Flow: Please improve error reporting

[mvysny]

Vaadin 14.3.3, flow 2.3.3. I am working on an unfamiliar code base, and the browser suddenly shows the following issue:

(ReferenceError) : Polymer is not defined client-5F17FE7D56927576AB18BC8D06949321.cache.js:212:20
    XC client-5F17FE7D56927576AB18BC8D06949321.cache.js:212
    Xn client-5F17FE7D56927576AB18BC8D06949321.cache.js:1003
    Wn client-5F17FE7D56927576AB18BC8D06949321.cache.js:774
    Yn client-5F17FE7D56927576AB18BC8D06949321.cache.js:594
    cu client-5F17FE7D56927576AB18BC8D06949321.cache.js:1016
    bu client-5F17FE7D56927576AB18BC8D06949321.cache.js:973
    _t client-5F17FE7D56927576AB18BC8D06949321.cache.js:575

The stacktrace tells nothing to me since it's an obfuscated GWT product which Flow uses internally.

Luckily there is a warning line The error has occurred in the JS code: '$0, Polymer.RenderStatus.beforeNextRender($0, () => $0.render());' which contains a lead that navigates me to the following server-side Java code:

attachEvent.getUI().getPage().executeJavaScript("Polymer.RenderStatus.beforeNextRender($0, () => $0.render());", calendar.getElement());

The exception should clearly state that the JavaScript code is coming from a server-side call to executeJavaScript() or similar. If that's not possible, then the warning line should be an error line clearly stating what's wrong and where the JavaScript code originates from.

[pleku]

For the server given JS executions, we should wrap those so that the failure is visible in the UI on development mode and like pointed out ^ make it clear that what is the source of the exception. For production mode the error should be highlighted in the console (but not UI).