tests/ui/const-generics/occurs-check/unused-substs-2.rs

   1 #![feature(generic_const_exprs)]
   2 #![allow(incomplete_features)]
   3
   4 // The goal is to get an unevaluated const `ct` with a `Ty::Infer(TyVar(_#1t)` subst.
   5 //
   6 // If we are then able to infer `ty::Infer(TyVar(_#1t) := Ty<ct>` we introduced an
   7 // artificial inference cycle.
   8 struct Foo<const N: usize>;
   9
  10 trait Bind<T> {
  11     fn bind() -> (T, Self);
  12 }
  13
  14 // `N` has to be `ConstKind::Unevaluated`.
  15 impl<T> Bind<T> for Foo<{ 6 + 1 }> {
  16     fn bind() -> (T, Self) {
  17         (panic!(), Foo)
  18     }
  19 }
  20
  21 fn main() {
  22     let (mut t, foo) = Foo::bind();
  23     // `t` is `ty::Infer(TyVar(_#1t))`
  24     // `foo` contains `ty::Infer(TyVar(_#1t))` in its substs
  25     t = foo;
  26     //~^ ERROR mismatched types
  27     //~| NOTE cyclic type
  28 }