checkForStyleEditorErrorsuc.js

// ==UserScript==
// @name            checkForStyleEditorErrors
// @include         chrome://devtools/content/shared/sourceeditor/codemirror/cmiframe.html
// ==/UserScript==

const {Services} = ChromeUtils.import('resource://gre/modules/Services.jsm');

let sss = Cc["@mozilla.org/content/style-sheet-service;1"].getService(Ci.nsIStyleSheetService);

sss.loadAndRegisterSheet(Services.io.newURI('data:text/css;charset=UTF-8,' + encodeURIComponent(`
  @-moz-document url('chrome://devtools/content/styleeditor/index.xhtml') {
    #errors label {
      cursor: pointer;
    }
  }
`)), sss.AUTHOR_SHEET);

keyset =  document.createXULElement('keyset');
document.documentElement.appendChild(keyset);
    
checkKey = document.createXULElement('key');
checkKey.setAttribute('id', 'xiao-check');
checkKey.setAttribute('modifiers', 'alt');
checkKey.setAttribute('key', 'C');
checkKey.setAttribute('oncommand', 'checkForErrors()');
keyset.appendChild(checkKey);

let doc = parent.document;

let errors = doc.getElementById('errors');

if (!errors) {
  errors = doc.createElement('vbox');
  errors.id = 'errors';
  errors.className = 'theme-toolbar';
  errors.style.display = 'none';
  doc.documentElement.appendChild(errors);
}

errors.addEventListener('click', function (e) {
  if (e.target == this)
    this.style.display = 'none';
});

function goToLine (line, col) {
	editor.focus();
  editor.setCursor({line: line - 1, ch: col});
}

docShell.cssErrorReportingEnabled = true;

function checkForErrors() {
  while (errors.hasChildNodes())
    errors.removeChild(errors.lastChild);

  let count = 0;

  let errorListener = {
    observe: function (message) {
      if (!count)
        errors.style.display = 'block';

      let error = message.QueryInterface(Ci.nsIScriptError);
      let newmessage = error.lineNumber + ':' + error.columnNumber + ' - ' + error.errorMessage;

      let label = doc.createElement('label');
      label.appendChild(doc.createTextNode(newmessage));
      label.addEventListener('click', function () {
        goToLine(error.lineNumber, error.columnNumber);
      });
      errors.appendChild(label);
      errors.appendChild(doc.createElement('br'));
      count++;

      if (count == 10) {
        errors.appendChild(doc.createTextNode('...'));
        Services.console.unregisterListener(this);
      }
    }
  }

  Services.console.registerListener(errorListener);

  let styleEl = document.createElement('style');
  styleEl.appendChild(document.createTextNode(editor.getText()));
  document.documentElement.appendChild(styleEl);
  styleEl.remove();

  // do this on a delay because of https://bugzilla.mozilla.org/show_bug.cgi?id=831428
  setTimeout(() => {
    if (count < 10)
      Services.console.unregisterListener(errorListener);
  });

  editor.focus();
}