Change:
// FIXME(inherent_associated_types): Acquiring the ParamEnv this early leads to cycle errors // when inside of an ADT (#108491) or where clause. let param_env = tcx.param_env(block.owner); <del> let cause = ObligationCause::misc(span, block.owner.def_id); let mut fulfillment_errors = Vec::new(); let mut applicable_candidates: Vec<_> = infcx.probe(|_| { // Regions are not considered during selection. let self_ty = self_ty .fold_with(&mut BoundVarEraser { tcx, universe: infcx.create_next_universe() }); struct BoundVarEraser<'tcx> { tcx: TyCtxt<'tcx>, universe: ty::UniverseIndex, } // FIXME(non_lifetime_binders): Don't assign the same universe to each placeholder. impl<'tcx> TypeFolder<TyCtxt<'tcx>> for BoundVarEraser<'tcx> { fn interner(&self) -> TyCtxt<'tcx> { self.tcx } </del> <ins> let mut universes = if self_ty.has_escaping_bound_vars() { vec![None; self_ty.outer_exclusive_binder().as_usize()] } else { vec![] }; </ins> <del> fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { // FIXME(@lcnr): This is broken, erasing bound regions // impacts selection as it results in different types. if r.is_bound() { self.tcx.lifetimes.re_erased } else { r } } </del> <ins> let (impl_, (assoc_item, def_scope)) = crate::traits::project::with_replaced_escaping_bound_vars( infcx, &mut universes, self_ty, |self_ty| { self.select_inherent_assoc_type_candidates( infcx, name, span, self_ty, param_env, candidates, ) }, )?; self.check_assoc_ty(assoc_item, name, def_scope, block, span); // FIXME(fmease): Currently creating throwaway `parent_args` to please // `create_args_for_associated_item`. Modify the latter instead (or sth. similar) to // not require the parent args logic. let parent_args = ty::GenericArgs::identity_for_item(tcx, impl_); let args = self.create_args_for_associated_item(span, assoc_item, segment, parent_args); let args = tcx.mk_args_from_iter( std::iter::once(ty::GenericArg::from(self_ty)) .chain(args.into_iter().skip(parent_args.len())), ); </ins> <del> fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> { match *ty.kind() { ty::Bound(_, bv) => Ty::new_placeholder( self.tcx, ty::PlaceholderType { universe: self.universe, bound: bv }, ), _ => ty.super_fold_with(self), } } </del> <ins> let ty = Ty::new_alias(tcx, ty::Inherent, ty::AliasTy::new(tcx, assoc_item, args)); </ins> <del> fn fold_const( &mut self, ct: ty::Const<'tcx>, ) -> <TyCtxt<'tcx> as rustc_type_ir::Interner>::Const { assert!(!ct.ty().has_escaping_bound_vars()); match ct.kind() { ty::ConstKind::Bound(_, bv) => ty::Const::new_placeholder( self.tcx, ty::PlaceholderConst { universe: self.universe, bound: bv }, ct.ty(), ), _ => ct.super_fold_with(self), } } } </del> <ins> Ok(Some((ty, assoc_item))) } </ins> <del> let InferOk { value: self_ty, obligations } = infcx.at(&cause, param_env).normalize(self_ty); </del> <ins> fn select_inherent_assoc_type_candidates( &self, infcx: &InferCtxt<'tcx>, name: Ident, span: Span, self_ty: Ty<'tcx>, param_env: ParamEnv<'tcx>, candidates: Vec<(DefId, (DefId, DefId))>, ) -> Result<(DefId, (DefId, DefId)), ErrorGuaranteed> { let tcx = self.tcx(); let mut fulfillment_errors = Vec::new(); </ins> <del> candidates .iter() .copied() .filter(|&(impl_, _)| { infcx.probe(|_| { let ocx = ObligationCtxt::new(infcx); ocx.register_obligations(obligations.clone()); let impl_args = infcx.fresh_args_for_item(span, impl_); let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args); let impl_ty = ocx.normalize(&cause, param_env, impl_ty); // Check that the self types can be related. if ocx.eq(&ObligationCause::dummy(), param_env, impl_ty, self_ty).is_err() { return false; } </del> <ins> let applicable_candidates: Vec<_> = candidates .iter() .copied() .filter(|&(impl_, _)| { infcx.probe(|_| { let ocx = ObligationCtxt::new(infcx); let self_ty = ocx.normalize(&ObligationCause::dummy(), param_env, self_ty); let impl_args = infcx.fresh_args_for_item(span, impl_); let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args); let impl_ty = ocx.normalize(&ObligationCause::dummy(), param_env, impl_ty); // Check that the self types can be related. if ocx.eq(&ObligationCause::dummy(), param_env, impl_ty, self_ty).is_err() { return false; } </ins> <del> // Check whether the impl imposes obligations we have to worry about. let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args); let impl_bounds = ocx.normalize(&cause, param_env, impl_bounds); let impl_obligations = traits::predicates_for_generics( |_, _| cause.clone(), param_env, impl_bounds, ); ocx.register_obligations(impl_obligations); </del> <ins> // Check whether the impl imposes obligations we have to worry about. let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args); let impl_bounds = ocx.normalize(&ObligationCause::dummy(), param_env, impl_bounds); let impl_obligations = traits::predicates_for_generics( |_, _| ObligationCause::dummy(), param_env, impl_bounds, ); ocx.register_obligations(impl_obligations); </ins> <del> let mut errors = ocx.select_where_possible(); if !errors.is_empty() { fulfillment_errors.append(&mut errors); return false; } </del> <ins> let mut errors = ocx.select_where_possible(); if !errors.is_empty() { fulfillment_errors.append(&mut errors); return false; } </ins> <del> true }) </del> <ins> true </ins> }) <del> .collect() }); </del> <ins> }) .collect(); </ins> <del> if applicable_candidates.len() > 1 { return Err(self.complain_about_ambiguous_inherent_assoc_type( </del> <ins> match &applicable_candidates[..] { &[] => Err(self.complain_about_inherent_assoc_type_not_found( </ins> name, <del> applicable_candidates.into_iter().map(|(_, (candidate, _))| candidate).collect(), </del> <ins> self_ty, candidates, fulfillment_errors, </ins> span, <del> )); } </del> <ins> )), </ins> <del> if let Some((impl_, (assoc_item, def_scope))) = applicable_candidates.pop() { self.check_assoc_ty(assoc_item, name, def_scope, block, span); // FIXME(fmease): Currently creating throwaway `parent_args` to please // `create_args_for_associated_item`. Modify the latter instead (or sth. similar) to // not require the parent args logic. let parent_args = ty::GenericArgs::identity_for_item(tcx, impl_); let args = self.create_args_for_associated_item(span, assoc_item, segment, parent_args); let args = tcx.mk_args_from_iter( std::iter::once(ty::GenericArg::from(self_ty)) .chain(args.into_iter().skip(parent_args.len())), ); let ty = Ty::new_alias(tcx, ty::Inherent, ty::AliasTy::new(tcx, assoc_item, args)); </del> <ins> &[applicable_candidate] => Ok(applicable_candidate), </ins> <del> return Ok(Some((ty, assoc_item))); </del> <ins> &[_, ..] => Err(self.complain_about_ambiguous_inherent_assoc_type( name, applicable_candidates.into_iter().map(|(_, (candidate, _))| candidate).collect(), span, )), </ins> } <del> Err(self.complain_about_inherent_assoc_type_not_found( name, self_ty, candidates, fulfillment_errors, span, )) </del> } fn lookup_assoc_ty(

Discussion:
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Ow, my bad! claim