LibJS: Use Identifier to represent name of ClassExpression

By using Identifier class to represent the name of a class expression,
it becomes possible to consistently store information within the
identifier object, indicating whether the name refers to a local
variable or not.

Userland/Libraries/LibJS/AST.cpp

@@ -1852,7 +1852,7 @@ Completion ClassExpression::execute(Interpreter& interpreter) const
 
     // 1. Let className be StringValue of BindingIdentifier.
     // 2. Let value be ? ClassDefinitionEvaluation of ClassTail with arguments className and className.
-    auto* value = TRY(class_definition_evaluation(interpreter.vm(), m_name, m_name.is_null() ? "" : m_name));
+    auto* value = TRY(class_definition_evaluation(interpreter.vm(), name(), name()));
 
     // 3. Set value.[[SourceText]] to the source text matched by ClassExpression.
     value->set_source_text(m_source_text);
@@ -2311,7 +2311,7 @@ ThrowCompletionOr<void> ClassDeclaration::for_each_bound_name(ThrowCompletionOrV
 void ClassExpression::dump(int indent) const
 {
     print_indent(indent);
-    outln("ClassExpression: \"{}\"", m_name);
+    outln("ClassExpression: \"{}\"", name());
 
     print_indent(indent);
     outln("(Constructor)");

Userland/Libraries/LibJS/AST.h

@@ -1405,7 +1405,7 @@ public:
 
 class ClassExpression final : public Expression {
 public:
-    ClassExpression(SourceRange source_range, DeprecatedString name, DeprecatedString source_text, RefPtr<FunctionExpression const> constructor, RefPtr<Expression const> super_class, Vector<NonnullRefPtr<ClassElement const>> elements)
+    ClassExpression(SourceRange source_range, RefPtr<Identifier const> name, DeprecatedString source_text, RefPtr<FunctionExpression const> constructor, RefPtr<Expression const> super_class, Vector<NonnullRefPtr<ClassElement const>> elements)
         : Expression(source_range)
         , m_name(move(name))
         , m_source_text(move(source_text))
@@ -1415,7 +1415,8 @@ public:
     {
     }
 
-    StringView name() const { return m_name; }
+    StringView name() const { return m_name ? m_name->string().view() : ""sv; }
+
     DeprecatedString const& source_text() const { return m_source_text; }
     RefPtr<FunctionExpression const> constructor() const { return m_constructor; }
 
@@ -1424,7 +1425,7 @@ public:
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode(Bytecode::Generator&) const override;
     virtual Bytecode::CodeGenerationErrorOr<void> generate_bytecode_with_lhs_name(Bytecode::Generator&, Optional<Bytecode::IdentifierTableIndex> lhs_name) const;
 
-    bool has_name() const { return !m_name.is_empty(); }
+    bool has_name() const { return m_name; }
 
     ThrowCompletionOr<ECMAScriptFunctionObject*> class_definition_evaluation(VM&, DeprecatedFlyString const& binding_name = {}, DeprecatedFlyString const& class_name = {}) const;
     ThrowCompletionOr<ECMAScriptFunctionObject*> create_class_constructor(VM&, Environment* class_environment, Environment* environment, Value super_class, DeprecatedFlyString const& binding_name = {}, DeprecatedFlyString const& class_name = {}) const;
@@ -1432,7 +1433,7 @@ public:
 private:
     virtual bool is_class_expression() const override { return true; }
 
-    DeprecatedString m_name;
+    RefPtr<Identifier const> m_name;
     DeprecatedString m_source_text;
     RefPtr<FunctionExpression const> m_constructor;
     RefPtr<Expression const> m_super_class;

Userland/Libraries/LibJS/Bytecode/ASTCodegen.cpp

@@ -2323,7 +2323,7 @@ Bytecode::CodeGenerationErrorOr<void> ClassExpression::generate_bytecode_with_lh
 
     if (has_name() || !lhs_name.has_value()) {
         // NOTE: Step 3.a is not a part of NewClass instruction because it is assumed to be done before super class expression evaluation
-        auto interned_index = generator.intern_identifier(m_name);
+        auto interned_index = generator.intern_identifier(name());
         generator.emit<Bytecode::Op::CreateVariable>(interned_index, Bytecode::Op::EnvironmentMode::Lexical, true);
     }
 

Userland/Libraries/LibJS/Parser.cpp

@@ -1071,12 +1071,17 @@ NonnullRefPtr<ClassExpression const> Parser::parse_class_expression(bool expect_
     RefPtr<FunctionExpression const> constructor;
     HashTable<DeprecatedFlyString> found_private_names;
 
-    DeprecatedFlyString class_name = expect_class_name || match_identifier() || match(TokenType::Yield) || match(TokenType::Await)
-        ? consume_identifier_reference().DeprecatedFlyString_value()
-        : "";
+    RefPtr<Identifier const> class_name { nullptr };
+    if (expect_class_name || match_identifier() || match(TokenType::Yield) || match(TokenType::Await)) {
+        class_name = create_ast_node<Identifier const>(
+            { m_source_code, rule_start.position(), position() },
+            consume_identifier_reference().DeprecatedFlyString_value()
+        );
+    }
 
-    check_identifier_name_for_assignment_validity(class_name, true);
-    if (m_state.in_class_static_init_block && class_name == "await"sv)
+    if (class_name)
+        check_identifier_name_for_assignment_validity(class_name->string(), true);
+    if (m_state.in_class_static_init_block && class_name && class_name->string() == "await"sv)
         syntax_error("Identifier must not be a reserved word in modules ('await')");
 
     if (match(TokenType::Extends)) {
@@ -1365,12 +1370,12 @@ NonnullRefPtr<ClassExpression const> Parser::parse_class_expression(bool expect_
             constructor_body->append(create_ast_node<ReturnStatement>({ m_source_code, rule_start.position(), position() }, move(super_call)));
 
             constructor = create_ast_node<FunctionExpression>(
-                { m_source_code, rule_start.position(), position() }, class_name, "",
+                { m_source_code, rule_start.position(), position() }, class_name ? class_name->string() : "", "",
                 move(constructor_body), Vector { FunctionParameter { move(argument_name), nullptr, true } }, 0, FunctionKind::Normal,
                 /* is_strict_mode */ true, /* might_need_arguments_object */ false, /* contains_direct_call_to_eval */ false);
         } else {
             constructor = create_ast_node<FunctionExpression>(
-                { m_source_code, rule_start.position(), position() }, class_name, "",
+                { m_source_code, rule_start.position(), position() }, class_name ? class_name->string() : "", "",
                 move(constructor_body), Vector<FunctionParameter> {}, 0, FunctionKind::Normal,
                 /* is_strict_mode */ true, /* might_need_arguments_object */ false, /* contains_direct_call_to_eval */ false);
         }