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LibJS: Do more comprehensive check if next() fast path is possible

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Before this change each built-in iterator object has a boolean
`m_next_method_was_redefined`. If user code later changed the iterator’s
prototype (e.g. `Object.setPrototypeOf()`), we still believed the
built-in fast-path was safe and skipped the user supplied override,
producing wrong results.

With this change
`BuiltinIterator::as_builtin_iterator_if_next_is_not_redefined()` looks
up the current `next` property and verifies that it is still the
built-in native function.
This commit is contained in:
Aliaksandr Kalenik 2025-06-01 18:44:18 +02:00 • committed by Alexander Kalenik
parent 0fcb574041
commit 285bc005cb
Notes: github-actions[bot] 2025-06-01 22:16:38 +00:00
25 changed files with 168 additions and 98 deletions
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15
Libraries/LibJS/Runtime/ArrayIterator.cpp
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@ -29,8 +29,6 @@ ArrayIterator::ArrayIterator(Value array, Object::PropertyKind iteration_kind, O
, m_array(array)
, m_iteration_kind(iteration_kind)
{
auto& array_iterator_prototype = as<ArrayIteratorPrototype>(prototype);
m_next_method_was_redefined = array_iterator_prototype.next_method_was_redefined();
}
void ArrayIterator::visit_edges(Cell::Visitor& visitor)
@ -39,6 +37,19 @@ void ArrayIterator::visit_edges(Cell::Visitor& visitor)
visitor.visit(m_array);
}
BuiltinIterator* ArrayIterator::as_builtin_iterator_if_next_is_not_redefined(IteratorRecord const& iterator_record)
{
if (iterator_record.next_method.is_object()) {
auto const& next_function = iterator_record.next_method.as_object();
if (next_function.is_native_function()) {
auto const& native_function = static_cast<NativeFunction const&>(next_function);
if (native_function.is_array_prototype_next_builtin())
return this;
}
}
return nullptr;
}
ThrowCompletionOr<void> ArrayIterator::next(VM& vm, bool& done, Value& value)
{
// 1. Let O be the this value.