ladybird/Libraries/LibWeb/CodeGenerators/WrapperGenerator.cpp

/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <AK/ByteBuffer.h>
#include <AK/GenericLexer.h>
#include <AK/HashMap.h>
#include <AK/LexicalPath.h>
#include <AK/SourceGenerator.h>
#include <AK/StringBuilder.h>
#include <LibCore/ArgsParser.h>
#include <LibCore/File.h>
#include <ctype.h>

static String snake_name(const StringView& title_name)
{
    StringBuilder builder;
    bool first = true;
    bool last_was_uppercase = false;
    for (auto ch : title_name) {
        if (isupper(ch)) {
            if (!first && !last_was_uppercase)
                builder.append('_');
            builder.append(tolower(ch));
        } else {
            builder.append(ch);
        }
        first = false;
        last_was_uppercase = isupper(ch);
    }
    return builder.to_string();
}

static String make_input_acceptable_cpp(const String& input)
{
    if (input.is_one_of("class", "template", "for", "default", "char")) {
        StringBuilder builder;
        builder.append(input);
        builder.append('_');
        return builder.to_string();
    }

    String input_without_dashes = input;
    input_without_dashes.replace("-", "_");

    return input_without_dashes;
}

static void report_parsing_error(StringView message, StringView filename, StringView input, size_t offset)
{
    // FIXME: Spaghetti code ahead.

    size_t lineno = 1;
    size_t colno = 1;
    size_t start_line = 0;
    size_t line_length = 0;
    for (size_t index = 0; index < input.length(); ++index) {
        if (offset == index)
            colno = index - start_line + 1;

        if (input[index] == '\n') {
            if (index >= offset)
                break;

            start_line = index + 1;
            line_length = 0;
            ++lineno;
        } else {
            ++line_length;
        }
    }

    StringBuilder error_message;
    error_message.appendff("{}\n", input.substring_view(start_line, line_length));
    for (size_t i = 0; i < colno - 1; ++i)
        error_message.append(' ');
    error_message.append("\033[1;31m^\n");
    error_message.appendff("{}:{}: error: {}\033[0m\n", filename, lineno, message);

    warnln("{}", error_message.string_view());
    exit(EXIT_FAILURE);
}

namespace IDL {

struct Type {
    String name;
    bool nullable { false };
};

struct Parameter {
    Type type;
    String name;
    bool optional { false };
};

struct Function {
    Type return_type;
    String name;
    Vector<Parameter> parameters;
    HashMap<String, String> extended_attributes;

    size_t length() const
    {
        // FIXME: This seems to produce a length that is way over what it's supposed to be.
        //        For example, getElementsByTagName has its length set to 20 when it should be 1.
        size_t length = 0;
        for (auto& parameter : parameters) {
            if (!parameter.optional)
                length++;
        }
        return length;
    }
};

struct Attribute {
    bool readonly { false };
    bool unsigned_ { false };
    Type type;
    String name;
    HashMap<String, String> extended_attributes;

    // Added for convenience after parsing
    String getter_callback_name;
    String setter_callback_name;
};

struct Interface {
    String name;
    String parent_name;

    Vector<Attribute> attributes;
    Vector<Function> functions;

    // Added for convenience after parsing
    String wrapper_class;
    String wrapper_base_class;
    String fully_qualified_name;
};

static OwnPtr<Interface> parse_interface(StringView filename, const StringView& input)
{
    auto interface = make<Interface>();

    GenericLexer lexer(input);

    auto assert_specific = [&](char ch) {
        if (!lexer.consume_specific(ch))
            report_parsing_error(String::formatted("expected '{}'", ch), filename, input, lexer.tell());
    };

    auto consume_whitespace = [&] {
        bool consumed = true;
        while (consumed) {
            consumed = lexer.consume_while([](char ch) { return isspace(ch); }).length() > 0;

            if (lexer.consume_specific("//")) {
                lexer.consume_until('\n');
                consumed = true;
            }
        }
    };

    auto assert_string = [&](const StringView& expected) {
        if (!lexer.consume_specific(expected))
            report_parsing_error(String::formatted("expected '{}'", expected), filename, input, lexer.tell());
    };

    assert_string("interface");
    consume_whitespace();
    interface->name = lexer.consume_until([](auto ch) { return isspace(ch); });
    consume_whitespace();
    if (lexer.consume_specific(':')) {
        consume_whitespace();
        interface->parent_name = lexer.consume_until([](auto ch) { return isspace(ch); });
        consume_whitespace();
    }
    assert_specific('{');

