LibJS: Add support for public fields in classes

9 files changed, 265 insertions, 11 deletions

diff --git a/Userland/Libraries/LibJS/AST.cpp b/Userland/Libraries/LibJS/AST.cpp
index 78d1694d98..8cc535d1fd 100644
--- a/Userland/Libraries/LibJS/AST.cpp
+++ b/Userland/Libraries/LibJS/AST.cpp
@@ -310,7 +310,8 @@ Value SuperCall::execute(Interpreter& interpreter, GlobalObject& global_object)
     [[maybe_unused]] auto& f = this_er.function_object();
 
     // 11. Perform ? InitializeInstanceElements(result, F).
-    // FIXME: This is missing here.
+    VERIFY(result.is_object());
+    vm.initialize_instance_elements(result.as_object(), f);
 
     // 12. Return result.
     return result;
@@ -867,6 +868,12 @@ Value ClassMethod::execute(Interpreter& interpreter, GlobalObject& global_object
     return m_function->execute(interpreter, global_object);
 }
 
+Value ClassField::execute(Interpreter& interpreter, GlobalObject&) const
+{
+    InterpreterNodeScope node_scope { interpreter, *this };
+    return {};
+}
+
 Value ClassExpression::execute(Interpreter& interpreter, GlobalObject& global_object) const
 {
     InterpreterNodeScope node_scope { interpreter, *this };
@@ -923,7 +930,7 @@ Value ClassExpression::execute(Interpreter& interpreter, GlobalObject& global_ob
         interpreter.vm().throw_exception<TypeError>(global_object, ErrorType::NotAnObject, "Class prototype");
         return {};
     }
-    for (const auto& method : m_methods) {
+    for (auto const& method : m_methods) {
         auto method_value = method.execute(interpreter, global_object);
         if (interpreter.exception())
             return {};
@@ -960,6 +967,40 @@ Value ClassExpression::execute(Interpreter& interpreter, GlobalObject& global_ob
             return {};
     }
 
+    for (auto& field : m_fields) {
+        auto key = field.key().execute(interpreter, global_object);
+        if (interpreter.exception())
+            return {};
+
+        auto property_key = key.to_property_key(global_object);
+        if (interpreter.exception())
+            return {};
+
+        FunctionObject* initializer = nullptr;
+        if (field.initializer()) {
+            auto copy_initializer = field.initializer();
+            auto body = create_ast_node<ExpressionStatement>(field.initializer()->source_range(), copy_initializer.release_nonnull());
+            // FIXME: A potential optimization is not creating the functions here since these are never directly accessible.
+            initializer = OrdinaryFunctionObject::create(interpreter.global_object(), property_key.to_display_string(), *body, {}, 0, interpreter.lexical_environment(), FunctionKind::Regular, false);
+            initializer->set_home_object(field.is_static() ? class_constructor : &class_prototype.as_object());
+        }
+
+        if (field.is_static()) {
+            Value field_value = js_undefined();
+            if (initializer) {
+                field_value = interpreter.vm().call(*initializer, class_constructor_value);
+                if (interpreter.exception())
+                    return {};
+            }
+
+            class_constructor->create_data_property_or_throw(property_key, field_value);
+            if (interpreter.exception())
+                return {};
+        } else {
+            class_constructor->add_field(property_key, initializer);
+        }
+    }
+
     return class_constructor;
 }
 
@@ -1186,6 +1227,11 @@ void ClassExpression::dump(int indent) const
     outln("(Methods)");
     for (auto& method : m_methods)
         method.dump(indent + 1);
+
+    print_indent(indent);
+    outln("(Fields)");
+    for (auto& field : m_fields)
+        field.dump(indent + 1);
 }
 
 void ClassMethod::dump(int indent) const
@@ -1219,6 +1265,23 @@ void ClassMethod::dump(int indent) const
     m_function->dump(indent + 1);
 }
 
