Auto merge of #108075 - WaffleLapkin:de-arena-allocates-you-OwO, r=Nilstrieb

Remove `arena_cache` modifier from `associated_item` query & copy `ty::AssocItem` instead of passing by ref

r? `@ghost`

18 files changed, 93 insertions, 101 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 5f1add2679c..04396c883d3 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -537,7 +537,7 @@ fn check_item_type(tcx: TyCtxt<'_>, id: hir::ItemId) {
             let assoc_items = tcx.associated_items(id.owner_id);
             check_on_unimplemented(tcx, id);
 
-            for assoc_item in assoc_items.in_definition_order() {
+            for &assoc_item in assoc_items.in_definition_order() {
                 match assoc_item.kind {
                     ty::AssocKind::Fn => {
                         let abi = tcx.fn_sig(assoc_item.def_id).skip_binder().abi();
@@ -670,7 +670,7 @@ pub(super) fn check_on_unimplemented(tcx: TyCtxt<'_>, item: hir::ItemId) {
 pub(super) fn check_specialization_validity<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_def: &ty::TraitDef,
-    trait_item: &ty::AssocItem,
+    trait_item: ty::AssocItem,
     impl_id: DefId,
     impl_item: DefId,
 ) {
@@ -767,17 +767,17 @@ 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_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_ref);
             }
         }
 
         check_specialization_validity(
             tcx,
             trait_def,
-            &ty_trait_item,
+            ty_trait_item,
             impl_id.to_def_id(),
             impl_item,
         );
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index 4fd06c23e10..a07a46da21f 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -37,8 +37,8 @@ use std::iter;
 /// - `impl_trait_ref`: the TraitRef corresponding to the trait implementation
 pub(super) fn compare_impl_method<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) {
     debug!("compare_impl_method(impl_trait_ref={:?})", impl_trait_ref);
@@ -129,8 +129,8 @@ pub(super) fn compare_impl_method<'tcx>(
 #[instrument(level = "debug", skip(tcx, impl_trait_ref))]
 fn compare_method_predicate_entailment<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
     check_implied_wf: CheckImpliedWfMode,
 ) -> Result<(), ErrorGuaranteed> {
@@ -381,8 +381,8 @@ fn compare_method_predicate_entailment<'tcx>(
 fn extract_bad_args_for_implies_lint<'tcx>(
     tcx: TyCtxt<'tcx>,
     errors: &[infer::RegionResolutionError<'tcx>],
-    (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
-    (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
+    (trait_m, trait_sig): (ty::AssocItem, ty::FnSig<'tcx>),
+    (impl_m, impl_sig): (ty::AssocItem, ty::FnSig<'tcx>),
     hir_id: hir::HirId,
 ) -> Vec<(Span, Option<String>)> {
     let mut blame_generics = vec![];
@@ -476,7 +476,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RemapLateBound<'_, 'tcx> {
 
 fn emit_implied_wf_lint<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
     hir_id: hir::HirId,
     bad_args: Vec<(Span, Option<String>)>,
 ) {
@@ -523,8 +523,8 @@ enum CheckImpliedWfMode {
 
 fn compare_asyncness<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
 ) -> Result<(), ErrorGuaranteed> {
     if tcx.asyncness(trait_m.def_id) == hir::IsAsync::Async {
         match tcx.fn_sig(impl_m.def_id).skip_binder().skip_binder().output().kind() {
@@ -869,8 +869,8 @@ fn report_trait_method_mismatch<'tcx>(
     infcx: &InferCtxt<'tcx>,
     mut cause: ObligationCause<'tcx>,
     terr: TypeError<'tcx>,
-    (trait_m, trait_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
-    (impl_m, impl_sig): (&ty::AssocItem, ty::FnSig<'tcx>),
+    (trait_m, trait_sig): (ty::AssocItem, ty::FnSig<'tcx>),
+    (impl_m, impl_sig): (ty::AssocItem, ty::FnSig<'tcx>),
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> ErrorGuaranteed {
     let tcx = infcx.tcx;
@@ -963,8 +963,8 @@ fn report_trait_method_mismatch<'tcx>(
 
