error[E0277]: the size for values of type `Self` cannot be known at compilation time
  --> $DIR/issue-27078.rs:3:12
   |
LL |     fn foo(self) -> &'static i32 {
   |            ^^^^ doesn't have a size known at compile-time
   |
   = help: unsized fn params are gated as an unstable feature
help: consider further restricting `Self`
   |
LL |     fn foo(self) -> &'static i32 where Self: Sized {
   |                                  +++++++++++++++++
help: function arguments must have a statically known size, borrowed types always have a known size
   |
LL |     fn foo(&self) -> &'static i32 {
   |            +

error: aborting due to 1 previous error

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