error: the `Self` constructor can only be used with tuple or unit structs
  --> $DIR/issue-56835.rs:4:12
   |
LL |     fn bar(Self(foo): Self) {}
   |            ^^^^^^^^^ help: use curly brackets: `Self { /* fields */ }`

error[E0164]: expected tuple struct or tuple variant, found self constructor `Self`
  --> $DIR/issue-56835.rs:4:12
   |
LL |     fn bar(Self(foo): Self) {}
   |            ^^^^^^^^^ not a tuple variant or struct

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0164`.