error[E0404]: expected trait, found type alias `Strings`
  --> $DIR/suggest-trait-alias-instead-of-type.rs:10:18
   |
LL | struct Struct<S: Strings>(S);
   |                  ^^^^^^^ type aliases cannot be used as traits
   |
help: you might have meant to use `#![feature(trait_alias)]` instead of a `type` alias
   |
LL | trait Strings = Iterator<Item=String>;
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0404`.