ladybird/Libraries/LibJS/Runtime/ArgumentsObject.cpp

/*
 * Copyright (c) 2021-2025, Andreas Kling <andreas@ladybird.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibJS/Runtime/ArgumentsObject.h>
#include <LibJS/Runtime/Completion.h>
#include <LibJS/Runtime/GlobalObject.h>

namespace JS {

GC_DEFINE_ALLOCATOR(ArgumentsObject);

ArgumentsObject::ArgumentsObject(Realm& realm, Environment& environment)
    : Object(realm.intrinsics().mapped_arguments_object_shape(), MayInterfereWithIndexedPropertyAccess::Yes)
    , m_environment(environment)
{
}

void ArgumentsObject::initialize(Realm& realm)
{
    Base::initialize(realm);
    set_has_parameter_map();
}

void ArgumentsObject::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_environment);
}

bool ArgumentsObject::parameter_map_has(PropertyKey const& key) const
{
    return key.is_number()
        && key.as_number() < m_mapped_names.size()
        && !m_mapped_names[key.as_number()].is_empty();
}

// 10.4.4.3 [[Get]] ( P, Receiver ), https://tc39.es/ecma262/#sec-arguments-exotic-objects-get-p-receiver
ThrowCompletionOr<Value> ArgumentsObject::internal_get(PropertyKey const& property_key, Value receiver, CacheablePropertyMetadata* cacheable_metadata, PropertyLookupPhase phase) const
{
    // 1. Let map be args.[[ParameterMap]].
    // 2. Let isMapped be ! HasOwnProperty(map, P).
    bool is_mapped = parameter_map_has(property_key);

    // 3. If isMapped is false, then
    if (!is_mapped) {
        // a. Return ? OrdinaryGet(args, P, Receiver).
        return Object::internal_get(property_key, receiver, cacheable_metadata, phase);
    }

    // a. Assert: map contains a formal parameter mapping for P.
    // b. Return ! Get(map, P).
    return get_from_parameter_map(property_key);
}

// 10.4.4.4 [[Set]] ( P, V, Receiver ), https://tc39.es/ecma262/#sec-arguments-exotic-objects-set-p-v-receiver
ThrowCompletionOr<bool> ArgumentsObject::internal_set(PropertyKey const& property_key, Value value, Value receiver, CacheablePropertyMetadata*, PropertyLookupPhase)
{
    bool is_mapped = false;

    // 1. If SameValue(args, Receiver) is false, then
    if (!same_value(this, receiver)) {
        // a. Let isMapped be false.
        is_mapped = false;
    } else {
        // a. Let map be args.[[ParameterMap]].
        // b. Let isMapped be ! HasOwnProperty(map, P).
        is_mapped = parameter_map_has(property_key);
    }

    // 3. If isMapped is true, then
    if (is_mapped) {
        // a. Assert: The following Set will succeed, since formal parameters mapped by arguments objects are always writable.
        // b. Perform ! Set(map, P, V, false).
        set_in_parameter_map(property_key, value);
    }

    // 4. Return ? OrdinarySet(args, P, V, Receiver).
    return Object::internal_set(property_key, value, receiver);
}

// 10.4.4.5 [[Delete]] ( P ), https://tc39.es/ecma262/#sec-arguments-exotic-objects-delete-p
ThrowCompletionOr<bool> ArgumentsObject::internal_delete(PropertyKey const& property_key)
{
    // 1. Let map be args.[[ParameterMap]].
    // 2. Let isMapped be ! HasOwnProperty(map, P).
    bool is_mapped = parameter_map_has(property_key);

    // 3. Let result be ? OrdinaryDelete(args, P).
    bool result = TRY(Object::internal_delete(property_key));

    // 4. If result is true and isMapped is true, then
    if (result && is_mapped) {
        // a. Perform ! map.[[Delete]](P).
        delete_from_parameter_map(property_key);
    }