+void ClassField::dump(int indent) const
+{
+    ASTNode::dump(indent);
+    print_indent(indent);
+    outln("(Key)");
+    m_key->dump(indent + 1);
+
+    print_indent(indent);
+    outln("Static: {}", m_is_static);
+
+    if (m_initializer) {
+        print_indent(indent);
+        outln("(Initializer)");
+        m_initializer->dump(indent + 1);
+    }
+}
+
 void StringLiteral::dump(int indent) const
 {
     print_indent(indent);
diff --git a/Userland/Libraries/LibJS/AST.h b/Userland/Libraries/LibJS/AST.h
index 838450e8a4..b400640bce 100644
--- a/Userland/Libraries/LibJS/AST.h
+++ b/Userland/Libraries/LibJS/AST.h
@@ -933,6 +933,30 @@ private:
     bool m_is_static;
 };
 
+class ClassField final : public ASTNode {
+public:
+    ClassField(SourceRange source_range, NonnullRefPtr<Expression> key, RefPtr<Expression> init, bool is_static)
+        : ASTNode(source_range)
+        , m_key(move(key))
+        , m_initializer(move(init))
+        , m_is_static(is_static)
+    {
+    }
+
+    Expression const& key() const { return *m_key; }
+    bool is_static() const { return m_is_static; }
+    RefPtr<Expression> const& initializer() const { return m_initializer; }
+    RefPtr<Expression>& initializer() { return m_initializer; }
+
+    virtual Value execute(Interpreter&, GlobalObject&) const override;
+    virtual void dump(int indent) const override;
+
+private:
+    NonnullRefPtr<Expression> m_key;
+    RefPtr<Expression> m_initializer;
+    bool m_is_static;
+};
+
 class SuperExpression final : public Expression {
 public:
     explicit SuperExpression(SourceRange source_range)
@@ -948,12 +972,13 @@ public:
 
 class ClassExpression final : public Expression {
 public:
-    ClassExpression(SourceRange source_range, String name, RefPtr<FunctionExpression> constructor, RefPtr<Expression> super_class, NonnullRefPtrVector<ClassMethod> methods)
+    ClassExpression(SourceRange source_range, String name, RefPtr<FunctionExpression> constructor, RefPtr<Expression> super_class, NonnullRefPtrVector<ClassMethod> methods, NonnullRefPtrVector<ClassField> fields)
         : Expression(source_range)
         , m_name(move(name))
         , m_constructor(move(constructor))
         , m_super_class(move(super_class))
         , m_methods(move(methods))
+        , m_fields(move(fields))
     {
     }
 
@@ -968,6 +993,7 @@ private:
     RefPtr<FunctionExpression> m_constructor;
     RefPtr<Expression> m_super_class;
     NonnullRefPtrVector<ClassMethod> m_methods;
+    NonnullRefPtrVector<ClassField> m_fields;
 };
 
 class ClassDeclaration final : public Declaration {
diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index 8dfe614e6a..d1528e64f9 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -643,6 +643,7 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
     consume(TokenType::Class);
 
     NonnullRefPtrVector<ClassMethod> methods;
+    NonnullRefPtrVector<ClassField> fields;
     RefPtr<Expression> super_class;
     RefPtr<FunctionExpression> constructor;
 
@@ -693,8 +694,8 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
             is_generator = true;
         }
 
+        StringView name;
         if (match_property_key()) {
-            StringView name;
             if (!is_generator && m_state.current_token.original_value() == "static"sv) {
                 if (match(TokenType::Identifier)) {
                     consume();
@@ -707,12 +708,12 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
             }
 
             if (match(TokenType::Identifier)) {
-                auto identifier_name = m_state.current_token.value();
+                auto identifier_name = m_state.current_token.original_value();
 
