Use iterators instead of slices at more sites

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -316,7 +316,7 @@ fn visit_implementation_of_dispatch_from_dyn<'tcx>(tcx: TyCtxt<'tcx>, impl_did:
                             dispatch_from_dyn_trait,
                             0,
                             field.ty(tcx, substs_a),
-                            &[field.ty(tcx, substs_b).into()],
+                            [field.ty(tcx, substs_b).into()],
                         )
                     }),
                 );
@@ -558,7 +558,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUn
     // Register an obligation for `A: Trait<B>`.
     let cause = traits::ObligationCause::misc(span, impl_hir_id);
     let predicate =
-        predicate_for_trait_def(tcx, param_env, cause, trait_def_id, 0, source, &[target.into()]);
+        predicate_for_trait_def(tcx, param_env, cause, trait_def_id, 0, source, [target.into()]);
     let errors = traits::fully_solve_obligation(&infcx, predicate);
     if !errors.is_empty() {
         infcx.err_ctxt().report_fulfillment_errors(&errors, None);

compiler/rustc_hir_typeck/src/coercion.rs

@@ -631,7 +631,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             coerce_unsized_did,
             0,
             coerce_source,
-            &[coerce_target.into()]
+            [coerce_target.into()]
         )];
 
         let mut has_unsized_tuple_coercion = false;

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -241,7 +241,7 @@ impl<'tcx> ConstToPat<'tcx> {
             partial_eq_trait_id,
             0,
             ty,
-            &[any_ty],
+            [any_ty],
         );
         // FIXME: should this call a `predicate_must_hold` variant instead?
 

compiler/rustc_trait_selection/src/lib.rs

@@ -11,6 +11,7 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(associated_type_bounds)]
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
 #![feature(drain_filter)]

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -1108,7 +1108,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     obligation.predicate.def_id(),
                     obligation.recursion_depth + 1,
                     source_tail,
-                    &[target_tail.into()],
+                    [target_tail.into()],
                 ));
             }
 
@@ -1139,7 +1139,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         obligation.predicate.def_id(),
                         obligation.recursion_depth + 1,
                         a_last,
-                        &[b_last.into()],
+                        [b_last.into()],
                     )
                 }));
             }

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -2101,7 +2101,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     trait_def_id,
                     recursion_depth,
                     normalized_ty,
-                    &[],
+                    [],
                 );
                 obligations.push(placeholder_obligation);
                 obligations

compiler/rustc_trait_selection/src/traits/util.rs

@@ -239,9 +239,9 @@ pub fn predicate_for_trait_def<'tcx>(
     trait_def_id: DefId,
     recursion_depth: usize,
     self_ty: Ty<'tcx>,
-    params: &[GenericArg<'tcx>],
+    params: impl IntoIterator<Item = GenericArg<'tcx>, IntoIter: ExactSizeIterator>,
 ) -> PredicateObligation<'tcx> {
-    let trait_ref = tcx.mk_trait_ref(trait_def_id, self_ty, params.iter().copied());
+    let trait_ref = tcx.mk_trait_ref(trait_def_id, self_ty, params);
     predicate_for_trait_ref(tcx, cause, param_env, trait_ref, recursion_depth)
 }