ices/44861.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#44861

// https://github.com/rust-lang/rust/issues/44861
// Playground: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=bdd59503a0dc2d33c60a949fc7c57633
// You need to select `build` instead of `run`.

#![crate_type = "lib"]
#![feature(specialization)]
#![feature(unsize, coerce_unsized)]

use std::ops::CoerceUnsized;
use std::marker::Unsize;

pub struct SmartassPtr<A: Smartass+?Sized>(A::Data);

pub trait Smartass {
    type Data;
    type Data2: CoerceUnsized<*const [u8]>;
}

pub trait MaybeObjectSafe {}

impl MaybeObjectSafe for () {}

impl<T> Smartass for T {
    type Data = <Self as Smartass>::Data2;
    default type Data2 = ();
}

impl Smartass for () {
    type Data2 = *const [u8; 1];
}

impl Smartass for MaybeObjectSafe {
    type Data = *const [u8];
    type Data2 = *const [u8; 0];
}

impl<U: Smartass+?Sized, T: Smartass+?Sized> CoerceUnsized<SmartassPtr<T>> for SmartassPtr<U>
    where <U as Smartass>::Data: std::ops::CoerceUnsized<<T as Smartass>::Data>
{}

pub fn conv(s: SmartassPtr<()>) -> SmartassPtr<MaybeObjectSafe> {
    s
}

=== stdout ===
=== stderr ===
warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /home/runner/work/glacier/glacier/ices/44861.rs:6:12
  |
6 | #![feature(specialization)]
  |            ^^^^^^^^^^^^^^
  |
  = note: `#[warn(incomplete_features)]` on by default
  = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information

warning: unused import: `std::marker::Unsize`
  --> /home/runner/work/glacier/glacier/ices/44861.rs:10:5
   |
10 | use std::marker::Unsize;
   |     ^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

warning: trait objects without an explicit `dyn` are deprecated
  --> /home/runner/work/glacier/glacier/ices/44861.rs:32:19
   |
32 | impl Smartass for MaybeObjectSafe {
   |                   ^^^^^^^^^^^^^^^ help: use `dyn`: `dyn MaybeObjectSafe`
   |
   = note: `#[warn(bare_trait_objects)]` on by default

warning: trait objects without an explicit `dyn` are deprecated
  --> /home/runner/work/glacier/glacier/ices/44861.rs:41:48
   |
41 | pub fn conv(s: SmartassPtr<()>) -> SmartassPtr<MaybeObjectSafe> {
   |                                                ^^^^^^^^^^^^^^^ help: use `dyn`: `dyn MaybeObjectSafe`

error[E0277]: the trait bound `(): std::ops::CoerceUnsized<*const [u8]>` is not satisfied
  --> /home/runner/work/glacier/glacier/ices/44861.rs:25:5
   |
16 |     type Data2: CoerceUnsized<*const [u8]>;
   |     --------------------------------------- required by `Smartass::Data2`
...
25 |     default type Data2 = ();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::ops::CoerceUnsized<*const [u8]>` is not implemented for `()`

error: aborting due to previous error; 4 warnings emitted

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