LibJS: Allow constructing generator from function with null "prototype"

Fixes 4 test262 tests and simplifies some upcoming stuff.

Author: awesomekling

Libraries/LibJS/Runtime/AsyncGenerator.cpp

@@ -24,15 +24,17 @@ ThrowCompletionOr<GC::Ref<AsyncGenerator>> AsyncGenerator::create(Realm& realm,
     // This is "g1.prototype" in figure-2 (https://tc39.es/ecma262/img/figure-2.png)
     static Bytecode::PropertyLookupCache cache;
     auto generating_function_prototype = TRY(generating_function->get(vm.names.prototype, cache));
-    auto generating_function_prototype_object = TRY(generating_function_prototype.to_object(vm));
+    GC::Ptr<Object> generating_function_prototype_object = nullptr;
+    if (!generating_function_prototype.is_nullish())
+        generating_function_prototype_object = MUST(generating_function_prototype.to_object(vm));
     auto object = realm.create<AsyncGenerator>(realm, generating_function_prototype_object, move(execution_context));
     object->m_generating_function = generating_function;
     object->m_previous_value = initial_value;
     return object;
 }
 
-AsyncGenerator::AsyncGenerator(Realm&, Object& prototype, NonnullOwnPtr<ExecutionContext> context)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+AsyncGenerator::AsyncGenerator(Realm& realm, Object* prototype, NonnullOwnPtr<ExecutionContext> context)
+    : Object(realm, prototype)
     , m_async_generator_context(move(context))
 {
 }

Libraries/LibJS/Runtime/AsyncGenerator.h

@@ -44,7 +44,7 @@ class AsyncGenerator final : public Object {
     Optional<String> const& generator_brand() const { return m_generator_brand; }
 
 private:
-    AsyncGenerator(Realm&, Object& prototype, NonnullOwnPtr<ExecutionContext>);
+    AsyncGenerator(Realm&, Object* prototype, NonnullOwnPtr<ExecutionContext>);
 
     virtual void visit_edges(Cell::Visitor&) override;
 

Libraries/LibJS/Runtime/GeneratorObject.cpp

@@ -32,15 +32,17 @@ ThrowCompletionOr<GC::Ref<GeneratorObject>> GeneratorObject::create(Realm& realm
         static Bytecode::PropertyLookupCache cache;
         generating_function_prototype = TRY(generating_function->get(vm.names.prototype, cache));
     }
-    auto generating_function_prototype_object = TRY(generating_function_prototype.to_object(vm));
+    GC::Ptr<Object> generating_function_prototype_object = nullptr;
+    if (!generating_function_prototype.is_nullish())
+        generating_function_prototype_object = MUST(generating_function_prototype.to_object(vm));
     auto object = realm.create<GeneratorObject>(realm, generating_function_prototype_object, move(execution_context));
     object->m_generating_function = generating_function;
     object->m_previous_value = initial_value;
     return object;
 }
 
-GeneratorObject::GeneratorObject(Realm&, Object& prototype, NonnullOwnPtr<ExecutionContext> context, Optional<StringView> generator_brand)
-    : Object(ConstructWithPrototypeTag::Tag, prototype)
+GeneratorObject::GeneratorObject(Realm& realm, Object* prototype, NonnullOwnPtr<ExecutionContext> context, Optional<StringView> generator_brand)
+    : Object(realm, prototype)
     , m_execution_context(move(context))
     , m_generator_brand(move(generator_brand))
 {

Libraries/LibJS/Runtime/GeneratorObject.h

@@ -46,7 +46,7 @@ class GeneratorObject : public Object {
     void set_generator_state(GeneratorState generator_state) { m_generator_state = generator_state; }
 
 protected:
-    GeneratorObject(Realm&, Object& prototype, NonnullOwnPtr<ExecutionContext>, Optional<StringView> generator_brand = {});
+    GeneratorObject(Realm&, Object* prototype, NonnullOwnPtr<ExecutionContext>, Optional<StringView> generator_brand = {});
 
     ThrowCompletionOr<GeneratorState> validate(VM&, Optional<StringView> const& generator_brand);
     virtual ThrowCompletionOr<IterationResult> execute(VM&, JS::Completion const& completion);

Libraries/LibJS/Runtime/IteratorHelper.cpp

@@ -19,7 +19,7 @@ ThrowCompletionOr<GC::Ref<IteratorHelper>> IteratorHelper::create(Realm& realm,
 }
 
 IteratorHelper::IteratorHelper(Realm& realm, Object& prototype, GC::Ref<IteratorRecord> underlying_iterator, GC::Ref<Closure> closure, GC::Ptr<AbruptClosure> abrupt_closure)
-    : GeneratorObject(realm, prototype, realm.vm().running_execution_context().copy(), "Iterator Helper"sv)
+    : GeneratorObject(realm, &prototype, realm.vm().running_execution_context().copy(), "Iterator Helper"sv)
     , m_underlying_iterator(move(underlying_iterator))
     , m_closure(closure)
     , m_abrupt_closure(abrupt_closure)