ladybird/Userland/Libraries/LibJS/Runtime/ProxyObject.cpp

/*
 * Copyright (c) 2020, Matthew Olsson <mattco@serenityos.org>
 * Copyright (c) 2021-2023, Linus Groh <linusg@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/Accessor.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/PropertyDescriptor.h>
#include <LibJS/Runtime/ProxyObject.h>
#include <LibJS/Runtime/ValueInlines.h>

namespace JS {

JS_DEFINE_ALLOCATOR(ProxyObject);

NonnullGCPtr<ProxyObject> ProxyObject::create(Realm& realm, Object& target, Object& handler)
{
    return realm.heap().allocate<ProxyObject>(realm, target, handler, realm.intrinsics().object_prototype());
}

ProxyObject::ProxyObject(Object& target, Object& handler, Object& prototype)
    : FunctionObject(prototype, MayInterfereWithIndexedPropertyAccess::Yes)
    , m_target(target)
    , m_handler(handler)
{
}

static Value property_key_to_value(VM& vm, PropertyKey const& property_key)
{
    VERIFY(property_key.is_valid());
    if (property_key.is_symbol())
        return property_key.as_symbol();

    if (property_key.is_string())
        return PrimitiveString::create(vm, property_key.as_string());

    VERIFY(property_key.is_number());
    return PrimitiveString::create(vm, ByteString::number(property_key.as_number()));
}

// 10.5.1 [[GetPrototypeOf]] ( ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-getprototypeof
ThrowCompletionOr<Object*> ProxyObject::internal_get_prototype_of() const
{
    auto& vm = this->vm();

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "getPrototypeOf").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.getPrototypeOf));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[GetPrototypeOf]]().
        return TRY(m_target->internal_get_prototype_of());
    }

    // 7. Let handlerProto be ? Call(trap, handler, « target »).
    auto handler_proto = TRY(call(vm, *trap, m_handler, m_target));

    // 8. If Type(handlerProto) is neither Object nor Null, throw a TypeError exception.
    if (!handler_proto.is_object() && !handler_proto.is_null())
        return vm.throw_completion<TypeError>(ErrorType::ProxyGetPrototypeOfReturn);

    // 9. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 10. If extensibleTarget is true, return handlerProto.
    if (extensible_target)
        return handler_proto.is_null() ? nullptr : &handler_proto.as_object();

    // 11. Let targetProto be ? target.[[GetPrototypeOf]]().
    auto* target_proto = TRY(m_target->internal_get_prototype_of());

    // 12. If SameValue(handlerProto, targetProto) is false, throw a TypeError exception.
    if (!same_value(handler_proto, target_proto))
        return vm.throw_completion<TypeError>(ErrorType::ProxyGetPrototypeOfNonExtensible);

    // 13. Return handlerProto.
    return handler_proto.is_null() ? nullptr : &handler_proto.as_object();
}

// 10.5.2 [[SetPrototypeOf]] ( V ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-setprototypeof-v
ThrowCompletionOr<bool> ProxyObject::internal_set_prototype_of(Object* prototype)
{
    auto& vm = this->vm();

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "setPrototypeOf").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.setPrototypeOf));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[SetPrototypeOf]](V).
        return m_target->internal_set_prototype_of(prototype);
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target, V »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, prototype)).to_boolean();

    // 8. If booleanTrapResult is false, return false.
    if (!trap_result)
        return false;

    // 9. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 10. If extensibleTarget is true, return true.
    if (extensible_target)
        return true;

    // 11. Let targetProto be ? target.[[GetPrototypeOf]]().
    auto* target_proto = TRY(m_target->internal_get_prototype_of());

    // 12. If SameValue(V, targetProto) is false, throw a TypeError exception.
    if (!same_value(prototype, target_proto))
        return vm.throw_completion<TypeError>(ErrorType::ProxySetPrototypeOfNonExtensible);

    // 13. Return true.
    return true;
}

// 10.5.3 [[IsExtensible]] ( ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-isextensible
ThrowCompletionOr<bool> ProxyObject::internal_is_extensible() const
{
    auto& vm = this->vm();

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "isExtensible").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.isExtensible));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? IsExtensible(target).
        return m_target->is_extensible();
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target)).to_boolean();

