| //@ compile-flags: -Znext-solver |
| |
| // Proving `W<?0>: Trait` instantiates `?0` with `(W<?1>, W<?2>)` and then |
| // proves `W<?1>: Trait` and `W<?2>: Trait`, resulting in a coinductive cycle. |
| // |
| // Proving coinductive cycles runs until we reach a fixpoint. However, after |
| // computing `try_evaluate_added_goals` in the second fixpoint iteration, the |
| // self type already has a depth equal to the number of steps. This results |
| // in enormous constraints, causing the canonicalizer to hang without ever |
| // reaching the recursion limit. We currently avoid that by erasing the constraints |
| // from overflow. |
| // |
| // This previously caused a hang in the trait solver, see |
| // https://github.com/rust-lang/trait-system-refactor-initiative/issues/13. |
| |
| #![feature(rustc_attrs)] |
| |
| #[rustc_coinductive] |
| trait Trait {} |
| |
| struct W<T>(T); |
| |
| impl<T, U> Trait for W<(W<T>, W<U>)> |
| where |
| W<T>: Trait, |
| W<U>: Trait, |
| { |
| } |
| |
| fn impls<T: Trait>() {} |
| |
| fn main() { |
| impls::<W<_>>(); |
| //~^ ERROR overflow evaluating the requirement |
| } |
