From 6e0e8a824296558b2d2eb9a18084820c8178eab8 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 14 Jun 2021 10:52:15 +0200
Subject: [PATCH] LibJS: Teach Reference to access call frame arguments
 directly

---
 Userland/Libraries/LibJS/AST.cpp               |  2 ++
 Userland/Libraries/LibJS/Runtime/Reference.cpp |  8 ++++++++
 Userland/Libraries/LibJS/Runtime/Reference.h   | 10 ++++++++++
 3 files changed, 20 insertions(+)

diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index 669968a1ad..8a8908ed2c 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -668,6 +668,8 @@ Reference Expression::to_reference(Interpreter&, GlobalObject&) const
 
 Reference Identifier::to_reference(Interpreter& interpreter, GlobalObject&) const
 {
+    if (m_argument_index.has_value())
+        return Reference(Reference::CallFrameArgument, m_argument_index.value(), string());
     return interpreter.vm().get_reference(string());
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/Reference.cpp b/Userland/Libraries/LibJS/Runtime/Reference.cpp
index 2bc6b466f8..76ccbb042e 100644
--- a/Userland/Libraries/LibJS/Runtime/Reference.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Reference.cpp
@@ -19,6 +19,11 @@ void Reference::put(GlobalObject& global_object, Value value)
         return;
     }
 
+    if (m_call_frame_argument_index.has_value()) {
+        global_object.vm().call_frame().arguments[m_call_frame_argument_index.value()] = value;
+        return;
+    }
+
     if (is_local_variable() || is_global_variable()) {
         if (is_local_variable())
             vm.set_variable(m_name.to_string(), value, global_object);
@@ -68,6 +73,9 @@ Value Reference::get(GlobalObject& global_object)
         return {};
     }
 
+    if (m_call_frame_argument_index.has_value())
+        return global_object.vm().argument(m_call_frame_argument_index.value());
+
     if (is_local_variable() || is_global_variable()) {
         Value value;
         if (is_local_variable())
diff --git a/Userland/Libraries/LibJS/Runtime/Reference.h b/Userland/Libraries/LibJS/Runtime/Reference.h
index 864d7855c4..337d852623 100644
--- a/Userland/Libraries/LibJS/Runtime/Reference.h
+++ b/Userland/Libraries/LibJS/Runtime/Reference.h
@@ -40,6 +40,15 @@ public:
     {
     }
 
+    enum CallFrameArgumentTag { CallFrameArgument };
+    Reference(CallFrameArgumentTag, size_t index, FlyString const& name)
+        : m_base(js_null())
+        , m_name(name)
+        , m_call_frame_argument_index(index)
+        , m_local_variable(true)
+    {
+    }
+
     Value base() const { return m_base; }
     const PropertyName& name() const { return m_name; }
     bool is_strict() const { return m_strict; }
@@ -74,6 +83,7 @@ private:
 
     Value m_base;
     PropertyName m_name;
+    Optional<size_t> m_call_frame_argument_index;
     bool m_strict { false };
     bool m_local_variable { false };
     bool m_global_variable { false };