    // 8. Let targetResult be ? IsExtensible(target).
    auto target_result = TRY(m_target->is_extensible());

    // 9. If SameValue(booleanTrapResult, targetResult) is false, throw a TypeError exception.
    if (trap_result != target_result)
        return vm.throw_completion<TypeError>(ErrorType::ProxyIsExtensibleReturn);

    // 10. Return booleanTrapResult.
    return trap_result;
}

// 10.5.4 [[PreventExtensions]] ( ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-preventextensions
ThrowCompletionOr<bool> ProxyObject::internal_prevent_extensions()
{
    auto& vm = this->vm();

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "preventExtensions").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.preventExtensions));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[PreventExtensions]]().
        return m_target->internal_prevent_extensions();
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target)).to_boolean();

    // 8. If booleanTrapResult is true, then
    if (trap_result) {
        // a. Let extensibleTarget be ? IsExtensible(target).
        auto extensible_target = TRY(m_target->is_extensible());

        // b. If extensibleTarget is true, throw a TypeError exception.
        if (extensible_target)
            return vm.throw_completion<TypeError>(ErrorType::ProxyPreventExtensionsReturn);
    }

    // 9. Return booleanTrapResult.
    return trap_result;
}

// 10.5.5 [[GetOwnProperty]] ( P ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-getownproperty-p
ThrowCompletionOr<Optional<PropertyDescriptor>> ProxyObject::internal_get_own_property(PropertyKey const& property_key) const
{
    auto& vm = this->vm();

    VERIFY(property_key.is_valid());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "getOwnPropertyDescriptor").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.getOwnPropertyDescriptor));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[GetOwnProperty]](P).
        return m_target->internal_get_own_property(property_key);
    }

    // 7. Let trapResultObj be ? Call(trap, handler, « target, P »).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key)));

    // 8. If Type(trapResultObj) is neither Object nor Undefined, throw a TypeError exception.
    if (!trap_result.is_object() && !trap_result.is_undefined())
        return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorReturn);

    // 9. Let targetDesc be ? target.[[GetOwnProperty]](P).
    auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

    // 10. If trapResultObj is undefined, then
    if (trap_result.is_undefined()) {
        // a. If targetDesc is undefined, return undefined.
        if (!target_descriptor.has_value())
            return Optional<PropertyDescriptor> {};

        // b. If targetDesc.[[Configurable]] is false, throw a TypeError exception.
        if (!*target_descriptor->configurable)
            return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorNonConfigurable);

        // c. Let extensibleTarget be ? IsExtensible(target).
        auto extensible_target = TRY(m_target->is_extensible());

        // d. If extensibleTarget is false, throw a TypeError exception.
        if (!extensible_target)
            return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorUndefinedReturn);

        // e. Return undefined.
        return Optional<PropertyDescriptor> {};
    }

    // 11. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 12. Let resultDesc be ? ToPropertyDescriptor(trapResultObj).
    auto result_desc = TRY(to_property_descriptor(vm, trap_result));

    // 13. Perform CompletePropertyDescriptor(resultDesc).
    result_desc.complete();

    // 14. Let valid be IsCompatiblePropertyDescriptor(extensibleTarget, resultDesc, targetDesc).
    auto valid = is_compatible_property_descriptor(extensible_target, result_desc, target_descriptor);

    // 15. If valid is false, throw a TypeError exception.
    if (!valid)
        return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorInvalidDescriptor);

    // 16. If resultDesc.[[Configurable]] is false, then
    if (!*result_desc.configurable) {
        // a. If targetDesc is undefined or targetDesc.[[Configurable]] is true, then
        if (!target_descriptor.has_value() || *target_descriptor->configurable)
            // i. Throw a TypeError exception.
            return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorInvalidNonConfig);

        // b. If resultDesc has a [[Writable]] field and resultDesc.[[Writable]] is false, then
        if (result_desc.writable.has_value() && !*result_desc.writable) {
            // i. If targetDesc.[[Writable]] is true, throw a TypeError exception.
            if (*target_descriptor->writable)
                return vm.throw_completion<TypeError>(ErrorType::ProxyGetOwnDescriptorNonConfigurableNonWritable);
        }
    }

