diff --git a/compiler/rustc_hir_analysis/src/astconv/mod.rs b/compiler/rustc_hir_analysis/src/astconv/mod.rs index 1ae3ebaebbb..657de8ae9ad 100644 --- a/compiler/rustc_hir_analysis/src/astconv/mod.rs +++ b/compiler/rustc_hir_analysis/src/astconv/mod.rs @@ -1671,9 +1671,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o { .is_accessible_from(self.item_def_id(), tcx) && tcx.all_impls(*trait_def_id) .any(|impl_def_id| { - let trait_ref = tcx.impl_trait_ref(impl_def_id); - trait_ref.is_some_and(|trait_ref| { - let impl_ = trait_ref.instantiate( + let impl_header = tcx.impl_trait_header(impl_def_id); + impl_header.is_some_and(|header| { + let header = header.instantiate( tcx, infcx.fresh_args_for_item(DUMMY_SP, impl_def_id), ); @@ -1685,11 +1685,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o { infcx .can_eq( ty::ParamEnv::empty(), - impl_.self_ty(), + header.trait_ref.self_ty(), value, - ) + ) && header.polarity != ty::ImplPolarity::Negative }) - && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative }) }) .map(|trait_def_id| tcx.def_path_str(trait_def_id)) @@ -1735,13 +1734,13 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o { } else { // Find all the types that have an `impl` for the trait. tcx.all_impls(trait_def_id) - .filter(|impl_def_id| { + .filter_map(|impl_def_id| tcx.impl_trait_header(impl_def_id)) + .filter(|header| { // Consider only accessible traits tcx.visibility(trait_def_id).is_accessible_from(self.item_def_id(), tcx) - && tcx.impl_polarity(impl_def_id) != ty::ImplPolarity::Negative + && header.skip_binder().polarity != ty::ImplPolarity::Negative }) - .filter_map(|impl_def_id| tcx.impl_trait_ref(impl_def_id)) - .map(|impl_| impl_.instantiate_identity().self_ty()) + .map(|header| header.instantiate_identity().trait_ref.self_ty()) // We don't care about blanket impls. .filter(|self_ty| !self_ty.has_non_region_param()) .map(|self_ty| tcx.erase_regions(self_ty).to_string()) diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs index 7250dc81faf..2bdf8f9326d 100644 --- a/compiler/rustc_hir_analysis/src/check/check.rs +++ b/compiler/rustc_hir_analysis/src/check/check.rs @@ -474,8 +474,12 @@ pub(crate) fn check_item_type(tcx: TyCtxt<'_>, def_id: LocalDefId) { } DefKind::Fn => {} // entirely within check_item_body DefKind::Impl { of_trait } => { - if of_trait && let Some(impl_trait_ref) = tcx.impl_trait_ref(def_id) { - check_impl_items_against_trait(tcx, def_id, impl_trait_ref.instantiate_identity()); + if of_trait && let Some(impl_trait_header) = tcx.impl_trait_header(def_id) { + check_impl_items_against_trait( + tcx, + def_id, + impl_trait_header.instantiate_identity(), + ); check_on_unimplemented(tcx, def_id); } } @@ -666,19 +670,19 @@ pub(super) fn check_specialization_validity<'tcx>( fn check_impl_items_against_trait<'tcx>( tcx: TyCtxt<'tcx>, impl_id: LocalDefId, - impl_trait_ref: ty::TraitRef<'tcx>, + impl_trait_header: ty::ImplTraitHeader<'tcx>, ) { // If the trait reference itself is erroneous (so the compilation is going // to fail), skip checking the items here -- the `impl_item` table in `tcx` // isn't populated for such impls. - if impl_trait_ref.references_error() { + if impl_trait_header.references_error() { return; } let impl_item_refs = tcx.associated_item_def_ids(impl_id); // Negative impls are not expected to have any items - match tcx.impl_polarity(impl_id) { + match impl_trait_header.polarity { ty::ImplPolarity::Reservation | ty::ImplPolarity::Positive => {} ty::ImplPolarity::Negative => { if let [first_item_ref, ..] = impl_item_refs { @@ -695,7 +699,7 @@ fn check_impl_items_against_trait<'tcx>( } } - let trait_def = tcx.trait_def(impl_trait_ref.def_id); + let trait_def = tcx.trait_def(impl_trait_header.trait_ref.def_id); for &impl_item in impl_item_refs { let ty_impl_item = tcx.associated_item(impl_item); @@ -714,10 +718,10 @@ fn check_impl_items_against_trait<'tcx>( )); } ty::AssocKind::Fn => { - compare_impl_method(tcx, ty_impl_item, ty_trait_item, impl_trait_ref); + compare_impl_method(tcx, ty_impl_item, ty_trait_item, impl_trait_header.trait_ref); } ty::AssocKind::Type => { - compare_impl_ty(tcx, ty_impl_item, ty_trait_item, impl_trait_ref); + compare_impl_ty(tcx, ty_impl_item, ty_trait_item, impl_trait_header.trait_ref); } } @@ -737,7 +741,7 @@ fn check_impl_items_against_trait<'tcx>( let mut must_implement_one_of: Option<&[Ident]> = trait_def.must_implement_one_of.as_deref(); - for &trait_item_id in tcx.associated_item_def_ids(impl_trait_ref.def_id) { + for &trait_item_id in tcx.associated_item_def_ids(impl_trait_header.trait_ref.def_id) { let leaf_def = ancestors.leaf_def(tcx, trait_item_id); let is_implemented = leaf_def @@ -815,7 +819,7 @@ fn check_impl_items_against_trait<'tcx>( if let Some(missing_items) = must_implement_one_of { let attr_span = tcx - .get_attr(impl_trait_ref.def_id, sym::rustc_must_implement_one_of) + .get_attr(impl_trait_header.trait_ref.def_id, sym::rustc_must_implement_one_of) .map(|attr| attr.span); missing_items_must_implement_one_of_err( diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs index 646a84b043c..6eba853af30 100644 --- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs +++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs @@ -245,9 +245,9 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<() // won't be allowed unless there's an *explicit* implementation of `Send` // for `T` hir::ItemKind::Impl(impl_) => { - let is_auto = tcx - .impl_trait_ref(def_id) - .is_some_and(|trait_ref| tcx.trait_is_auto(trait_ref.skip_binder().def_id)); + let header = tcx.impl_trait_header(def_id); + let is_auto = header + .is_some_and(|header| tcx.trait_is_auto(header.skip_binder().trait_ref.def_id)); let mut res = Ok(()); if let (hir::Defaultness::Default { .. }, true) = (impl_.defaultness, is_auto) { let sp = impl_.of_trait.as_ref().map_or(item.span, |t| t.path.span); @@ -259,11 +259,12 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<() .emit()); } // We match on both `ty::ImplPolarity` and `ast::ImplPolarity` just to get the `!` span. - match tcx.impl_polarity(def_id) { - ty::ImplPolarity::Positive => { + match header.map(|h| h.skip_binder().polarity) { + // `None` means this is an inherent impl + Some(ty::ImplPolarity::Positive) | None => { res = res.and(check_impl(tcx, item, impl_.self_ty, &impl_.of_trait)); } - ty::ImplPolarity::Negative => { + Some(ty::ImplPolarity::Negative) => { let ast::ImplPolarity::Negative(span) = impl_.polarity else { bug!("impl_polarity query disagrees with impl's polarity in AST"); }; @@ -280,7 +281,7 @@ fn check_item<'tcx>(tcx: TyCtxt<'tcx>, item: &'tcx hir::Item<'tcx>) -> Result<() .emit()); } } - ty::ImplPolarity::Reservation => { + Some(ty::ImplPolarity::Reservation) => { // FIXME: what amount of WF checking do we need for reservation impls? } } diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs index 7fc51e36a2b..ab5c0f32705 100644 --- a/compiler/rustc_hir_typeck/src/method/suggest.rs +++ b/compiler/rustc_hir_typeck/src/method/suggest.rs @@ -3134,12 +3134,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { if self .tcx .all_impls(candidate.def_id) - .filter(|imp_did| { - self.tcx.impl_polarity(*imp_did) == ty::ImplPolarity::Negative + .map(|imp_did| { + self.tcx.impl_trait_header(imp_did).expect( + "inherent impls can't be candidates, only trait impls can be", + ) }) - .any(|imp_did| { - let imp = - self.tcx.impl_trait_ref(imp_did).unwrap().instantiate_identity(); + .filter(|header| { + header.skip_binder().polarity == ty::ImplPolarity::Negative + }) + .any(|header| { + let imp = header.instantiate_identity().trait_ref; let imp_simp = simplify_type(self.tcx, imp.self_ty(), TreatParams::ForLookup); imp_simp.is_some_and(|s| s == simp_rcvr_ty) diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs index a45cd9aa396..e64ebae255f 100644 --- a/compiler/rustc_middle/src/ty/mod.rs +++ b/compiler/rustc_middle/src/ty/mod.rs @@ -1590,15 +1590,16 @@ impl<'tcx> TyCtxt<'tcx> { def_id1: DefId, def_id2: DefId, ) -> Option { - let impl_trait_ref1 = self.impl_trait_ref(def_id1).unwrap().instantiate_identity(); - let impl_trait_ref2 = self.impl_trait_ref(def_id2).unwrap().instantiate_identity(); + let impl1 = self.impl_trait_header(def_id1).unwrap().instantiate_identity(); + let impl2 = self.impl_trait_header(def_id2).unwrap().instantiate_identity(); + // If either trait impl references an error, they're allowed to overlap, // as one of them essentially doesn't exist. - if impl_trait_ref1.references_error() || impl_trait_ref2.references_error() { + if impl1.references_error() || impl2.references_error() { return Some(ImplOverlapKind::Permitted { marker: false }); } - match (self.impl_polarity(def_id1), self.impl_polarity(def_id2)) { + match (impl1.polarity, impl2.polarity) { (ImplPolarity::Reservation, _) | (_, ImplPolarity::Reservation) => { // `#[rustc_reservation_impl]` impls don't overlap with anything return Some(ImplOverlapKind::Permitted { marker: false }); @@ -1615,7 +1616,7 @@ impl<'tcx> TyCtxt<'tcx> { let is_marker_overlap = { let is_marker_impl = |trait_ref: TraitRef<'_>| -> bool { self.trait_def(trait_ref.def_id).is_marker }; - is_marker_impl(impl_trait_ref1) && is_marker_impl(impl_trait_ref2) + is_marker_impl(impl1.trait_ref) && is_marker_impl(impl2.trait_ref) }; if is_marker_overlap { diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs index 149e4c2cb08..e34194f0bb0 100644 --- a/compiler/rustc_monomorphize/src/collector.rs +++ b/compiler/rustc_monomorphize/src/collector.rs @@ -1347,8 +1347,11 @@ fn create_mono_items_for_default_impls<'tcx>( item: hir::ItemId, output: &mut MonoItems<'tcx>, ) { - let polarity = tcx.impl_polarity(item.owner_id); - if matches!(polarity, ty::ImplPolarity::Negative) { + let Some(impl_) = tcx.impl_trait_header(item.owner_id) else { + return; + }; + + if matches!(impl_.skip_binder().polarity, ty::ImplPolarity::Negative) { return; } @@ -1356,10 +1359,6 @@ fn create_mono_items_for_default_impls<'tcx>( return; } - let Some(trait_ref) = tcx.impl_trait_ref(item.owner_id) else { - return; - }; - // Lifetimes never affect trait selection, so we are allowed to eagerly // instantiate an instance of an impl method if the impl (and method, // which we check below) is only parameterized over lifetime. In that case, @@ -1376,7 +1375,7 @@ fn create_mono_items_for_default_impls<'tcx>( } }; let impl_args = GenericArgs::for_item(tcx, item.owner_id.to_def_id(), only_region_params); - let trait_ref = trait_ref.instantiate(tcx, impl_args); + let trait_ref = impl_.instantiate(tcx, impl_args).trait_ref; // Unlike 'lazy' monomorphization that begins by collecting items transitively // called by `main` or other global items, when eagerly monomorphizing impl diff --git a/compiler/rustc_trait_selection/src/solve/trait_goals.rs b/compiler/rustc_trait_selection/src/solve/trait_goals.rs index 044832224e5..42ae82a907f 100644 --- a/compiler/rustc_trait_selection/src/solve/trait_goals.rs +++ b/compiler/rustc_trait_selection/src/solve/trait_goals.rs @@ -39,15 +39,18 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> { ) -> Result, NoSolution> { let tcx = ecx.tcx(); - let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap(); + let impl_trait_header = tcx.impl_trait_header(impl_def_id).unwrap(); let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::ForLookup }; - if !drcx.args_may_unify(goal.predicate.trait_ref.args, impl_trait_ref.skip_binder().args) { + if !drcx.args_may_unify( + goal.predicate.trait_ref.args, + impl_trait_header.skip_binder().trait_ref.args, + ) { return Err(NoSolution); } - let impl_polarity = tcx.impl_polarity(impl_def_id); // An upper bound of the certainty of this goal, used to lower the certainty // of reservation impl to ambiguous during coherence. + let impl_polarity = impl_trait_header.skip_binder().polarity; let