    // 5. Return result.
    return result;
}

// 10.4.4.1 [[GetOwnProperty]] ( P ), https://tc39.es/ecma262/#sec-arguments-exotic-objects-getownproperty-p
ThrowCompletionOr<Optional<PropertyDescriptor>> ArgumentsObject::internal_get_own_property(PropertyKey const& property_key) const
{
    // 1. Let desc be OrdinaryGetOwnProperty(args, P).
    auto desc = MUST(Object::internal_get_own_property(property_key));

    // 2. If desc is undefined, return desc.
    if (!desc.has_value())
        return desc;

    // 3. Let map be args.[[ParameterMap]].
    // 4. Let isMapped be ! HasOwnProperty(map, P).
    bool is_mapped = parameter_map_has(property_key);

    // 5. If isMapped is true, then
    if (is_mapped) {
        // a. Set desc.[[Value]] to ! Get(map, P).
        desc->value = get_from_parameter_map(property_key);
    }

    // 6. Return desc.
    return desc;
}

// 10.4.4.2 [[DefineOwnProperty]] ( P, Desc ), https://tc39.es/ecma262/#sec-arguments-exotic-objects-defineownproperty-p-desc
ThrowCompletionOr<bool> ArgumentsObject::internal_define_own_property(PropertyKey const& property_key, PropertyDescriptor const& descriptor, Optional<PropertyDescriptor>* precomputed_get_own_property)
{
    // 1. Let map be args.[[ParameterMap]].
    // 2. Let isMapped be ! HasOwnProperty(map, P).
    bool is_mapped = parameter_map_has(property_key);

    // 3. Let newArgDesc be Desc.
    auto new_arg_desc = descriptor;

    // 4. If isMapped is true and IsDataDescriptor(Desc) is true, then
    if (is_mapped && descriptor.is_data_descriptor()) {
        // a. If Desc does not have a [[Value]] field and Desc has a [[Writable]] field, and Desc.[[Writable]] is false, then
        if (!descriptor.value.has_value() && descriptor.writable.has_value() && descriptor.writable == false) {
            // i. Set newArgDesc to a copy of Desc.
            new_arg_desc = descriptor;
            // ii. Set newArgDesc.[[Value]] to ! Get(map, P).
            new_arg_desc.value = get_from_parameter_map(property_key);
        }
    }

    // 5. Let allowed be ! OrdinaryDefineOwnProperty(args, P, newArgDesc).
    bool allowed = MUST(Object::internal_define_own_property(property_key, new_arg_desc, precomputed_get_own_property));

    // 6. If allowed is false, return false.
    if (!allowed)
        return false;

    // 7. If isMapped is true, then
    if (is_mapped) {
        // a. If IsAccessorDescriptor(Desc) is true, then
        if (descriptor.is_accessor_descriptor()) {
            // i. Perform ! map.[[Delete]](P).
            delete_from_parameter_map(property_key);
        } else {
            // i. If Desc has a [[Value]] field, then
            if (descriptor.value.has_value()) {
                // 1. Assert: The following Set will succeed, since formal parameters mapped by arguments objects are always writable.

                // 2. Perform ! Set(map, P, Desc.[[Value]], false).
                set_in_parameter_map(property_key, descriptor.value.value());
            }
            // ii. If Desc has a [[Writable]] field and Desc.[[Writable]] is false, then
            if (descriptor.writable == false) {
                // 1. Perform ! map.[[Delete]](P).
                delete_from_parameter_map(property_key);
            }
        }
    }

    // 8. Return true.
    return true;
}

void ArgumentsObject::delete_from_parameter_map(PropertyKey const& property_key)
{
    m_mapped_names[property_key.as_number()] = FlyString {};
}

Value ArgumentsObject::get_from_parameter_map(PropertyKey const& property_key) const
{
    return MUST(m_environment->get_binding_value(vm(), m_mapped_names[property_key.as_number()], false));
}

void ArgumentsObject::set_in_parameter_map(PropertyKey const& property_key, Value value)
{
    MUST(m_environment->set_mutable_binding(vm(), m_mapped_names[property_key.as_number()], value, false));
}

}