ices/79422.rs: fixed with errors

[github-actions]

Issue: rust-lang/rust#79422

#![feature(generic_associated_types)]
#![allow(incomplete_features)]

trait RefCont<'a, T> {
    fn t(&'a self) -> &'a T;
}

impl<'a, T> RefCont<'a, T> for &'a T {
    fn t(&'a self) -> &'a T {
        self
    }
}

impl<'a, T> RefCont<'a, T> for Box<T> {
    fn t(&'a self) -> &'a T {
        self.as_ref()
    }
}

trait MapLike<K, V> {
    type VRefCont<'a>: RefCont<'a, V>;
    fn get<'a>(&'a self, key: &K) -> Option<Self::VRefCont<'a>>;
}

impl<K: Ord, V: 'static> MapLike<K, V> for std::collections::BTreeMap<K, V> {
    type VRefCont<'a> = &'a V;
    fn get<'a>(&'a self, key: &K) -> Option<&'a V> {
        std::collections::BTreeMap::get(self, key)
    }
}

struct Source;

impl<K, V: Default> MapLike<K, V> for Source {
    type VRefCont<'a> = Box<V>;
    fn get<'a>(&self, _: &K) -> Option<Box<V>> {
        Some(Box::new(V::default()))
    }
}

fn main() {
    let m = Box::new(std::collections::BTreeMap::<u8, u8>::new())
        as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
}

=== stdout ===
=== stderr ===
error[E0107]: missing generics for associated type `MapLike::VRefCont`
  --> /home/runner/work/glacier/glacier/ices/79422.rs:21:10
   |
21 |     type VRefCont<'a>: RefCont<'a, V>;
   |          ^^^^^^^^ expected 1 lifetime argument
   |
note: associated type defined here, with 1 lifetime parameter: `'a`
  --> /home/runner/work/glacier/glacier/ices/79422.rs:21:10
   |
21 |     type VRefCont<'a>: RefCont<'a, V>;
   |          ^^^^^^^^ --
help: use angle brackets to add missing lifetime argument
   |
21 |     type VRefCont<'a><'a>: RefCont<'a, V>;
   |                  ^^^^

error[E0038]: the trait `MapLike` cannot be made into an object
  --> /home/runner/work/glacier/glacier/ices/79422.rs:43:12
   |
43 |         as Box<dyn MapLike<u8, u8, VRefCont = dyn RefCont<'_, u8>>>;
   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` cannot be made into an object
   |
   = help: consider moving `get` to another trait
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /home/runner/work/glacier/glacier/ices/79422.rs:22:38
   |
20 | trait MapLike<K, V> {
   |       ------- this trait cannot be made into an object...
21 |     type VRefCont<'a>: RefCont<'a, V>;
22 |     fn get<'a>(&'a self, key: &K) -> Option<Self::VRefCont<'a>>;
   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^ ...because method `get` references the `Self` type in its return type

error[E0038]: the trait `MapLike` cannot be made into an object
  --> /home/runner/work/glacier/glacier/ices/79422.rs:42:13
   |
42 |     let m = Box::new(std::collections::BTreeMap::<u8, u8>::new())
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `MapLike` cannot be made into an object
   |
   = help: consider moving `get` to another trait
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /home/runner/work/glacier/glacier/ices/79422.rs:22:38
   |
20 | trait MapLike<K, V> {
   |       ------- this trait cannot be made into an object...
21 |     type VRefCont<'a>: RefCont<'a, V>;
22 |     fn get<'a>(&'a self, key: &K) -> Option<Self::VRefCont<'a>>;
   |                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^ ...because method `get` references the `Self` type in its return type
   = note: required because of the requirements on the impl of `CoerceUnsized<Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>>` for `Box<BTreeMap<u8, u8>>`
   = note: required by cast to type `Box<dyn MapLike<u8, u8, VRefCont = (dyn RefCont<'_, u8> + 'static)>>`

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0038, E0107.
For more information about an error, try `rustc --explain E0038`.
==============