1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
2 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
3 use clippy_utils::sugg::has_enclosing_paren;
4 use clippy_utils::ty::{expr_sig, is_copy, peel_mid_ty_refs, ty_sig, variant_of_res};
6 fn_def_id, get_parent_expr, get_parent_expr_for_hir, is_lint_allowed, meets_msrv, msrvs, path_to_local,
9 use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
10 use rustc_data_structures::fx::FxIndexMap;
11 use rustc_errors::Applicability;
12 use rustc_hir::intravisit::{walk_ty, Visitor};
14 self as hir, def_id::DefId, BindingAnnotation, Body, BodyId, BorrowKind, Closure, Expr, ExprKind, FnRetTy,
15 GenericArg, HirId, ImplItem, ImplItemKind, Item, ItemKind, Local, MatchSource, Mutability, Node, Pat, PatKind,
16 Path, QPath, TraitItem, TraitItemKind, TyKind, UnOp,
18 use rustc_index::bit_set::BitSet;
19 use rustc_infer::infer::TyCtxtInferExt;
20 use rustc_lint::{LateContext, LateLintPass};
21 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
22 use rustc_middle::ty::{
23 self, subst::Subst, Binder, BoundVariableKind, EarlyBinder, FnSig, GenericArgKind, List, ParamTy, PredicateKind,
24 ProjectionPredicate, Ty, TyCtxt, TypeVisitable, TypeckResults,
26 use rustc_semver::RustcVersion;
27 use rustc_session::{declare_tool_lint, impl_lint_pass};
28 use rustc_span::{symbol::sym, Span, Symbol, DUMMY_SP};
29 use rustc_trait_selection::infer::InferCtxtExt as _;
30 use rustc_trait_selection::traits::{query::evaluate_obligation::InferCtxtExt as _, Obligation, ObligationCause};
31 use std::collections::VecDeque;
33 declare_clippy_lint! {
35 /// Checks for explicit `deref()` or `deref_mut()` method calls.
37 /// ### Why is this bad?
38 /// Dereferencing by `&*x` or `&mut *x` is clearer and more concise,
39 /// when not part of a method chain.
43 /// use std::ops::Deref;
44 /// let a: &mut String = &mut String::from("foo");
45 /// let b: &str = a.deref();
50 /// let a: &mut String = &mut String::from("foo");
54 /// This lint excludes:
56 /// let _ = d.unwrap().deref();
58 #[clippy::version = "1.44.0"]
59 pub EXPLICIT_DEREF_METHODS,
61 "Explicit use of deref or deref_mut method while not in a method chain."
64 declare_clippy_lint! {
66 /// Checks for address of operations (`&`) that are going to
67 /// be dereferenced immediately by the compiler.
69 /// ### Why is this bad?
70 /// Suggests that the receiver of the expression borrows
75 /// fn fun(_a: &i32) {}
77 /// let x: &i32 = &&&&&&5;
83 /// # fn fun(_a: &i32) {}
87 #[clippy::version = "pre 1.29.0"]
90 "taking a reference that is going to be automatically dereferenced"
93 declare_clippy_lint! {
95 /// Checks for `ref` bindings which create a reference to a reference.
97 /// ### Why is this bad?
98 /// The address-of operator at the use site is clearer about the need for a reference.
102 /// let x = Some("");
103 /// if let Some(ref x) = x {
110 /// let x = Some("");
111 /// if let Some(x) = x {
115 #[clippy::version = "1.54.0"]
116 pub REF_BINDING_TO_REFERENCE,
118 "`ref` binding to a reference"
121 declare_clippy_lint! {
123 /// Checks for dereferencing expressions which would be covered by auto-deref.
125 /// ### Why is this bad?
126 /// This unnecessarily complicates the code.
130 /// let x = String::new();
131 /// let y: &str = &*x;
135 /// let x = String::new();
136 /// let y: &str = &x;
138 #[clippy::version = "1.60.0"]
139 pub EXPLICIT_AUTO_DEREF,
141 "dereferencing when the compiler would automatically dereference"
144 impl_lint_pass!(Dereferencing => [
145 EXPLICIT_DEREF_METHODS,
147 REF_BINDING_TO_REFERENCE,
152 pub struct Dereferencing {
153 state: Option<(State, StateData)>,
155 // While parsing a `deref` method call in ufcs form, the path to the function is itself an
156 // expression. This is to store the id of that expression so it can be skipped when
157 // `check_expr` is called for it.
158 skip_expr: Option<HirId>,
160 /// The body the first local was found in. Used to emit lints when the traversal of the body has
161 /// been finished. Note we can't lint at the end of every body as they can be nested within each
163 current_body: Option<BodyId>,
165 /// The list of locals currently being checked by the lint.
166 /// If the value is `None`, then the binding has been seen as a ref pattern, but is not linted.
167 /// This is needed for or patterns where one of the branches can be linted, but another can not
170 /// e.g. `m!(x) | Foo::Bar(ref x)`
171 ref_locals: FxIndexMap<HirId, Option<RefPat>>,
173 // `IntoIterator` for arrays requires Rust 1.53.
174 msrv: Option<RustcVersion>,
179 pub fn new(msrv: Option<RustcVersion>) -> Self {
182 ..Dereferencing::default()
188 /// Span of the top level expression
194 struct DerefedBorrow {
197 snip_expr: Option<HirId>,
201 // Any number of deref method calls.
