error[E0277]: the size for values of type `str` cannot be known at compilation time
  --> $DIR/unsized-ret.rs:9:27
   |
LL |     foo::<fn() -> str, _>(None, ());
   |     --------------------- ^^^^ doesn't have a size known at compile-time
   |     |
   |     required by a bound introduced by this call
   |
   = help: within `fn() -> str`, the trait `Sized` is not implemented for `str`
   = note: required because it appears within the type `fn() -> str`
note: required by a bound in `foo`
  --> $DIR/unsized-ret.rs:4:11
   |
LL | fn foo<F: Fn<T>, T>(f: Option<F>, t: T) {
   |           ^^^^^ required by this bound in `foo`

error[E0277]: the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time
  --> $DIR/unsized-ret.rs:12:66
   |
LL |     foo::<for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),));
   |     ------------------------------------------------------------ ^^^^ doesn't have a size known at compile-time
   |     |
   |     required by a bound introduced by this call
   |
   = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)`
   = note: required because it appears within the type `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`
note: required by a bound in `foo`
  --> $DIR/unsized-ret.rs:4:11
   |
LL | fn foo<F: Fn<T>, T>(f: Option<F>, t: T) {
   |           ^^^^^ required by this bound in `foo`

error: aborting due to 2 previous errors

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