-                if (identifier_name == "get") {
+                if (identifier_name == "get"sv) {
                     method_kind = ClassMethod::Kind::Getter;
                     consume();
-                } else if (identifier_name == "set") {
+                } else if (identifier_name == "set"sv) {
                     method_kind = ClassMethod::Kind::Setter;
                     consume();
                 }
@@ -740,7 +741,7 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
                 //   It is a Syntax Error if PropName of MethodDefinition is "prototype".
                 if (is_static && name == "prototype"sv)
                     syntax_error("Classes may not have a static property named 'prototype'");
-            } else if (match(TokenType::ParenOpen) && (is_static || method_kind != ClassMethod::Kind::Method)) {
+            } else if ((match(TokenType::ParenOpen) || match(TokenType::Equals)) && (is_static || method_kind != ClassMethod::Kind::Method)) {
                 switch (method_kind) {
                 case ClassMethod::Kind::Method:
                     VERIFY(is_static);
@@ -762,7 +763,7 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
             }
 
             // Constructor may be a StringLiteral or an Identifier.
-            if (!is_static && name == "constructor") {
+            if (!is_static && name == "constructor"sv) {
                 if (method_kind != ClassMethod::Kind::Method)
                     syntax_error("Class constructor may not be an accessor");
                 if (!constructor.is_null())
@@ -792,9 +793,29 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
             } else {
                 syntax_error("No key for class method");
             }
-        } else {
+        } else if (is_generator) {
             expected("ParenOpen");
             consume();
+        } else if (property_key.is_null()) {
+            expected("property key");
+            consume();
+        } else {
+            if (name == "constructor"sv)
+                syntax_error("Class cannot have field named 'constructor'");
+
+            RefPtr<Expression> initializer;
+
+            if (match(TokenType::Equals)) {
+                consume();
+
+                TemporaryChange super_property_access_rollback(m_state.allow_super_property_lookup, true);
+                TemporaryChange field_initializer_rollback(m_state.in_class_field_initializer, true);
+                initializer = parse_expression(2);
+            }
+
+            fields.append(create_ast_node<ClassField>({ m_state.current_token.filename(), rule_start.position(), position() }, property_key.release_nonnull(), move(initializer), is_static));
+
+            consume_or_insert_semicolon();
         }
     }
 
@@ -821,7 +842,7 @@ NonnullRefPtr<ClassExpression> Parser::parse_class_expression(bool expect_class_
         }
     }
 
-    return create_ast_node<ClassExpression>({ m_state.current_token.filename(), rule_start.position(), position() }, move(class_name), move(constructor), move(super_class), move(methods));
+    return create_ast_node<ClassExpression>({ m_state.current_token.filename(), rule_start.position(), position() }, move(class_name), move(constructor), move(super_class), move(methods), move(fields));
 }
 
 Parser::PrimaryExpressionParseResult Parser::parse_primary_expression()
@@ -1535,6 +1556,7 @@ NonnullRefPtr<AssignmentExpression> Parser::parse_assignment_expression(Assignme
             parser.m_state.in_break_context = m_state.in_break_context;
             parser.m_state.in_continue_context = m_state.in_continue_context;
             parser.m_state.string_legacy_octal_escape_sequence_in_scope = m_state.string_legacy_octal_escape_sequence_in_scope;
+            parser.m_state.in_class_field_initializer = m_state.in_class_field_initializer;
 
             auto result = parser.parse_binding_pattern();
             if (parser.has_errors())
@@ -1577,6 +1599,8 @@ NonnullRefPtr<Identifier> Parser::parse_identifier()
 {
     auto identifier_start = position();
     auto token = consume_identifier();
+    if (m_state.in_class_field_initializer && token.value() == "arguments"sv)
+        syntax_error("'arguments' is not allowed in class field initializer");
     return create_ast_node<Identifier>(
         { m_state.current_token.filename(), identifier_start, position() },
         token.value());
@@ -1757,6 +1781,7 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u8 parse_options)
     TemporaryChange super_constructor_call_rollback(m_state.allow_super_constructor_call, !!(parse_options & FunctionNodeParseOptions::AllowSuperConstructorCall));
     TemporaryChange break_context_rollback(m_state.in_break_context, false);
     TemporaryChange continue_context_rollback(m_state.in_continue_context, false);
+    TemporaryChange class_field_initializer_rollback(m_state.in_class_field_initializer, false);
 
