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Rollup merge of #124106 - compiler-errors:tait-lifetime-dedup, r=oli-obk

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Don't repeatedly duplicate TAIT lifetimes for each subsequently nested TAIT

Make it so that nested TAITs inherit the lifetimes from their parent item, not their parent TAIT. This is because we don't need to re-duplicate lifetimes for nested TAITs over and over, since the only lifetimes they can capture are from the parent item anyways.

This mirrors how RPITs work. This is **not** a functional change that should be observable, since the whole point of duplicating lifetimes and marking the shadowed ones (and uncaptured ones) as bivariant is designed to *not* be observable.

r? oli-obk
This commit is contained in:
Matthias Krüger 2024-04-19 19:30:49 +02:00 committed by GitHub
commit 26d4b1bfba
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3 changed files with 88 additions and 7 deletions
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15
compiler/rustc_hir_analysis/src/collect/generics_of.rs
View File

@ -195,16 +195,19 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
}
Some(fn_def_id.to_def_id())
}
ItemKind::OpaqueTy(hir::OpaqueTy {
origin: hir::OpaqueTyOrigin::TyAlias { .. },
ItemKind::OpaqueTy(&hir::OpaqueTy {
origin: hir::OpaqueTyOrigin::TyAlias { parent, in_assoc_ty },
..
}) => {
let parent_id = tcx.hir().get_parent_item(hir_id);
assert_ne!(parent_id, hir::CRATE_OWNER_ID);
debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent_id);
if in_assoc_ty {
assert!(matches!(tcx.def_kind(parent), DefKind::AssocTy));
} else {
assert!(matches!(tcx.def_kind(parent), DefKind::TyAlias));
}
debug!("generics_of: parent of opaque ty {:?} is {:?}", def_id, parent);
// Opaque types are always nested within another item, and
// inherit the generics of the item.
Some(parent_id.to_def_id())
Some(parent.to_def_id())
}
_ => None,
},

24
tests/ui/type-alias-impl-trait/variance.rs
View File

@ -52,4 +52,28 @@ impl<'i> Foo<'i> for () {
//~^ ERROR: unconstrained opaque type
}
trait Nesting<'a> {
type Output;
}
impl<'a> Nesting<'a> for &'a () {
type Output = &'a ();
}
type NestedDeeply<'a> =
impl Nesting< //~ [*, o]
'a,
Output = impl Nesting< //~ [*, o]
'a,
Output = impl Nesting< //~ [*, o]
'a,
Output = impl Nesting< //~ [*, o]
'a,
Output = impl Nesting<'a> //~ [*, o]
>
>,
>,
>;
fn test<'a>() -> NestedDeeply<'a> {
&()
}
fn main() {}

56
tests/ui/type-alias-impl-trait/variance.stderr
View File

@ -176,6 +176,60 @@ error: [*, *, o, o]
LL | type ExplicitCaptureFromGat<'a> = impl Sized + Captures<'a>;
| ^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 24 previous errors
error: [*, o]
--> $DIR/variance.rs:62:5
|
LL | / impl Nesting<
LL | | 'a,
LL | | Output = impl Nesting<
LL | | 'a,
... |
LL | | >,
LL | | >;
| |_____^
error: [*, o]
--> $DIR/variance.rs:64:18
|
LL | Output = impl Nesting<
| __________________^
LL | | 'a,
LL | | Output = impl Nesting<
LL | | 'a,
... |
LL | | >,
LL | | >,
| |_________^
error: [*, o]
--> $DIR/variance.rs:66:22
|
LL | Output = impl Nesting<
| ______________________^
LL | | 'a,
LL | | Output = impl Nesting<
LL | | 'a,
LL | | Output = impl Nesting<'a>
LL | | >
LL | | >,
| |_____________^
error: [*, o]
--> $DIR/variance.rs:68:26
|
LL | Output = impl Nesting<
| __________________________^
LL | | 'a,
LL | | Output = impl Nesting<'a>
LL | | >
| |_________________^
error: [*, o]
--> $DIR/variance.rs:70:30
|
LL | Output = impl Nesting<'a>
| ^^^^^^^^^^^^^^^^
error: aborting due to 29 previous errors
For more information about this error, try `rustc --explain E0657`.