LibJS: Start implementing ShadowRealm

This commit adds the ShadowRealm object itself, its constructor, and
prototype (currently empty).

Userland/Libraries/LibJS/Runtime/ShadowRealmConstructor.cpp

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/ShadowRealm.h>
+#include <LibJS/Runtime/ShadowRealmConstructor.h>
+
+namespace JS {
+
+// 3.2 The ShadowRealm Constructor, https://tc39.es/proposal-shadowrealm/#sec-shadowrealm-constructor
+ShadowRealmConstructor::ShadowRealmConstructor(GlobalObject& global_object)
+    : NativeFunction(vm().names.ShadowRealm.as_string(), *global_object.function_prototype())
+{
+}
+
+void ShadowRealmConstructor::initialize(GlobalObject& global_object)
+{
+    auto& vm = this->vm();
+    NativeFunction::initialize(global_object);
+
+    // 3.3.1 ShadowRealm.prototype, https://tc39.es/proposal-shadowrealm/#sec-shadowrealm.prototype
+    define_direct_property(vm.names.prototype, global_object.shadow_realm_prototype(), 0);
+
+    define_direct_property(vm.names.length, Value(0), Attribute::Configurable);
+}
+
+// 3.2.1 ShadowRealm ( ), https://tc39.es/proposal-shadowrealm/#sec-shadowrealm
+Value ShadowRealmConstructor::call()
+{
+    auto& vm = this->vm();
+
+    // 1. If NewTarget is undefined, throw a TypeError exception.
+    vm.throw_exception<TypeError>(global_object(), ErrorType::ConstructorWithoutNew, vm.names.ShadowRealm);
+    return {};
+}
+
+// 3.2.1 ShadowRealm ( ), https://tc39.es/proposal-shadowrealm/#sec-shadowrealm
+Value ShadowRealmConstructor::construct(FunctionObject& new_target)
+{
+    auto& vm = this->vm();
+    auto& global_object = this->global_object();
+
+    // 3. Let realmRec be CreateRealm().
+    auto* realm = Realm::create(vm);
+
+    // 5. Let context be a new execution context.
+    auto context = ExecutionContext { vm.heap() };
+
+    // 6. Set the Function of context to null.
+    context.function = nullptr;
+
+    // 7. Set the Realm of context to realmRec.
+    context.realm = realm;
+
+    // 8. Set the ScriptOrModule of context to null.
+    // FIXME: Our execution context struct currently does not track this item.
+
+    // 2. Let O be ? OrdinaryCreateFromConstructor(NewTarget, "%ShadowRealm.prototype%", « [[ShadowRealm]], [[ExecutionContext]] »).
+    // 4. Set O.[[ShadowRealm]] to realmRec.
+    // 9. Set O.[[ExecutionContext]] to context.
+    auto* object = TRY_OR_DISCARD(ordinary_create_from_constructor<ShadowRealm>(global_object, new_target, &GlobalObject::shadow_realm_prototype, *realm, move(context)));
+
+    // 10. Perform ? SetRealmGlobalObject(realmRec, undefined, undefined).
+    auto* new_global_object = vm.heap().allocate_without_global_object<GlobalObject>();
+    new_global_object->initialize_global_object();
+    realm->set_global_object(*new_global_object, nullptr);
+
+    // TODO: I don't think we should have these exactly like this, that doesn't work well with how
+    //       we create global objects. Still, it should be possible to make a ShadowRealm with a
+    //       non-LibJS GlobalObject somehow.
+    // 11. Perform ? SetDefaultGlobalBindings(O.[[ShadowRealm]]).
+    // 12. Perform ? HostInitializeShadowRealm(O.[[ShadowRealm]]).
+
+    // 13. Return O.
+    return object;
+}
+
+}