    // 17. Return resultDesc.
    return result_desc;
}

// 10.5.6 [[DefineOwnProperty]] ( P, Desc ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-defineownproperty-p-desc
ThrowCompletionOr<bool> ProxyObject::internal_define_own_property(PropertyKey const& property_key, PropertyDescriptor const& property_descriptor)
{
    auto& vm = this->vm();

    VERIFY(property_key.is_valid());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "defineProperty").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.defineProperty));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[DefineOwnProperty]](P, Desc).
        return m_target->internal_define_own_property(property_key, property_descriptor);
    }

    // 7. Let descObj be FromPropertyDescriptor(Desc).
    auto descriptor_object = from_property_descriptor(vm, property_descriptor);

    // 8. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target, P, descObj »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key), descriptor_object)).to_boolean();

    // 9. If booleanTrapResult is false, return false.
    if (!trap_result)
        return false;

    // 10. Let targetDesc be ? target.[[GetOwnProperty]](P).
    auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

    // 11. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 12. Else, let settingConfigFalse be false.
    bool setting_config_false = false;

    // 13. If Desc has a [[Configurable]] field and if Desc.[[Configurable]] is false, then
    if (property_descriptor.configurable.has_value() && !*property_descriptor.configurable) {
        // a. Let settingConfigFalse be true.
        setting_config_false = true;
    }

    // 14. If targetDesc is undefined, then
    if (!target_descriptor.has_value()) {
        // a. If extensibleTarget is false, throw a TypeError exception.
        if (!extensible_target)
            return vm.throw_completion<TypeError>(ErrorType::ProxyDefinePropNonExtensible);

        // b. If settingConfigFalse is true, throw a TypeError exception.
        if (setting_config_false)
            return vm.throw_completion<TypeError>(ErrorType::ProxyDefinePropNonConfigurableNonExisting);
    }
    // 15. Else,
    else {
        // a. If IsCompatiblePropertyDescriptor(extensibleTarget, Desc, targetDesc) is false, throw a TypeError exception.
        if (!is_compatible_property_descriptor(extensible_target, property_descriptor, target_descriptor))
            return vm.throw_completion<TypeError>(ErrorType::ProxyDefinePropIncompatibleDescriptor);

        // b. If settingConfigFalse is true and targetDesc.[[Configurable]] is true, throw a TypeError exception.
        if (setting_config_false && *target_descriptor->configurable)
            return vm.throw_completion<TypeError>(ErrorType::ProxyDefinePropExistingConfigurable);

        // c. If IsDataDescriptor(targetDesc) is true, targetDesc.[[Configurable]] is false, and targetDesc.[[Writable]] is true, then
        if (target_descriptor->is_data_descriptor() && !*target_descriptor->configurable && *target_descriptor->writable) {
            // i. If Desc has a [[Writable]] field and Desc.[[Writable]] is false, throw a TypeError exception.
            if (property_descriptor.writable.has_value() && !*property_descriptor.writable)
                return vm.throw_completion<TypeError>(ErrorType::ProxyDefinePropNonWritable);
        }
    }

    // 16. Return true.
    return true;
}

// 10.5.7 [[HasProperty]] ( P ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-hasproperty-p
ThrowCompletionOr<bool> ProxyObject::internal_has_property(PropertyKey const& property_key) const
{
    auto& vm = this->vm();

    VERIFY(property_key.is_valid());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // NOTE: We need to protect ourselves from a Proxy with the handler's prototype set to the
    // Proxy itself, which would by default bounce between these functions indefinitely and lead to
    // a stack overflow when the Proxy's (p) or Proxy handler's (h) Object::get() is called and the
    // handler doesn't have a `has` trap:
    //
    // 1. p -> ProxyObject::internal_has_property()  <- you are here
    // 2. target -> Object::internal_has_property()
    // 3. target.[[Prototype]] (which is internal_has_property) -> Object::internal_has_property()
    //
    // In JS code: `const proxy = new Proxy({}, {}); proxy.__proto__ = Object.create(proxy); "foo" in proxy;`
    if (vm.did_reach_stack_space_limit())
        return vm.throw_completion<InternalError>(ErrorType::CallStackSizeExceeded);

