Enable iter_on_single_items

Author: nickdrozd

clippy_lints/src/ptr.rs

@@ -691,7 +691,7 @@ fn matches_preds<'tcx>(
         .iter()
         .all(|&p| match cx.tcx.instantiate_bound_regions_with_erased(p) {
             ExistentialPredicate::Trait(p) => infcx
-                .type_implements_trait(p.def_id, [ty.into()].into_iter().chain(p.args.iter()), cx.param_env)
+                .type_implements_trait(p.def_id, iter::once(ty.into()).chain(p.args.iter()), cx.param_env)
                 .must_apply_modulo_regions(),
             ExistentialPredicate::Projection(p) => infcx.predicate_must_hold_modulo_regions(&Obligation::new(
                 cx.tcx,

clippy_utils/src/ty/mod.rs

@@ -291,7 +291,7 @@ pub fn implements_trait_with_env_from_iter<'tcx>(
         .map(|arg| arg.into().unwrap_or_else(|| infcx.next_ty_var(DUMMY_SP).into()))
         .collect::<Vec<_>>();
 
-    let trait_ref = TraitRef::new(tcx, trait_id, [GenericArg::from(ty)].into_iter().chain(args));
+    let trait_ref = TraitRef::new(tcx, trait_id, iter::once(GenericArg::from(ty)).chain(args));
 
     debug_assert_matches!(
         tcx.def_kind(trait_id),

tests/dogfood.rs

@@ -92,6 +92,8 @@ fn run_clippy_for_package(project: &str) -> bool {
         "-D",
         "clippy::dbg_macro",
         "-D",
+        "clippy::iter_on_single_items",
+        "-D",
         "clippy::needless_pass_by_ref_mut",
         "-D",
         "clippy::significant_drop_tightening",