    auto parse_type = [&] {
        auto name = lexer.consume_until([](auto ch) { return isspace(ch) || ch == '?'; });
        auto nullable = lexer.consume_specific('?');
        return Type { name, nullable };
    };

    auto parse_attribute = [&](HashMap<String, String>& extended_attributes) {
        bool readonly = lexer.consume_specific("readonly");
        if (readonly)
            consume_whitespace();

        if (lexer.consume_specific("attribute"))
            consume_whitespace();

        bool unsigned_ = lexer.consume_specific("unsigned");
        if (unsigned_)
            consume_whitespace();

        auto type = parse_type();
        consume_whitespace();
        auto name = lexer.consume_until([](auto ch) { return isspace(ch) || ch == ';'; });
        consume_whitespace();
        assert_specific(';');
        Attribute attribute;
        attribute.readonly = readonly;
        attribute.unsigned_ = unsigned_;
        attribute.type = type;
        attribute.name = name;
        attribute.getter_callback_name = String::format("%s_getter", snake_name(attribute.name).characters());
        attribute.setter_callback_name = String::format("%s_setter", snake_name(attribute.name).characters());
        attribute.extended_attributes = move(extended_attributes);
        interface->attributes.append(move(attribute));
    };

    auto parse_function = [&](HashMap<String, String>& extended_attributes) {
        auto return_type = parse_type();
        consume_whitespace();
        auto name = lexer.consume_until([](auto ch) { return isspace(ch) || ch == '('; });
        consume_whitespace();
        assert_specific('(');

        Vector<Parameter> parameters;

        for (;;) {
            if (lexer.consume_specific(')'))
                break;
            bool optional = lexer.consume_specific("optional");
            if (optional)
                consume_whitespace();
            auto type = parse_type();
            consume_whitespace();
            auto name = lexer.consume_until([](auto ch) { return isspace(ch) || ch == ',' || ch == ')'; });
            parameters.append({ move(type), move(name), optional });
            if (lexer.consume_specific(')'))
                break;
            assert_specific(',');
            consume_whitespace();
        }

        consume_whitespace();
        assert_specific(';');

        interface->functions.append(Function { return_type, name, move(parameters), move(extended_attributes) });
    };

    auto parse_extended_attributes = [&] {
        HashMap<String, String> extended_attributes;
        for (;;) {
            consume_whitespace();
            if (lexer.consume_specific(']'))
                break;
            auto name = lexer.consume_until([](auto ch) { return ch == ']' || ch == '=' || ch == ','; });
            if (lexer.consume_specific('=')) {
                auto value = lexer.consume_until([](auto ch) { return ch == ']' || ch == ','; });
                extended_attributes.set(name, value);
            } else {
                extended_attributes.set(name, {});
            }
            lexer.consume_specific(',');
        }
        consume_whitespace();
        return extended_attributes;
    };

    for (;;) {
        HashMap<String, String> extended_attributes;

        consume_whitespace();

        if (lexer.consume_specific('}'))
            break;

        if (lexer.consume_specific('[')) {
            extended_attributes = parse_extended_attributes();
        }

        if (lexer.next_is("readonly") || lexer.next_is("attribute")) {
            parse_attribute(extended_attributes);
            continue;
        }

        parse_function(extended_attributes);
    }

    interface->wrapper_class = String::format("%sWrapper", interface->name.characters());
    interface->wrapper_base_class = String::format("%sWrapper", interface->parent_name.is_empty() ? "" : interface->parent_name.characters());

    return interface;
}

}

static void generate_header(const IDL::Interface&);
static void generate_implementation(const IDL::Interface&);

int main(int argc, char** argv)
{
    Core::ArgsParser args_parser;
    const char* path = nullptr;
    bool header_mode = false;
    bool implementation_mode = false;
    args_parser.add_option(header_mode, "Generate the wrapper .h file", "header", 'H');
    args_parser.add_option(implementation_mode, "Generate the wrapper .cpp file", "implementation", 'I');
    args_parser.add_positional_argument(path, "IDL file", "idl-file");
    args_parser.parse(argc, argv);

    auto file_or_error = Core::File::open(path, Core::IODevice::ReadOnly);
    if (file_or_error.is_error()) {
        fprintf(stderr, "Cannot open %s\n", path);
        return 1;
    }