     ScopePusher scope(*this, ScopePusher::Var, Parser::Scope::Function);
 
diff --git a/Userland/Libraries/LibJS/Parser.h b/Userland/Libraries/LibJS/Parser.h
index 12cf4d089e..41b6cef2c8 100644
--- a/Userland/Libraries/LibJS/Parser.h
+++ b/Userland/Libraries/LibJS/Parser.h
@@ -258,6 +258,7 @@ private:
         bool in_break_context { false };
         bool in_continue_context { false };
         bool string_legacy_octal_escape_sequence_in_scope { false };
+        bool in_class_field_initializer { false };
 
         ParserState(Lexer, Program::Type);
     };
diff --git a/Userland/Libraries/LibJS/Runtime/FunctionObject.cpp b/Userland/Libraries/LibJS/Runtime/FunctionObject.cpp
index bf4e02b0f6..da1f410294 100644
--- a/Userland/Libraries/LibJS/Runtime/FunctionObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/FunctionObject.cpp
@@ -66,6 +66,23 @@ BoundFunction* FunctionObject::bind(Value bound_this_value, Vector<Value> argume
     return heap().allocate<BoundFunction>(global_object(), global_object(), target_function, bound_this_object, move(all_bound_arguments), computed_length, constructor_prototype);
 }
 
+void FunctionObject::add_field(StringOrSymbol property_key, FunctionObject* initializer)
+{
+    m_fields.empend(property_key, initializer);
+}
+
+// 7.3.31 DefineField ( receiver, fieldRecord ), https://tc39.es/ecma262/#sec-definefield
+void FunctionObject::InstanceField::define_field(VM& vm, Object& receiver) const
+{
+    Value init_value = js_undefined();
+    if (initializer) {
+        init_value = vm.call(*initializer, receiver.value_of());
+        if (vm.exception())
+            return;
+    }
+    receiver.create_data_property_or_throw(name, init_value);
+}
+
 void FunctionObject::visit_edges(Visitor& visitor)
 {
     Object::visit_edges(visitor);
@@ -75,6 +92,9 @@ void FunctionObject::visit_edges(Visitor& visitor)
 
     for (auto argument : m_bound_arguments)
         visitor.visit(argument);
+
+    for (auto& field : m_fields)
+        visitor.visit(field.initializer);
 }
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/FunctionObject.h b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
index 5b089877b1..3cfa762166 100644
--- a/Userland/Libraries/LibJS/Runtime/FunctionObject.h
+++ b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
@@ -63,6 +63,17 @@ public:
     // This is for IsSimpleParameterList (static semantics)
     bool has_simple_parameter_list() const { return m_has_simple_parameter_list; }
 
+    // [[Fields]]
+    struct InstanceField {
+        StringOrSymbol name;
+        FunctionObject* initializer { nullptr };
+
+        void define_field(VM& vm, Object& receiver) const;
+    };
+
+    Vector<InstanceField> const& fields() const { return m_fields; }
+    void add_field(StringOrSymbol property_key, FunctionObject* initializer);
+
 protected:
     virtual void visit_edges(Visitor&) override;
 
@@ -79,6 +90,7 @@ private:
     ConstructorKind m_constructor_kind = ConstructorKind::Base;
     ThisMode m_this_mode { ThisMode::Global };
     bool m_has_simple_parameter_list { false };
+    Vector<InstanceField> m_fields;
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/VM.cpp b/Userland/Libraries/LibJS/Runtime/VM.cpp
index f8ebdab071..a0e0acceb8 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.cpp
+++ b/Userland/Libraries/LibJS/Runtime/VM.cpp
@@ -457,6 +457,16 @@ static void append_bound_and_passed_arguments(MarkedValueList& arguments, Vector
     }
 }
 
