error[E0307]: invalid `self` parameter type: T
  --> $DIR/issue-66312.rs:4:22
   |
LL |     fn is_some(self: T);
   |                      ^
   |
   = note: type of `self` must be `Self` or a type that dereferences to it
   = help: consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one of the previous types except `Self`)

error: aborting due to previous error

For more information about this error, try `rustc --explain E0307`.