    LexicalPath lexical_path(path);
    auto namespace_ = lexical_path.parts().at(lexical_path.parts().size() - 2);

    auto data = file_or_error.value()->read_all();
    auto interface = IDL::parse_interface(path, data);

    if (!interface) {
        warnln("Cannot parse {}", path);
        return 1;
    }

    if (namespace_.is_one_of("DOM", "HTML", "UIEvents", "HighResolutionTime", "SVG")) {
        StringBuilder builder;
        builder.append(namespace_);
        builder.append("::");
        builder.append(interface->name);
        interface->fully_qualified_name = builder.to_string();
    } else {
        interface->fully_qualified_name = interface->name;
    }

#if 0
    dbg() << "Attributes:";
    for (auto& attribute : interface->attributes) {
        dbg() << "  " << (attribute.readonly ? "Readonly " : "")
              << attribute.type.name << (attribute.type.nullable ? "?" : "")
              << " " << attribute.name;
    }

    dbg() << "Functions:";
    for (auto& function : interface->functions) {
        dbg() << "  " << function.return_type.name << (function.return_type.nullable ? "?" : "")
              << " " << function.name;
        for (auto& parameter : function.parameters) {
            dbg() << "    " << parameter.type.name << (parameter.type.nullable ? "?" : "") << " " << parameter.name;
        }
    }
#endif

    if (header_mode)
        generate_header(*interface);

    if (implementation_mode)
        generate_implementation(*interface);

    return 0;
}

static bool should_emit_wrapper_factory(const IDL::Interface& interface)
{
    // FIXME: This is very hackish.
    if (interface.name == "Event")
        return false;
    if (interface.name == "EventTarget")
        return false;
    if (interface.name == "Node")
        return false;
    if (interface.name == "Text")
        return false;
    if (interface.name == "Document")
        return false;
    if (interface.name == "DocumentType")
        return false;
    if (interface.name.ends_with("Element"))
        return false;
    return true;
}

static bool is_wrappable_type(const IDL::Type& type)
{
    if (type.name == "Node")
        return true;
    if (type.name == "Document")
        return true;
    if (type.name == "Text")
        return true;
    if (type.name == "DocumentType")
        return true;
    if (type.name.ends_with("Element"))
        return true;
    if (type.name == "ImageData")
        return true;
    return false;
}

static void generate_header(const IDL::Interface& interface)
{
    StringBuilder builder;
    SourceGenerator generator { builder };

    generator.set("name", interface.name);
    generator.set("fully_qualified_name", interface.fully_qualified_name);
    generator.set("wrapper_base_class", interface.wrapper_base_class);
    generator.set("wrapper_class", interface.wrapper_class);
    generator.set("wrapper_class:snakecase", snake_name(interface.wrapper_class));

    generator.append(R"~~~(
#pragma once

#include <LibWeb/Bindings/Wrapper.h>

// FIXME: This is very strange.
#if __has_include(<LibWeb/DOM/@name@.h>)
#    include <LibWeb/DOM/@name@.h>
#elif __has_include(<LibWeb/HTML/@name@.h>)
#    include <LibWeb/HTML/@name@.h>
#elif __has_include(<LibWeb/UIEvents/@name@.h>)
#    include <LibWeb/UIEvents/@name@.h>
#elif __has_include(<LibWeb/HighResolutionTime/@name@.h>)
#    include <LibWeb/HighResolutionTime/@name@.h>
#elif __has_include(<LibWeb/SVG/@name@.h>)
#    include <LibWeb/SVG/@name@.h>
#endif
)~~~");

    if (interface.wrapper_base_class != "Wrapper") {
        generator.append(R"~~~(
#include <LibWeb/Bindings/@wrapper_base_class@.h>
)~~~");
    }

    generator.append(R"~~~(
namespace Web::Bindings {

class @wrapper_class@ : public @wrapper_base_class@ {
    JS_OBJECT(@wrapper_class@, @wrapper_base_class@);
public:
    @wrapper_class@(JS::GlobalObject&, @fully_qualified_name@&);
    virtual void initialize(JS::GlobalObject&) override;
    virtual ~@wrapper_class@() override;
)~~~");