203 // The number of calls in a sequence which changed the referenced type
204 ty_changed_count: usize,
206 /// The required mutability
207 target_mut: Mutability,
209 DerefedBorrow(DerefedBorrow),
211 mutability: Option<Mutability>,
217 mutability: Mutability,
220 mutability: Mutability,
224 // A reference operation considered by this lint pass
232 /// Whether every usage of the binding is dereferenced.
234 /// The spans of all the ref bindings for this local.
236 /// The applicability of this suggestion.
238 /// All the replacements which need to be made.
239 replacements: Vec<(Span, String)>,
240 /// The [`HirId`] that the lint should be emitted at.
244 impl<'tcx> LateLintPass<'tcx> for Dereferencing {
245 #[expect(clippy::too_many_lines)]
246 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
247 // Skip path expressions from deref calls. e.g. `Deref::deref(e)`
248 if Some(expr.hir_id) == self.skip_expr.take() {
252 if let Some(local) = path_to_local(expr) {
253 self.check_local_usage(cx, expr, local);
256 // Stop processing sub expressions when a macro call is seen
257 if expr.span.from_expansion() {
258 if let Some((state, data)) = self.state.take() {
259 report(cx, expr, state, data);
264 let typeck = cx.typeck_results();
265 let (kind, sub_expr) = if let Some(x) = try_parse_ref_op(cx.tcx, typeck, expr) {
268 // The whole chain of reference operations has been seen
269 if let Some((state, data)) = self.state.take() {
270 report(cx, expr, state, data);
275 match (self.state.take(), kind) {
277 let expr_ty = typeck.expr_ty(expr);
278 let (position, adjustments) = walk_parents(cx, expr, self.msrv);
282 if let Position::FieldAccess(name) = position
283 && !ty_contains_field(typeck.expr_ty(sub_expr), name)
286 State::ExplicitDerefField { name },
287 StateData { span: expr.span, hir_id: expr.hir_id, position },
289 } else if position.is_deref_stable() {
291 State::ExplicitDeref { mutability: None },
292 StateData { span: expr.span, hir_id: expr.hir_id, position },
296 RefOp::Method(target_mut)
297 if !is_lint_allowed(cx, EXPLICIT_DEREF_METHODS, expr.hir_id)
298 && position.lint_explicit_deref() =>
302 ty_changed_count: if deref_method_same_type(expr_ty, typeck.expr_ty(sub_expr)) {
307 is_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
317 RefOp::AddrOf(mutability) => {
318 // Find the number of times the borrow is auto-derefed.
319 let mut iter = adjustments.iter();
320 let mut deref_count = 0usize;
321 let next_adjust = loop {
324 if !matches!(adjust.kind, Adjust::Deref(_)) {
326 } else if !adjust.target.is_ref() {
336 // Determine the required number of references before any can be removed. In all cases the
337 // reference made by the current expression will be removed. After that there are four cases to
340 // 1. Auto-borrow will trigger in the current position, so no further references are required.
341 // 2. Auto-deref ends at a reference, or the underlying type, so one extra needs to be left to
342 // handle the automatically inserted re-borrow.
343 // 3. Auto-deref hits a user-defined `Deref` impl, so at least one reference needs to exist to
345 // 4. If the chain of non-user-defined derefs ends with a mutable re-borrow, and re-borrow
346 // adjustments will not be inserted automatically, then leave one further reference to avoid
347 // moving a mutable borrow.
349 // fn foo<T>(x: &mut Option<&mut T>, y: &mut T) {
351 // // Removing the borrow will cause `x` to be moved
352 // Some(x) => &mut *x,
357 "this expression creates a reference which is immediately dereferenced by the compiler";
358 let borrow_msg = "this expression borrows a value the compiler would automatically borrow";
359 let impl_msg = "the borrowed expression implements the required traits";
361 let (required_refs, msg, snip_expr) = if position.can_auto_borrow() {
362 (1, if deref_count == 1 { borrow_msg } else { deref_msg }, None)
363 } else if let Position::ImplArg(hir_id) = position {
364 (0, impl_msg, Some(hir_id))
365 } else if let Some(&Adjust::Borrow(AutoBorrow::Ref(_, mutability))) =
366 next_adjust.map(|a| &a.kind)
368 if matches!(mutability, AutoBorrowMutability::Mut { .. }) && !position.is_reborrow_stable()
378 if deref_count >= required_refs {
380 State::DerefedBorrow(DerefedBorrow {
381 // One of the required refs is for the current borrow expression, the remaining ones
382 // can't be removed without breaking the code. See earlier comment.
