Unexpected results if using microseconds in web

[kinex]

Both print statements in this sample code output the same value:

void main() {
  final now = DateTime.now();
  print(now.microsecondsSinceEpoch);
  final later = now.add(Duration(microseconds: 1));
  print(later.microsecondsSinceEpoch);
}

I noticed this while trying my Flutter app in web, because it caused an infinite loop (works fine in mobile). My app is using microseconds extensively for different DateTime calculations, so it seems I have to do a lot of refactoring to make my app compatible with web.

This limitation is indirectly documented here: https://api.dart.dev/stable/2.10.4/dart-core/DateTime/microsecondsSinceEpoch.html

I think this should be documented more clearly at least in DateTime.add and in Duration. Also an analyzer warning would be good.

It is also unclear is it safe to use getter Duration.inMicroseconds in web.

[mraleph]

/cc @lrhn

[jamesderlin]

This would be a limitation of DateTime objects for the web in general and wouldn't specifically be about adding. See #44876.