 fn check_region_bounds_on_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
     delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     let impl_generics = tcx.generics_of(impl_m.def_id);
@@ -1038,7 +1038,7 @@ fn check_region_bounds_on_impl_item<'tcx>(
             .sess
             .create_err(LifetimesOrBoundsMismatchOnTrait {
                 span,
-                item_kind: assoc_item_kind_str(impl_m),
+                item_kind: assoc_item_kind_str(&impl_m),
                 ident: impl_m.ident(tcx),
                 generics_span,
                 bounds_span,
@@ -1056,8 +1056,8 @@ fn extract_spans_for_error_reporting<'tcx>(
     infcx: &infer::InferCtxt<'tcx>,
     terr: TypeError<'_>,
     cause: &ObligationCause<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
 ) -> (Span, Option<Span>) {
     let tcx = infcx.tcx;
     let mut impl_args = {
@@ -1080,8 +1080,8 @@ fn extract_spans_for_error_reporting<'tcx>(
 
 fn compare_self_type<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
     // Try to give more informative error messages about self typing
@@ -1092,7 +1092,7 @@ fn compare_self_type<'tcx>(
     // inscrutable, particularly for cases where one method has no
     // self.
 
-    let self_string = |method: &ty::AssocItem| {
+    let self_string = |method: ty::AssocItem| {
         let untransformed_self_ty = match method.container {
             ty::ImplContainer => impl_trait_ref.self_ty(),
             ty::TraitContainer => tcx.types.self_param,
@@ -1182,8 +1182,8 @@ fn compare_self_type<'tcx>(
 /// [`compare_generic_param_kinds`]. This function also does not handle lifetime parameters
 fn compare_number_of_generics<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_: &ty::AssocItem,
-    trait_: &ty::AssocItem,
+    impl_: ty::AssocItem,
+    trait_: ty::AssocItem,
     delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     let trait_own_counts = tcx.generics_of(trait_.def_id).own_counts();
@@ -1203,7 +1203,7 @@ fn compare_number_of_generics<'tcx>(
         ("const", trait_own_counts.consts, impl_own_counts.consts),
     ];
 
-    let item_kind = assoc_item_kind_str(impl_);
+    let item_kind = assoc_item_kind_str(&impl_);
 
     let mut err_occurred = None;
     for (kind, trait_count, impl_count) in matchings {
@@ -1325,8 +1325,8 @@ fn compare_number_of_generics<'tcx>(
 
 fn compare_number_of_method_arguments<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
 ) -> Result<(), ErrorGuaranteed> {
     let impl_m_fty = tcx.fn_sig(impl_m.def_id);
     let trait_m_fty = tcx.fn_sig(trait_m.def_id);
@@ -1405,8 +1405,8 @@ fn compare_number_of_method_arguments<'tcx>(
 
 fn compare_synthetic_generics<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_m: &ty::AssocItem,
-    trait_m: &ty::AssocItem,
+    impl_m: ty::AssocItem,
+    trait_m: ty::AssocItem,
 ) -> Result<(), ErrorGuaranteed> {
     // FIXME(chrisvittal) Clean up this function, list of FIXME items:
     //     1. Better messages for the span labels
@@ -1559,8 +1559,8 @@ fn compare_synthetic_generics<'tcx>(
 /// This function does not handle lifetime parameters
 fn compare_generic_param_kinds<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_item: &ty::AssocItem,
-    trait_item: &ty::AssocItem,
+    impl_item: ty::AssocItem,
+    trait_item: ty::AssocItem,
     delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     assert_eq!(impl_item.kind, trait_item.kind);
@@ -1736,8 +1736,8 @@ pub(super) fn compare_impl_const_raw(
 