383 count: deref_count - required_refs,
387 StateData { span: expr.span, hir_id: expr.hir_id, position },
389 } else if position.is_deref_stable()
390 // Auto-deref doesn't combine with other adjustments
391 && next_adjust.map_or(true, |a| matches!(a.kind, Adjust::Deref(_) | Adjust::Borrow(_)))
392 && iter.all(|a| matches!(a.kind, Adjust::Deref(_) | Adjust::Borrow(_)))
395 State::Borrow { mutability },
404 RefOp::Method(..) => (),
420 ty_changed_count: if deref_method_same_type(typeck.expr_ty(expr), typeck.expr_ty(sub_expr)) {
425 is_final_ufcs: matches!(expr.kind, ExprKind::Call(..)),
431 (Some((State::DerefedBorrow(state), data)), RefOp::AddrOf(_)) if state.count != 0 => {
433 State::DerefedBorrow(DerefedBorrow {
434 count: state.count - 1,
440 (Some((State::DerefedBorrow(state), data)), RefOp::AddrOf(mutability)) => {
441 let position = data.position;
442 report(cx, expr, State::DerefedBorrow(state), data);
443 if position.is_deref_stable() {
445 State::Borrow { mutability },
454 (Some((State::DerefedBorrow(state), data)), RefOp::Deref) => {
455 let position = data.position;
456 report(cx, expr, State::DerefedBorrow(state), data);
457 if let Position::FieldAccess(name) = position
458 && !ty_contains_field(typeck.expr_ty(sub_expr), name)
461 State::ExplicitDerefField { name },
462 StateData { span: expr.span, hir_id: expr.hir_id, position },
464 } else if position.is_deref_stable() {
466 State::ExplicitDeref { mutability: None },
467 StateData { span: expr.span, hir_id: expr.hir_id, position },
472 (Some((State::Borrow { mutability }, data)), RefOp::Deref) => {
473 if typeck.expr_ty(sub_expr).is_ref() {
474 self.state = Some((State::Reborrow { mutability }, data));
477 State::ExplicitDeref {
478 mutability: Some(mutability),
484 (Some((State::Reborrow { mutability }, data)), RefOp::Deref) => {
486 State::ExplicitDeref {
487 mutability: Some(mutability),
492 (state @ Some((State::ExplicitDeref { .. }, _)), RefOp::Deref) => {
495 (Some((State::ExplicitDerefField { name }, data)), RefOp::Deref)
496 if !ty_contains_field(typeck.expr_ty(sub_expr), name) =>
498 self.state = Some((State::ExplicitDerefField { name }, data));
501 (Some((state, data)), _) => report(cx, expr, state, data),
505 fn check_pat(&mut self, cx: &LateContext<'tcx>, pat: &'tcx Pat<'_>) {
506 if let PatKind::Binding(BindingAnnotation::REF, id, name, _) = pat.kind {
507 if let Some(opt_prev_pat) = self.ref_locals.get_mut(&id) {
508 // This binding id has been seen before. Add this pattern to the list of changes.
509 if let Some(prev_pat) = opt_prev_pat {
510 if pat.span.from_expansion() {
511 // Doesn't match the context of the previous pattern. Can't lint here.
512 *opt_prev_pat = None;
514 prev_pat.spans.push(pat.span);
515 prev_pat.replacements.push((
517 snippet_with_context(cx, name.span, pat.span.ctxt(), "..", &mut prev_pat.app)
527 if !pat.span.from_expansion();
528 if let ty::Ref(_, tam, _) = *cx.typeck_results().pat_ty(pat).kind();
529 // only lint immutable refs, because borrowed `&mut T` cannot be moved out
530 if let ty::Ref(_, _, Mutability::Not) = *tam.kind();
532 let mut app = Applicability::MachineApplicable;
533 let snip = snippet_with_context(cx, name.span, pat.span.ctxt(), "..", &mut app).0;
534 self.current_body = self.current_body.or(cx.enclosing_body);
535 self.ref_locals.insert(
539 spans: vec![pat.span],
541 replacements: vec![(pat.span, snip.into())],
550 fn check_body_post(&mut self, cx: &LateContext<'tcx>, body: &'tcx Body<'_>) {
551 if Some(body.id()) == self.current_body {
552 for pat in self.ref_locals.drain(..).filter_map(|(_, x)| x) {
553 let replacements = pat.replacements;
555 let lint = if pat.always_deref {
558 REF_BINDING_TO_REFERENCE
560 span_lint_hir_and_then(
565 "this pattern creates a reference to a reference",
567 diag.multipart_suggestion("try this", replacements, app);
571 self.current_body = None;
575 extract_msrv_attr!(LateContext);
578 fn try_parse_ref_op<'tcx>(
580 typeck: &'tcx TypeckResults<'_>,
581 expr: &'tcx Expr<'_>,
582 ) -> Option<(RefOp, &'tcx Expr<'tcx>)> {
583 let (def_id, arg) = match expr.kind {
584 ExprKind::MethodCall(_, arg, [], _) => (typeck.type_dependent_def_id(expr.hir_id)?, arg),
587 kind: ExprKind::Path(path),
592 ) => (typeck.qpath_res(path, *hir_id).opt_def_id()?, arg),
593 ExprKind::Unary(UnOp::Deref, sub_expr) if !typeck.expr_ty(sub_expr).is_unsafe_ptr() => {
594 return Some((RefOp::Deref, sub_expr));
596 ExprKind::AddrOf(BorrowKind::Ref, mutability, sub_expr) => return Some((RefOp::AddrOf(mutability), sub_expr)),
599 if tcx.is_diagnostic_item(sym::deref_method, def_id) {
600 Some((RefOp::Method(Mutability::Not), arg))
601 } else if tcx.trait_of_item(def_id)? == tcx.lang_items().deref_mut_trait()? {
602 Some((RefOp::Method(Mutability::Mut), arg))
608 // Checks whether the type for a deref call actually changed the type, not just the mutability of
610 fn deref_method_same_type<'tcx>(result_ty: Ty<'tcx>, arg_ty: Ty<'tcx>) -> bool {
611 match (result_ty.kind(), arg_ty.kind()) {
612 (ty::Ref(_, result_ty, _), ty::Ref(_, arg_ty, _)) => result_ty == arg_ty,
614 // The result type for a deref method is always a reference
615 // Not matching the previous pattern means the argument type is not a reference
616 // This means that the type did change
621 /// The position of an expression relative to it's parent.
