error[E0116]: cannot define inherent `impl` for a type outside of the crate where the type is defined
  --> $DIR/trait-or-new-type-instead.rs:1:1
   |
LL | / impl<T> Option<T> {
LL | |
LL | |     pub fn foo(&self) { }
LL | | }
   | |_^ impl for type defined outside of crate.
   |
   = note: define and implement a trait or new type instead

error: aborting due to previous error

For more information about this error, try `rustc --explain E0116`.