maximal_certainty = match impl_polarity { ty::ImplPolarity::Positive | ty::ImplPolarity::Negative => { match impl_polarity == goal.predicate.polarity { @@ -63,7 +66,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> { ecx.probe_trait_candidate(CandidateSource::Impl(impl_def_id)).enter(|ecx| { let impl_args = ecx.fresh_args_for_item(impl_def_id); - let impl_trait_ref = impl_trait_ref.instantiate(tcx, impl_args); + let impl_trait_ref = impl_trait_header.instantiate(tcx, impl_args).trait_ref; ecx.eq(goal.param_env, goal.predicate.trait_ref, impl_trait_ref)?; let where_clause_bounds = tcx diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs index 7d14395850b..8fa5cd5c522 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs @@ -1980,13 +1980,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { .tcx .all_impls(trait_pred.def_id()) .filter_map(|def_id| { - if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative + let imp = self.tcx.impl_trait_header(def_id).unwrap().skip_binder(); + if imp.polarity == ty::ImplPolarity::Negative || !self.tcx.is_user_visible_dep(def_id.krate) { return None; } - - let imp = self.tcx.impl_trait_ref(def_id).unwrap().skip_binder(); + let imp = imp.trait_ref; self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false).map( |similarity| ImplCandidate { trait_ref: imp, similarity, impl_def_id: def_id }, @@ -2165,12 +2165,13 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> { .tcx .all_impls(def_id) // Ignore automatically derived impls and `!Trait` impls. - .filter(|&def_id| { - self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative + .filter_map(|def_id| self.tcx.impl_trait_header(def_id)) + .map(ty::EarlyBinder::instantiate_identity) + .filter(|header| { + header.polarity != ty::ImplPolarity::Negative || self.tcx.is_automatically_derived(def_id) }) - .filter_map(|def_id| self.tcx.impl_trait_ref(def_id)) - .map(ty::EarlyBinder::instantiate_identity) + .map(|header| header.trait_ref) .filter(|trait_ref| { let self_ty = trait_ref.self_ty(); // Avoid mentioning type parameters. 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 f9a292c2bd7..b6f672bfabe 100644 --- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs +++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs @@ -560,20 +560,22 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // Before we create the substitutions and everything, first // consider a "quick reject". This avoids creating more types // and so forth that we need to. - let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap(); - if !drcx.args_may_unify(obligation_args, impl_trait_ref.skip_binder().args) { + let impl_trait_header = self.tcx().impl_trait_header(impl_def_id).unwrap(); + if !drcx + .args_may_unify(obligation_args, impl_trait_header.skip_binder().trait_ref.args) + { return; } if self.reject_fn_ptr_impls( impl_def_id, obligation, - impl_trait_ref.skip_binder().self_ty(), + impl_trait_header.skip_binder().trait_ref.self_ty(), ) { return; } self.infcx.probe(|_| { - if let Ok(_args) = self.match_impl(impl_def_id, impl_trait_ref, obligation) { + if let Ok(_args) = self.match_impl(impl_def_id, impl_trait_header, obligation) { candidates.vec.push(ImplCandidate(impl_def_id)); } }); diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index ac6cfcdeb59..5f11bb600e3 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -2404,8 +2404,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> { impl_def_id: DefId, obligation: &PolyTraitObligation<'tcx>, ) -> Normalized<'tcx, GenericArgsRef<'tcx>> { - let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap(); - match self.match_impl(impl_def_id, impl_trait_ref, obligation) { + let impl_trait_header = self.tcx().impl_trait_header(impl_def_id).unwrap(); + match self.match_impl(impl_def_id, impl_trait_header, obligation) { Ok(args) => args, Err(()) => { // FIXME: A rematch may fail when a candidate cache hit occurs @@ -2438,7 +2438,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> { fn match_impl( &mut self, impl_def_id: DefId, - impl_trait_ref: EarlyBinder>, + impl_trait_header: EarlyBinder>, obligation: &PolyTraitObligation<'tcx>, ) -> Result>, ()> { let placeholder_obligation = @@ -2447,12 +2447,12 @@ impl<'tcx> SelectionContext<'_, 'tcx> { let impl_args = self.infcx.fresh_args_for_item(obligation.cause.span, impl_def_id); - let impl_trait_ref = impl_trait_ref.instantiate(self.tcx(), impl_args); - if impl_trait_ref.references_error() { + let impl_trait_header = impl_trait_header.instantiate(self.tcx(), impl_args); + if impl_trait_header.references_error() { return Err(()); } - debug!(?impl_trait_ref); + debug!(?impl_trait_header); let Normalized { value: impl_trait_ref, obligations: mut nested_obligations } = ensure_sufficient_stack(|| { @@ -2461,7 +2461,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> { obligation.param_env, obligation.cause.clone(), obligation.recursion_depth + 1, - impl_trait_ref, + impl_trait_header.trait_ref, ) }); @@ -2482,9 +2482,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> { })?; nested_obligations.extend(obligations); - if !self.is_intercrate() - && self.tcx().impl_polarity(impl_def_id) == ty::ImplPolarity::Reservation - { + if !self.is_intercrate() && impl_trait_header.polarity == ty::ImplPolarity::Reservation { debug!("reservation impls only apply in intercrate mode"); return Err(()); } diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs index 8e0fa79c977..6de839f5d98 100644 --- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs @@ -168,6 +168,8 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId, } } + let impl1_trait_header = tcx.impl_trait_header(impl1_def_id).unwrap().instantiate_identity(); + // We determine whether there's a subset relationship by: // // - replacing bound vars with placeholders in impl1, @@ -181,21 +183,25 @@ pub(super) fn specializes(tcx: TyCtxt<'_>, (impl1_def_id, impl2_def_id): (DefId, // See RFC 1210 for more details and justification. // Currently we do not allow e.g., a negative impl to specialize a positive one - if tcx.impl_polarity(impl1_def_id) != tcx.impl_polarity(impl2_def_id) { + if impl1_trait_header.polarity != tcx.impl_polarity(impl2_def_id) { return false; } // create a parameter environment corresponding to a (placeholder) instantiation of impl1 let penv = tcx.param_env(impl1_def_id); - let impl1_trait_ref = tcx.impl_trait_ref(impl1_def_id).unwrap().instantiate_identity(); // Create an infcx, taking the predicates of impl1 as assumptions: let infcx = tcx.infer_ctxt().build(); // Attempt to prove that impl2 applies, given all of the above. - fulfill_implication(&infcx, penv, impl1_trait_ref, impl1_def_id, impl2_def_id, |_, _| { - ObligationCause::dummy() - }) + fulfill_implication( + &infcx, + penv, + impl1_trait_header.trait_ref, + impl1_def_id, + impl2_def_id, + |_, _| ObligationCause::dummy(), + ) .is_ok() } diff --git a/compiler/rustc_ty_utils/src/ty.rs b/compiler/rustc_ty_utils/src/ty.rs index 60b1bbe8c2a..b725eda33ce 100644 --- a/compiler/rustc_ty_utils/src/ty.rs +++ b/compiler/rustc_ty_utils/src/ty.rs @@ -257,14 +257,15 @@ fn param_env_reveal_all_normalized(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamE fn issue33140_self_ty(tcx: TyCtxt<'_>, def_id: DefId) -> Option>> { debug!("issue33140_self_ty({:?})", def_id); - let trait_ref = tcx - .impl_trait_ref(def_id) + let impl_ = tcx + .impl_trait_header(def_id) .unwrap_or_else(|| bug!("issue33140_self_ty called on inherent impl {:?}", def_id)) .skip_binder(); + let trait_ref = impl_.trait_ref; debug!("issue33140_self_ty({:?}), trait-ref={:?}", def_id, trait_ref); - let is_marker_like = tcx.impl_polarity(def_id) == ty::ImplPolarity::Positive + let is_marker_like = impl_.polarity == ty::ImplPolarity::Positive && tcx.associated_item_def_ids(trait_ref.def_id).is_empty(); // Check whether these impls would be ok for a marker trait.