error[E0520]: `from` specializes an item from a parent `impl`, but that item is not marked `default`
  --> $DIR/issue-111232.rs:15:5
   |
LL | impl<T> From<T> for T {
   | --------------------- parent `impl` is here
...
LL |     fn from(s: S) -> S {
   |     ^^^^^^^^^^^^^^^^^^ cannot specialize default item `from`
   |
   = note: to specialize, `from` in the parent `impl` must be marked `default`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0520`.