From 566a8dfd93ac78516f8571ba1f2c98d779821c96 Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Sun, 16 Jul 2023 14:37:35 -0400
Subject: [PATCH] LibJS: Allow GeneratorObject to be subclassed

In the Iterator Helpers proposal, we must create a generator object with
additional internal slots and behavior differences.

GeneratorObject is currently implemented assuming it wraps around an
ECMAScriptFunctionObject with generated bytecode. In this proposal, we
instead have "Abstract Closure" blocks. So this marks the `execute`
method as virtual, to allow the future subclass to essentially just
invoke those closures.

We will also require mutable access to the [[GeneratorState]] internal
slot.
---
 Userland/Libraries/LibJS/Print.cpp                  |  8 ++++----
 .../Libraries/LibJS/Runtime/GeneratorObject.cpp     |  3 ++-
 Userland/Libraries/LibJS/Runtime/GeneratorObject.h  | 13 ++++++++-----
 3 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/Userland/Libraries/LibJS/Print.cpp b/Userland/Libraries/LibJS/Print.cpp
index 2ae606baf78..11d95eacb1a 100644
--- a/Userland/Libraries/LibJS/Print.cpp
+++ b/Userland/Libraries/LibJS/Print.cpp
@@ -421,15 +421,15 @@ ErrorOr<void> print_shadow_realm(JS::PrintContext& print_context, JS::ShadowReal
     return {};
 }
 
-ErrorOr<void> print_generator(JS::PrintContext& print_context, JS::GeneratorObject const&, HashTable<JS::Object*>&)
+ErrorOr<void> print_generator(JS::PrintContext& print_context, JS::GeneratorObject const& generator, HashTable<JS::Object*>&)
 {
-    TRY(print_type(print_context, "Generator"sv));
+    TRY(print_type(print_context, generator.class_name()));
     return {};
 }
 
-ErrorOr<void> print_async_generator(JS::PrintContext& print_context, JS::AsyncGenerator const&, HashTable<JS::Object*>&)
+ErrorOr<void> print_async_generator(JS::PrintContext& print_context, JS::AsyncGenerator const& generator, HashTable<JS::Object*>&)
 {
-    TRY(print_type(print_context, "AsyncGenerator"sv));
+    TRY(print_type(print_context, generator.class_name()));
     return {};
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp b/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
index f5400323261..39ab4e66fc3 100644
--- a/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/GeneratorObject.cpp
@@ -35,9 +35,10 @@ ThrowCompletionOr<NonnullGCPtr<GeneratorObject>> GeneratorObject::create(Realm&
     return object;
 }
 
-GeneratorObject::GeneratorObject(Realm&, Object& prototype, ExecutionContext context)
+GeneratorObject::GeneratorObject(Realm&, Object& prototype, ExecutionContext context, Optional<StringView> generator_brand)
     : Object(ConstructWithPrototypeTag::Tag, prototype)
     , m_execution_context(move(context))
+    , m_generator_brand(move(generator_brand))
 {
 }
 
diff --git a/Userland/Libraries/LibJS/Runtime/GeneratorObject.h b/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
index 2989d41dd64..1217870e92e 100644
--- a/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
+++ b/Userland/Libraries/LibJS/Runtime/GeneratorObject.h
@@ -12,7 +12,7 @@
 
 namespace JS {
 
-class GeneratorObject final : public Object {
+class GeneratorObject : public Object {
     JS_OBJECT(GeneratorObject, Object);
 
 public:
@@ -23,19 +23,22 @@ public:
     ThrowCompletionOr<Value> resume(VM&, Value value, Optional<StringView> const& generator_brand);
     ThrowCompletionOr<Value> resume_abrupt(VM&, JS::Completion abrupt_completion, Optional<StringView> const& generator_brand);
 
-private:
-    GeneratorObject(Realm&, Object& prototype, ExecutionContext);
-
     enum class GeneratorState {
         SuspendedStart,
         SuspendedYield,
         Executing,
         Completed,
     };
+    GeneratorState generator_state() const { return m_generator_state; }
+    void set_generator_state(GeneratorState generator_state) { m_generator_state = generator_state; }
+
+protected:
+    GeneratorObject(Realm&, Object& prototype, ExecutionContext, Optional<StringView> generator_brand = {});
 
     ThrowCompletionOr<GeneratorState> validate(VM&, Optional<StringView> const& generator_brand);
-    ThrowCompletionOr<Value> execute(VM&, JS::Completion const& completion);
+    virtual ThrowCompletionOr<Value> execute(VM&, JS::Completion const& completion);
 
+private:
     ExecutionContext m_execution_context;
     GCPtr<ECMAScriptFunctionObject> m_generating_function;
     Value m_previous_value;