622 #[derive(Clone, Copy)]
625 /// The method is defined on a reference type. e.g. `impl Foo for &T`
626 MethodReceiverRefImpl,
632 /// Any other location which will trigger auto-deref to a specific time.
633 /// Contains the precedence of the parent expression and whether the target type is sized.
634 DerefStable(i8, bool),
635 /// Any other location which will trigger auto-reborrowing.
636 /// Contains the precedence of the parent expression.
638 /// Contains the precedence of the parent expression.
642 fn is_deref_stable(self) -> bool {
643 matches!(self, Self::DerefStable(..))
646 fn is_reborrow_stable(self) -> bool {
647 matches!(self, Self::DerefStable(..) | Self::ReborrowStable(_))
650 fn can_auto_borrow(self) -> bool {
651 matches!(self, Self::MethodReceiver | Self::FieldAccess(_) | Self::Callee)
654 fn lint_explicit_deref(self) -> bool {
655 matches!(self, Self::Other(_) | Self::DerefStable(..) | Self::ReborrowStable(_))
658 fn precedence(self) -> i8 {
661 | Self::MethodReceiverRefImpl
663 | Self::FieldAccess(_)
664 | Self::Postfix => PREC_POSTFIX,
665 Self::ImplArg(_) | Self::Deref => PREC_PREFIX,
666 Self::DerefStable(p, _) | Self::ReborrowStable(p) | Self::Other(p) => p,
671 /// Walks up the parent expressions attempting to determine both how stable the auto-deref result
672 /// is, and which adjustments will be applied to it. Note this will not consider auto-borrow
673 /// locations as those follow different rules.
674 #[expect(clippy::too_many_lines)]
675 fn walk_parents<'tcx>(
676 cx: &LateContext<'tcx>,
678 msrv: Option<RustcVersion>,
679 ) -> (Position, &'tcx [Adjustment<'tcx>]) {
680 let mut adjustments = [].as_slice();
681 let mut precedence = 0i8;
682 let ctxt = e.span.ctxt();
683 let position = walk_to_expr_usage(cx, e, &mut |parent, child_id| {
684 // LocalTableInContext returns the wrong lifetime, so go use `expr_adjustments` instead.
685 if adjustments.is_empty() && let Node::Expr(e) = cx.tcx.hir().get(child_id) {
686 adjustments = cx.typeck_results().expr_adjustments(e);
689 Node::Local(Local { ty: Some(ty), span, .. }) if span.ctxt() == ctxt => {
690 Some(binding_ty_auto_deref_stability(cx, ty, precedence, List::empty()))
693 kind: ItemKind::Static(..) | ItemKind::Const(..),
698 | Node::TraitItem(&TraitItem {
699 kind: TraitItemKind::Const(..),
704 | Node::ImplItem(&ImplItem {
705 kind: ImplItemKind::Const(..),
709 }) if span.ctxt() == ctxt => {
710 let ty = cx.tcx.type_of(def_id);
711 Some(ty_auto_deref_stability(cx, ty, precedence).position_for_result(cx))
715 kind: ItemKind::Fn(..),
720 | Node::TraitItem(&TraitItem {
721 kind: TraitItemKind::Fn(..),
726 | Node::ImplItem(&ImplItem {
727 kind: ImplItemKind::Fn(..),
731 }) if span.ctxt() == ctxt => {
734 .erase_late_bound_regions(cx.tcx.fn_sig(def_id.to_def_id()).output());
735 Some(ty_auto_deref_stability(cx, output, precedence).position_for_result(cx))
738 Node::ExprField(field) if field.span.ctxt() == ctxt => match get_parent_expr_for_hir(cx, field.hir_id) {
741 kind: ExprKind::Struct(path, ..),
743 }) => variant_of_res(cx, cx.qpath_res(path, *hir_id))
744 .and_then(|variant| variant.fields.iter().find(|f| f.name == field.ident.name))
746 ty_auto_deref_stability(cx, cx.tcx.type_of(field_def.did), precedence).position_for_arg()
751 Node::Expr(parent) if parent.span.ctxt() == ctxt => match parent.kind {
752 ExprKind::Ret(_) => {
753 let owner_id = cx.tcx.hir().body_owner(cx.enclosing_body.unwrap());
756 closure_expr @ Expr {
757 kind: ExprKind::Closure(closure),
760 ) = cx.tcx.hir().get(owner_id)
762 closure_result_position(cx, closure, cx.typeck_results().expr_ty(closure_expr), precedence)
766 .erase_late_bound_regions(cx.tcx.fn_sig(cx.tcx.hir().local_def_id(owner_id)).output());
767 ty_auto_deref_stability(cx, output, precedence).position_for_result(cx)
771 ExprKind::Closure(closure) => Some(closure_result_position(
774 cx.typeck_results().expr_ty(parent),
777 ExprKind::Call(func, _) if func.hir_id == child_id => {
778 (child_id == e.hir_id).then_some(Position::Callee)
780 ExprKind::Call(func, args) => args
782 .position(|arg| arg.hir_id == child_id)
783 .zip(expr_sig(cx, func))
784 .and_then(|(i, sig)| {
785 sig.input_with_hir(i).map(|(hir_ty, ty)| match hir_ty {
786 // Type inference for closures can depend on how they're called. Only go by the explicit
788 Some(hir_ty) => binding_ty_auto_deref_stability(cx, hir_ty, precedence, ty.bound_vars()),
790 if let ty::Param(param_ty) = ty.skip_binder().kind() {
791 needless_borrow_impl_arg_position(cx, parent, i, *param_ty, e, precedence, msrv)
793 ty_auto_deref_stability(cx, cx.tcx.erase_late_bound_regions(ty), precedence)
799 ExprKind::MethodCall(_, receiver, args, _) => {
800 let id = cx.typeck_results().type_dependent_def_id(parent.hir_id).unwrap();
801 if receiver.hir_id == child_id {
802 // Check for calls to trait methods where the trait is implemented on a reference.
