diff options
Diffstat (limited to 'tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.rs')
-rw-r--r-- | tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.rs | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.rs b/tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.rs new file mode 100644 index 000000000..efeb8d023 --- /dev/null +++ b/tests/ui/traits/next-solver/cycles/inductive-fixpoint-hang.rs @@ -0,0 +1,33 @@ +// 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 +} |