existential predicate dedup + inference vars is incomplete

[lcnr]

trait Super {
    type Assoc;
}

trait Trait<T>: Super<Assoc = u32> {}

trait Eq<T: ?Sized> {}
impl<T: ?Sized> Eq<T> for T {}

trait Constrain<T: ?Sized, U: ?Sized> {}
impl<T: ?Sized, U: ?Sized> Constrain<T, U> for ()
where
    dyn Trait<U, Assoc = U>: Eq<T>,
    dyn Trait<u32, Assoc = u32>: Eq<T>,

{}

fn foo<T: Constrain<U, V>, U: ?Sized, V: ?Sized>() {}
fn main() {
    foo::<(), _, _>();
} 

results in the following error with both the new and old solver

error[E0277]: the trait bound `(dyn Trait<u32> + 'static): Eq<(dyn Trait<_, Assoc = _> + 'static)>` is not satisfied
  --> <source>:20:11
   |
20 |     foo::<(), _, _>();
   |           ^^ the trait `Eq<(dyn Trait<_, Assoc = _> + 'static)>` is not implemented for `(dyn Trait<u32> + 'static)`

however, the underlying issue results in an ICE in tests/ui/issues/issue-59326.rs while equating canonical var values in a proof tree visitor.

[lcnr]

ICE with both old and new solver:

trait Super {
    type Assoc;
}

trait Trait<T>: Super<Assoc = u32> {}

trait Eq<T: ?Sized> {}
impl<T: ?Sized> Eq<T> for T {}
trait Constrain<T: ?Sized, U: ?Sized> {}
impl<U: ?Sized> Constrain<dyn Trait<U, Assoc = U>, U> for ()
where
    u32: Eq<U>,
{}

fn foo<T: Constrain<U, V>, U: ?Sized, V: ?Sized>() {}
fn main() {
    foo::<(), _, _>();
}

[lcnr]

will be fixed by rust-lang/rust#136458