LibJS: De-duplicate ClassFieldDefinition Records

This was defined twice, despite being the very same thing:
- ClassElement::ClassFieldDefinition
- ECMAScriptFunctionObject::InstanceField

Move the former to a new header and use it everywhere. Also update the
define_field() AO to take a single field instead of separate name and
initializer arguments.

Userland/Libraries/LibJS/AST.cpp

@@ -1487,13 +1487,13 @@ Completion ClassElement::execute(Interpreter&, GlobalObject&) const
     VERIFY_NOT_REACHED();
 }
 
-static ThrowCompletionOr<ClassElement::ClassElementName> class_key_to_property_name(Interpreter& interpreter, GlobalObject& global_object, Expression const& key)
+static ThrowCompletionOr<ClassElementName> class_key_to_property_name(Interpreter& interpreter, GlobalObject& global_object, Expression const& key)
 {
     if (is<PrivateIdentifier>(key)) {
         auto& private_identifier = static_cast<PrivateIdentifier const&>(key);
         auto* private_environment = interpreter.vm().running_execution_context().private_environment;
         VERIFY(private_environment);
-        return ClassElement::ClassElementName { private_environment->resolve_private_identifier(private_identifier.string()) };
+        return ClassElementName { private_environment->resolve_private_identifier(private_identifier.string()) };
     }
 
     auto prop_key = TRY(key.execute(interpreter, global_object)).release_value();
@@ -1502,7 +1502,7 @@ static ThrowCompletionOr<ClassElement::ClassElementName> class_key_to_property_n
         prop_key = TRY(prop_key.to_primitive(global_object, Value::PreferredType::String));
 
     auto property_key = TRY(PropertyKey::from_value(global_object, prop_key));
-    return ClassElement::ClassElementName { property_key };
+    return ClassElementName { property_key };
 }
 
 // 15.4.5 Runtime Semantics: MethodDefinitionEvaluation, https://tc39.es/ecma262/#sec-runtime-semantics-methoddefinitionevaluation
@@ -1838,11 +1838,11 @@ ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_e
 
     prototype->define_direct_property(vm.names.constructor, class_constructor, Attribute::Writable | Attribute::Configurable);
 
-    using StaticElement = Variant<ClassElement::ClassFieldDefinition, Handle<ECMAScriptFunctionObject>>;
+    using StaticElement = Variant<ClassFieldDefinition, Handle<ECMAScriptFunctionObject>>;
 
     Vector<PrivateElement> static_private_methods;
     Vector<PrivateElement> instance_private_methods;
-    Vector<ClassElement::ClassFieldDefinition> instance_fields;
+    Vector<ClassFieldDefinition> instance_fields;
     Vector<StaticElement> static_elements;
 
     for (auto const& element : m_elements) {
@@ -1871,7 +1871,7 @@ ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_e
 
             if (!added_to_existing)
                 container.append(move(element_value.get<PrivateElement>()));
-        } else if (auto* class_field_definition_ptr = element_value.get_pointer<ClassElement::ClassFieldDefinition>()) {
+        } else if (auto* class_field_definition_ptr = element_value.get_pointer<ClassFieldDefinition>()) {
             if (element.is_static())
                 static_elements.append(move(*class_field_definition_ptr));
             else
@@ -1892,7 +1892,7 @@ ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_e
         MUST(class_scope->initialize_binding(global_object, binding_name, class_constructor));
 
     for (auto& field : instance_fields)
-        class_constructor->add_field(field.name, field.initializer.is_null() ? nullptr : field.initializer.cell());
+        class_constructor->add_field(field);
 
     for (auto& private_method : instance_private_methods)
         class_constructor->add_private_method(private_method);
@@ -1902,8 +1902,8 @@ ThrowCompletionOr<ECMAScriptFunctionObject*> ClassExpression::class_definition_e
 
     for (auto& element : static_elements) {
         TRY(element.visit(
-            [&](ClassElement::ClassFieldDefinition& field) -> ThrowCompletionOr<void> {
-                return TRY(class_constructor->define_field(field.name, field.initializer.is_null() ? nullptr : field.initializer.cell()));
+            [&](ClassFieldDefinition& field) -> ThrowCompletionOr<void> {
+                return TRY(class_constructor->define_field(field));
             },
             [&](Handle<ECMAScriptFunctionObject> static_block_function) -> ThrowCompletionOr<void> {
                 VERIFY(!static_block_function.is_null());

