How to know when the user has entered an invalid date?

[JanderSilv]

I'd like to be able to trigger a warning message to the user, when it tries to type an invalid date.
The reason is, when date picker autocorrects the date, some users don't realize that the date has changed.

Other possibility is preserve the invalid date, and let the user change for a valid one by himself. These two scenarios works for me.

I read about this on some issues and PRs like: #773, #2756 but I still don't get how to do it.