)
    {
        return pair_int_hash(key.attributes.bits(), Traits<JS::StringOrSymbol>::hash(key.property_key));
    }
};