diff options
| -rw-r--r-- | compiler/rustc_typeck/src/collect/type_of.rs | 33 |
1 files changed, 21 insertions, 12 deletions
diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs index 571b91cf254..7fa58dcd5f4 100644 --- a/compiler/rustc_typeck/src/collect/type_of.rs +++ b/compiler/rustc_typeck/src/collect/type_of.rs @@ -29,20 +29,28 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option< let parent_node = tcx.hir().get(parent_node_id); match parent_node { - // This matches on types who's paths couldn't be resolved without typeck'ing e.g. + // This match arm is for when the def_id appears in a GAT whose + // path can't be resolved without typechecking e.g. // // trait Foo { - // type Assoc<const N1: usize>; + // type Assoc<const N: usize>; // fn foo() -> Self::Assoc<3>; - // // note: if the def_id argument is the 3 then in this example - // // parent_node would be the node for Self::Assoc<_> // } - // We didnt write <Self as Foo>::Assoc so the Self::Assoc<_> is lowered to QPath::TypeRelative. + // + // In the above code we would call this query with the def_id of 3 and + // the parent_node we match on would be the hir node for Self::Assoc<3> + // + // `Self::Assoc<3>` cant be resolved without typchecking here as we + // didnt write <Self as Foo>::Assoc<3>. If we did then another match + // arm would handle this. + // // I believe this match arm is only needed for GAT but I am not 100% sure - BoxyUwU Node::Ty(hir_ty @ Ty { kind: TyKind::Path(QPath::TypeRelative(_, segment)), .. }) => { - // Walk up from the parent_node to find an item so that - // we can resolve the relative path to an actual associated type. - // For the code example above, this item would be the Foo trait. + // Find the Item containing the associated type so we can create an ItemCtxt. + // Using the ItemCtxt convert the HIR for the unresolved assoc type into a + // ty which is a fully resolved projection. + // For the code example above, this would mean converting Self::Assoc<3> + // into a ty::Projection(<Self as Foo>::Assoc<3>) let item_hir_id = tcx .hir() .parent_iter(hir_id) @@ -52,11 +60,12 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option< .unwrap(); let item_did = tcx.hir().local_def_id(item_hir_id).to_def_id(); let item_ctxt = &ItemCtxt::new(tcx, item_did) as &dyn crate::astconv::AstConv<'_>; - - // This ty will be the actual associated type so that we can - // go through its generics to find which param our def_id corresponds to. - // For the code example above, this ty would be the Assoc<const N1: usize>. let ty = item_ctxt.ast_ty_to_ty(hir_ty); + + // Iterate through the generics of the projection to find the one that corresponds to + // the def_id that this query was called with. We filter to only const args here as a + // precaution for if it's ever allowed to elide lifetimes in GAT's. It currently isn't + // but it can't hurt to be safe ^^ if let ty::Projection(projection) = ty.kind() { let generics = tcx.generics_of(projection.item_def_id); |