803 // Two cases need to be handled:
804 // * `self` methods on `&T` will never have auto-borrow
805 // * `&self` methods on `&T` can have auto-borrow, but `&self` methods on `T` will take
807 if e.hir_id != child_id {
808 return Some(Position::ReborrowStable(precedence))
809 } else if let Some(trait_id) = cx.tcx.trait_of_item(id)
810 && let arg_ty = cx.tcx.erase_regions(cx.typeck_results().expr_ty_adjusted(e))
811 && let ty::Ref(_, sub_ty, _) = *arg_ty.kind()
812 && let subs = match cx
814 .node_substs_opt(parent.hir_id)
815 .and_then(|subs| subs.get(1..))
817 Some(subs) => cx.tcx.mk_substs(subs.iter().copied()),
818 None => cx.tcx.mk_substs(std::iter::empty::<ty::subst::GenericArg<'_>>()),
819 } && let impl_ty = if cx.tcx.fn_sig(id).skip_binder().inputs()[0].is_ref() {
820 // Trait methods taking `&self`
823 // Trait methods taking `self`
825 } && impl_ty.is_ref()
826 && cx.tcx.infer_ctxt().enter(|infcx|
828 .type_implements_trait(trait_id, impl_ty, subs, cx.param_env)
829 .must_apply_modulo_regions()
832 return Some(Position::MethodReceiverRefImpl)
834 return Some(Position::MethodReceiver);
836 args.iter().position(|arg| arg.hir_id == child_id).map(|i| {
837 let ty = cx.tcx.fn_sig(id).skip_binder().inputs()[i + 1];
838 if let ty::Param(param_ty) = ty.kind() {
839 needless_borrow_impl_arg_position(cx, parent, i + 1, *param_ty, e, precedence, msrv)
841 ty_auto_deref_stability(
843 cx.tcx.erase_late_bound_regions(cx.tcx.fn_sig(id).input(i + 1)),
850 ExprKind::Field(child, name) if child.hir_id == e.hir_id => Some(Position::FieldAccess(name.name)),
851 ExprKind::Unary(UnOp::Deref, child) if child.hir_id == e.hir_id => Some(Position::Deref),
852 ExprKind::Match(child, _, MatchSource::TryDesugar | MatchSource::AwaitDesugar)
853 | ExprKind::Index(child, _)
854 if child.hir_id == e.hir_id =>
856 Some(Position::Postfix)
858 _ if child_id == e.hir_id => {
859 precedence = parent.precedence().order();
867 .unwrap_or(Position::Other(precedence));
868 (position, adjustments)
871 fn closure_result_position<'tcx>(
872 cx: &LateContext<'tcx>,
873 closure: &'tcx Closure<'_>,
877 match closure.fn_decl.output {
878 FnRetTy::Return(hir_ty) => {
879 if let Some(sig) = ty_sig(cx, ty)
880 && let Some(output) = sig.output()
882 binding_ty_auto_deref_stability(cx, hir_ty, precedence, output.bound_vars())
884 Position::Other(precedence)
887 FnRetTy::DefaultReturn(_) => Position::Other(precedence),
891 // Checks the stability of auto-deref when assigned to a binding with the given explicit type.
894 // let x = Box::new(Box::new(0u32));
895 // let y1: &Box<_> = x.deref();
896 // let y2: &Box<_> = &x;
898 // Here `y1` and `y2` would resolve to different types, so the type `&Box<_>` is not stable when
899 // switching to auto-dereferencing.
900 fn binding_ty_auto_deref_stability<'tcx>(
901 cx: &LateContext<'tcx>,
902 ty: &'tcx hir::Ty<'_>,
904 binder_args: &'tcx List<BoundVariableKind>,
906 let TyKind::Rptr(_, ty) = &ty.kind else {
907 return Position::Other(precedence);
912 break match ty.ty.kind {
913 TyKind::Rptr(_, ref ref_ty) => {
918 QPath::TypeRelative(_, path)
922 segments: [.., path], ..
926 if let Some(args) = path.args
927 && args.args.iter().any(|arg| match arg {
928 GenericArg::Infer(_) => true,
929 GenericArg::Type(ty) => ty_contains_infer(ty),
933 Position::ReborrowStable(precedence)
935 Position::DerefStable(
938 .erase_late_bound_regions(Binder::bind_with_vars(
939 cx.typeck_results().node_type(ty.ty.hir_id),
942 .is_sized(cx.tcx.at(DUMMY_SP), cx.param_env.without_caller_bounds()),
946 TyKind::Slice(_) => Position::DerefStable(precedence, false),
947 TyKind::Array(..) | TyKind::Ptr(_) | TyKind::BareFn(_) => Position::DerefStable(precedence, true),
950 | TyKind::Path(_) => Position::DerefStable(
953 .erase_late_bound_regions(Binder::bind_with_vars(
954 cx.typeck_results().node_type(ty.ty.hir_id),
957 .is_sized(cx.tcx.at(DUMMY_SP), cx.param_env.without_caller_bounds()),
959 TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(..) | TyKind::TraitObject(..) | TyKind::Err => {
960 Position::ReborrowStable(precedence)
966 // Checks whether a type is inferred at some point.
