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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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17
Libraries/LibJS/Runtime/StringIterator.cpp
View file

@ -6,8 +6,8 @@
#include <AK/Utf8View.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/NativeFunction.h>
#include <LibJS/Runtime/StringIterator.h>
#include <LibJS/Runtime/StringIteratorPrototype.h>
namespace JS {
@ -23,8 +23,19 @@ StringIterator::StringIterator(String string, Object& prototype)
, m_string(move(string))
, m_iterator(Utf8View(m_string).begin())
{
auto& string_iterator_prototype = as<StringIteratorPrototype>(prototype);
m_next_method_was_redefined = string_iterator_prototype.next_method_was_redefined();
}
BuiltinIterator* StringIterator::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_string_prototype_next_builtin())
return this;
}
}
return nullptr;
}
ThrowCompletionOr<void> StringIterator::next(VM& vm, bool& done, Value& value)