| //@ revisions: current next |
| //@[next] compile-flags: -Znext-solver=coherence |
| //@ ignore-compare-mode-next-solver (explicit revisions) |
| //@ check-pass |
| |
| // A regression test for `paperclip-core`. This previously failed to compile |
| // in the new solver. |
| // |
| // Behavior in old solver: |
| // We prove `Projection(<W<?0> as Unconstrained>::Assoc, ())`. This |
| // normalizes `<W<?0> as Unconstrained>::Assoc` to `?1` with nested goals |
| // `[Projection(<?0 as Unconstrained>::Assoc, ?1), Trait(?1: NoImpl)]`. |
| // We then unify `?1` with `()`. At this point `?1: NoImpl` does not hold, |
| // and we get an error. |
| // |
| // Previous behavior of the new solver: |
| // We prove `Projection(<W<?0> as Unconstrained>::Assoc, ())`. This normalizes |
| // `<W<?0> as Unconstrained>::Assoc` to `?1` and eagerly computes the nested |
| // goals `[Projection(<?0 as Unconstrained>::Assoc, ?1), Trait(?1: NoImpl)]`. |
| // These goals are both ambiguous. `NormalizesTo`` then returns `?1` as the |
| // normalized-to type. It discards the nested goals, forcing the certainty of |
| // the normalization to `Maybe`. Unifying `?1` with `()` succeeds¹. However, |
| // this is never propagated to the `?1: NoImpl` goal, as it only exists inside |
| // of the `NormalizesTo` goal. The normalized-to term always starts out as |
| // unconstrained. |
| // |
| // We fix this regression by returning the nested goals of `NormalizesTo` goals |
| // to the `AliasRelate`. This results in us checking `(): NoImpl`, same as the |
| // old solver. |
| |
| struct W<T: ?Sized>(T); |
| trait NoImpl {} |
| trait Unconstrained { |
| type Assoc; |
| } |
| impl<T: Unconstrained<Assoc = U>, U: NoImpl> Unconstrained for W<T> { |
| type Assoc = U; |
| } |
| |
| |
| trait Overlap {} |
| impl<T: Unconstrained<Assoc = ()>> Overlap for T {} |
| impl<U> Overlap for W<U> {} |
| |
| fn main() {} |
