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LibJS: Implement a very hackish "arguments" object

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We now lazily create an "arguments" array inside functions when code
tries to access it.

This doesn't follow the spec at all but still covers a lot of the
basic uses of arguments, i.e "arguments.length" and "arguments[n]"
This commit is contained in:
Andreas Kling 2020-12-05 16:38:29 +01:00
parent e6dadd9e5b
commit cc14b5a6d7
4 changed files with 39 additions and 0 deletions
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21
Libraries/LibJS/Runtime/VM.cpp
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@ -27,6 +27,7 @@
#include <AK/ScopeGuard.h>
#include <AK/StringBuilder.h>
#include <LibJS/Interpreter.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/Reference.h>
@ -116,6 +117,8 @@ void VM::gather_roots(HashTable<Cell*>& roots)
for (auto& call_frame : m_call_stack) {
if (call_frame->this_value.is_cell())
roots.set(call_frame->this_value.as_cell());
if (call_frame->arguments_object)
roots.set(call_frame->arguments_object);
for (auto& argument : call_frame->arguments) {
if (argument.is_cell())
roots.set(argument.as_cell());
@ -166,6 +169,24 @@ void VM::set_variable(const FlyString& name, Value value, GlobalObject& global_o
Value VM::get_variable(const FlyString& name, GlobalObject& global_object)
{
if (m_call_stack.size()) {
if (name == names.arguments) {
// HACK: Special handling for the name "arguments":
// If the name "arguments" is defined in the current scope, for example via
// a function parameter, or by a local var declaration, we use that.
// Otherwise, we return a lazily constructed Array with all the argument values.
// FIXME: Do something much more spec-compliant.
auto possible_match = current_scope()->get_from_scope(name);
if (possible_match.has_value())
return possible_match.value().value;
if (!call_frame().arguments_object) {
call_frame().arguments_object = Array::create(global_object);
for (auto argument : call_frame().arguments) {
call_frame().arguments_object->indexed_properties().append(argument);
}
}
return call_frame().arguments_object;
}
for (auto* scope = current_scope(); scope; scope = scope->parent()) {
auto possible_match = scope->get_from_scope(name);
if (possible_match.has_value())