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// 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
}
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