diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs index 8f2f02a5e41..e3da87a2210 100644 --- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs +++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs @@ -745,7 +745,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { match (source.kind(), target.kind()) { // Trait+Kx+'a -> Trait+Ky+'b (upcasts). - (&ty::Dynamic(ref data_a, _, ty::Dyn), &ty::Dynamic(ref data_b, _, ty::Dyn)) => { + ( + &ty::Dynamic(ref a_data, a_region, ty::Dyn), + &ty::Dynamic(ref b_data, b_region, ty::Dyn), + ) => { // Upcast coercions permit several things: // // 1. Dropping auto traits, e.g., `Foo + Send` to `Foo` @@ -757,19 +760,19 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // // We always perform upcasting coercions when we can because of reason // #2 (region bounds). - let auto_traits_compatible = data_b + let auto_traits_compatible = b_data .auto_traits() // All of a's auto traits need to be in b's auto traits. - .all(|b| data_a.auto_traits().any(|a| a == b)); + .all(|b| a_data.auto_traits().any(|a| a == b)); if auto_traits_compatible { - let principal_def_id_a = data_a.principal_def_id(); - let principal_def_id_b = data_b.principal_def_id(); + let principal_def_id_a = a_data.principal_def_id(); + let principal_def_id_b = b_data.principal_def_id(); if principal_def_id_a == principal_def_id_b { // no cyclic candidates.vec.push(BuiltinUnsizeCandidate); } else if principal_def_id_a.is_some() && principal_def_id_b.is_some() { // not casual unsizing, now check whether this is trait upcasting coercion. - let principal_a = data_a.principal().unwrap(); + let principal_a = a_data.principal().unwrap(); let target_trait_did = principal_def_id_b.unwrap(); let source_trait_ref = principal_a.with_self_ty(self.tcx(), source); if let Some(deref_trait_ref) = self.need_migrate_deref_output_trait_object( @@ -785,9 +788,23 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { for (idx, upcast_trait_ref) in util::supertraits(self.tcx(), source_trait_ref).enumerate() { - if upcast_trait_ref.def_id() == target_trait_did { - candidates.vec.push(TraitUpcastingUnsizeCandidate(idx)); - } + self.infcx.probe(|_| { + if upcast_trait_ref.def_id() == target_trait_did + && let Ok(nested) = self.match_upcast_principal( + obligation, + upcast_trait_ref, + a_data, + b_data, + a_region, + b_region, + ) + { + if nested.is_none() { + candidates.ambiguous = true; + } + candidates.vec.push(TraitUpcastingUnsizeCandidate(idx)); + } + }) } } } diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs index 3d6df08f6db..65d43b55b90 100644 --- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs +++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs @@ -890,89 +890,16 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { let unnormalized_upcast_principal = util::supertraits(tcx, source_principal).nth(idx).unwrap(); - let mut nested = vec![]; - let upcast_principal = normalize_with_depth_to( - self, - obligation.param_env, - obligation.cause.clone(), - obligation.recursion_depth + 1, - unnormalized_upcast_principal, - &mut nested, - ); - - for bound in b_data { - match bound.skip_binder() { - // Check that a's supertrait (upcast_principal) is compatible - // with the target (b_ty). - ty::ExistentialPredicate::Trait(target_principal) => { - nested.extend( - self.infcx - .at(&obligation.cause, obligation.param_env) - .sup( - DefineOpaqueTypes::No, - upcast_principal.map_bound(|trait_ref| { - ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref) - }), - bound.rebind(target_principal), - ) - .map_err(|_| SelectionError::Unimplemented)? - .into_obligations(), - ); - } - // Check that b_ty's projection is satisfied by exactly one of - // a_ty's projections. First, we look through the list to see if - // any match. If not, error. Then, if *more* than one matches, we - // return ambiguity. Otherwise, if exactly one matches, equate - // it with b_ty's projection. - ty::ExistentialPredicate::Projection(target_projection) => { - let target_projection = bound.rebind(target_projection); - let mut matching_projections = - a_data.projection_bounds().filter(|source_projection| { - // Eager normalization means that we can just use can_eq - // here instead of equating and processing obligations. - source_projection.item_def_id() == target_projection.item_def_id() - && self.infcx.can_eq( - obligation.param_env, - *source_projection, - target_projection, - ) - }); - let Some(source_projection) = matching_projections.next() else { - return Err(SelectionError::Unimplemented); - }; - if