Have FutureOr extensions not show-up in the autocompletion of non-FutureOr objects.

[rrousselGit]

Hello!

Spawned from Discord thread: https://discord.com/channels/608014603317936148/1171510601655275612/1182766954805735514

Currently if we make an extension Name on FutureOr {...}, whatever extension we wrote will show up everywhere.
But although it makes sense from a compiler point of view for those extensions to work everywhere, from a user perspective, they pollute the autocompletion in unrelated places.

Could we do that FutureOr extensions only show-up in autocompletion if a variable is explicitly typed as FutureOr?

Such that we have:

FutureOr<int> futureOr;
futureOr. // < extensions show-up in the autocompletion here

int value;
value. // < but they won't show-up here

Future<int> future;
future. // < and possibly not here either

[bwilkerson]

Definitely an interesting idea. Yes, I believe that it's technically feasible.

[lrhn]

If someone puts an extension on FutureOr<String>, it could very well be because they want the operation to work on both Future<String> and String, not just on something explicitly typed as FutureOr<String>. Not showing it for a String doesn't seem right in that case. Not showing it for Future<String> doesn't seem right, ever. (I something works on FutureOr<T>, it's because it's async aware, and then it should most likely work on Future<T> too.)

Could it be something one should opt in to? Like @onlyOnFutures extension ... on FutureOr<...> which only appears for FutureOr<...> or Future<...>, because you're expected to do something more direct for known synchronous values?