LibJS: Begin implementing Atomics

This adds the Atomics object to the global object and sets up only its
@@toStringTag property.

Userland/Libraries/LibJS/CMakeLists.txt

@@ -35,6 +35,7 @@ set(SOURCES
     Runtime/ArrayIterator.cpp
     Runtime/ArrayIteratorPrototype.cpp
     Runtime/ArrayPrototype.cpp
+    Runtime/AtomicsObject.cpp
     Runtime/BigInt.cpp
     Runtime/BigIntConstructor.cpp
     Runtime/BigIntObject.cpp

Userland/Libraries/LibJS/Runtime/AtomicsObject.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AtomicsObject.h>
+#include <LibJS/Runtime/GlobalObject.h>
+
+namespace JS {
+
+AtomicsObject::AtomicsObject(GlobalObject& global_object)
+    : Object(*global_object.object_prototype())
+{
+}
+
+void AtomicsObject::initialize(GlobalObject& global_object)
+{
+    Object::initialize(global_object);
+
+    auto& vm = this->vm();
+
+    // 25.4.15 Atomics [ @@toStringTag ], https://tc39.es/ecma262/#sec-atomics-@@tostringtag
+    define_direct_property(*vm.well_known_symbol_to_string_tag(), js_string(global_object.heap(), "Atomics"), Attribute::Configurable);
+}
+
+}

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021, Tim Flynn <trflynn89@pm.me>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibJS/Runtime/Object.h>
+
+namespace JS {
+
+class AtomicsObject : public Object {
+    JS_OBJECT(AtomicsObject, Object);
+
+public:
+    explicit AtomicsObject(GlobalObject&);
+    virtual void initialize(GlobalObject&) override;
+    virtual ~AtomicsObject() override = default;
+};
+
+}

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -17,6 +17,7 @@ namespace JS {
     P(__defineSetter__)                      \
     P(__lookupGetter__)                      \
     P(__lookupSetter__)                      \
+    P(Atomics)                               \
     P(BYTES_PER_ELEMENT)                     \
     P(BigInt)                                \
     P(Boolean)                               \

Userland/Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -20,6 +20,7 @@
 #include <LibJS/Runtime/ArrayConstructor.h>
 #include <LibJS/Runtime/ArrayIteratorPrototype.h>
 #include <LibJS/Runtime/ArrayPrototype.h>
+#include <LibJS/Runtime/AtomicsObject.h>
 #include <LibJS/Runtime/BigIntConstructor.h>
 #include <LibJS/Runtime/BigIntPrototype.h>
 #include <LibJS/Runtime/BooleanConstructor.h>
@@ -184,6 +185,7 @@ void GlobalObject::initialize_global_object()
 
     define_direct_property(vm.names.globalThis, this, attr);
     define_direct_property(vm.names.console, heap().allocate<ConsoleObject>(*this, *this), attr);
+    define_direct_property(vm.names.Atomics, heap().allocate<AtomicsObject>(*this, *this), attr);
     define_direct_property(vm.names.Math, heap().allocate<MathObject>(*this, *this), attr);
     define_direct_property(vm.names.JSON, heap().allocate<JSONObject>(*this, *this), attr);
     define_direct_property(vm.names.Reflect, heap().allocate<ReflectObject>(*this, *this), attr);

Userland/Libraries/LibJS/Tests/builtins/Atomics/Atomics.@@toStringTag.js

@@ -0,0 +1,4 @@
+test("basic functionality", () => {
+    expect(Atomics[Symbol.toStringTag]).toBe("Atomics");
+    expect(Atomics.toString()).toBe("[object Atomics]");
+});