    if (interface.wrapper_base_class == "Wrapper") {
        generator.append(R"~~~(
    @fully_qualified_name@& impl() { return *m_impl; }
    const @fully_qualified_name@& impl() const { return *m_impl; }
)~~~");
    } else {
        generator.append(R"~~~(
    @fully_qualified_name@& impl() { return static_cast<@fully_qualified_name@&>(@wrapper_base_class@::impl()); }
    const @fully_qualified_name@& impl() const { return static_cast<const @fully_qualified_name@&>(@wrapper_base_class@::impl()); }
)~~~");
    }

    generator.append(R"~~~(
private:
    virtual bool is_@wrapper_class:snakecase@() const final { return true; }
)~~~");

    for (auto& function : interface.functions) {
        auto function_generator = generator.fork();
        function_generator.set("function.name:snakecase", snake_name(function.name));
        function_generator.append(R"~~~(
    JS_DECLARE_NATIVE_FUNCTION(@function.name:snakecase@);
        )~~~");
    }

    for (auto& attribute : interface.attributes) {
        auto attribute_generator = generator.fork();
        attribute_generator.set("attribute.name:snakecase", snake_name(attribute.name));
        attribute_generator.append(R"~~~(
    JS_DECLARE_NATIVE_GETTER(@attribute.name:snakecase@_getter);
)~~~");

        if (!attribute.readonly) {
            attribute_generator.append(R"~~~(
    JS_DECLARE_NATIVE_SETTER(@attribute.name:snakecase@_setter);
)~~~");
        }
    }

    if (interface.wrapper_base_class == "Wrapper") {
        generator.append(R"~~~(
    NonnullRefPtr<@fully_qualified_name@> m_impl;
        )~~~");
    }

    generator.append(R"~~~(
};
)~~~");

    if (should_emit_wrapper_factory(interface)) {
        generator.append(R"~~~(
@wrapper_class@* wrap(JS::GlobalObject&, @fully_qualified_name@&);
)~~~");
    }

    generator.append(R"~~~(
} // namespace Web::Bindings
)~~~");

    outln("{}", generator.as_string_view());
}

void generate_implementation(const IDL::Interface& interface)
{
    StringBuilder builder;
    SourceGenerator generator { builder };

    generator.set("wrapper_class", interface.wrapper_class);
    generator.set("wrapper_base_class", interface.wrapper_base_class);
    generator.set("fully_qualified_name", interface.fully_qualified_name);

    generator.append(R"~~~(
#include <AK/FlyString.h>
#include <LibJS/Runtime/Array.h>
#include <LibJS/Runtime/Error.h>
#include <LibJS/Runtime/Function.h>
#include <LibJS/Runtime/GlobalObject.h>
#include <LibJS/Runtime/Uint8ClampedArray.h>
#include <LibJS/Runtime/Value.h>
#include <LibWeb/Bindings/@wrapper_class@.h>
#include <LibWeb/Bindings/CanvasRenderingContext2DWrapper.h>
#include <LibWeb/Bindings/CommentWrapper.h>
#include <LibWeb/Bindings/DOMImplementationWrapper.h>
#include <LibWeb/Bindings/DocumentFragmentWrapper.h>
#include <LibWeb/Bindings/DocumentTypeWrapper.h>
#include <LibWeb/Bindings/DocumentWrapper.h>
#include <LibWeb/Bindings/EventTargetWrapperFactory.h>
#include <LibWeb/Bindings/HTMLCanvasElementWrapper.h>
#include <LibWeb/Bindings/HTMLHeadElementWrapper.h>
#include <LibWeb/Bindings/HTMLImageElementWrapper.h>
#include <LibWeb/Bindings/ImageDataWrapper.h>
#include <LibWeb/Bindings/NodeWrapperFactory.h>
#include <LibWeb/Bindings/TextWrapper.h>
#include <LibWeb/Bindings/WindowObject.h>
#include <LibWeb/DOM/Element.h>
#include <LibWeb/DOM/EventListener.h>
#include <LibWeb/HTML/HTMLElement.h>
#include <LibWeb/Origin.h>

