diff options
| -rw-r--r-- | compiler/rustc_hir_analysis/src/check/check.rs | 37 |
1 files changed, 30 insertions, 7 deletions
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs index 727eeafc491..4379d7b77b1 100644 --- a/compiler/rustc_hir_analysis/src/check/check.rs +++ b/compiler/rustc_hir_analysis/src/check/check.rs @@ -506,13 +506,6 @@ fn sanity_check_found_hidden_type<'tcx>( }); // Get the hidden type. let mut hidden_ty = tcx.type_of(key.def_id).instantiate(tcx, key.args); - // In case it is in a nested opaque type, find that opaque type's - // usage in the function signature and use the generic arguments from the usage site. - // We need to do because RPITs ignore the lifetimes of the function, - // as they have their own copies of all the lifetimes they capture. - // So the only way to get the lifetimes represented in terms of the function, - // is to look how they are used in the function signature (or do some other fancy - // recording of this mapping at ast -> hir lowering time). if let hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) = origin { if hidden_ty != ty.ty { hidden_ty = find_and_apply_rpit_args( @@ -534,6 +527,36 @@ fn sanity_check_found_hidden_type<'tcx>( } } +/// In case it is in a nested opaque type, find that opaque type's +/// usage in the function signature and use the generic arguments from the usage site. +/// We need to do because RPITs ignore the lifetimes of the function, +/// as they have their own copies of all the lifetimes they capture. +/// So the only way to get the lifetimes represented in terms of the function, +/// is to look how they are used in the function signature (or do some other fancy +/// recording of this mapping at ast -> hir lowering time). +/// +/// As an example: +/// ```text +/// trait Id { +/// type Assoc; +/// } +/// impl<'a> Id for &'a () { +/// type Assoc = &'a (); +/// } +/// fn func<'a>(x: &'a ()) -> impl Id<Assoc = impl Sized + 'a> { x } +/// // desugared to +/// +/// // hidden type is `&'bDup ()` +/// // During wfcheck the hidden type of `Inner` is `&'a ()`, but +/// // `typeof(Inner<'b, 'bDup>) = &'bDup ()`. +/// // So we walk the signature of `func` to find the use of `Inner<'static, 'a>` +/// // and then use that to replace the lifetimes in the hidden type, obtaining +/// // `&'a ()`. +/// type Outer<'b, 'bDup> = impl Id<Assoc = Inner<'b, 'bDup>>; +/// // hidden type is `&'cDup ()` +/// type Inner<'c, 'cDup> = impl Sized + 'cDup; +/// fn func<'a>(x: &'a () -> Outer<'static, 'a> { x } +/// ``` fn find_and_apply_rpit_args<'tcx>( tcx: TyCtxt<'tcx>, mut hidden_ty: Ty<'tcx>, |