    // 5. Let trap be ? GetMethod(handler, "has").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.has));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[HasProperty]](P).
        return m_target->internal_has_property(property_key);
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target, P »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key))).to_boolean();

    // 8. If booleanTrapResult is false, then
    if (!trap_result) {
        // a. Let targetDesc be ? target.[[GetOwnProperty]](P).
        auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

        // b. If targetDesc is not undefined, then
        if (target_descriptor.has_value()) {
            // i. If targetDesc.[[Configurable]] is false, throw a TypeError exception.
            if (!*target_descriptor->configurable)
                return vm.throw_completion<TypeError>(ErrorType::ProxyHasExistingNonConfigurable);

            // ii. Let extensibleTarget be ? IsExtensible(target).
            auto extensible_target = TRY(m_target->is_extensible());

            // iii. If extensibleTarget is false, throw a TypeError exception.
            if (!extensible_target)
                return vm.throw_completion<TypeError>(ErrorType::ProxyHasExistingNonExtensible);
        }
    }

    // 9. Return booleanTrapResult.
    return trap_result;
}

// 10.5.8 [[Get]] ( P, Receiver ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-get-p-receiver
ThrowCompletionOr<Value> ProxyObject::internal_get(PropertyKey const& property_key, Value receiver, CacheablePropertyMetadata*) const
{
    // NOTE: We don't return any cacheable metadata for proxy lookups.

    VERIFY(!receiver.is_empty());

    auto& vm = this->vm();

    VERIFY(property_key.is_valid());
    VERIFY(!receiver.is_empty());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // NOTE: We need to protect ourselves from a Proxy with its (or handler's) prototype set to the
    // Proxy itself, which would by default bounce between these functions indefinitely and lead to
    // a stack overflow when the Proxy's (p) or Proxy handler's (h) Object::get() is called and the
    // handler doesn't have a `get` trap:
    //
    // 1. p -> ProxyObject::internal_get()  <- you are here
    // 2. h -> Value::get_method()
    // 3. h -> Value::get()
    // 4. h -> Object::internal_get()
    // 5. h -> Object::internal_get_prototype_of() (result is p)
    // 6. goto 1
    //
    // In JS code: `h = {}; p = new Proxy({}, h); h.__proto__ = p; p.foo // or h.foo`
    if (vm.did_reach_stack_space_limit())
        return vm.throw_completion<InternalError>(ErrorType::CallStackSizeExceeded);

    // 5. Let trap be ? GetMethod(handler, "get").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.get));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[Get]](P, Receiver).
        return m_target->internal_get(property_key, receiver);
    }

    // 7. Let trapResult be ? Call(trap, handler, « target, P, Receiver »).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key), receiver));

    // 8. Let targetDesc be ? target.[[GetOwnProperty]](P).
    auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

    // 9. If targetDesc is not undefined and targetDesc.[[Configurable]] is false, then
    if (target_descriptor.has_value() && !*target_descriptor->configurable) {
        // a. If IsDataDescriptor(targetDesc) is true and targetDesc.[[Writable]] is false, then
        if (target_descriptor->is_data_descriptor() && !*target_descriptor->writable) {
            // i. If SameValue(trapResult, targetDesc.[[Value]]) is false, throw a TypeError exception.
            if (!same_value(trap_result, *target_descriptor->value))
                return vm.throw_completion<TypeError>(ErrorType::ProxyGetImmutableDataProperty);
        }
        // b. If IsAccessorDescriptor(targetDesc) is true and targetDesc.[[Get]] is undefined, then
        if (target_descriptor->is_accessor_descriptor() && !*target_descriptor->get) {
            // i. If trapResult is not undefined, throw a TypeError exception.
            if (!trap_result.is_undefined())
                return vm.throw_completion<TypeError>(ErrorType::ProxyGetNonConfigurableAccessor);
        }
    }

    // 10. Return trapResult.
    return trap_result;
}

// 10.5.9 [[Set]] ( P, V, Receiver ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-set-p-v-receiver
ThrowCompletionOr<bool> ProxyObject::internal_set(PropertyKey const& property_key, Value value, Value receiver, CacheablePropertyMetadata*)
{
    auto& vm = this->vm();