// FIXME: This is a total hack until we can figure out the namespace for a given type somehow.
using namespace Web::DOM;
using namespace Web::HTML;

namespace Web::Bindings {

)~~~");

    if (interface.wrapper_base_class == "Wrapper") {
        generator.append(R"~~~(
@wrapper_class@::@wrapper_class@(JS::GlobalObject& global_object, @fully_qualified_name@& impl)
: Wrapper(*global_object.object_prototype())
, m_impl(impl)
{
}
)~~~");
    } else {
        generator.append(R"~~~(
@wrapper_class@::@wrapper_class@(JS::GlobalObject& global_object, @fully_qualified_name@& impl)
: @wrapper_base_class@(global_object, impl)
{
}
)~~~");
    }

    generator.append(R"~~~(
void @wrapper_class@::initialize(JS::GlobalObject& global_object)
{
    [[maybe_unused]] u8 default_attributes = JS::Attribute::Enumerable | JS::Attribute::Configurable;

    @wrapper_base_class@::initialize(global_object);
)~~~");

    for (auto& attribute : interface.attributes) {
        auto attribute_generator = generator.fork();
        attribute_generator.set("attribute.name", attribute.name);
        attribute_generator.set("attribute.getter_callback", attribute.getter_callback_name);

        if (attribute.readonly)
            attribute_generator.set("attribute.setter_callback", "nullptr");
        else
            attribute_generator.set("attribute.setter_callback", attribute.setter_callback_name);

        attribute_generator.append(R"~~~(
    define_native_property("@attribute.name@", @attribute.getter_callback@, @attribute.setter_callback@, default_attributes);
)~~~");
    }

    for (auto& function : interface.functions) {
        auto function_generator = generator.fork();
        function_generator.set("function.name", function.name);
        function_generator.set("function.name:snakecase", snake_name(function.name));
        function_generator.set("function.name:length", String::number(function.name.length()));

        function_generator.append(R"~~~(
    define_native_function("@function.name@", @function.name:snakecase@, @function.name:length@, default_attributes);
)~~~");
    }

    generator.append(R"~~~(
}

@wrapper_class@::~@wrapper_class@()
{
}
)~~~");

    if (!interface.attributes.is_empty() || !interface.functions.is_empty()) {
        generator.append(R"~~~(
static @fully_qualified_name@* impl_from(JS::VM& vm, JS::GlobalObject& global_object)
{
    auto* this_object = vm.this_value(global_object).to_object(global_object);
    if (!this_object)
        return {};
    if (!this_object->inherits("@wrapper_class@")) {
        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::NotA, "@fully_qualified_name@");
        return nullptr;
    }

    return &static_cast<@wrapper_class@*>(this_object)->impl();
    }
)~~~");
    }

    auto generate_to_cpp = [&](auto& parameter, auto& js_name, const auto& js_suffix, auto cpp_name, bool return_void = false, bool legacy_null_to_empty_string = false, bool optional = false) {
        auto scoped_generator = generator.fork();
        scoped_generator.set("cpp_name", cpp_name);
        scoped_generator.set("js_name", js_name);
        scoped_generator.set("js_suffix", js_suffix);
        scoped_generator.set("legacy_null_to_empty_string", legacy_null_to_empty_string ? "true" : "false");
        scoped_generator.set("parameter.type.name", parameter.type.name);

        if (return_void)
            scoped_generator.set("return_statement", "return;");
        else
            scoped_generator.set("return_statement", "return {};");

        // FIXME: Add support for optional to all types
        if (parameter.type.name == "DOMString") {
            if (!optional) {
                scoped_generator.append(R"~~~(
    auto @cpp_name@ = @js_name@@js_suffix@.to_string(global_object, @legacy_null_to_empty_string@);
    if (vm.exception())
        @return_statement@
)~~~");
            } else {
                scoped_generator.append(R"~~~(
    String @cpp_name@;
    if (!@js_name@@js_suffix@.is_undefined()) {
        @cpp_name@ = @js_name@@js_suffix@.to_string(global_object, @legacy_null_to_empty_string@);
        if (vm.exception())
            @return_statement@
    }
)~~~");
            }
        } else if (parameter.type.name == "EventListener") {
            scoped_generator.append(R"~~~(
    if (!@js_name@@js_suffix@.is_function()) {
        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::NotA, "Function");
        @return_statement@
    }
    auto @cpp_name@ = adopt(*new EventListener(JS::make_handle(&@js_name@@js_suffix@.as_function())));
)~~~");
        } else if (is_wrappable_type(parameter.type)) {
            scoped_generator.append(R"~~~(
    auto @cpp_name@_object = @js_name@@js_suffix@.to_object(global_object);
    if (vm.exception())
        @return_statement@