967 // e.g. `_`, `Box<_>`, `[_]`
968 fn ty_contains_infer(ty: &hir::Ty<'_>) -> bool {
970 impl Visitor<'_> for V {
971 fn visit_ty(&mut self, ty: &hir::Ty<'_>) {
975 TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(_) | TyKind::Err
984 fn visit_generic_arg(&mut self, arg: &GenericArg<'_>) {
985 if self.0 || matches!(arg, GenericArg::Infer(_)) {
987 } else if let GenericArg::Type(ty) = arg {
992 let mut v = V(false);
998 // * child is an expression of the form `&e` in an argument position requiring an `impl Trait`
999 // * `e`'s type implements `Trait` and is copyable
1000 // If the conditions are met, returns `Some(Position::ImplArg(..))`; otherwise, returns `None`.
1001 // The "is copyable" condition is to avoid the case where removing the `&` means `e` would have to
1002 // be moved, but it cannot be.
1003 fn needless_borrow_impl_arg_position<'tcx>(
1004 cx: &LateContext<'tcx>,
1005 parent: &Expr<'tcx>,
1008 mut expr: &Expr<'tcx>,
1010 msrv: Option<RustcVersion>,
1012 let destruct_trait_def_id = cx.tcx.lang_items().destruct_trait();
1013 let sized_trait_def_id = cx.tcx.lang_items().sized_trait();
1015 let Some(callee_def_id) = fn_def_id(cx, parent) else { return Position::Other(precedence) };
1016 let fn_sig = cx.tcx.fn_sig(callee_def_id).skip_binder();
1017 let substs_with_expr_ty = cx
1019 .node_substs(if let ExprKind::Call(callee, _) = parent.kind {
1025 let predicates = cx.tcx.param_env(callee_def_id).caller_bounds();
1026 let projection_predicates = predicates
1028 .filter_map(|predicate| {
1029 if let PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
1030 Some(projection_predicate)
1035 .collect::<Vec<_>>();
1037 let mut trait_with_ref_mut_self_method = false;
1039 // If no traits were found, or only the `Destruct`, `Sized`, or `Any` traits were found, return.
1042 .filter_map(|predicate| {
1043 if let PredicateKind::Trait(trait_predicate) = predicate.kind().skip_binder()
1044 && trait_predicate.trait_ref.self_ty() == param_ty.to_ty(cx.tcx)
1046 Some(trait_predicate.trait_ref.def_id)
1051 .inspect(|trait_def_id| {
1052 trait_with_ref_mut_self_method |= has_ref_mut_self_method(cx, *trait_def_id);
1054 .all(|trait_def_id| {
1055 Some(trait_def_id) == destruct_trait_def_id
1056 || Some(trait_def_id) == sized_trait_def_id
1057 || cx.tcx.is_diagnostic_item(sym::Any, trait_def_id)
1060 return Position::Other(precedence);
1063 // `substs_with_referent_ty` can be constructed outside of `check_referent` because the same
1064 // elements are modified each time `check_referent` is called.
1065 let mut substs_with_referent_ty = substs_with_expr_ty.to_vec();
1067 let mut check_referent = |referent| {
1068 let referent_ty = cx.typeck_results().expr_ty(referent);
1070 if !is_copy(cx, referent_ty) {
1074 // https://github.com/rust-lang/rust-clippy/pull/9136#pullrequestreview-1037379321
1075 if trait_with_ref_mut_self_method && !matches!(referent_ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
1085 &projection_predicates,
1086 &mut substs_with_referent_ty,
1091 predicates.iter().all(|predicate| {
1092 if let PredicateKind::Trait(trait_predicate) = predicate.kind().skip_binder()
1093 && cx.tcx.is_diagnostic_item(sym::IntoIterator, trait_predicate.trait_ref.def_id)
1094 && let ty::Param(param_ty) = trait_predicate.self_ty().kind()
1095 && let GenericArgKind::Type(ty) = substs_with_referent_ty[param_ty.index as usize].unpack()
1097 && !meets_msrv(msrv, msrvs::ARRAY_INTO_ITERATOR)
1102 let predicate = EarlyBinder(predicate).subst(cx.tcx, &substs_with_referent_ty);
1103 let obligation = Obligation::new(ObligationCause::dummy(), cx.param_env, predicate);
1106 .enter(|infcx| infcx.predicate_must_hold_modulo_regions(&obligation))
1110 let mut needless_borrow = false;
1111 while let ExprKind::AddrOf(_, _, referent) = expr.kind {
1112 if !check_referent(referent) {
1116 needless_borrow = true;
1119 if needless_borrow {
1120 Position::ImplArg(expr.hir_id)
1122 Position::Other(precedence)
1126 fn has_ref_mut_self_method(cx: &LateContext<'_>, trait_def_id: DefId) -> bool {
1128 .associated_items(trait_def_id)
1129 .in_definition_order()
1131 if assoc_item.fn_has_self_parameter {
1132 let self_ty = cx.tcx.fn_sig(assoc_item.def_id).skip_binder().inputs()[0];
1133 matches!(self_ty.kind(), ty::Ref(_, _, Mutability::Mut))
1140 // Iteratively replaces `param_ty` with `new_ty` in `substs`, and similarly for each resulting
1141 // projected type that is a type parameter. Returns `false` if replacing the types would have an
1142 // effect on the function signature beyond substituting `new_ty` for `param_ty`.