 pub(super) fn compare_impl_ty<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_ty: &ty::AssocItem,
-    trait_ty: &ty::AssocItem,
+    impl_ty: ty::AssocItem,
+    trait_ty: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) {
     debug!("compare_impl_type(impl_trait_ref={:?})", impl_trait_ref);
@@ -1754,8 +1754,8 @@ pub(super) fn compare_impl_ty<'tcx>(
 /// instead of associated functions.
 fn compare_type_predicate_entailment<'tcx>(
     tcx: TyCtxt<'tcx>,
-    impl_ty: &ty::AssocItem,
-    trait_ty: &ty::AssocItem,
+    impl_ty: ty::AssocItem,
+    trait_ty: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
     let impl_substs = InternalSubsts::identity_for_item(tcx, impl_ty.def_id);
@@ -1855,8 +1855,8 @@ fn compare_type_predicate_entailment<'tcx>(
 #[instrument(level = "debug", skip(tcx))]
 pub(super) fn check_type_bounds<'tcx>(
     tcx: TyCtxt<'tcx>,
-    trait_ty: &ty::AssocItem,
-    impl_ty: &ty::AssocItem,
+    trait_ty: ty::AssocItem,
+    impl_ty: ty::AssocItem,
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
     // Given
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index 4d2d1ca9b3e..9acfc1b3d29 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -199,7 +199,7 @@ fn report_forbidden_specialization(tcx: TyCtxt<'_>, impl_item: DefId, parent_imp
 fn missing_items_err(
     tcx: TyCtxt<'_>,
     impl_span: Span,
-    missing_items: &[&ty::AssocItem],
+    missing_items: &[ty::AssocItem],
     full_impl_span: Span,
 ) {
     let missing_items_msg = missing_items
@@ -225,7 +225,7 @@ fn missing_items_err(
     let padding =
         tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());
 
-    for trait_item in missing_items {
+    for &trait_item in missing_items {
         let snippet = suggestion_signature(trait_item, tcx);
         let code = format!("{}{}\n{}", padding, snippet, padding);
         let msg = format!("implement the missing item: `{snippet}`");
@@ -272,7 +272,7 @@ fn default_body_is_unstable(
     reason: Option<Symbol>,
     issue: Option<NonZeroU32>,
 ) {
-    let missing_item_name = &tcx.associated_item(item_did).name;
+    let missing_item_name = tcx.associated_item(item_did).name;
     let use_of_unstable_library_feature_note = match reason {
         Some(r) => format!("use of unstable library feature '{feature}': {r}"),
         None => format!("use of unstable library feature '{feature}'"),
@@ -365,7 +365,7 @@ fn fn_sig_suggestion<'tcx>(
     sig: ty::FnSig<'tcx>,
     ident: Ident,
     predicates: ty::GenericPredicates<'tcx>,
-    assoc: &ty::AssocItem,
+    assoc: ty::AssocItem,
 ) -> String {
     let args = sig
         .inputs()
@@ -433,7 +433,7 @@ pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
 /// Return placeholder code for the given associated item.
 /// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
 /// structured suggestion.
-fn suggestion_signature(assoc: &ty::AssocItem, tcx: TyCtxt<'_>) -> String {
+fn suggestion_signature(assoc: ty::AssocItem, tcx: TyCtxt<'_>) -> String {
     match assoc.kind {
         ty::AssocKind::Fn => {
             // We skip the binder here because the binder would deanonymize all
diff --git a/compiler/rustc_hir_analysis/src/check/wfcheck.rs b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
index ab47d393a06..66c3904af96 100644
--- a/compiler/rustc_hir_analysis/src/check/wfcheck.rs
+++ b/compiler/rustc_hir_analysis/src/check/wfcheck.rs
@@ -1180,7 +1180,7 @@ fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
 ///
 /// Assuming the defaults are used, check that all predicates (bounds on the
 /// assoc type and where clauses on the trait) hold.
-fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: &ty::AssocItem, span: Span) {
+fn check_associated_type_bounds(wfcx: &WfCheckingCtxt<'_, '_>, item: ty::AssocItem, span: Span) {
     let bounds = wfcx.tcx().explicit_item_bounds(item.def_id);
 