    VERIFY(property_key.is_valid());
    VERIFY(!value.is_empty());
    VERIFY(!receiver.is_empty());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // NOTE: We need to protect ourselves from a Proxy with its prototype set to the
    // Proxy itself, which would by default bounce between these functions indefinitely and lead to
    // a stack overflow when the Proxy's (p) or Proxy handler's (h) Object::get() is called and the
    // handler doesn't have a `has` trap:
    //
    // 1. p -> ProxyObject::internal_set()  <- you are here
    // 2. target -> Object::internal_set()
    // 3. target -> Object::ordinary_set_with_own_descriptor()
    // 4. target.[[Prototype]] -> Object::internal_set()
    // 5. target.[[Prototype]] -> Object::ordinary_set_with_own_descriptor()
    // 6. target.[[Prototype]].[[Prototype]] (which is ProxyObject) -> Object::internal_set()
    //
    // In JS code: `const proxy = new Proxy({}, {}); proxy.__proto__ = Object.create(proxy); proxy["foo"] = "bar";`
    if (vm.did_reach_stack_space_limit())
        return vm.throw_completion<InternalError>(ErrorType::CallStackSizeExceeded);

    // 5. Let trap be ? GetMethod(handler, "set").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.set));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[Set]](P, V, Receiver).
        return m_target->internal_set(property_key, value, receiver);
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target, P, V, Receiver »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key), value, receiver)).to_boolean();

    // 8. If booleanTrapResult is false, return false.
    if (!trap_result)
        return false;

    // 9. Let targetDesc be ? target.[[GetOwnProperty]](P).
    auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

    // 10. If targetDesc is not undefined and targetDesc.[[Configurable]] is false, then
    if (target_descriptor.has_value() && !*target_descriptor->configurable) {
        // a. If IsDataDescriptor(targetDesc) is true and targetDesc.[[Writable]] is false, then
        if (target_descriptor->is_data_descriptor() && !*target_descriptor->writable) {
            // i. If SameValue(V, targetDesc.[[Value]]) is false, throw a TypeError exception.
            if (!same_value(value, *target_descriptor->value))
                return vm.throw_completion<TypeError>(ErrorType::ProxySetImmutableDataProperty);
        }
        // b. If IsAccessorDescriptor(targetDesc) is true, then
        if (target_descriptor->is_accessor_descriptor()) {
            // i. If targetDesc.[[Set]] is undefined, throw a TypeError exception.
            if (!*target_descriptor->set)
                return vm.throw_completion<TypeError>(ErrorType::ProxySetNonConfigurableAccessor);
        }
    }

    // 11. Return true.
    return true;
}

// 10.5.10 [[Delete]] ( P ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-delete-p
ThrowCompletionOr<bool> ProxyObject::internal_delete(PropertyKey const& property_key)
{
    auto& vm = this->vm();

    VERIFY(property_key.is_valid());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "deleteProperty").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.deleteProperty));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[Delete]](P).
        return m_target->internal_delete(property_key);
    }

    // 7. Let booleanTrapResult be ToBoolean(? Call(trap, handler, « target, P »)).
    auto trap_result = TRY(call(vm, *trap, m_handler, m_target, property_key_to_value(vm, property_key))).to_boolean();

    // 8. If booleanTrapResult is false, return false.
    if (!trap_result)
        return false;

    // 9. Let targetDesc be ? target.[[GetOwnProperty]](P).
    auto target_descriptor = TRY(m_target->internal_get_own_property(property_key));

    // 10. If targetDesc is undefined, return true.
    if (!target_descriptor.has_value())
        return true;

    // 11. If targetDesc.[[Configurable]] is false, throw a TypeError exception.
    if (!*target_descriptor->configurable)
        return vm.throw_completion<TypeError>(ErrorType::ProxyDeleteNonConfigurable);

    // 12. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 13. If extensibleTarget is false, throw a TypeError exception.
    if (!extensible_target)
        return vm.throw_completion<TypeError>(ErrorType::ProxyDeleteNonExtensible);

    // 14. Return true.
    return true;
}

// 10.5.11 [[OwnPropertyKeys]] ( ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-ownpropertykeys
ThrowCompletionOr<MarkedVector<Value>> ProxyObject::internal_own_property_keys() const
{
    auto& vm = this->vm();

