Allow iterators instead of requiring slices that will get turned into iterators

11 files changed, 24 insertions, 30 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/auto_trait.rs b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
index 3dab34747f7..c7dc7b1049c 100644
--- a/compiler/rustc_trait_selection/src/traits/auto_trait.rs
+++ b/compiler/rustc_trait_selection/src/traits/auto_trait.rs
@@ -86,7 +86,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     ) -> AutoTraitResult<A> {
         let tcx = self.tcx;
 
-        let trait_ref = tcx.mk_trait_ref(trait_did, ty, &[]);
+        let trait_ref = tcx.mk_trait_ref(trait_did, ty, []);
 
         let trait_pred = ty::Binder::dummy(trait_ref);
 
@@ -260,7 +260,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
         let mut already_visited = FxHashSet::default();
         let mut predicates = VecDeque::new();
         predicates.push_back(ty::Binder::dummy(ty::TraitPredicate {
-            trait_ref: infcx.tcx.mk_trait_ref(trait_did, ty, &[]),
+            trait_ref: infcx.tcx.mk_trait_ref(trait_did, ty, []),
 
             constness: ty::BoundConstness::NotConst,
             // Auto traits are positive
diff --git a/compiler/rustc_trait_selection/src/traits/engine.rs b/compiler/rustc_trait_selection/src/traits/engine.rs
index 97f4f7d795d..09c2449bdae 100644
--- a/compiler/rustc_trait_selection/src/traits/engine.rs
+++ b/compiler/rustc_trait_selection/src/traits/engine.rs
@@ -93,7 +93,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
         def_id: DefId,
     ) {
         let tcx = self.infcx.tcx;
-        let trait_ref = tcx.mk_trait_ref(def_id, ty, &[]);
+        let trait_ref = tcx.mk_trait_ref(def_id, ty, []);
         self.register_obligation(Obligation {
             cause,
             recursion_depth: 0,
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index cb9902bed54..3d0f87942c3 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -347,8 +347,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                     span: DUMMY_SP,
                     kind: TypeVariableOriginKind::MiscVariable,
                 });
-                let trait_ref =
-                    self.tcx.mk_trait_ref(trait_def_id, ty.skip_binder(), &[var.into()]);
+                let trait_ref = self.tcx.mk_trait_ref(trait_def_id, ty.skip_binder(), [var.into()]);
                 let obligation = Obligation::new(
                     self.tcx,
                     ObligationCause::dummy(),
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
index 445b5696d20..4b6d8177381 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
@@ -2985,7 +2985,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     self.tcx.mk_projection(
                         item_def_id,
                         // Future::Output has no substs
-                        self.tcx.mk_substs_trait(trait_pred.self_ty(), &[]),
+                        self.tcx.mk_substs_trait(trait_pred.self_ty(), []),
                     )
                 });
                 let projection_ty = normalize_to(
@@ -3068,13 +3068,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // Ensure all fields impl the trait.
                 adt.all_fields().all(|field| {
                     let field_ty = field.ty(self.tcx, substs);
-                    let trait_substs;
-                    let trait_substs: &[_] = match diagnostic_name {
+                    let trait_substs = match diagnostic_name {
                         sym::PartialEq | sym::PartialOrd => {
-                            trait_substs = [field_ty.into()];
-                            &trait_substs
+                            Some(field_ty.into())
                         }
-                        _ => &[],
+                        _ => None,
                     };
                     let trait_pred = trait_pred.map_bound_ref(|tr| ty::TraitPredicate {
                         trait_ref: self.tcx.mk_trait_ref(
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 227a7f0a112..7eb21e156fd 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -143,7 +143,7 @@ pub fn type_known_to_meet_bound_modulo_regions<'tcx>(
     def_id: DefId,
     span: Span,
 ) -> bool {
-    let trait_ref = ty::Binder::dummy(infcx.tcx.mk_trait_ref(def_id, ty, &[]));
+    let trait_ref = ty::Binder::dummy(infcx.tcx.mk_trait_ref(def_id, ty, []));
     pred_known_to_hold_modulo_regions(infcx, param_env, trait_ref.without_const(), span)
 }
 
@@ -902,7 +902,7 @@ pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
     // this has been typecked-before, so diagnostics is not really needed.
     let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
 
-    let trait_ref = tcx.mk_trait_ref(unsize_trait_did, source, &[target.into()]);
+    let trait_ref = tcx.mk_trait_ref(unsize_trait_did, source, [target.into()]);
 
     match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), ty::Binder::dummy(trait_ref))) {
         Ok(ImplSource::TraitUpcasting(implsrc_traitcasting)) => {
diff --git a/compiler/rustc_trait_selection/src/traits/object_safety.rs b/compiler/rustc_trait_selection/src/traits/object_safety.rs
index 20826f2c541..29b315bff16 100644
--- a/compiler/rustc_trait_selection/src/traits/object_safety.rs
+++ b/compiler/rustc_trait_selection/src/traits/object_safety.rs
@@ -688,7 +688,7 @@ fn receiver_is_dispatchable<'tcx>(
         let unsize_predicate = ty::Binder::dummy(tcx.mk_trait_ref(
             unsize_did,
             tcx.types.self_param,
-            &[unsized_self_ty.into()],
+            [unsized_self_ty.into()],
         ))
         .without_const()
         .to_predicate(tcx);
@@ -724,7 +724,7 @@ fn receiver_is_dispatchable<'tcx>(
         let predicate = ty::Binder::dummy(tcx.mk_trait_ref(
             dispatch_from_dyn_did,
             receiver_ty,
-            &[unsized_receiver_ty.into()],
+            [unsized_receiver_ty.into()],
         ))
         .without_const();
 