     debug!("check_associated_type_bounds: bounds={:?}", bounds);
@@ -1630,7 +1630,7 @@ const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut se
 fn check_method_receiver<'tcx>(
     wfcx: &WfCheckingCtxt<'_, 'tcx>,
     fn_sig: &hir::FnSig<'_>,
-    method: &ty::AssocItem,
+    method: ty::AssocItem,
     self_ty: Ty<'tcx>,
 ) {
     let tcx = wfcx.tcx();
diff --git a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
index a9331af4eab..7bca4edcc8c 100644
--- a/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
+++ b/compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs
@@ -27,8 +27,8 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
     /// namespace.
     fn impls_have_common_items(
         &self,
-        impl_items1: &ty::AssocItems<'_>,
-        impl_items2: &ty::AssocItems<'_>,
+        impl_items1: &ty::AssocItems,
+        impl_items2: &ty::AssocItems,
     ) -> bool {
         let mut impl_items1 = &impl_items1;
         let mut impl_items2 = &impl_items2;
@@ -38,10 +38,10 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
             std::mem::swap(&mut impl_items1, &mut impl_items2);
         }
 
-        for item1 in impl_items1.in_definition_order() {
+        for &item1 in impl_items1.in_definition_order() {
             let collision = impl_items2
                 .filter_by_name_unhygienic(item1.name)
-                .any(|item2| self.compare_hygienically(item1, item2));
+                .any(|&item2| self.compare_hygienically(item1, item2));
 
             if collision {
                 return true;
@@ -51,7 +51,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
         false
     }
 
-    fn compare_hygienically(&self, item1: &ty::AssocItem, item2: &ty::AssocItem) -> bool {
+    fn compare_hygienically(&self, item1: ty::AssocItem, item2: ty::AssocItem) -> bool {
         // Symbols and namespace match, compare hygienically.
         item1.kind.namespace() == item2.kind.namespace()
             && item1.ident(self.tcx).normalize_to_macros_2_0()
@@ -98,10 +98,10 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
         let impl_items1 = self.tcx.associated_items(impl1);
         let impl_items2 = self.tcx.associated_items(impl2);
 
-        for item1 in impl_items1.in_definition_order() {
+        for &item1 in impl_items1.in_definition_order() {
             let collision = impl_items2
                 .filter_by_name_unhygienic(item1.name)
-                .find(|item2| self.compare_hygienically(item1, item2));
+                .find(|&&item2| self.compare_hygienically(item1, item2));
 
             if let Some(item2) = collision {
                 let name = item1.ident(self.tcx).normalize_to_macros_2_0();
diff --git a/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs b/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
index 9133e6540d4..560ffc620e0 100644
--- a/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
+++ b/compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs
@@ -423,7 +423,7 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
 
     fn get_unbound_associated_types(&self) -> Vec<String> {
         if self.tcx.is_trait(self.def_id) {
-            let items: &AssocItems<'_> = self.tcx.associated_items(self.def_id);
+            let items: &AssocItems = self.tcx.associated_items(self.def_id);
             items
                 .in_definition_order()
                 .filter(|item| item.kind == AssocKind::Type)
diff --git a/compiler/rustc_hir_typeck/src/method/probe.rs b/compiler/rustc_hir_typeck/src/method/probe.rs
index 0e3a16ac717..0b9226802cf 100644
--- a/compiler/rustc_hir_typeck/src/method/probe.rs
+++ b/compiler/rustc_hir_typeck/src/method/probe.rs
@@ -735,7 +735,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             debug!("impl_ty: {:?}", impl_ty);
 
             // Determine the receiver type that the method itself expects.
-            let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs);
+            let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(item, impl_ty, impl_substs);
             debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty);
 
             // We can't use normalize_associated_types_in as it will pollute the
@@ -796,7 +796,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             let new_trait_ref = this.erase_late_bound_regions(new_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
-                this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs);
+                this.xform_self_ty(item, new_trait_ref.self_ty(), new_trait_ref.substs);
             this.push_candidate(
                 Candidate {
                     xform_self_ty,
@@ -846,7 +846,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             let trait_ref = this.erase_late_bound_regions(poly_trait_ref);
 
             let (xform_self_ty, xform_ret_ty) =
-                this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs);
+                this.xform_self_ty(item, trait_ref.self_ty(), trait_ref.substs);
 
