Fix the lint in clippy itself

Author: sgued

clippy_lints/src/dereference.rs

@@ -760,7 +760,7 @@ fn walk_parents<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> (Position, &
  .and_then(|subs| subs.get(1..))
  {
  Some(subs) => cx.tcx.mk_substs(subs.iter().copied()),
- None => cx.tcx.mk_substs([].iter()),
+ None => cx.tcx.mk_substs(std::iter::empty::<ty::subst::GenericArg<'_>>()),
  } && let impl_ty = if cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref() {
  // Trait methods taking `&self`
  sub_ty

clippy_lints/src/derive.rs

@@ -516,7 +516,10 @@ fn param_env_for_derived_eq(tcx: TyCtxt<'_>, did: DefId, eq_trait_id: DefId) ->
  tcx.mk_predicates(ty_predicates.iter().map(|&(p, _)| p).chain(
  params.iter().filter(|&&(_, needs_eq)| needs_eq).map(|&(param, _)| {
  tcx.mk_predicate(Binder::dummy(PredicateKind::Trait(TraitPredicate {
- trait_ref: TraitRef::new(eq_trait_id, tcx.mk_substs([tcx.mk_param_from_def(param)].into_iter())),
+ trait_ref: TraitRef::new(
+ eq_trait_id,
+ tcx.mk_substs(std::iter::once(tcx.mk_param_from_def(param))),
+ ),
  constness: BoundConstness::NotConst,
  polarity: ImplPolarity::Positive,
  })))

clippy_lints/src/redundant_slicing.rs

@@ -11,6 +11,8 @@ use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::subst::GenericArg;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 
+use std::iter;
+
 declare_clippy_lint! {
  /// ### What it does
  /// Checks for redundant slicing expressions which use the full range, and
@@ -134,7 +136,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
  } else if let Some(target_id) = cx.tcx.lang_items().deref_target() {
  if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions(
  cx.param_env,
- cx.tcx.mk_projection(target_id, cx.tcx.mk_substs([GenericArg::from(indexed_ty)].into_iter())),
+ cx.tcx.mk_projection(target_id, cx.tcx.mk_substs(iter::once(GenericArg::from(indexed_ty)))),
  ) {
  if deref_ty == expr_ty {
  let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;

clippy_lints/src/types/mod.rs

@@ -490,6 +490,7 @@ impl Types {
  }
  }
  }
+ #[allow(clippy::iter_empty)]
  match *qpath {
  QPath::Resolved(Some(ty), p) => {
  context.is_nested_call = true;

clippy_lints/src/utils/conf.rs

@@ -350,7 +350,7 @@ define_Conf! {
  /// Lint: DISALLOWED_SCRIPT_IDENTS.
  ///
  /// The list of unicode scripts allowed to be used in the scope.
- (allowed_scripts: Vec<String> = ["Latin"].iter().map(ToString::to_string).collect()),
+ (allowed_scripts: Vec<String> = vec!["Latin".to_string()]),
  /// Lint: NON_SEND_FIELDS_IN_SEND_TY.
  ///
  /// Whether to apply the raw pointer heuristic to determine if a type is `Send`.

clippy_lints/src/utils/internal_lints/metadata_collector.rs

@@ -797,7 +797,7 @@ fn get_lint_group_and_level_or_lint(
  let result = cx.lint_store.check_lint_name(
  lint_name,
  Some(sym::clippy),
- &[Ident::with_dummy_span(sym::clippy)].into_iter().collect(),
+ &std::iter::once(Ident::with_dummy_span(sym::clippy)).collect(),
  );
  if let CheckLintNameResult::Tool(Ok(lint_lst)) = result {
  if let Some(group) = get_lint_group(cx, lint_lst[0]) {