From 8a47b442c431efcaba7e257c509b9b8d2337e37a Mon Sep 17 00:00:00 2001 From: lcnr Date: Tue, 3 Dec 2024 13:49:12 +0100 Subject: [PATCH] closure requirements: don't replace bivariant opaque args It is unnecessary, these get constrained when checking that the opaque type is well-formed. It also results in the opaque type no longer being well formed. If you've got `fn foo<'a>() -> impl Sized + 'a` the opaque is `type Opaque<'a, 'aDummy> where 'a: 'aDummy, 'aDummy: 'a` where `'aDummy` is bivariant. If we call `foo::<'b>()` inside of a closure and its return type ends up in a type test, we start out with the WF `Opaque<'b, 'b>`, and then replace the bivariant `'b` with `'static`. `Opaque<'b, 'static>` is no longer well-formed. Given how these type tests are used, I don't think this caused any practical issues. --- .../rustc_borrowck/src/region_infer/mod.rs | 30 ------------------- 1 file changed, 30 deletions(-) diff --git a/compiler/rustc_borrowck/src/region_infer/mod.rs b/compiler/rustc_borrowck/src/region_infer/mod.rs index f4f87fa9f650..691709e53ee6 100644 --- a/compiler/rustc_borrowck/src/region_infer/mod.rs +++ b/compiler/rustc_borrowck/src/region_infer/mod.rs @@ -1068,37 +1068,7 @@ impl<'tcx> RegionInferenceContext<'tcx> { ty: Ty<'tcx>, ) -> Option> { let tcx = infcx.tcx; - - // Opaque types' args may include useless lifetimes. - // We will replace them with ReStatic. - struct OpaqueFolder<'tcx> { - tcx: TyCtxt<'tcx>, - } - impl<'tcx> ty::TypeFolder> for OpaqueFolder<'tcx> { - fn cx(&self) -> TyCtxt<'tcx> { - self.tcx - } - fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { - use ty::TypeSuperFoldable as _; - let tcx = self.tcx; - let &ty::Alias(ty::Opaque, ty::AliasTy { args, def_id, .. }) = t.kind() else { - return t.super_fold_with(self); - }; - let args = std::iter::zip(args, tcx.variances_of(def_id)).map(|(arg, v)| { - match (arg.unpack(), v) { - (ty::GenericArgKind::Lifetime(_), ty::Bivariant) => { - tcx.lifetimes.re_static.into() - } - _ => arg.fold_with(self), - } - }); - Ty::new_opaque(tcx, def_id, tcx.mk_args_from_iter(args)) - } - } - - let ty = ty.fold_with(&mut OpaqueFolder { tcx }); let mut failed = false; - let ty = fold_regions(tcx, ty, |r, _depth| { let r_vid = self.to_region_vid(r); let r_scc = self.constraint_sccs.scc(r_vid);