1143 // See: https://github.com/rust-lang/rust-clippy/pull/9136#discussion_r927212757
1144 fn replace_types<'tcx>(
1145 cx: &LateContext<'tcx>,
1148 fn_sig: FnSig<'tcx>,
1150 projection_predicates: &[ProjectionPredicate<'tcx>],
1151 substs: &mut [ty::GenericArg<'tcx>],
1153 let mut replaced = BitSet::new_empty(substs.len());
1155 let mut deque = VecDeque::with_capacity(substs.len());
1156 deque.push_back((param_ty, new_ty));
1158 while let Some((param_ty, new_ty)) = deque.pop_front() {
1159 // If `replaced.is_empty()`, then `param_ty` and `new_ty` are those initially passed in.
1164 .all(|(i, ty)| (replaced.is_empty() && i == arg_index) || !ty.contains(param_ty.to_ty(cx.tcx)))
1169 substs[param_ty.index as usize] = ty::GenericArg::from(new_ty);
1171 // The `replaced.insert(...)` check provides some protection against infinite loops.
1172 if replaced.insert(param_ty.index) {
1173 for projection_predicate in projection_predicates {
1174 if projection_predicate.projection_ty.self_ty() == param_ty.to_ty(cx.tcx)
1175 && let Some(term_ty) = projection_predicate.term.ty()
1176 && let ty::Param(term_param_ty) = term_ty.kind()
1178 let item_def_id = projection_predicate.projection_ty.item_def_id;
1179 let assoc_item = cx.tcx.associated_item(item_def_id);
1180 let projection = cx.tcx
1181 .mk_projection(assoc_item.def_id, cx.tcx.mk_substs_trait(new_ty, &[]));
1183 if let Ok(projected_ty) = cx.tcx.try_normalize_erasing_regions(cx.param_env, projection)
1184 && substs[term_param_ty.index as usize] != ty::GenericArg::from(projected_ty)
1186 deque.push_back((*term_param_ty, projected_ty));
1196 struct TyPosition<'tcx> {
1198 ty: Option<Ty<'tcx>>,
1200 impl From<Position> for TyPosition<'_> {
1201 fn from(position: Position) -> Self {
1202 Self { position, ty: None }
1205 impl<'tcx> TyPosition<'tcx> {
1206 fn new_deref_stable_for_result(precedence: i8, ty: Ty<'tcx>) -> Self {
1208 position: Position::ReborrowStable(precedence),
1212 fn position_for_result(self, cx: &LateContext<'tcx>) -> Position {
1213 match (self.position, self.ty) {
1214 (Position::ReborrowStable(precedence), Some(ty)) => {
1215 Position::DerefStable(precedence, ty.is_sized(cx.tcx.at(DUMMY_SP), cx.param_env))
1217 (position, _) => position,
1220 fn position_for_arg(self) -> Position {
1225 // Checks whether a type is stable when switching to auto dereferencing,
1226 fn ty_auto_deref_stability<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, precedence: i8) -> TyPosition<'tcx> {
1227 let ty::Ref(_, mut ty, _) = *ty.kind() else {
1228 return Position::Other(precedence).into();
1232 break match *ty.kind() {
1233 ty::Ref(_, ref_ty, _) => {
1237 ty::Param(_) => TyPosition::new_deref_stable_for_result(precedence, ty),
1238 ty::Infer(_) | ty::Error(_) | ty::Bound(..) | ty::Opaque(..) | ty::Placeholder(_) | ty::Dynamic(..) => {
1239 Position::ReborrowStable(precedence).into()
1241 ty::Adt(..) if ty.has_placeholders() || ty.has_opaque_types() => {
1242 Position::ReborrowStable(precedence).into()
1244 ty::Adt(_, substs) if substs.has_param_types_or_consts() => {
1245 TyPosition::new_deref_stable_for_result(precedence, ty)
1254 | ty::FnPtr(_) => Position::DerefStable(precedence, true).into(),
1255 ty::Str | ty::Slice(..) => Position::DerefStable(precedence, false).into(),
1260 | ty::GeneratorWitness(..)
1264 | ty::Projection(_) => Position::DerefStable(
1266 ty.is_sized(cx.tcx.at(DUMMY_SP), cx.param_env.without_caller_bounds()),
1273 fn ty_contains_field(ty: Ty<'_>, name: Symbol) -> bool {
1274 if let ty::Adt(adt, _) = *ty.kind() {
1275 adt.is_struct() && adt.all_fields().any(|f| f.name == name)
1281 #[expect(clippy::needless_pass_by_value, clippy::too_many_lines)]
1282 fn report<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, state: State, data: StateData) {
1284 State::DerefMethod {
1289 let mut app = Applicability::MachineApplicable;
1290 let (expr_str, expr_is_macro_call) = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app);
1291 let ty = cx.typeck_results().expr_ty(expr);
1292 let (_, ref_count) = peel_mid_ty_refs(ty);
1293 let deref_str = if ty_changed_count >= ref_count && ref_count != 0 {
1294 // a deref call changing &T -> &U requires two deref operators the first time
1295 // this occurs. One to remove the reference, a second to call the deref impl.
1296 "*".repeat(ty_changed_count + 1)
1298 "*".repeat(ty_changed_count)
1300 let addr_of_str = if ty_changed_count < ref_count {
1301 // Check if a reborrow from &mut T -> &T is required.
