LibJS: Add AsyncGenerator / AsyncGeneratorPrototype

Not implementing any prototype functions yet, but stubbing out async
generator infrastructure will allow us to make some progress in that
direction.

Userland/Libraries/LibJS/CMakeLists.txt

@@ -49,8 +49,10 @@ set(SOURCES
     Runtime/AsyncFunctionConstructor.cpp
     Runtime/AsyncFunctionDriverWrapper.cpp
     Runtime/AsyncFunctionPrototype.cpp
+    Runtime/AsyncGenerator.cpp
     Runtime/AsyncGeneratorFunctionConstructor.cpp
     Runtime/AsyncGeneratorFunctionPrototype.cpp
+    Runtime/AsyncGeneratorPrototype.cpp
     Runtime/AsyncIteratorPrototype.cpp
     Runtime/AtomicsObject.cpp
     Runtime/BigInt.cpp

Userland/Libraries/LibJS/Forward.h

@@ -196,8 +196,10 @@ class ProxyObject;
 class ProxyConstructor;
 
 // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct constructor
-class GeneratorPrototype;
 class AsyncFromSyncIteratorPrototype;
+class AsyncGenerator;
+class AsyncGeneratorPrototype;
+class GeneratorPrototype;
 
 class TypedArrayConstructor;
 class TypedArrayPrototype;

Userland/Libraries/LibJS/Runtime/AsyncGenerator.cpp

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AsyncGenerator.h>
+#include <LibJS/Runtime/AsyncGeneratorPrototype.h>
+#include <LibJS/Runtime/GlobalObject.h>
+
+namespace JS {
+
+AsyncGenerator::AsyncGenerator(Object& prototype)
+    : Object(prototype)
+{
+}
+
+void AsyncGenerator::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+    for (auto const& request : m_async_generator_queue) {
+        if (request.completion.value().has_value())
+            visitor.visit(*request.completion.value());
+        visitor.visit(request.capability.promise);
+        visitor.visit(request.capability.reject);
+        visitor.visit(request.capability.resolve);
+    }
+}
+
+}

Userland/Libraries/LibJS/Runtime/AsyncGenerator.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Variant.h>
+#include <LibJS/Runtime/AsyncGeneratorRequest.h>
+#include <LibJS/Runtime/ExecutionContext.h>
+#include <LibJS/Runtime/Object.h>
+
+namespace JS {
+
+// 27.6.2 Properties of AsyncGenerator Instances, https://tc39.es/ecma262/#sec-properties-of-asyncgenerator-intances
+class AsyncGenerator final : public Object {
+    JS_OBJECT(AsyncGenerator, Object);
+
+public:
+    enum class State {
+        SuspendedStart,
+        SuspendedYield,
+        Executing,
+        AwaitingReturn,
+        Completed,
+    };
+
+    explicit AsyncGenerator(Object& prototype);
+    virtual ~AsyncGenerator() override = default;
+
+private:
+    virtual void visit_edges(Cell::Visitor&) override;
+
+    // At the time of constructing an AsyncGenerator, we still need to point to an
+    // execution context on the stack, but later need to 'adopt' it.
+    using ExecutionContextVariant = Variant<ExecutionContext, ExecutionContext*, Empty>;
+
+    Optional<State> m_async_generator_state;               // [[AsyncGeneratorState]]
+    ExecutionContextVariant m_async_generator_context;     // [[AsyncGeneratorContext]]
+    Vector<AsyncGeneratorRequest> m_async_generator_queue; // [[AsyncGeneratorQueue]]
+    Optional<String> m_generator_brand;                    // [[GeneratorBrand]]
+};
+
+}

Userland/Libraries/LibJS/Runtime/AsyncGeneratorFunctionPrototype.cpp

@@ -6,6 +6,7 @@
 
 #include <LibJS/Runtime/AsyncGeneratorFunctionConstructor.h>
 #include <LibJS/Runtime/AsyncGeneratorFunctionPrototype.h>
+#include <LibJS/Runtime/AsyncGeneratorPrototype.h>
 #include <LibJS/Runtime/GlobalObject.h>
 
 namespace JS {
@@ -23,8 +24,7 @@ void AsyncGeneratorFunctionPrototype::initialize(GlobalObject& global_object)
     // The constructor cannot be set at this point since it has not been initialized.
 
     // 27.4.3.2 AsyncGeneratorFunction.prototype.prototype, https://tc39.es/ecma262/#sec-asyncgeneratorfunction-prototype-prototype
-    // FIXME: AsyncGenerator does not exist yet.
-    // define_direct_property(vm.names.prototype, global_object.async_generator_prototype(), Attribute::Configurable);
+    define_direct_property(vm.names.prototype, global_object.async_generator_prototype(), Attribute::Configurable);
 
     // 27.4.3.3 AsyncGeneratorFunction.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-asyncgeneratorfunction-prototype-tostringtag
     define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(vm, vm.names.AsyncGeneratorFunction.as_string()), Attribute::Configurable);

Userland/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.cpp

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AsyncGeneratorPrototype.h>
+
+namespace JS {
+
+// 27.6.1 Properties of the AsyncGenerator Prototype Object, https://tc39.es/ecma262/#sec-properties-of-asyncgenerator-prototype
+AsyncGeneratorPrototype::AsyncGeneratorPrototype(GlobalObject& global_object)
+    : PrototypeObject(*global_object.async_iterator_prototype())
+{
+}
+
+void AsyncGeneratorPrototype::initialize(GlobalObject& global_object)
+{
+    auto& vm = this->vm();
+    Object::initialize(global_object);
+
+    // 27.6.1.5 AsyncGenerator.prototype [ @@toStringTag ], https://tc39.es/ecma262/#sec-asyncgenerator-prototype-tostringtag
+    define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(vm, "AsyncGenerator"), Attribute::Configurable);
+}
+
+}

