Clone a GObject

clone.js

const Gtk = imports.gi.Gtk;
const GObject = imports.gi.GObject;
const Gir = imports.gi.GIRepository;

// G_PARAM_READWRITE is not yet properly introspected
const READWRITE = GObject.ParamFlags.READABLE | GObject.ParamFlags.WRITABLE;

const dontCloneTheseProperties = [
    ['Gtk', 'Widget', 'parent'], // would try to add the new widget to the same parent
    ['Gtk', 'Widget', 'margin'], // sets all margin properties at once
    ['Gtk', 'Widget', 'expand'], // sets all expand properties at once
];

function ignoreInfoEqual(arg1, arg2) {
    return arg1[0] === arg2[0] && arg1[1] === arg2[1] && arg1[2] === arg2[2];
}

function getWritablePropertyNamesForObjectInfo(info) {
    let propertyNames = [];
    let nProperties = Gir.object_info_get_n_properties(info);
    for(let ix = 0; ix < nProperties; ix++) {
        let propertyInfo = Gir.object_info_get_property(info, ix);
        let flags = Gir.property_info_get_flags(propertyInfo);
        if ((flags & READWRITE) == READWRITE) {
            let name = propertyInfo.get_name();
            let ignoreInfo = [info.get_namespace(), info.get_name(), name];
            if (!dontCloneTheseProperties.some(ignoreInfoEqual.bind(null, ignoreInfo)))
                propertyNames.push(name);
        }
    }
    return propertyNames;
}

function clone(obj) {
    // This seems like it ought to work, but segfaults:
    // let typeClass = GObject.TypeClass.ref(obj.constructor.$gtype);
    // let props = GObject.ObjectClass.prototype.list_properties.call(typeClass);
    // let obj2 = new obj.constructor(props);
    // return obj2;

    let repository = Gir.Repository.get_default();
    let baseInfo = repository.find_by_gtype(obj.constructor.$gtype);
    let propertyNames = [];
    for (let info = baseInfo; info !== null; info = Gir.object_info_get_parent(info)) {
        propertyNames = propertyNames.concat(getWritablePropertyNamesForObjectInfo(info));
    }
    let constructProps = {};
    propertyNames.forEach(function (name) {
        constructProps[name] = obj[name];
    });
    return new obj.constructor(constructProps);
}

Gtk.init(null);
let win = new Gtk.Window();
let grid = new Gtk.Grid();
let button1 = new Gtk.Button({
    label: 'I am a button!',
    margin_left: 20,
    tooltip_text: 'I am a tooltip!',
    vexpand: true,
});
let button2 = clone(button1);
grid.add(button1);
grid.add(button2);
win.add(grid);
win.connect('destroy', Gtk.main_quit);
win.show_all();
Gtk.main();