    if (!@cpp_name@_object->inherits("@parameter.type.name@Wrapper")) {
        vm.throw_exception<JS::TypeError>(global_object, JS::ErrorType::NotA, "@parameter.type.name@");
        @return_statement@
    }

    auto& @cpp_name@ = static_cast<@parameter.type.name@Wrapper*>(@cpp_name@_object)->impl();
)~~~");
        } else if (parameter.type.name == "double") {
            scoped_generator.append(R"~~~(
    auto @cpp_name@ = @js_name@@js_suffix@.to_double(global_object);
    if (vm.exception())
        @return_statement@
)~~~");
        } else if (parameter.type.name == "boolean") {
            scoped_generator.append(R"~~~(
    auto @cpp_name@ = @js_name@@js_suffix@.to_boolean();
)~~~");
        } else {
            dbgln("Unimplemented JS-to-C++ conversion: {}", parameter.type.name);
            ASSERT_NOT_REACHED();
        }
    };

    auto generate_arguments = [&](auto& parameters, auto& arguments_builder, bool return_void = false) {
        auto arguments_generator = generator.fork();

        Vector<String> parameter_names;
        size_t argument_index = 0;
        for (auto& parameter : parameters) {
            parameter_names.append(snake_name(parameter.name));
            arguments_generator.set("argument.index", String::number(argument_index));

            arguments_generator.append(R"~~~(
    auto arg@argument.index@ = vm.argument(@argument.index@);
)~~~");
            // FIXME: Parameters can have [LegacyNullToEmptyString] attached.
            generate_to_cpp(parameter, "arg", String::number(argument_index), snake_name(parameter.name), return_void, false, parameter.optional);
            ++argument_index;
        }

        arguments_builder.join(", ", parameter_names);
    };

    auto generate_return_statement = [&](auto& return_type) {
        auto scoped_generator = generator.fork();
        scoped_generator.set("return_type", return_type.name);

        if (return_type.name == "void") {
            scoped_generator.append(R"~~~(
    return JS::js_undefined();
)~~~");
            return;
        }

        if (return_type.nullable) {
            if (return_type.name == "DOMString") {
                scoped_generator.append(R"~~~(
    if (retval.is_null())
        return JS::js_null();
)~~~");
            } else {
                scoped_generator.append(R"~~~(
    if (!retval)
        return JS::js_null();
)~~~");
            }
        }

        if (return_type.name == "DOMString") {
            scoped_generator.append(R"~~~(
    return JS::js_string(vm, retval);
)~~~");
        } else if (return_type.name == "ArrayFromVector") {
            // FIXME: Remove this fake type hack once it's no longer needed.
            //        Basically once we have NodeList we can throw this out.
            scoped_generator.append(R"~~~(
    auto* new_array = JS::Array::create(global_object);
    for (auto& element : retval)
        new_array->indexed_properties().append(wrap(global_object, element));

    return new_array;
)~~~");
        } else if (return_type.name == "long" || return_type.name == "double" || return_type.name == "boolean" || return_type.name == "short") {
            scoped_generator.append(R"~~~(
    return JS::Value(retval);
)~~~");
        } else if (return_type.name == "Uint8ClampedArray") {
            scoped_generator.append(R"~~~(
    return retval;
)~~~");
        } else {
            scoped_generator.append(R"~~~(
    return wrap(global_object, const_cast<@return_type@&>(*retval));
)~~~");
        }
    };

    for (auto& attribute : interface.attributes) {
        auto attribute_generator = generator.fork();
        attribute_generator.set("attribute.getter_callback", attribute.getter_callback_name);
        attribute_generator.set("attribute.setter_callback", attribute.setter_callback_name);
        attribute_generator.set("attribute.name:snakecase", snake_name(attribute.name));

        if (attribute.extended_attributes.contains("Reflect")) {
            auto attribute_name = attribute.extended_attributes.get("Reflect").value();
            if (attribute_name.is_null())
                attribute_name = attribute.name;
            attribute_name = make_input_acceptable_cpp(attribute_name);

            attribute_generator.set("attribute.reflect_name", attribute_name);
        } else {
            attribute_generator.set("attribute.reflect_name", snake_name(attribute.name));
        }

        attribute_generator.append(R"~~~(
JS_DEFINE_NATIVE_GETTER(@wrapper_class@::@attribute.getter_callback@)
{
    auto* impl = impl_from(vm, global_object);
    if (!impl)
        return {};
)~~~");