Userland/Libraries/LibJS/Runtime/AsyncGeneratorPrototype.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/AsyncGenerator.h>
+#include <LibJS/Runtime/PrototypeObject.h>
+
+namespace JS {
+
+class AsyncGeneratorPrototype final : public PrototypeObject<AsyncGeneratorPrototype, AsyncGenerator> {
+    JS_PROTOTYPE_OBJECT(AsyncGeneratorPrototype, AsyncGenerator, AsyncGenerator)
+
+public:
+    explicit AsyncGeneratorPrototype(GlobalObject&);
+    virtual void initialize(GlobalObject&) override;
+    virtual ~AsyncGeneratorPrototype() override = default;
+};
+
+}

Userland/Libraries/LibJS/Runtime/AsyncGeneratorRequest.h

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Completion.h>
+#include <LibJS/Runtime/PromiseReaction.h>
+
+namespace JS {
+
+// 27.6.3.1 AsyncGeneratorRequest Records, https://tc39.es/ecma262/#sec-asyncgeneratorrequest-records
+struct AsyncGeneratorRequest {
+    Completion completion;        // [[Completion]]
+    PromiseCapability capability; // [[Capability]]
+};
+
+}

Userland/Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -28,6 +28,7 @@
 #include <LibJS/Runtime/AsyncFunctionPrototype.h>
 #include <LibJS/Runtime/AsyncGeneratorFunctionConstructor.h>
 #include <LibJS/Runtime/AsyncGeneratorFunctionPrototype.h>
+#include <LibJS/Runtime/AsyncGeneratorPrototype.h>
 #include <LibJS/Runtime/AsyncIteratorPrototype.h>
 #include <LibJS/Runtime/AtomicsObject.h>
 #include <LibJS/Runtime/BigIntConstructor.h>
@@ -177,12 +178,10 @@ void GlobalObject::initialize_global_object()
     JS_ENUMERATE_ITERATOR_PROTOTYPES
 #undef __JS_ENUMERATE
 
-    // %GeneratorFunction.prototype.prototype% must be initialized separately as it has no
-    // companion constructor
-    m_generator_prototype = heap().allocate<GeneratorPrototype>(*this, *this);
-
+    // These must be initialized separately as they have no companion constructor
     m_async_from_sync_iterator_prototype = heap().allocate<AsyncFromSyncIteratorPrototype>(*this, *this);
-
+    m_async_generator_prototype = heap().allocate<AsyncGeneratorPrototype>(*this, *this);
+    m_generator_prototype = heap().allocate<GeneratorPrototype>(*this, *this);
     m_intl_segments_prototype = heap().allocate<Intl::SegmentsPrototype>(*this, *this);
 
 #define __JS_ENUMERATE(ClassName, snake_name, PrototypeName, ConstructorName, ArrayType) \
@@ -298,6 +297,9 @@ void GlobalObject::initialize_global_object()
     // 27.5.1.1 Generator.prototype.constructor, https://tc39.es/ecma262/#sec-generator.prototype.constructor
     m_generator_prototype->define_direct_property(vm.names.constructor, m_generator_function_prototype, Attribute::Configurable);
 
+    // 27.6.1.1 AsyncGenerator.prototype.constructor, https://tc39.es/ecma262/#sec-asyncgenerator-prototype-constructor
+    m_async_generator_prototype->define_direct_property(vm.names.constructor, m_async_generator_function_prototype, Attribute::Configurable);
+
     m_array_prototype_values_function = &m_array_prototype->get_without_side_effects(vm.names.values).as_function();
     m_date_constructor_now_function = &m_date_constructor->get_without_side_effects(vm.names.now).as_function();
     m_eval_function = &get_without_side_effects(vm.names.eval).as_function();
@@ -315,8 +317,9 @@ void GlobalObject::visit_edges(Visitor& visitor)
     visitor.visit(m_new_object_shape);
     visitor.visit(m_new_ordinary_function_prototype_object_shape);
     visitor.visit(m_proxy_constructor);
-    visitor.visit(m_generator_prototype);
     visitor.visit(m_async_from_sync_iterator_prototype);
+    visitor.visit(m_async_generator_prototype);
+    visitor.visit(m_generator_prototype);
     visitor.visit(m_intl_segments_prototype);
     visitor.visit(m_array_prototype_values_function);
     visitor.visit(m_date_constructor_now_function);

Userland/Libraries/LibJS/Runtime/GlobalObject.h

@@ -37,6 +37,7 @@ public:
 
     // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct constructor
     Object* async_from_sync_iterator_prototype() { return m_async_from_sync_iterator_prototype; }
+    Object* async_generator_prototype() { return m_async_generator_prototype; }
     Object* generator_prototype() { return m_generator_prototype; }
 
     // Not included in JS_ENUMERATE_INTL_OBJECTS due to missing distinct constructor
@@ -109,6 +110,7 @@ private:
 
     // Not included in JS_ENUMERATE_NATIVE_OBJECTS due to missing distinct constructor
     Object* m_async_from_sync_iterator_prototype { nullptr };
+    Object* m_async_generator_prototype { nullptr };
     Object* m_generator_prototype { nullptr };
 
     // Not included in JS_ENUMERATE_INTL_OBJECTS due to missing distinct constructor