blob: efeb8d0231e25ad5ace5f85ef6163c531982a63b (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
// compile-flags: -Znext-solver
// This currently hangs if we do not erase constraints from
// overflow.
//
// We set the provisional result of `W<?0>` to `?0 := W<_>`.
// The next iteration does not simply result in a `?0 := W<W<_>` constraint as
// one might expect, but instead each time we evaluate the nested `W<T>` goal we
// apply the previously returned constraints: the first fixpoint iteration goes
// as follows: `W<?1>: Trait` constrains `?1` to `W<?2>`, we then evaluate
// `W<W<?2>>: Trait` the next time we try to prove the nested goal. This results
// inn `W<W<W<?3>>>` and so on. This goes on until we reach overflow in
// `try_evaluate_added_goals`. This means the provisional result after the
// second fixpoint iteration is already `W<W<W<...>>>` with a size proportional
// to the number of steps in `try_evaluate_added_goals`. The size then continues
// to grow. The exponential blowup from having 2 nested goals per impl causes
// the solver to hang without hitting the recursion limit.
trait Trait {}
struct W<T: ?Sized>(*const T);
impl<T: ?Sized> Trait for W<W<T>>
where
W<T>: Trait,
W<T>: Trait,
{}
fn impls_trait<T: Trait>() {}
fn main() {
impls_trait::<W<_>>();
//~^ ERROR overflow evaluating the requirement
}
|
