74 lines
2.0 KiB
Rust
74 lines
2.0 KiB
Rust
// compile-flags: -Ztrait-solver=next
|
|
// check-pass
|
|
|
|
// A minimization of an ambiguity when using typenum. See
|
|
// https://github.com/rust-lang/trait-system-refactor-initiative/issues/55
|
|
// for more details.
|
|
trait Id {
|
|
type Assoc: ?Sized;
|
|
}
|
|
impl<T: ?Sized> Id for T {
|
|
type Assoc = T;
|
|
}
|
|
|
|
trait WithAssoc<T: ?Sized> {
|
|
type Assoc: ?Sized;
|
|
}
|
|
|
|
|
|
struct Leaf;
|
|
struct Wrapper<U: ?Sized>(U);
|
|
|
|
impl<U: ?Sized> WithAssoc<U> for Leaf {
|
|
type Assoc = U;
|
|
}
|
|
|
|
impl<Ul: ?Sized, Ur: ?Sized> WithAssoc<Wrapper<Ur>> for Wrapper<Ul>
|
|
where
|
|
Ul: WithAssoc<Ur>,
|
|
{
|
|
type Assoc = <<Ul as WithAssoc<Ur>>::Assoc as Id>::Assoc;
|
|
}
|
|
|
|
fn bound<T: ?Sized, U: ?Sized, V: ?Sized>()
|
|
where
|
|
T: WithAssoc<U, Assoc = V>,
|
|
{
|
|
}
|
|
|
|
// normalize self type to `Wrapper<Leaf>`
|
|
// This succeeds, HOWEVER, instantiating the query response previously
|
|
// incremented the universe index counter.
|
|
// equate impl headers:
|
|
// <Wrapper<Leaf> as WithAssoc<<Wrapper<Leaf> as Id>::Assoc>>
|
|
// <Wrapper<?2t> as WithAssoc<Wrapper<?3t>>>
|
|
// ~> AliasRelate(<Wrapper<Leaf> as Id>::Assoc, Equate, Wrapper<?3t>)
|
|
// add where bounds:
|
|
// ~> Leaf: WithAssoc<?3t>
|
|
// equate with assoc type:
|
|
// ?0t
|
|
// <Leaf as WithAssoc<?3t>>::Assoc as Id>::Assoc
|
|
// ~> AliasRelate(
|
|
// <<Leaf as WithAssoc<?3t>>::Assoc as Id>::Assoc,
|
|
// Equate,
|
|
// <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc,
|
|
// )
|
|
//
|
|
// We do not reuse `?3t` during generalization because `?0t` cannot name `?4t` as we created
|
|
// it after incrementing the universe index while normalizing the self type.
|
|
//
|
|
// evaluate_added_goals_and_make_query_response:
|
|
// AliasRelate(<Wrapper<Leaf> as Id>::Assoc, Equate, Wrapper<?3t>)
|
|
// YES, constrains ?3t to Leaf
|
|
// AliasRelate(
|
|
// <<Leaf as WithAssoc<Leaf>>::Assoc as Id>::Assoc,
|
|
// Equate,
|
|
// <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc,
|
|
// )
|
|
//
|
|
// Normalizing <<Leaf as WithAssoc<?4t>>::Assoc as Id>::Assoc then *correctly*
|
|
// results in ambiguity.
|
|
fn main() {
|
|
bound::<<Wrapper<Leaf> as Id>::Assoc, <Wrapper<Leaf> as Id>::Assoc, _>()
|
|
}
|