error[E0308]: mismatched types
  --> $DIR/ice-trait-with-default-method-but-no-impl-broken-mir-109869-1.rs:16:9
   |
LL |     fn from((from, ()): Spanned<F>) -> Self {
   |                                        ---- expected `(dyn Span<T> + 'static)` because of return type
LL |         (T::from(from), ())
   |         ^^^^^^^^^^^^^^^^^^^ expected `dyn Span`, found `(T, ())`
   |
   = note: expected trait object `(dyn Span<T> + 'static)`
                     found tuple `(T, ())`
   = help: `(T, ())` implements `Span` so you could box the found value and coerce it to the trait object `Box<dyn Span>`, you will have to change the expected type as well
help: call `Into::into` on this expression to convert `(T, ())` into `(dyn Span<T> + 'static)`
   |
LL |         (T::from(from), ()).into()
   |                            +++++++

error: aborting due to 1 previous error

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