matching_projections.next().is_some() { - // This is incomplete but I don't care. We should never - // have more than one projection that ever applies with - // eager norm and actually implementable traits, since - // you can't have two supertraits like: - // `trait A: B + B` - return Err(SelectionError::Unimplemented); - } - nested.extend( - self.infcx - .at(&obligation.cause, obligation.param_env) - .sup(DefineOpaqueTypes::No, source_projection, target_projection) - .map_err(|_| SelectionError::Unimplemented)? - .into_obligations(), - ); - } - // Check that b_ty's auto trait is present in a_ty's bounds. - ty::ExistentialPredicate::AutoTrait(def_id) => { - if !a_data.auto_traits().any(|source_def_id| source_def_id == def_id) { - return Err(SelectionError::Unimplemented); - } - } - } - } - - // Also require that a_ty's lifetime outlives b_ty's lifetime. - nested.push(Obligation::with_depth( - tcx, - obligation.cause.clone(), - obligation.recursion_depth + 1, - obligation.param_env, - ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region)), - )); + let nested = self + .match_upcast_principal( + obligation, + unnormalized_upcast_principal, + a_data, + b_data, + a_region, + b_region, + )? + .expect("did not expect ambiguity during confirmation"); let vtable_segment_callback = { let mut vptr_offset = 0; diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index 5da8d838db2..f1bd9f8b71a 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -2477,6 +2477,98 @@ impl<'tcx> SelectionContext<'_, 'tcx> { Ok(Normalized { value: impl_args, obligations: nested_obligations }) } + fn match_upcast_principal( + &mut self, + obligation: &PolyTraitObligation<'tcx>, + unnormalized_upcast_principal: ty::PolyTraitRef<'tcx>, + a_data: &'tcx ty::List>, + b_data: &'tcx ty::List>, + a_region: ty::Region<'tcx>, + b_region: ty::Region<'tcx>, + ) -> SelectionResult<'tcx, Vec>> { + let tcx = self.tcx(); + let mut nested = vec![]; + + let upcast_principal = normalize_with_depth_to( + self, + obligation.param_env, + obligation.cause.clone(), + obligation.recursion_depth + 1, + unnormalized_upcast_principal, + &mut nested, + ); + + for bound in b_data { + match bound.skip_binder() { + // Check that a_ty's supertrait (upcast_principal) is compatible + // with the target (b_ty). + ty::ExistentialPredicate::Trait(target_principal) => { + nested.extend( + self.infcx + .at(&obligation.cause, obligation.param_env) + .sup( + DefineOpaqueTypes::No, + upcast_principal.map_bound(|trait_ref| { + ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref) + }), + bound.rebind(target_principal), + ) + .map_err(|_| SelectionError::Unimplemented)? + .into_obligations(), + ); + } + // Check that b_ty's projection is satisfied by exactly one of + // a_ty's projections. First, we look through the list to see if + // any match. If not, error. Then, if *more* than one matches, we + // return ambiguity. Otherwise, if exactly one matches, equate + // it with b_ty's projection. + ty::ExistentialPredicate::Projection(target_projection) => { + let target_projection = bound.rebind(target_projection); + let mut matching_projections = + a_data.projection_bounds().filter(|source_projection| { + // Eager normalization means that we can just use can_eq + // here instead of equating and processing obligations. + source_projection.item_def_id() == target_projection.item_def_id() + && self.infcx.can_eq( + obligation.param_env, + *source_projection, + target_projection, + ) + }); + let Some(source_projection) = matching_projections.next() else { + return Err(SelectionError::Unimplemented); + }; + if matching_projections.next().is_some() { + return Ok(None); + } + nested.extend( + self.infcx + .at(&obligation.cause, obligation.param_env) + .sup(DefineOpaqueTypes::No, source_projection, target_projection) + .map_err(|_| SelectionError::Unimplemented)? + .into_obligations(), + ); + } + // Check that b_ty's auto traits are present in a_ty's bounds. + ty::ExistentialPredicate::AutoTrait(def_id) => { + if !a_data.auto_traits().any(|source_def_id| source_def_id == def_id) { + return Err(SelectionError::Unimplemented); + } + } + } + } + + nested.push(Obligation::with_depth( + tcx, + obligation.cause.clone(), + obligation.recursion_depth + 1, + obligation.param_env, + ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region)), + )); + + Ok(Some(nested)) + } + /// Normalize `where_clause_trait_ref` and try to match it against /// `obligation`. If successful, return any predicates that /// result from the normalization.