Userland/Libraries/LibJS/AST.h

@@ -19,6 +19,7 @@
 #include <LibJS/Bytecode/CodeGenerationError.h>
 #include <LibJS/Forward.h>
 #include <LibJS/Heap/Handle.h>
+#include <LibJS/Runtime/ClassFieldDefinition.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/EnvironmentCoordinate.h>
 #include <LibJS/Runtime/FunctionKind.h>
@@ -1248,13 +1249,6 @@ public:
     virtual ElementKind class_element_kind() const = 0;
     bool is_static() const { return m_is_static; }
 
-    using ClassElementName = Variant<PropertyKey, PrivateName>;
-
-    struct ClassFieldDefinition {
-        ClassElementName name;
-        Handle<ECMAScriptFunctionObject> initializer;
-    };
-
     // We use the Completion also as a ClassStaticBlockDefinition Record.
     using ClassValue = Variant<ClassFieldDefinition, Completion, PrivateElement>;
     virtual ThrowCompletionOr<ClassValue> class_element_evaluation(Interpreter&, GlobalObject&, Object& home_object) const = 0;

Userland/Libraries/LibJS/Forward.h

@@ -141,6 +141,7 @@ class BoundFunction;
 class Cell;
 class CellAllocator;
 class ClassExpression;
+struct ClassFieldDefinition;
 class Completion;
 class Console;
 class DeclarativeEnvironment;

Userland/Libraries/LibJS/Runtime/ClassFieldDefinition.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2022, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <LibJS/Forward.h>
+
+namespace JS {
+
+using ClassElementName = Variant<PropertyKey, PrivateName>;
+
+// 6.2.10 The ClassFieldDefinition Record Specification Type, https://tc39.es/ecma262/#sec-classfielddefinition-record-specification-type
+struct ClassFieldDefinition {
+    ClassElementName name;                        // [[Name]]
+    Handle<ECMAScriptFunctionObject> initializer; // [[Initializer]]
+};
+
+}

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp

@@ -299,8 +299,6 @@ void ECMAScriptFunctionObject::visit_edges(Visitor& visitor)
     for (auto& field : m_fields) {
         if (auto* property_key_ptr = field.name.get_pointer<PropertyKey>(); property_key_ptr && property_key_ptr->is_symbol())
             visitor.visit(property_key_ptr->as_symbol());
-
-        visitor.visit(field.initializer);
     }
 }
 
@@ -886,9 +884,4 @@ void ECMAScriptFunctionObject::set_name(FlyString const& name)
     VERIFY(success);
 }
 
-void ECMAScriptFunctionObject::add_field(ClassElement::ClassElementName property_key, ECMAScriptFunctionObject* initializer)
-{
-    m_fields.empend(property_key, initializer);
-}
-
 }

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -68,13 +68,8 @@ public:
     String const& source_text() const { return m_source_text; }
     void set_source_text(String source_text) { m_source_text = move(source_text); }
 
-    struct InstanceField {
-        Variant<PropertyKey, PrivateName> name;
-        ECMAScriptFunctionObject* initializer { nullptr };
-    };
-
-    Vector<InstanceField> const& fields() const { return m_fields; }
-    void add_field(Variant<PropertyKey, PrivateName> property_key, ECMAScriptFunctionObject* initializer);
+    Vector<ClassFieldDefinition> const& fields() const { return m_fields; }
+    void add_field(ClassFieldDefinition field) { m_fields.append(move(field)); }
 