             // Because this trait derives from a where-clause, it
             // should not contain any inference variables or other
@@ -917,7 +917,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
 
     fn matches_return_type(
         &self,
-        method: &ty::AssocItem,
+        method: ty::AssocItem,
         self_ty: Option<Ty<'tcx>>,
         expected: Ty<'tcx>,
     ) -> bool {
@@ -966,11 +966,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                     } else {
                         let new_trait_ref = self.erase_late_bound_regions(bound_trait_ref);
 
-                        let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(
-                            &item,
-                            new_trait_ref.self_ty(),
-                            new_trait_ref.substs,
-                        );
+                        let (xform_self_ty, xform_ret_ty) =
+                            self.xform_self_ty(item, new_trait_ref.self_ty(), new_trait_ref.substs);
                         self.push_candidate(
                             Candidate {
                                 xform_self_ty,
@@ -998,7 +995,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 }
 
                 let (xform_self_ty, xform_ret_ty) =
-                    self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs);
+                    self.xform_self_ty(item, trait_ref.self_ty(), trait_substs);
                 self.push_candidate(
                     Candidate {
                         xform_self_ty,
@@ -1025,7 +1022,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             .filter(|candidate| candidate_filter(&candidate.item))
             .filter(|candidate| {
                 if let Some(return_ty) = self.return_type {
-                    self.matches_return_type(&candidate.item, None, return_ty)
+                    self.matches_return_type(candidate.item, None, return_ty)
                 } else {
                     true
                 }
@@ -1884,7 +1881,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     #[instrument(level = "debug", skip(self))]
     fn xform_self_ty(
         &self,
-        item: &ty::AssocItem,
+        item: ty::AssocItem,
         impl_ty: Ty<'tcx>,
         substs: SubstsRef<'tcx>,
     ) -> (Ty<'tcx>, Option<Ty<'tcx>>) {
diff --git a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
index 2b1d99ef445..b33729d0be5 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs
@@ -326,7 +326,7 @@ impl<T> Trait<T> for X {
                         diag,
                         &trait_ref,
                         pred.bounds,
-                        &assoc,
+                        assoc,
                         assoc_substs,
                         ty,
                         msg,
@@ -624,7 +624,7 @@ fn foo(&self) -> Self::T { String::new() }
         diag: &mut Diagnostic,
         trait_ref: &ty::TraitRef<'tcx>,
         bounds: hir::GenericBounds<'_>,
-        assoc: &ty::AssocItem,
+        assoc: ty::AssocItem,
         assoc_substs: &[ty::GenericArg<'tcx>],
         ty: Ty<'tcx>,
         msg: &str,
@@ -667,7 +667,7 @@ fn foo(&self) -> Self::T { String::new() }
         &self,
         diag: &mut Diagnostic,
         span: Span,
-        assoc: &ty::AssocItem,
+        assoc: ty::AssocItem,
         assoc_substs: &[ty::GenericArg<'tcx>],
         ty: Ty<'tcx>,
         msg: &str,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 1ccad25fe08..cf4d9b4b005 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -729,15 +729,14 @@ rustc_queries! {
     }
 
