4ed2291624
Emit feature gate *warning* for `auto` traits pre-expansion Auto traits were introduced before we were more careful about not stabilizing new syntax pre-expansion. This is a more conservative step in the general direction we want to go in https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Removal.20of.20.60auto.20trait.60.20syntax. Fixes #116121