error[E0308]: mismatched types
  --> $DIR/issue-90213-expected-boxfuture-self-ice.rs:9:19
   |
LL |         Self::foo(None)
   |         --------- ^^^^ expected struct `Box`, found enum `Option`
   |         |
   |         arguments to this function are incorrect
   |
   = note: expected struct `Box<Option<S>>`
                found enum `Option<_>`
   = note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html
note: associated function defined here
  --> $DIR/issue-90213-expected-boxfuture-self-ice.rs:7:8
   |
LL |     fn foo(_: Box<Option<S>>) {}
   |        ^^^ -----------------
help: store this in the heap by calling `Box::new`
   |
LL |         Self::foo(Box::new(None))
   |                   +++++++++    +

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.