error: unnamed receiver type is only allowed if the surrounding extern block contains exactly one extern type; use `self: &mut TheType`
 --> $DIR/unnamed_receiver.rs:6:14
  |
6 |         fn f(&mut self);
  |              ^^^^^^^^^

error: unnamed receiver type is only allowed if the surrounding extern block contains exactly one extern type; use `self: &TheType`
  --> $DIR/unnamed_receiver.rs:10:20
   |
10 |         fn f(self: &Self);
   |                    ^^^^^