     /// Maps from a trait item to the trait item "descriptor".
-    query associated_item(key: DefId) -> &'tcx ty::AssocItem {
+    query associated_item(key: DefId) -> ty::AssocItem {
         desc { |tcx| "computing associated item data for `{}`", tcx.def_path_str(key) }
-        arena_cache
         cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
     /// Collects the associated items defined on a trait or impl.
-    query associated_items(key: DefId) -> &'tcx ty::AssocItems<'tcx> {
+    query associated_items(key: DefId) -> &'tcx ty::AssocItems {
         arena_cache
         desc { |tcx| "collecting associated items of `{}`", tcx.def_path_str(key) }
     }
diff --git a/compiler/rustc_middle/src/traits/specialization_graph.rs b/compiler/rustc_middle/src/traits/specialization_graph.rs
index 2f52767d12a..4019cf8ceee 100644
--- a/compiler/rustc_middle/src/traits/specialization_graph.rs
+++ b/compiler/rustc_middle/src/traits/specialization_graph.rs
@@ -133,11 +133,7 @@ impl Node {
     ///
     /// If this returns `None`, the item can potentially still be found in
     /// parents of this node.
-    pub fn item<'tcx>(
-        &self,
-        tcx: TyCtxt<'tcx>,
-        trait_item_def_id: DefId,
-    ) -> Option<&'tcx ty::AssocItem> {
+    pub fn item<'tcx>(&self, tcx: TyCtxt<'tcx>, trait_item_def_id: DefId) -> Option<ty::AssocItem> {
         match *self {
             Node::Trait(_) => Some(tcx.associated_item(trait_item_def_id)),
             Node::Impl(impl_def_id) => {
@@ -239,7 +235,7 @@ impl<'tcx> Ancestors<'tcx> {
                     }
                 }
 
-                Some(LeafDef { item: *item, defining_node: node, finalizing_node })
+                Some(LeafDef { item, defining_node: node, finalizing_node })
             } else {
                 // Item not mentioned. This "finalizes" any defaulted item provided by an ancestor.
                 finalizing_node = Some(node);
diff --git a/compiler/rustc_middle/src/ty/assoc.rs b/compiler/rustc_middle/src/ty/assoc.rs
index 756776dc294..f1a9e50a4f0 100644
--- a/compiler/rustc_middle/src/ty/assoc.rs
+++ b/compiler/rustc_middle/src/ty/assoc.rs
@@ -129,13 +129,13 @@ impl std::fmt::Display for AssocKind {
 /// it is relatively expensive. Instead, items are indexed by `Symbol` and hygienic comparison is
 /// done only on items with the same name.
 #[derive(Debug, Clone, PartialEq, HashStable)]
-pub struct AssocItems<'tcx> {
-    items: SortedIndexMultiMap<u32, Symbol, &'tcx ty::AssocItem>,
+pub struct AssocItems {
+    items: SortedIndexMultiMap<u32, Symbol, ty::AssocItem>,
 }
 
-impl<'tcx> AssocItems<'tcx> {
+impl AssocItems {
     /// Constructs an `AssociatedItems` map from a series of `ty::AssocItem`s in definition order.
-    pub fn new(items_in_def_order: impl IntoIterator<Item = &'tcx ty::AssocItem>) -> Self {
+    pub fn new(items_in_def_order: impl IntoIterator<Item = ty::AssocItem>) -> Self {
         let items = items_in_def_order.into_iter().map(|item| (item.name, item)).collect();
         AssocItems { items }
     }
@@ -145,7 +145,7 @@ impl<'tcx> AssocItems<'tcx> {
     /// New code should avoid relying on definition order. If you need a particular associated item
     /// for a known trait, make that trait a lang item instead of indexing this array.
     pub fn in_definition_order(&self) -> impl '_ + Iterator<Item = &ty::AssocItem> {
-        self.items.iter().map(|(_, v)| *v)
+        self.items.iter().map(|(_, v)| v)
     }
 
     pub fn len(&self) -> usize {
@@ -157,7 +157,7 @@ impl<'tcx> AssocItems<'tcx> {
         &self,
         name: Symbol,
     ) -> impl '_ + Iterator<Item = &ty::AssocItem> {
-        self.items.get_by_key(name).copied()
+        self.items.get_by_key(name)
     }
 
     /// Returns the associated item with the given name and `AssocKind`, if one exists.
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 4b4f62b67f2..d183a1a3fb0 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -2206,7 +2206,7 @@ impl<'tcx> TyCtxt<'tcx> {
         Some(Ident::new(def, span))
     }
 
