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| 1 | +use rustc_hir::def_id::DefId; |
| 2 | + |
| 3 | +use crate::ty::{self, ExistentialPredicateStableCmpExt, TyCtxt}; |
| 4 | + |
| 5 | +impl<'tcx> TyCtxt<'tcx> { |
| 6 | + /// Given a `def_id` of a trait or impl method, compute whether that method needs to |
| 7 | + /// have an RPITIT shim applied to it for it to be object safe. If so, return the |
| 8 | + /// `def_id` of the RPITIT, and also the args of trait method that returns the RPITIT. |
| 9 | + /// |
| 10 | + /// NOTE that these args are not, in general, the same as than the RPITIT's args. They |
| 11 | + /// are a subset of those args, since they do not include the late-bound lifetimes of |
| 12 | + /// the RPITIT. Depending on the context, these will need to be dealt with in different |
| 13 | + /// ways -- in codegen, it's okay to fill them with ReErased. |
| 14 | + pub fn return_position_impl_trait_in_trait_shim_data( |
| 15 | + self, |
| 16 | + def_id: DefId, |
| 17 | + ) -> Option<(DefId, ty::EarlyBinder<'tcx, ty::GenericArgsRef<'tcx>>)> { |
| 18 | + let assoc_item = self.opt_associated_item(def_id)?; |
| 19 | + |
| 20 | + let (trait_item_def_id, opt_impl_def_id) = match assoc_item.container { |
| 21 | + ty::AssocItemContainer::Impl => { |
| 22 | + (assoc_item.trait_item_def_id?, Some(self.parent(def_id))) |
| 23 | + } |
| 24 | + ty::AssocItemContainer::Trait => (def_id, None), |
| 25 | + }; |
| 26 | + |
| 27 | + let sig = self.fn_sig(trait_item_def_id); |
| 28 | + |
| 29 | + // Check if the trait returns an RPITIT. |
| 30 | + let ty::Alias(ty::Projection, ty::AliasTy { def_id, .. }) = |
| 31 | + *sig.skip_binder().skip_binder().output().kind() |
| 32 | + else { |
| 33 | + return None; |
| 34 | + }; |
| 35 | + if !self.is_impl_trait_in_trait(def_id) { |
| 36 | + return None; |
| 37 | + } |
| 38 | + |
| 39 | + let args = if let Some(impl_def_id) = opt_impl_def_id { |
| 40 | + // Rebase the args from the RPITIT onto the impl trait ref, so we can later |
| 41 | + // substitute them with the method args of the *impl* method, since that's |
| 42 | + // the instance we're building a vtable shim for. |
| 43 | + ty::GenericArgs::identity_for_item(self, trait_item_def_id).rebase_onto( |
| 44 | + self, |
| 45 | + self.parent(trait_item_def_id), |
| 46 | + self.impl_trait_ref(impl_def_id) |
| 47 | + .expect("expected impl trait ref from parent of impl item") |
| 48 | + .instantiate_identity() |
| 49 | + .args, |
| 50 | + ) |
| 51 | + } else { |
| 52 | + // This is when we have a default trait implementation. |
| 53 | + ty::GenericArgs::identity_for_item(self, trait_item_def_id) |
| 54 | + }; |
| 55 | + |
| 56 | + Some((def_id, ty::EarlyBinder::bind(args))) |
| 57 | + } |
| 58 | + |
| 59 | + /// Given a `DefId` of an RPITIT and its args, return the existential predicates |
| 60 | + /// that corresponds to the RPITIT's bounds with the self type erased. |
| 61 | + pub fn item_bounds_to_existential_predicates( |
| 62 | + self, |
| 63 | + def_id: DefId, |
| 64 | + args: ty::GenericArgsRef<'tcx>, |
| 65 | + ) -> &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> { |
| 66 | + let mut bounds: Vec<_> = self |
| 67 | + .item_super_predicates(def_id) |
| 68 | + .iter_instantiated(self, args) |
| 69 | + .filter_map(|clause| { |
| 70 | + clause |
| 71 | + .kind() |
| 72 | + .map_bound(|clause| match clause { |
| 73 | + ty::ClauseKind::Trait(trait_pred) => Some(ty::ExistentialPredicate::Trait( |
| 74 | + ty::ExistentialTraitRef::erase_self_ty(self, trait_pred.trait_ref), |
| 75 | + )), |
| 76 | + ty::ClauseKind::Projection(projection_pred) => { |
| 77 | + Some(ty::ExistentialPredicate::Projection( |
| 78 | + ty::ExistentialProjection::erase_self_ty(self, projection_pred), |
| 79 | + )) |
| 80 | + } |
| 81 | + ty::ClauseKind::TypeOutlives(_) => { |
| 82 | + // Type outlives bounds don't really turn into anything, |
| 83 | + // since we must use an intersection region for the `dyn*`'s |
| 84 | + // region anyways. |
| 85 | + None |
| 86 | + } |
| 87 | + _ => unreachable!("unexpected clause in item bounds: {clause:?}"), |
| 88 | + }) |
| 89 | + .transpose() |
| 90 | + }) |
| 91 | + .collect(); |
| 92 | + bounds.sort_by(|a, b| a.skip_binder().stable_cmp(self, &b.skip_binder())); |
| 93 | + self.mk_poly_existential_predicates(&bounds) |
| 94 | + } |
| 95 | +} |
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