diff --git a/compiler/rustc_trait_selection/src/traits/project.rs b/compiler/rustc_trait_selection/src/traits/project.rs
index e1b30112e39..b8fe4c86405 100644
--- a/compiler/rustc_trait_selection/src/traits/project.rs
+++ b/compiler/rustc_trait_selection/src/traits/project.rs
@@ -1712,7 +1712,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                                 selcx.tcx(),
                                 ty::Binder::dummy(selcx.tcx().mk_trait_ref(
                                     selcx.tcx().require_lang_item(LangItem::Sized, None),
-                                    self_ty, &[],
+                                    self_ty, [],
                                 ))
                                 .without_const(),
                             ),
@@ -1969,7 +1969,7 @@ fn confirm_pointee_candidate<'cx, 'tcx>(
         let sized_predicate = ty::Binder::dummy(tcx.mk_trait_ref(
             tcx.require_lang_item(LangItem::Sized, None),
             self_ty,
-            &[],
+            [],
         ))
         .without_const();
         obligations.push(obligation.with(tcx, sized_predicate));
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 6b19b9297c5..b11f2c8e6a4 100644
--- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs
@@ -714,7 +714,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
 
         // <ty as Deref>
-        let trait_ref = tcx.mk_trait_ref(tcx.lang_items().deref_trait()?, ty, &[]);
+        let trait_ref = tcx.mk_trait_ref(tcx.lang_items().deref_trait()?, ty, []);
 
         let obligation = traits::Obligation::new(
             tcx,
diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
index 6d737b455bf..5c3a132bb5c 100644
--- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs
@@ -635,7 +635,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let tr = ty::Binder::dummy(self.tcx().mk_trait_ref(
             self.tcx().require_lang_item(LangItem::Sized, None),
             output_ty,
-            &[],
+            [],
         ));
         nested.push(Obligation::new(
             self.infcx.tcx,
@@ -1000,7 +1000,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let tr = ty::Binder::dummy(tcx.mk_trait_ref(
                     tcx.require_lang_item(LangItem::Sized, None),
                     source,
-                    &[],
+                    [],
                 ));
                 nested.push(predicate_to_obligation(tr.without_const().to_predicate(tcx)));
 
@@ -1258,7 +1258,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                             trait_ref: self.tcx().mk_trait_ref(
                                 self.tcx().require_lang_item(LangItem::Destruct, None),
                                 nested_ty,
-                                &[],
+                                [],
                             ),
                             constness: ty::BoundConstness::ConstIfConst,
                             polarity: ty::ImplPolarity::Positive,
@@ -1283,7 +1283,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         trait_ref: self.tcx().mk_trait_ref(
                             self.tcx().require_lang_item(LangItem::Destruct, None),
                             nested_ty,
-                            &[],
+                            [],
                         ),
                         constness: ty::BoundConstness::ConstIfConst,
                         polarity: ty::ImplPolarity::Positive,
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 21c79461eda..41798e00caa 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -241,7 +241,7 @@ pub fn predicate_for_trait_def<'tcx>(
     self_ty: Ty<'tcx>,
     params: &[GenericArg<'tcx>],
 ) -> PredicateObligation<'tcx> {
-    let trait_ref = tcx.mk_trait_ref(trait_def_id, self_ty, params);
+    let trait_ref = tcx.mk_trait_ref(trait_def_id, self_ty, params.iter().copied());
     predicate_for_trait_ref(tcx, cause, param_env, trait_ref, recursion_depth)
 }
 
@@ -304,7 +304,7 @@ pub fn closure_trait_ref_and_return_type<'tcx>(
         TupleArgumentsFlag::Yes => tcx.intern_tup(sig.skip_binder().inputs()),
     };
     debug_assert!(!self_ty.has_escaping_bound_vars());
-    let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, self_ty, &[arguments_tuple.into()]);
+    let trait_ref = tcx.mk_trait_ref(fn_trait_def_id, self_ty, [arguments_tuple.into()]);
     sig.map_bound(|sig| (trait_ref, sig.output()))
 }
 
@@ -316,7 +316,7 @@ pub fn generator_trait_ref_and_outputs<'tcx>(
 ) -> ty::Binder<'tcx, (ty::TraitRef<'tcx>, Ty<'tcx>, Ty<'tcx>)> {
     debug_assert!(!self_ty.has_escaping_bound_vars());
     let trait_ref =
-        tcx.mk_trait_ref(fn_trait_def_id, self_ty, &[sig.skip_binder().resume_ty.into()]);
+        tcx.mk_trait_ref(fn_trait_def_id, self_ty, [sig.skip_binder().resume_ty.into()]);
     sig.map_bound(|sig| (trait_ref, sig.yield_ty, sig.return_ty))
 }
 
diff --git a/compiler/rustc_trait_selection/src/traits/wf.rs b/compiler/rustc_trait_selection/src/traits/wf.rs
index 3fe019cb7de..378e6738795 100644
--- a/compiler/rustc_trait_selection/src/traits/wf.rs
+++ b/compiler/rustc_trait_selection/src/traits/wf.rs
@@ -421,11 +421,8 @@ impl<'tcx> WfPredicates<'tcx> {
     fn require_sized(&mut self, subty: Ty<'tcx>, cause: traits::ObligationCauseCode<'tcx>) {
         if !subty.has_escaping_bound_vars() {
             let cause = self.cause(cause);
-            let trait_ref = self.tcx.mk_trait_ref(
-                self.tcx.require_lang_item(LangItem::Sized, None),
-                subty,
-                &[],
-            );
+            let trait_ref =
+                self.tcx.mk_trait_ref(self.tcx.require_lang_item(LangItem::Sized, None), subty, []);
             self.out.push(traits::Obligation::with_depth(
                 self.tcx,
                 cause,