error[E0118]: no nominal type found for inherent implementation
  --> $DIR/E0118-2.rs:3:6
   |
LL | impl &mut Foo {
   |      ^^^^^^^^ impl requires a nominal type
   |
   = note: either implement a trait on it or create a newtype to wrap it instead
   = note: you could also try moving the reference to uses of `Foo` (such as `self`) within the implementation

error: aborting due to previous error

For more information about this error, try `rustc --explain E0118`.