-    pub fn opt_associated_item(self, def_id: DefId) -> Option<&'tcx AssocItem> {
+    pub fn opt_associated_item(self, def_id: DefId) -> Option<AssocItem> {
         if let DefKind::AssocConst | DefKind::AssocFn | DefKind::AssocTy = self.def_kind(def_id) {
             Some(self.associated_item(def_id))
         } else {
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 93c3364de8f..df1aeed941d 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -97,7 +97,7 @@ fn check_is_object_safe(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
 /// object. Note that object-safe traits can have some
 /// non-vtable-safe methods, so long as they require `Self: Sized` or
 /// otherwise ensure that they cannot be used when `Self = Trait`.
-pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: &ty::AssocItem) -> bool {
+pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: ty::AssocItem) -> bool {
     debug_assert!(tcx.generics_of(trait_def_id).has_self);
     debug!("is_vtable_safe_method({:?}, {:?})", trait_def_id, method);
     // Any method that has a `Self: Sized` bound cannot be called.
@@ -120,8 +120,8 @@ fn object_safety_violations_for_trait(
         .associated_items(trait_def_id)
         .in_definition_order()
         .filter(|item| item.kind == ty::AssocKind::Fn)
-        .filter_map(|item| {
-            object_safety_violation_for_method(tcx, trait_def_id, &item)
+        .filter_map(|&item| {
+            object_safety_violation_for_method(tcx, trait_def_id, item)
                 .map(|(code, span)| ObjectSafetyViolation::Method(item.name, code, span))
         })
         .collect();
@@ -387,7 +387,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
 fn object_safety_violation_for_method(
     tcx: TyCtxt<'_>,
     trait_def_id: DefId,
-    method: &ty::AssocItem,
+    method: ty::AssocItem,
 ) -> Option<(MethodViolationCode, Span)> {
     debug!("object_safety_violation_for_method({:?}, {:?})", trait_def_id, method);
     // Any method that has a `Self : Sized` requisite is otherwise
@@ -420,7 +420,7 @@ fn object_safety_violation_for_method(
 fn virtual_call_violation_for_method<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_def_id: DefId,
-    method: &ty::AssocItem,
+    method: ty::AssocItem,
 ) -> Option<MethodViolationCode> {
     let sig = tcx.fn_sig(method.def_id).subst_identity();
 
@@ -722,7 +722,7 @@ fn object_ty_for_trait<'tcx>(
 #[allow(dead_code)]
 fn receiver_is_dispatchable<'tcx>(
     tcx: TyCtxt<'tcx>,
-    method: &ty::AssocItem,
+    method: ty::AssocItem,
     receiver_ty: Ty<'tcx>,
 ) -> bool {
     debug!("receiver_is_dispatchable: method = {:?}, receiver_ty = {:?}", method, receiver_ty);
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index 011fe742a69..c2388f9fa1b 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -2149,7 +2149,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
     } else {
         ty.map_bound(|ty| ty.into())
     };
-    if !check_substs_compatible(tcx, &assoc_ty.item, substs) {
+    if !check_substs_compatible(tcx, assoc_ty.item, substs) {
         let err = tcx.ty_error_with_message(
             obligation.cause.span,
             "impl item and trait item have different parameters",
@@ -2164,7 +2164,7 @@ fn confirm_impl_candidate<'cx, 'tcx>(
 // Verify that the trait item and its implementation have compatible substs lists
 fn check_substs_compatible<'tcx>(
     tcx: TyCtxt<'tcx>,
-    assoc_item: &ty::AssocItem,
+    assoc_item: ty::AssocItem,
     substs: ty::SubstsRef<'tcx>,
 ) -> bool {
     fn check_substs_compatible_inner<'tcx>(
@@ -2238,7 +2238,7 @@ fn confirm_impl_trait_in_trait_candidate<'tcx>(
         leaf_def.defining_node,
     );
 