+// 7.3.32 InitializeInstanceElements ( O, constructor ), https://tc39.es/ecma262/#sec-initializeinstanceelements
+void VM::initialize_instance_elements(Object& object, FunctionObject& constructor)
+{
+    for (auto& field : constructor.fields()) {
+        field.define_field(*this, object);
+        if (exception())
+            return;
+    }
+}
+
 Value VM::construct(FunctionObject& function, FunctionObject& new_target, Optional<MarkedValueList> arguments)
 {
     auto& global_object = function.global_object();
@@ -494,6 +504,14 @@ Value VM::construct(FunctionObject& function, FunctionObject& new_target, Option
 
     // If we are a Derived constructor, |this| has not been constructed before super is called.
     callee_context.this_value = this_argument;
+
+    if (function.constructor_kind() == FunctionObject::ConstructorKind::Base) {
+        VERIFY(this_argument.is_object());
+        initialize_instance_elements(this_argument.as_object(), function);
+        if (exception())
+            return {};
+    }
+
     auto result = function.construct(new_target);
 
     pop_execution_context();
diff --git a/Userland/Libraries/LibJS/Runtime/VM.h b/Userland/Libraries/LibJS/Runtime/VM.h
index 7b2981c686..4b25bb3e3b 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.h
+++ b/Userland/Libraries/LibJS/Runtime/VM.h
@@ -267,6 +267,8 @@ public:
     Function<void(const Promise&)> on_promise_unhandled_rejection;
     Function<void(const Promise&)> on_promise_rejection_handled;
 
+    void initialize_instance_elements(Object& object, FunctionObject& constructor);
+
 private:
     VM();
 
diff --git a/Userland/Libraries/LibJS/Tests/classes/class-public-fields.js b/Userland/Libraries/LibJS/Tests/classes/class-public-fields.js
new file mode 100644
index 0000000000..86c1e86de7
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/classes/class-public-fields.js
@@ -0,0 +1,87 @@
+test("basic functionality", () => {
+    class A {
+        number = 3;
+
+        string = "foo";
+
+        uninitialized;
+    }
+
+    const a = new A();
+    expect(a.number).toBe(3);
+    expect(a.string).toBe("foo");
+    expect(a.uninitialized).toBeUndefined();
+});
+
+test("extended name syntax", () => {
+    class A {
+        "field with space" = 1;
+
+        12 = "twelve";
+
+        [`he${"llo"}`] = 3;
+    }
+
+    const a = new A();
+    expect(a["field with space"]).toBe(1);
+    expect(a[12]).toBe("twelve");
+    expect(a.hello).toBe(3);
+});
+
+test("initializer has correct this value", () => {
+    class A {
+        this_val = this;
+
+        this_name = this.this_val;
+    }
+
+    const a = new A();
+    expect(a.this_val).toBe(a);
+    expect(a.this_name).toBe(a);
+});
+
+test("static fields", () => {
+    class A {
+        static simple = 1;
+        simple = 2;
+
+        static "with space" = 3;
+
+        static 24 = "two dozen";
+
+        static [`he${"llo"}`] = "friends";
+
+        static this_val = this;
+        static this_name = this.name;
+        static this_val2 = this.this_val;
+    }
+
+    expect(A.simple).toBe(1);
+    expect(A["with space"]).toBe(3);
+    expect(A[24]).toBe("two dozen");
+    expect(A.hello).toBe("friends");
+
+    expect(A.this_val).toBe(A);
+    expect(A.this_name).toBe("A");
+    expect(A.this_val2).toBe(A);
+
+    const a = new A();
+    expect(a.simple).toBe(2);
+});
+
+test("with super class", () => {
+    class A {
+        super_field = 3;
+    }
+
+    class B extends A {
+        references_super_field = super.super_field;
+        arrow_ref_super = () => (super.super_field = 4);
+    }
+
+    const b = new B();
+    expect(b.super_field).toBe(3);
+    expect(b.references_super_field).toBeUndefined();
+    b.arrow_ref_super();
+    expect(b.super_field).toBe(4);
+});