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LibJS: Implement [[Call]] and [[Construct]] internal slots properly

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This patch implements:

- Spec compliant [[Call]] and [[Construct]] internal slots, as virtual
  FunctionObject::internal_{call,construct}(). These effectively replace
  the old virtual FunctionObject::{call,construct}(), but with several
  advantages:
  - Clear and consistent naming, following the object internal methods
  - Use of completions
  - internal_construct() returns an Object, and not Value! This has been
    a source of confusion for a long time, since in the spec there's
    always an Object returned but the Value return type in LibJS meant
    that this could not be fully trusted and something could screw you
    over.
  - Arguments are passed explicitly in form of a MarkedValueList,
    allowing manipulation (BoundFunction). We still put them on the
    execution context as a lot of code depends on it (VM::arguments()),
    but not from the Call() / Construct() AOs anymore, which now allows
    for bypassing them and invoking [[Call]] / [[Construct]] directly.
    Nothing but Call() / Construct() themselves do that at the moment,
    but future additions to ECMA262 or already existing web specs might.
- Spec compliant, standalone Call() and Construct() AOs: currently the
  closest we have is VM::{call,construct}(), but those try to cater to
  all the different function object subclasses at once, resulting in a
  horrible mess and calling AOs with functions they should never be
  called with; most prominently PrepareForOrdinaryCall and
  OrdinaryCallBindThis, which are only for ECMAScriptFunctionObject.

As a result this also contains an implicit optimization: we no longer
need to create a new function environment for NativeFunctions - which,
worth mentioning, is what started this whole crusade in the first place
:^)
This commit is contained in:
Linus Groh 2021-10-08 20:37:21 +01:00
parent 58c34012dd
commit cf168fac50
16 changed files with 503 additions and 246 deletions
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162
Userland/Libraries/LibJS/Runtime/VM.cpp
View file