-    if !check_substs_compatible(tcx, &leaf_def.item, impl_fn_substs) {
+    if !check_substs_compatible(tcx, leaf_def.item, impl_fn_substs) {
         let err = tcx.ty_error_with_message(
             obligation.cause.span,
             "impl method and trait method have different parameters",
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
index c3dcd64b2c2..2e4a5cfe4bc 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/specialization_graph.rs
@@ -399,7 +399,7 @@ pub(crate) fn assoc_def(
     // If there is no such item in that impl, this function will fail with a
     // cycle error if the specialization graph is currently being built.
     if let Some(&impl_item_id) = tcx.impl_item_implementor_ids(impl_def_id).get(&assoc_def_id) {
-        let &item = tcx.associated_item(impl_item_id);
+        let item = tcx.associated_item(impl_item_id);
         let impl_node = Node::Impl(impl_def_id);
         return Ok(LeafDef {
             item,
diff --git a/compiler/rustc_trait_selection/src/traits/vtable.rs b/compiler/rustc_trait_selection/src/traits/vtable.rs
index 64daca714c3..9f5c5bbeac8 100644
--- a/compiler/rustc_trait_selection/src/traits/vtable.rs
+++ b/compiler/rustc_trait_selection/src/traits/vtable.rs
@@ -197,12 +197,12 @@ fn own_existential_vtable_entries(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &[Def
         .in_definition_order()
         .filter(|item| item.kind == ty::AssocKind::Fn);
     // Now list each method's DefId (for within its trait).
-    let own_entries = trait_methods.filter_map(move |trait_method| {
+    let own_entries = trait_methods.filter_map(move |&trait_method| {
         debug!("own_existential_vtable_entry: trait_method={:?}", trait_method);
         let def_id = trait_method.def_id;
 
         // Some methods cannot be called on an object; skip those.
-        if !is_vtable_safe_method(tcx, trait_def_id, &trait_method) {
+        if !is_vtable_safe_method(tcx, trait_def_id, trait_method) {
             debug!("own_existential_vtable_entry: not vtable safe");
             return None;
         }
diff --git a/compiler/rustc_ty_utils/src/assoc.rs b/compiler/rustc_ty_utils/src/assoc.rs
index a6e0f13f698..164cac6a010 100644
--- a/compiler/rustc_ty_utils/src/assoc.rs
+++ b/compiler/rustc_ty_utils/src/assoc.rs
@@ -26,7 +26,7 @@ fn associated_item_def_ids(tcx: TyCtxt<'_>, def_id: DefId) -> &[DefId] {
     }
 }
 
-fn associated_items(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AssocItems<'_> {
+fn associated_items(tcx: TyCtxt<'_>, def_id: DefId) -> ty::AssocItems {
     if tcx.is_trait_alias(def_id) {
         ty::AssocItems::new(Vec::new())
     } else {
diff --git a/src/librustdoc/passes/collect_intra_doc_links.rs b/src/librustdoc/passes/collect_intra_doc_links.rs
index edad773b05e..d2c6e7ab024 100644
--- a/src/librustdoc/passes/collect_intra_doc_links.rs
+++ b/src/librustdoc/passes/collect_intra_doc_links.rs
@@ -689,12 +689,12 @@ fn resolve_associated_trait_item<'a>(
             .find_by_name_and_namespace(cx.tcx, Ident::with_dummy_span(item_name), ns, trait_)
             .map(|trait_assoc| {
                 trait_assoc_to_impl_assoc_item(cx.tcx, impl_, trait_assoc.def_id)
-                    .unwrap_or(trait_assoc)
+                    .unwrap_or(*trait_assoc)
             })
     });
     // FIXME(#74563): warn about ambiguity
     debug!("the candidates were {:?}", candidates.clone().collect::<Vec<_>>());
-    candidates.next().copied()
+    candidates.next()
 }
 
 /// Find the associated item in the impl `impl_id` that corresponds to the
@@ -711,7 +711,7 @@ fn trait_assoc_to_impl_assoc_item<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_id: DefId,
     trait_assoc_id: DefId,
-) -> Option<&'tcx ty::AssocItem> {
+) -> Option<ty::AssocItem> {
     let trait_to_impl_assoc_map = tcx.impl_item_implementor_ids(impl_id);
     debug!(?trait_to_impl_assoc_map);
     let impl_assoc_id = *trait_to_impl_assoc_map.get(&trait_assoc_id)?;