warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
  --> $DIR/equality.rs:1:12
   |
LL | #![feature(specialization)]
   |            ^^^^^^^^^^^^^^
   |
   = note: `#[warn(incomplete_features)]` on by default
   = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
   = help: consider using `min_specialization` instead, which is more stable and complete

error[E0308]: mismatched types
  --> $DIR/equality.rs:15:5
   |
LL | fn two(x: bool) -> impl Foo {
   |                    -------- the expected opaque type
...
LL |     0_u32
   |     ^^^^^ expected `i32`, found `u32`
   |
   = note: expected opaque type `impl Foo`
                     found type `u32`

error[E0277]: cannot add `impl Foo` to `u32`
  --> $DIR/equality.rs:24:11
   |
LL |         n + sum_to(n - 1)
   |           ^ no implementation for `u32 + impl Foo`
   |
   = help: the trait `Add<impl Foo>` is not implemented for `u32`

error[E0283]: type annotations needed
  --> $DIR/equality.rs:21:5
   |
LL | /     if n == 0 {
LL | |         0
LL | |     } else {
LL | |         n + sum_to(n - 1)
LL | |
LL | |     }
   | |_____^ cannot infer type for type `{integer}`
   |
   = note: multiple `impl`s satisfying `{integer}: ToString` found in the `alloc` crate:
           - impl ToString for i8;
           - impl ToString for u8;
note: required because of the requirements on the impl of `Foo` for `{integer}`
  --> $DIR/equality.rs:5:26
   |
LL | impl<T: Copy + ToString> Foo for T {}
   |                          ^^^     ^

error: aborting due to 3 previous errors; 1 warning emitted

Some errors have detailed explanations: E0277, E0283, E0308.
For more information about an error, try `rustc --explain E0277`.