@ -13,6 +13,7 @@
#include <LibJS/Runtime/AbstractOperations.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/BoundFunction.h>
#include <LibJS/Runtime/Completion.h>
#include <LibJS/Runtime/ECMAScriptFunctionObject.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/FinalizationRegistry.h>
@ -477,116 +478,21 @@ Reference VM::resolve_binding(FlyString const& name, Environment* environment)
return get_identifier_reference(environment, name, strict);
}
static void append_bound_and_passed_arguments(MarkedValueList& arguments, Vector<Value> bound_arguments, Optional<MarkedValueList> passed_arguments)
{
arguments.ensure_capacity(bound_arguments.size());
arguments.extend(move(bound_arguments));
if (passed_arguments.has_value()) {
auto arguments_list = move(passed_arguments.release_value().values());
arguments.grow_capacity(arguments_list.size());
arguments.extend(move(arguments_list));
}
}
// 7.3.32 InitializeInstanceElements ( O, constructor ), https://tc39.es/ecma262/#sec-initializeinstanceelements
void VM::initialize_instance_elements(Object& object, ECMAScriptFunctionObject& constructor)
ThrowCompletionOr<void> VM::initialize_instance_elements(Object& object, ECMAScriptFunctionObject& constructor)
{
for (auto& field : constructor.fields()) {
field.define_field(*this, object);
if (exception())
return;
if (auto* exception = this->exception())
return JS::throw_completion(exception->value());
}
return {};
}
// FIXME: This function should not exist as-is, most of it should be moved to the individual
// [[Construct]] implementations so that this becomes the Construct() AO (3 steps).
// NOTE: This is a leftover from the old world of vm.call() and vm.construct(). Replace all uses with plain construct() and remove this.
Value VM::construct(FunctionObject& function, FunctionObject& new_target, Optional<MarkedValueList> arguments)
{
auto& global_object = function.global_object();
Value this_argument;
if (!is<ECMAScriptFunctionObject>(function) || static_cast<ECMAScriptFunctionObject&>(function).constructor_kind() == ECMAScriptFunctionObject::ConstructorKind::Base)
this_argument = TRY_OR_DISCARD(ordinary_create_from_constructor<Object>(global_object, new_target, &GlobalObject::object_prototype));
// FIXME: prepare_for_ordinary_call() is not supposed to receive a BoundFunction, ProxyObject, etc. - ever.
// This needs to be moved to NativeFunction/ECMAScriptFunctionObject's construct() (10.2.2 [[Construct]])
ExecutionContext callee_context(heap());
prepare_for_ordinary_call(function, callee_context, &new_target);
if (exception())
return {};
ArmedScopeGuard pop_guard = [&] {
pop_execution_context();
};
if (auto* interpreter = interpreter_if_exists())
callee_context.current_node = interpreter->current_node();
if (is<BoundFunction>(function)) {
auto& bound_function = static_cast<BoundFunction&>(function);
append_bound_and_passed_arguments(callee_context.arguments, bound_function.bound_arguments(), move(arguments));
} else {
append_bound_and_passed_arguments(callee_context.arguments, {}, move(arguments));
}
if (auto* environment = callee_context.lexical_environment) {
auto& function_environment = verify_cast<FunctionEnvironment>(*environment);
function_environment.set_new_target(&new_target);
if (!this_argument.is_empty() && function_environment.this_binding_status() != FunctionEnvironment::ThisBindingStatus::Lexical) {
function_environment.bind_this_value(global_object, this_argument);
if (exception())
return {};
}
}
// If we are a Derived constructor, |this| has not been constructed before super is called.
callee_context.this_value = this_argument;
if (is<ECMAScriptFunctionObject>(function) && static_cast<ECMAScriptFunctionObject&>(function).constructor_kind() == ECMAScriptFunctionObject::ConstructorKind::Base) {
VERIFY(this_argument.is_object());
initialize_instance_elements(this_argument.as_object(), static_cast<ECMAScriptFunctionObject&>(function));
if (exception())
return {};
}
auto* constructor_environment = callee_context.lexical_environment;
auto result = function.construct(new_target);
VERIFY(constructor_environment);
pop_execution_context();
pop_guard.disarm();
// If we are constructing an instance of a derived class,
// set the prototype on objects created by constructors that return an object (i.e. NativeFunction subclasses).
if ((!is<ECMAScriptFunctionObject>(function) || static_cast<ECMAScriptFunctionObject&>(function).constructor_kind() == ECMAScriptFunctionObject::ConstructorKind::Base)
&& is<ECMAScriptFunctionObject>(new_target) && static_cast<ECMAScriptFunctionObject&>(new_target).constructor_kind() == ECMAScriptFunctionObject::ConstructorKind::Derived
&& result.is_object()) {
verify_cast<FunctionEnvironment>(constructor_environment)->replace_this_binding(result);
auto prototype = TRY_OR_DISCARD(new_target.get(names.prototype));
if (prototype.is_object())
TRY_OR_DISCARD(result.as_object().internal_set_prototype_of(&prototype.as_object()));
return result;
}
if (exception())
return {};
if (result.is_object())
return result;
if (is<ECMAScriptFunctionObject>(function) && static_cast<ECMAScriptFunctionObject&>(function).constructor_kind() == ECMAScriptFunctionObject::ConstructorKind::Base)
return this_argument;
if (!result.is_empty() && !result.is_undefined()) {
throw_exception<TypeError>(global_object, ErrorType::DerivedConstructorReturningInvalidValue);
return {};
}
VERIFY(constructor_environment);
return constructor_environment->get_this_binding(global_object);
return TRY_OR_DISCARD(JS::construct(function.global_object(), function, move(arguments), &new_target));
}
void VM::throw_exception(Exception& exception)
@ -622,12 +528,8 @@ Value VM::get_new_target()
// 10.2.1.1 PrepareForOrdinaryCall ( F, newTarget ), https://tc39.es/ecma262/#sec-prepareforordinarycall
void VM::prepare_for_ordinary_call(FunctionObject& function, ExecutionContext& callee_context, Object* new_target)
{
// NOTE: This is a LibJS specific hack for NativeFunction to inherit the strictness of its caller.
// FIXME: I feel like we should be able to get rid of this.
if (is<NativeFunction>(function))
callee_context.is_strict_mode = in_strict_mode();
else
callee_context.is_strict_mode = function.is_strict_mode();
// Non-standard
callee_context.is_strict_mode = function.is_strict_mode();
// 1. Let callerContext be the running execution context.
// 2. Let calleeContext be a new ECMAScript code execution context.
@ -642,9 +544,13 @@ void VM::prepare_for_ordinary_call(FunctionObject& function, ExecutionContext& c
// 4. Let calleeRealm be F.[[Realm]].
auto* callee_realm = function.realm();
// FIXME: See FIXME in VM::call_internal() / VM::construct().
// NOTE: This non-standard fallback is needed until we can guarantee that literally
// every function has a realm - especially in LibWeb that's sometimes not the case
// when a function is created while no JS is running, as we currently need to rely on
// that (:acid2:, I know - see set_event_handler_attribute() for an example).
// If there's no 'current realm' either, we can't continue and crash.
if (!callee_realm)
callee_realm = current_realm();
callee_realm = vm.current_realm();
VERIFY(callee_realm);
// 5. Set the Realm of calleeContext to calleeRealm.
@ -703,46 +609,14 @@ void VM::ordinary_call_bind_this(FunctionObject& function, ExecutionContext& cal
callee_context.this_value = this_value;
}
// NOTE: This is only here because there's a million invocations of vm.call() - it used to be tied to the VM in weird ways.
// We should update all of those and then remove this, along with the call() template functions in VM.h, and use the standalone call() AO.
ThrowCompletionOr<Value> VM::call_internal(FunctionObject& function, Value this_value, Optional<MarkedValueList> arguments)
{
VERIFY(!exception());
VERIFY(!this_value.is_empty());
if (is<BoundFunction>(function)) {
auto& bound_function = static_cast<BoundFunction&>(function);
MarkedValueList with_bound_arguments { heap() };
append_bound_and_passed_arguments(with_bound_arguments, bound_function.bound_arguments(), move(arguments));
return call_internal(bound_function.bound_target_function(), bound_function.bound_this(), move(with_bound_arguments));
}
// FIXME: prepare_for_ordinary_call() is not supposed to receive a BoundFunction, ProxyObject, etc. - ever.
// This needs to be moved to NativeFunction/ECMAScriptFunctionObject's construct() (10.2.2 [[Construct]])
ExecutionContext callee_context(heap());
prepare_for_ordinary_call(function, callee_context, nullptr);
if (auto* exception = this->exception())
return JS::throw_completion(exception->value());
ScopeGuard pop_guard = [&] {
pop_execution_context();
};
if (auto* interpreter = interpreter_if_exists())
callee_context.current_node = interpreter->current_node();
callee_context.this_value = this_value;
append_bound_and_passed_arguments(callee_context.arguments, {}, move(arguments));
ordinary_call_bind_this(function, callee_context, this_value);
if (auto* exception = this->exception())
return JS::throw_completion(exception->value());
auto result = function.call();
if (auto* exception = this->exception())
return JS::throw_completion(exception->value());
return result;
return JS::call_impl(function.global_object(), &function, this_value, move(arguments));
}
bool VM::in_strict_mode() const