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "ownKeys").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.ownKeys));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? target.[[OwnPropertyKeys]]().
        return m_target->internal_own_property_keys();
    }

    // 7. Let trapResultArray be ? Call(trap, handler, « target »).
    auto trap_result_array = TRY(call(vm, *trap, m_handler, m_target));

    // 8. Let trapResult be ? CreateListFromArrayLike(trapResultArray, « String, Symbol »).
    HashTable<PropertyKey> unique_keys;
    auto trap_result = TRY(create_list_from_array_like(vm, trap_result_array, [&](auto value) -> ThrowCompletionOr<void> {
        if (!value.is_string() && !value.is_symbol())
            return vm.throw_completion<TypeError>(ErrorType::ProxyOwnPropertyKeysNotStringOrSymbol);
        auto property_key = MUST(value.to_property_key(vm));
        unique_keys.set(property_key, AK::HashSetExistingEntryBehavior::Keep);
        return {};
    }));

    // 9. If trapResult contains any duplicate entries, throw a TypeError exception.
    if (unique_keys.size() != trap_result.size())
        return vm.throw_completion<TypeError>(ErrorType::ProxyOwnPropertyKeysDuplicates);

    // 10. Let extensibleTarget be ? IsExtensible(target).
    auto extensible_target = TRY(m_target->is_extensible());

    // 11. Let targetKeys be ? target.[[OwnPropertyKeys]]().
    auto target_keys = TRY(m_target->internal_own_property_keys());

    // 12. Assert: targetKeys is a List of property keys.
    // 13. Assert: targetKeys contains no duplicate entries.

    // 14. Let targetConfigurableKeys be a new empty List.
    auto target_configurable_keys = MarkedVector<Value> { heap() };

    // 15. Let targetNonconfigurableKeys be a new empty List.
    auto target_nonconfigurable_keys = MarkedVector<Value> { heap() };

    // 16. For each element key of targetKeys, do
    for (auto& key : target_keys) {
        auto property_key = MUST(PropertyKey::from_value(vm, key));

        // a. Let desc be ? target.[[GetOwnProperty]](key).
        auto descriptor = TRY(m_target->internal_get_own_property(property_key));

        // b. If desc is not undefined and desc.[[Configurable]] is false, then
        if (descriptor.has_value() && !*descriptor->configurable) {
            // i. Append key as an element of targetNonconfigurableKeys.
            target_nonconfigurable_keys.append(key);
        }
        // c. Else,
        else {
            // i. Append key as an element of targetConfigurableKeys.
            target_configurable_keys.append(key);
        }
    }

    // 17. If extensibleTarget is true and targetNonconfigurableKeys is empty, then
    if (extensible_target && target_nonconfigurable_keys.is_empty()) {
        // a. Return trapResult.
        return { move(trap_result) };
    }

    // 18. Let uncheckedResultKeys be a List whose elements are the elements of trapResult.
    auto unchecked_result_keys = MarkedVector<Value> { heap() };
    unchecked_result_keys.extend(trap_result);

    // 19. For each element key of targetNonconfigurableKeys, do
    for (auto& key : target_nonconfigurable_keys) {
        // a. If key is not an element of uncheckedResultKeys, throw a TypeError exception.
        if (!unchecked_result_keys.contains_slow(key))
            return vm.throw_completion<TypeError>(ErrorType::ProxyOwnPropertyKeysSkippedNonconfigurableProperty, key.to_string_without_side_effects());

        // b. Remove key from uncheckedResultKeys.
        unchecked_result_keys.remove_first_matching([&](auto& value) {
            return same_value(value, key);
        });
    }

    // 20. If extensibleTarget is true, return trapResult.
    if (extensible_target)
        return { move(trap_result) };

    // 21. For each element key of targetConfigurableKeys, do
    for (auto& key : target_configurable_keys) {
        // a. If key is not an element of uncheckedResultKeys, throw a TypeError exception.
        if (!unchecked_result_keys.contains_slow(key))
            return vm.throw_completion<TypeError>(ErrorType::ProxyOwnPropertyKeysNonExtensibleSkippedProperty, key.to_string_without_side_effects());

