error[E0277]: can't compare `S` with `S`
  --> $DIR/E0277-3.rs:6:9
   |
LL |     foo(S);
   |     --- ^ no implementation for `S == S`
   |     |
   |     required by a bound introduced by this call
   |
   = help: the trait `PartialEq` is not implemented for `S`
note: required by a bound in `foo`
  --> $DIR/E0277-3.rs:1:11
   |
LL | fn foo<T: PartialEq>(_: T) {}
   |           ^^^^^^^^^ required by this bound in `foo`
help: consider annotating `S` with `#[derive(PartialEq)]`
   |
LL + #[derive(PartialEq)]
LL | struct S;
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.