tampermonkey-open-with-github-desktop.js

// ==UserScript==
// @name         GitLab: Open with GitHub Desktop
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description
// @match        http://gitlab.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=gitlab.com
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    const label='GitHub Desktop'
    const html = `<a class="dropdown-item open-with-link"><div class="gl-new-dropdown-item-text-wrapper">${label}</div></a>`
    const elem = new DOMParser().parseFromString(html, 'text/html').body.children[0];
    elem.href = "x-github-client://openRepo/" + document.getElementsByName('http_project_clone')[0].value.replace(/\.git$/, "");
    document.evaluate("//label[contains(text(),'Open in your IDE')]", document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue.parentNode.appendChild(elem);
})();