        // b. Remove key from uncheckedResultKeys.
        unchecked_result_keys.remove_first_matching([&](auto& value) {
            return same_value(value, key);
        });
    }

    // 22. If uncheckedResultKeys is not empty, throw a TypeError exception.
    if (!unchecked_result_keys.is_empty())
        return vm.throw_completion<TypeError>(ErrorType::ProxyOwnPropertyKeysNonExtensibleNewProperty, unchecked_result_keys[0].to_string_without_side_effects());

    // 23. Return trapResult.
    return { move(trap_result) };
}

// 10.5.12 [[Call]] ( thisArgument, argumentsList ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-call-thisargument-argumentslist
ThrowCompletionOr<Value> ProxyObject::internal_call(Value this_argument, ReadonlySpan<Value> arguments_list)
{
    auto& vm = this->vm();
    auto& realm = *vm.current_realm();

    // A Proxy exotic object only has a [[Call]] internal method if the initial value of its [[ProxyTarget]] internal slot is an object that has a [[Call]] internal method.
    VERIFY(is_function());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].

    // 5. Let trap be ? GetMethod(handler, "apply").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.apply));

    // 6. If trap is undefined, then
    if (!trap) {
        // a. Return ? Call(target, thisArgument, argumentsList).
        return call(vm, m_target, this_argument, arguments_list);
    }

    // 7. Let argArray be CreateArrayFromList(argumentsList).
    auto arguments_array = Array::create_from(realm, arguments_list);

    // 8. Return ? Call(trap, handler, « target, thisArgument, argArray »).
    return call(vm, trap, m_handler, m_target, this_argument, arguments_array);
}

bool ProxyObject::has_constructor() const
{
    // Note: A Proxy exotic object only has a [[Construct]] internal method if the initial value of
    //       its [[ProxyTarget]] internal slot is an object that has a [[Construct]] internal method.
    if (!is_function())
        return false;

    return static_cast<FunctionObject&>(*m_target).has_constructor();
}

// 10.5.13 [[Construct]] ( argumentsList, newTarget ), https://tc39.es/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-construct-argumentslist-newtarget
ThrowCompletionOr<NonnullGCPtr<Object>> ProxyObject::internal_construct(ReadonlySpan<Value> arguments_list, FunctionObject& new_target)
{
    auto& vm = this->vm();
    auto& realm = *vm.current_realm();

    // A Proxy exotic object only has a [[Construct]] internal method if the initial value of its [[ProxyTarget]] internal slot is an object that has a [[Construct]] internal method.
    VERIFY(is_function());

    // 1. Let handler be O.[[ProxyHandler]].

    // 2. If handler is null, throw a TypeError exception.
    if (m_is_revoked)
        return vm.throw_completion<TypeError>(ErrorType::ProxyRevoked);

    // 3. Assert: Type(handler) is Object.
    // 4. Let target be O.[[ProxyTarget]].
    // 5. Assert: IsConstructor(target) is true.

    // 6. Let trap be ? GetMethod(handler, "construct").
    auto trap = TRY(Value(m_handler).get_method(vm, vm.names.construct));

    // 7. If trap is undefined, then
    if (!trap) {
        // a. Return ? Construct(target, argumentsList, newTarget).
        return construct(vm, static_cast<FunctionObject&>(*m_target), arguments_list, &new_target);
    }

    // 8. Let argArray be CreateArrayFromList(argumentsList).
    auto arguments_array = Array::create_from(realm, arguments_list);

    // 9. Let newObj be ? Call(trap, handler, « target, argArray, newTarget »).
    auto new_object = TRY(call(vm, trap, m_handler, m_target, arguments_array, &new_target));

    // 10. If Type(newObj) is not Object, throw a TypeError exception.
    if (!new_object.is_object())
        return vm.throw_completion<TypeError>(ErrorType::ProxyConstructBadReturnType);

    // 11. Return newObj.
    return new_object.as_object();
}

void ProxyObject::visit_edges(Cell::Visitor& visitor)
{
    Base::visit_edges(visitor);
    visitor.visit(m_target);
    visitor.visit(m_handler);
}

DeprecatedFlyString const& ProxyObject::name() const
{
    VERIFY(is_function());
    return static_cast<FunctionObject&>(*m_target).name();
}

}