1302 if target_mut == Mutability::Not && matches!(ty.kind(), ty::Ref(_, _, Mutability::Mut)) {
1307 } else if target_mut == Mutability::Mut {
1313 let expr_str = if !expr_is_macro_call && is_final_ufcs && expr.precedence().order() < PREC_PREFIX {
1314 format!("({})", expr_str)
1316 expr_str.into_owned()
1321 EXPLICIT_DEREF_METHODS,
1324 Mutability::Not => "explicit `deref` method call",
1325 Mutability::Mut => "explicit `deref_mut` method call",
1328 format!("{}{}{}", addr_of_str, deref_str, expr_str),
1332 State::DerefedBorrow(state) => {
1333 let mut app = Applicability::MachineApplicable;
1334 let snip_expr = state.snip_expr.map_or(expr, |hir_id| cx.tcx.hir().expect_expr(hir_id));
1335 let (snip, snip_is_macro) = snippet_with_context(cx, snip_expr.span, data.span.ctxt(), "..", &mut app);
1336 span_lint_hir_and_then(cx, NEEDLESS_BORROW, data.hir_id, data.span, state.msg, |diag| {
1337 let calls_field = matches!(expr.kind, ExprKind::Field(..)) && matches!(data.position, Position::Callee);
1338 let sugg = if !snip_is_macro
1339 && !has_enclosing_paren(&snip)
1340 && (expr.precedence().order() < data.position.precedence() || calls_field)
1342 format!("({})", snip)
1346 diag.span_suggestion(data.span, "change this to", sugg, app);
1349 State::ExplicitDeref { mutability } => {
1353 | ExprKind::ConstBlock(_)
1355 | ExprKind::Loop(..)
1356 | ExprKind::Match(..)
1357 ) && matches!(data.position, Position::DerefStable(_, true))
1359 // Rustc bug: auto deref doesn't work on block expression when targeting sized types.
1363 let (prefix, precedence) = if let Some(mutability) = mutability
1364 && !cx.typeck_results().expr_ty(expr).is_ref()
1366 let prefix = match mutability {
1367 Mutability::Not => "&",
1368 Mutability::Mut => "&mut ",
1372 ("", data.position.precedence())
1374 span_lint_hir_and_then(
1376 EXPLICIT_AUTO_DEREF,
1379 "deref which would be done by auto-deref",
1381 let mut app = Applicability::MachineApplicable;
1382 let (snip, snip_is_macro) = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app);
1384 if !snip_is_macro && expr.precedence().order() < precedence && !has_enclosing_paren(&snip) {
1385 format!("{}({})", prefix, snip)
1387 format!("{}{}", prefix, snip)
1389 diag.span_suggestion(data.span, "try this", sugg, app);
1393 State::ExplicitDerefField { .. } => {
1397 | ExprKind::ConstBlock(_)
1399 | ExprKind::Loop(..)
1400 | ExprKind::Match(..)
1401 ) && matches!(data.position, Position::DerefStable(_, true))
1403 // Rustc bug: auto deref doesn't work on block expression when targeting sized types.
1407 span_lint_hir_and_then(
1409 EXPLICIT_AUTO_DEREF,
1412 "deref which would be done by auto-deref",
1414 let mut app = Applicability::MachineApplicable;
1415 let snip = snippet_with_context(cx, expr.span, data.span.ctxt(), "..", &mut app).0;
1416 diag.span_suggestion(data.span, "try this", snip.into_owned(), app);
1420 State::Borrow { .. } | State::Reborrow { .. } => (),
1424 impl Dereferencing {
1425 fn check_local_usage<'tcx>(&mut self, cx: &LateContext<'tcx>, e: &Expr<'tcx>, local: HirId) {
1426 if let Some(outer_pat) = self.ref_locals.get_mut(&local) {
1427 if let Some(pat) = outer_pat {
1428 // Check for auto-deref
1430 cx.typeck_results().expr_adjustments(e),
1433 kind: Adjust::Deref(_),
1437 kind: Adjust::Deref(_),
1443 match get_parent_expr(cx, e) {
1444 // Field accesses are the same no matter the number of references.
1446 kind: ExprKind::Field(..),
1451 kind: ExprKind::Unary(UnOp::Deref, _),
1453 }) if !span.from_expansion() => {
1454 // Remove explicit deref.
1455 let snip = snippet_with_context(cx, e.span, span.ctxt(), "..", &mut pat.app).0;
1456 pat.replacements.push((span, snip.into()));
1458 Some(parent) if !parent.span.from_expansion() => {
1459 // Double reference might be needed at this point.
1460 if parent.precedence().order() == PREC_POSTFIX {
1461 // Parentheses would be needed here, don't lint.
1464 pat.always_deref = false;
1465 let snip = snippet_with_context(cx, e.span, parent.span.ctxt(), "..", &mut pat.app).0;
1466 pat.replacements.push((e.span, format!("&{}", snip)));
1469 _ if !e.span.from_expansion() => {
1470 // Double reference might be needed at this point.
1471 pat.always_deref = false;
1472 let snip = snippet_with_applicability(cx, e.span, "..", &mut pat.app);
1473 pat.replacements.push((e.span, format!("&{}", snip)));
1475 // Edge case for macros. The span of the identifier will usually match the context of the
1476 // binding, but not if the identifier was created in a macro. e.g. `concat_idents` and proc
1478 _ => *outer_pat = None,