deprecate `avoid_returning_null`

[pq]

See: dart-archive/linter#2632 (comment)

[bwilkerson]

FWIW, it isn't clear to me that the rule has any value in a null safe world. If the return type is non-nullable, then returning null is a compiler error and a lint is useless. If the return type is nullable, then I'm proposing that we not produce a lint. Hence, I think the right course of action is to deprecate the lint and disable it in null safe code.

[pq]

Agreed.

[subzero911]

False positive

It states: "Avoid returning null from members whose return type is bool, double, int, or num"
but return type is not int but int?
consider improving this linter rule to distinct nullable types

[pq]

@subzero911: we've been mulling over whether there's value in this lint really at all in the presence of nullability. Is there any reason you still have it enabled?

[subzero911]

Most likely, no.
If your type is int / bool / double / num, you can't return null (because these types are not nullable themselves).
If your type is int? / bool? / double? / num?, it is supposed that you can assign null to it, so the lint makes no sense.

[pq]

Thanks for the feedback. Much appreciated!

[pq]

dart-archive/linter#2750 addresses the false positive.

[pq]

Pushing ahead on this, I wonder if anyone has any misgivings wrt to deprecating avoid_returning_null.

/cc @bwilkerson @eernstg @lrhn ?