        if (attribute.extended_attributes.contains("ReturnNullIfCrossOrigin")) {
            attribute_generator.append(R"~~~(
    if (!impl->may_access_from_origin(static_cast<WindowObject&>(global_object).origin()))
        return JS::js_null();
)~~~");
        }

        if (attribute.extended_attributes.contains("Reflect")) {
            if (attribute.type.name != "boolean") {
                attribute_generator.append(R"~~~(
    auto retval = impl->attribute(HTML::AttributeNames::@attribute.reflect_name@);
)~~~");
            } else {
                attribute_generator.append(R"~~~(
    auto retval = impl->has_attribute(HTML::AttributeNames::@attribute.reflect_name@);
)~~~");
            }
        } else {
            attribute_generator.append(R"~~~(
    auto retval = impl->@attribute.name:snakecase@();
)~~~");
        }

        generate_return_statement(attribute.type);

        attribute_generator.append(R"~~~(
}
)~~~");

        if (!attribute.readonly) {
            attribute_generator.append(R"~~~(
JS_DEFINE_NATIVE_SETTER(@wrapper_class@::@attribute.setter_callback@)
{
    auto* impl = impl_from(vm, global_object);
    if (!impl)
        return;
)~~~");

            generate_to_cpp(attribute, "value", "", "cpp_value", true, attribute.extended_attributes.contains("LegacyNullToEmptyString"));

            if (attribute.extended_attributes.contains("Reflect")) {
                if (attribute.type.name != "boolean") {
                    attribute_generator.append(R"~~~(
    impl->set_attribute(HTML::AttributeNames::@attribute.reflect_name@, cpp_value);
)~~~");
                } else {
                    attribute_generator.append(R"~~~(
    if (!cpp_value)
        impl->remove_attribute(HTML::AttributeNames::@attribute.reflect_name@);
    else
        impl->set_attribute(HTML::AttributeNames::@attribute.reflect_name@, String::empty());
)~~~");
                }
            } else {
                attribute_generator.append(R"~~~(
    impl->set_@attribute.name:snakecase@(cpp_value);
)~~~");
            }

            attribute_generator.append(R"~~~(
}
)~~~");
        }
    }

    // Implementation: Functions
    for (auto& function : interface.functions) {
        auto function_generator = generator.fork();
        function_generator.set("function.name", function.name);
        function_generator.set("function.name:snakecase", snake_name(function.name));
        function_generator.set("function.nargs", String::number(function.length()));

        function_generator.append(R"~~~(\
JS_DEFINE_NATIVE_FUNCTION(@wrapper_class@::@function.name:snakecase@)
{
    auto* impl = impl_from(vm, global_object);
    if (!impl)
        return {};
)~~~");

        if (function.length() > 0) {
            if (function.length() == 1) {
                function_generator.set(".bad_arg_count", "JS::ErrorType::BadArgCountOne");
                function_generator.set(".arg_count_suffix", "");
            } else {
                function_generator.set(".bad_arg_count", "JS::ErrorType::BadArgCountMany");
                function_generator.set(".arg_count_suffix", String::formatted(", \"{}\"", function.length()));
            }

            function_generator.append(R"~~~(
    if (vm.argument_count() < @function.nargs@) {
        vm.throw_exception<JS::TypeError>(global_object, @.bad_arg_count@, "@function.name@"@.arg_count_suffix@);
        return {};
    }
)~~~");
        }

        StringBuilder arguments_builder;
        generate_arguments(function.parameters, arguments_builder);

        function_generator.set(".arguments", arguments_builder.string_view());

        if (function.return_type.name != "void") {
            function_generator.append(R"~~~(
    auto retval = impl->@function.name:snakecase@(@.arguments@);
)~~~");
        } else {
            function_generator.append(R"~~~(
    impl->@function.name:snakecase@(@.arguments@);
)~~~");
        }

        generate_return_statement(function.return_type);

        function_generator.append(R"~~~(
}
)~~~");
    }

    if (should_emit_wrapper_factory(interface)) {
        generator.append(R"~~~(
@wrapper_class@* wrap(JS::GlobalObject& global_object, @fully_qualified_name@& impl)
{
    return static_cast<@wrapper_class@*>(wrap_impl(global_object, impl));
}
)~~~");
    }

    generator.append(R"~~~(
} // namespace Web::Bindings
)~~~");

    outln("{}", generator.as_string_view());
}