     Vector<PrivateElement> const& private_methods() const { return m_private_methods; }
     void add_private_method(PrivateElement method) { m_private_methods.append(move(method)); };
@@ -123,7 +118,7 @@ private:
     ScriptOrModule m_script_or_module;                                       // [[ScriptOrModule]]
     Object* m_home_object { nullptr };                                       // [[HomeObject]]
     String m_source_text;                                                    // [[SourceText]]
-    Vector<InstanceField> m_fields;                                          // [[Fields]]
+    Vector<ClassFieldDefinition> m_fields;                                   // [[Fields]]
     Vector<PrivateElement> m_private_methods;                                // [[PrivateMethods]]
     Variant<PropertyKey, PrivateName, Empty> m_class_field_initializer_name; // [[ClassFieldInitializerName]]
     ConstructorKind m_constructor_kind : 1 { ConstructorKind::Base };        // [[ConstructorKind]]

Userland/Libraries/LibJS/Runtime/Object.cpp

@@ -10,6 +10,7 @@
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Accessor.h>
 #include <LibJS/Runtime/Array.h>
+#include <LibJS/Runtime/ClassFieldDefinition.h>
 #include <LibJS/Runtime/ECMAScriptFunctionObject.h>
 #include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/GlobalObject.h>
@@ -556,17 +557,36 @@ ThrowCompletionOr<void> Object::private_set(PrivateName const& name, Value value
 }
 
 // 7.3.32 DefineField ( receiver, fieldRecord ), https://tc39.es/ecma262/#sec-definefield
-ThrowCompletionOr<void> Object::define_field(Variant<PropertyKey, PrivateName> name, ECMAScriptFunctionObject* initializer)
+ThrowCompletionOr<void> Object::define_field(ClassFieldDefinition const& field)
 {
-    Value init_value = js_undefined();
-    if (initializer)
-        init_value = TRY(call(global_object(), *initializer, this));
+    // 1. Let fieldName be fieldRecord.[[Name]].
+    auto const& field_name = field.name;
 
-    if (auto* property_key_ptr = name.get_pointer<PropertyKey>())
-        TRY(create_data_property_or_throw(*property_key_ptr, init_value));
-    else
-        TRY(private_field_add(name.get<PrivateName>(), init_value));
+    // 2. Let initializer be fieldRecord.[[Initializer]].
+    auto const& initializer = field.initializer;
 
+    auto init_value = js_undefined();
+
+    // 3. If initializer is not empty, then
+    if (!initializer.is_null()) {
+        // a. Let initValue be ? Call(initializer, receiver).
+        init_value = TRY(call(global_object(), initializer.cell(), this));
+    }
+    // 4. Else, let initValue be undefined.
+
+    // 5. If fieldName is a Private Name, then
+    if (field_name.has<PrivateName>()) {
+        // a. Perform ? PrivateFieldAdd(receiver, fieldName, initValue).
+        TRY(private_field_add(field_name.get<PrivateName>(), init_value));
+    }
+    // 6. Else,
+    else {
+        // a. Assert: IsPropertyKey(fieldName) is true.
+        // b. Perform ? CreateDataPropertyOrThrow(receiver, fieldName, initValue).
+        TRY(create_data_property_or_throw(field_name.get<PropertyKey>(), init_value));
+    }
+
+    // 7. Return unused.
     return {};
 }
 

Userland/Libraries/LibJS/Runtime/Object.h

@@ -110,7 +110,7 @@ public:
     ThrowCompletionOr<void> private_method_or_accessor_add(PrivateElement element);
     ThrowCompletionOr<Value> private_get(PrivateName const& name);
     ThrowCompletionOr<void> private_set(PrivateName const& name, Value value);
-    ThrowCompletionOr<void> define_field(Variant<PropertyKey, PrivateName> name, ECMAScriptFunctionObject* initializer);
+    ThrowCompletionOr<void> define_field(ClassFieldDefinition const&);
 
     // 10.1 Ordinary Object Internal Methods and Internal Slots, https://tc39.es/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots
 

Userland/Libraries/LibJS/Runtime/VM.cpp

@@ -600,7 +600,7 @@ ThrowCompletionOr<void> VM::initialize_instance_elements(Object& object, ECMAScr
         TRY(object.private_method_or_accessor_add(method));
 
     for (auto& field : constructor.fields())
-        TRY(object.define_field(field.name, field.initializer));
+        TRY(object.define_field(field));
     return {};
 }