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generalize hr alias: avoid unconstrainable infer vars
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36 changes: 36 additions & 0 deletions
36
tests/ui/traits/next-solver/generalize/hr-alias-non-hr-alias-self-ty-1.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,36 @@ | ||
| //@ revisions: old next | ||
| //@[next] compile-flags: -Znext-solver | ||
| //@ ignore-compare-mode-next-solver (explicit revisions) | ||
| //@ check-pass | ||
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| // Generalizing an alias referencing escaping bound variables | ||
| // is hard. We previously didn't replace this alias with inference | ||
| // variables but did replace nested alias which do not reference | ||
| // any bound variables. This caused us to stall with the following | ||
| // goal, which cannot make any progress: | ||
| // | ||
| // <<T as Id>::Refl as HigherRanked>::Output<'a> | ||
| // alias-relate | ||
| // <?unconstrained as HigherRanked>::Output<'a> | ||
| // | ||
| // | ||
| // cc trait-system-refactor-initiative#110 | ||
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| #![allow(unused)] | ||
| trait HigherRanked { | ||
| type Output<'a>; | ||
| } | ||
| trait Id { | ||
| type Refl: HigherRanked; | ||
| } | ||
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| fn foo<T: Id>() -> for<'a> fn(<<T as Id>::Refl as HigherRanked>::Output<'a>) { | ||
| todo!() | ||
| } | ||
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| fn bar<T: Id>() { | ||
| // we generalize here | ||
| let x = foo::<T>(); | ||
| } | ||
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| fn main() {} |
32 changes: 32 additions & 0 deletions
32
tests/ui/traits/next-solver/generalize/hr-alias-non-hr-alias-self-ty-2.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,32 @@ | ||
| //@ revisions: old next | ||
| //@[next] compile-flags: -Znext-solver | ||
| //@ ignore-compare-mode-next-solver (explicit revisions) | ||
| //@ check-pass | ||
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| // A minimization of an ambiguity error in `icu_provider`. | ||
| // | ||
| // cc trait-system-refactor-initiative#110 | ||
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| trait Yokeable<'a> { | ||
| type Output; | ||
| } | ||
| trait Id { | ||
| type Refl; | ||
| } | ||
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| fn into_deserialized<M: Id>() -> M | ||
| where | ||
| M::Refl: for<'a> Yokeable<'a>, | ||
| { | ||
| try_map_project::<M, _>(|_| todo!()) | ||
| } | ||
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| fn try_map_project<M: Id, F>(_f: F) -> M | ||
| where | ||
| M::Refl: for<'a> Yokeable<'a>, | ||
| F: for<'a> FnOnce(&'a ()) -> <<M as Id>::Refl as Yokeable<'a>>::Output, | ||
| { | ||
| todo!() | ||
| } | ||
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| fn main() {} |
51 changes: 51 additions & 0 deletions
51
tests/ui/traits/next-solver/generalize/hr-alias-universe-lowering-ambiguity.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,51 @@ | ||
| //@ compile-flags: -Znext-solver | ||
| //@ check-pass | ||
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| // A regression test for a fairly subtle issue with how we | ||
| // generalize aliases referencing higher-ranked regions | ||
| // which previously caused unexpected ambiguity errors. | ||
| // | ||
| // The explanations in the test may end up being out of date | ||
| // in the future as we may refine our approach to generalization | ||
| // going forward. | ||
| // | ||
| // cc trait-system-refactor-initiative#108 | ||
| trait Trait<'a> { | ||
| type Assoc; | ||
| } | ||
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| impl<'a> Trait<'a> for () { | ||
| type Assoc = (); | ||
| } | ||
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| fn foo<T: for<'a> Trait<'a>>(x: T) -> for<'a> fn(<T as Trait<'a>>::Assoc) { | ||
| |_| () | ||
| } | ||
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| fn unconstrained<T>() -> T { | ||
| todo!() | ||
| } | ||
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| fn main() { | ||
| // create `?x.0` in the root universe | ||
| let mut x = unconstrained(); | ||
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| // bump the current universe of the inference context | ||
| let bump: for<'a, 'b> fn(&'a (), &'b ()) = |_, _| (); | ||
| let _: for<'a> fn(&'a (), &'a ()) = bump; | ||
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| // create `?y.1` in a higher universe | ||
| let mut y = Default::default(); | ||
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| // relate `?x.0` with `for<'a> fn(<?y.1 as Trait<'a>>::Assoc)` | ||
| // -> instantiate `?x.0` with `for<'a> fn(<?y_new.0 as Trait<'a>>::Assoc)` | ||
| x = foo(y); | ||
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| // Constrain `?y.1` to `()` | ||
| let _: () = y; | ||
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| // `AliasRelate(<?y_new.0 as Trait<'a>>::Assoc, <() as Trait<'a>>::Assoc)` | ||
| // remains ambiguous unless we somehow constrain `?y_new.0` during | ||
| // generalization to be equal to `?y.1`, which is exactly what we | ||
| // did to fix this issue. | ||
| } |
1 change: 1 addition & 0 deletions
1
tests/ui/traits/next-solver/generalize/occurs-check-nested-alias.rs
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