Most promise chains should end with ".catch(Cu.reportError);" or ".catch(() => {});". We cannot detect all misuses, but we can likely detect the most common ones by checking that return value of ".then()" or a call to an async function is never ignored, but is stored in a variable, propagated via "return", or fed to ".catch()".

We could potentially use some or all of the rules from this plugin: https://github.com/xjamundx/eslint-plugin-promise