normalization may result in unconstrained regions #15
Comments
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Because proving alias-outlives bounds checks for equality between regions, this results in the undesirable errors: trait Super {
type SAssoc;
}
trait Trait<'a>: Super<SAssoc = <Self as Trait<'a>>::TAssoc> {
type TAssoc;
}
fn test<'a, T: 'a>() {}
fn unconstrained_lt<'arg, T: for<'a> Trait<'a>>(x: &'arg <T as Super>::SAssoc) {
test::<'arg, <T as Super>::SAssoc>();
}normalizing "through" the alias with unconstrained regions does compile: trait Super {
type SAssoc;
}
trait Trait<'a>: Super<SAssoc = <Self as Trait<'a>>::TAssoc> {
type TAssoc;
}
fn test<'a, T: 'a>() {}
fn unconstrained_lt<'arg, T: for<'a> Trait<'a, TAssoc = T>>(x: &'arg <T as Super>::SAssoc) {
test::<'arg, <T as Super>::SAssoc>();
} |
|
via alias-bound instead trait Super {
type SAssoc;
}
trait Trait<'a>: Super<SAssoc = <Self as Trait<'a>>::TAssoc> {
type TAssoc;
}
trait AliasBound {
type WithBound: for<'a> Trait<'a>;
}
fn unconstrained_lt<T: AliasBound>(x: <T::WithBound as Super>::SAssoc) {} |
bors
added a commit
to rust-lang-ci/rust
that referenced
this issue
Jan 30, 2025
… r=<try> elaborate: avoid projections with unconstrained bound regions Should only do this for where-bounds and item bounds. Gonna rewrite later I think. This means we'll no longer need to support unconstrained regions in implied bounds, see lcnr/random-rust-snippets#15. This fixes ```rust trait Super { type SAssoc; } trait Trait<'a>: Super<SAssoc = <Self as Trait<'a>>::TAssoc> { type TAssoc; } fn test<'a, T: 'a>() {} fn unconstrained_lt<'arg, T: for<'a> Trait<'a>>(x: &'arg <T as Super>::SAssoc) { test::<'arg, <T as Super>::SAssoc>(); } ``` but breaks ```rust trait Super { type SAssoc; } trait Trait<'a>: Super<SAssoc = <Self as Trait<'a>>::TAssoc> { type TAssoc; } fn test<'a, T: 'a>() {} fn unconstrained_lt<'arg, T: for<'a> Trait<'a, TAssoc = usize>>(x: <T as Super>::SAssoc) -> usize { x } ``` r? `@compiler-errors`
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The function argument of
unconstrained_ltnormalizes to<T as Trait<'unconstrained>>::TAssocThe text was updated successfully, but these errors were encountered: