Add explicit_auto_deref lint

CHANGELOG.md

@@ -3400,6 +3400,7 @@ Released 2018-09-13
 [`expect_fun_call`]: https://rust-lang.github.io/rust-clippy/master/index.html#expect_fun_call
 [`expect_used`]: https://rust-lang.github.io/rust-clippy/master/index.html#expect_used
 [`expl_impl_clone_on_copy`]: https://rust-lang.github.io/rust-clippy/master/index.html#expl_impl_clone_on_copy
+[`explicit_auto_deref`]: https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref
 [`explicit_counter_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#explicit_counter_loop
 [`explicit_deref_methods`]: https://rust-lang.github.io/rust-clippy/master/index.html#explicit_deref_methods
 [`explicit_into_iter_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#explicit_into_iter_loop

clippy_lints/src/dereference.rs

@@ -1,18 +1,21 @@
 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_hir_and_then};
 use clippy_utils::source::{snippet_with_applicability, snippet_with_context};
 use clippy_utils::sugg::has_enclosing_paren;
-use clippy_utils::ty::peel_mid_ty_refs;
-use clippy_utils::{get_parent_expr, get_parent_node, is_lint_allowed, path_to_local};
+use clippy_utils::ty::{expr_sig, peel_mid_ty_refs, variant_of_res};
+use clippy_utils::{
+    get_parent_expr, get_parent_node, is_lint_allowed, path_to_local, peel_hir_ty_refs, walk_to_expr_usage,
+};
 use rustc_ast::util::parser::{PREC_POSTFIX, PREC_PREFIX};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_errors::Applicability;
 use rustc_hir::{
-    BindingAnnotation, Body, BodyId, BorrowKind, Destination, Expr, ExprKind, HirId, MatchSource, Mutability, Node,
-    Pat, PatKind, UnOp,
+    self as hir, BindingAnnotation, Body, BodyId, BorrowKind, Destination, Expr, ExprKind, FnRetTy, GenericArg, HirId,
+    ImplItem, ImplItemKind, Item, ItemKind, Local, MatchSource, Mutability, Node, Pat, PatKind, Path, QPath, TraitItem,
+    TraitItemKind, TyKind, UnOp,
 };
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
-use rustc_middle::ty::{self, Ty, TyCtxt, TypeckResults};
+use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeckResults};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
 use rustc_span::{symbol::sym, Span};
 
@@ -104,10 +107,34 @@ declare_clippy_lint! {
     "`ref` binding to a reference"
 }
 
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for dereferencing expressions which would be covered by auto-deref.
+    ///
+    /// ### Why is this bad?
+    /// This unnecessarily complicates the code.
+    ///
+    /// ### Example
+    /// ```rust
+    /// let x = String::new();
+    /// let y: &str = &*x;
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let x = String::new();
+    /// let y: &str = &x;
+    /// ```
+    #[clippy::version = "1.60.0"]
+    pub EXPLICIT_AUTO_DEREF,
+    complexity,
+    "dereferencing when the compiler would automatically dereference"
+}
+
 impl_lint_pass!(Dereferencing => [
     EXPLICIT_DEREF_METHODS,
     NEEDLESS_BORROW,
     REF_BINDING_TO_REFERENCE,
+    EXPLICIT_AUTO_DEREF,
 ]);
 
 #[derive(Default)]
@@ -152,6 +179,11 @@ enum State {
         required_precedence: i8,
         msg: &'static str,
     },
+    ExplicitDeref {
+        deref_span: Span,
+        deref_hir_id: HirId,
+    },
+    Borrow,
 }
 
 // A reference operation considered by this lint pass
@@ -305,6 +337,14 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing {
                                     hir_id: expr.hir_id,
                                 },
                             ));
+                        } else if is_stable_auto_deref_position(cx, expr) {
+                            self.state = Some((
+                                State::Borrow,
+                                StateData {
+                                    span: expr.span,
+                                    hir_id: expr.hir_id,
+                                },
+                            ));
                         }
                     },
                     _ => (),
@@ -354,6 +394,18 @@ impl<'tcx> LateLintPass<'tcx> for Dereferencing {
                     data,
                 ));
             },
+            (Some((State::Borrow, data)), RefOp::Deref) => {
+                self.state = Some((
+                    State::ExplicitDeref {
+                        deref_span: expr.span,
+                        deref_hir_id: expr.hir_id,
+                    },
+                    data,
+                ));
+            },
+            (state @ Some((State::ExplicitDeref { .. }, _)), RefOp::Deref) => {
+                self.state = state;
+            },
 
             (Some((state, data)), _) => report(cx, expr, state, data),
         }
@@ -596,8 +648,230 @@ fn find_adjustments<'tcx>(
     }
 }
 
+// Checks if the expression for the given id occurs in a position which auto dereferencing applies.
+// Note that the target type must not be inferred in a way that may cause auto-deref to select a
+// different type, nor may the position be the result of a macro expansion.
+//
+// e.g. the following should not linted
+// macro_rules! foo { ($e:expr) => { let x: &str = $e; }}
+// foo!(&*String::new());
+// fn foo<T>(_: &T) {}
+// foo(&*String::new())
+fn is_stable_auto_deref_position<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> bool {
+    walk_to_expr_usage(cx, e, |node, child_id| match node {
+        Node::Local(&Local { ty: Some(ty), .. }) => Some(is_binding_ty_auto_deref_stable(ty)),
+        Node::Item(&Item {
+            kind: ItemKind::Static(..) | ItemKind::Const(..),
+            ..
+        })
+        | Node::TraitItem(&TraitItem {
+            kind: TraitItemKind::Const(..),
+            ..
+        })
+        | Node::ImplItem(&ImplItem {
+            kind: ImplItemKind::Const(..),
+            ..
+        }) => Some(true),
+
+        Node::Item(&Item {
+            kind: ItemKind::Fn(..),
+            def_id,
+            ..
+        })
+        | Node::TraitItem(&TraitItem {
+            kind: TraitItemKind::Fn(..),
+            def_id,
+            ..
+        })
+        | Node::ImplItem(&ImplItem {
+            kind: ImplItemKind::Fn(..),
+            def_id,
+            ..
+        }) => {
+            let output = cx.tcx.fn_sig(def_id.to_def_id()).skip_binder().output();
+            Some(!(output.has_placeholders() || output.has_opaque_types()))
+        },
+
+        Node::Expr(e) => match e.kind {
+            ExprKind::Ret(_) => {
+                let output = cx
+                    .tcx
+                    .fn_sig(cx.tcx.hir().body_owner_def_id(cx.enclosing_body.unwrap()))
+                    .skip_binder()
+                    .output();
+                Some(!(output.has_placeholders() || output.has_opaque_types()))
+            },
+            ExprKind::Call(func, args) => Some(
+                args.iter()
+                    .position(|arg| arg.hir_id == child_id)
+                    .zip(expr_sig(cx, func))
+                    .and_then(|(i, sig)| sig.input_with_hir(i))
+                    .map_or(false, |(hir_ty, ty)| match hir_ty {
+                        // Type inference for closures can depend on how they're called. Only go by the explicit
+                        // types here.
+                        Some(ty) => is_binding_ty_auto_deref_stable(ty),
+                        None => is_param_auto_deref_stable(ty.skip_binder()),
+                    }),
+            ),
+            ExprKind::MethodCall(_, [_, args @ ..], _) => {
+                let id = cx.typeck_results().type_dependent_def_id(e.hir_id).unwrap();
+                Some(args.iter().position(|arg| arg.hir_id == child_id).map_or(false, |i| {
+                    let arg = cx.tcx.fn_sig(id).skip_binder().inputs()[i + 1];
+                    is_param_auto_deref_stable(arg)
+                }))
+            },
+            ExprKind::Struct(path, fields, _) => {
+                let variant = variant_of_res(cx, cx.qpath_res(path, e.hir_id));
+                Some(
+                    fields
+                        .iter()
+                        .find(|f| f.expr.hir_id == child_id)
+                        .zip(variant)
+                        .and_then(|(field, variant)| variant.fields.iter().find(|f| f.name == field.ident.name))
+                        .map_or(false, |field| is_param_auto_deref_stable(cx.tcx.type_of(field.did))),
+                )
+            },
+            _ => None,
+        },
+        _ => None,
+    })
+    .unwrap_or(false)
+}
+
+// Checks whether auto-dereferencing any type into a binding of the given type will definitely
+// produce the same result.
+//
+// e.g.
+// let x = Box::new(Box::new(0u32));
+// let y1: &Box<_> = x.deref();
+// let y2: &Box<_> = &x;
+//
+// Here `y1` and `y2` would resolve to different types, so the type `&Box<_>` is not stable when
+// switching to auto-dereferencing.
+fn is_binding_ty_auto_deref_stable(ty: &hir::Ty<'_>) -> bool {
+    let (ty, count) = peel_hir_ty_refs(ty);
+    if count != 1 {
+        return false;
+    }
+
+    match &ty.kind {
+        TyKind::Rptr(_, ty) => is_binding_ty_auto_deref_stable(ty.ty),
+        &TyKind::Path(
+            QPath::TypeRelative(_, path)
+            | QPath::Resolved(
+                _,
+                Path {
+                    segments: [.., path], ..
+                },
+            ),
+        ) => {
+            if let Some(args) = path.args {
+                args.args.iter().all(|arg| {
+                    if let GenericArg::Type(ty) = arg {
+                        !ty_contains_infer(ty)
+                    } else {
+                        true
+                    }
+                })
+            } else {
+                true
+            }
+        },
+        TyKind::Slice(_)
+        | TyKind::Array(..)
+        | TyKind::BareFn(_)
+        | TyKind::Never
+        | TyKind::Tup(_)
+        | TyKind::Ptr(_)
+        | TyKind::TraitObject(..)
+        | TyKind::Path(_) => true,
+        TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(..) | TyKind::Err => false,
+    }
+}
+
+// Checks whether a type is inferred at some point.
+// e.g. `_`, `Box<_>`, `[_]`
+fn ty_contains_infer(ty: &hir::Ty<'_>) -> bool {
+    match &ty.kind {
+        TyKind::Slice(ty) | TyKind::Array(ty, _) => ty_contains_infer(ty),
+        TyKind::Ptr(ty) | TyKind::Rptr(_, ty) => ty_contains_infer(ty.ty),
+        TyKind::Tup(tys) => tys.iter().any(ty_contains_infer),
+        TyKind::BareFn(ty) => {
+            if ty.decl.inputs.iter().any(ty_contains_infer) {
+                return true;
+            }
+            if let FnRetTy::Return(ty) = &ty.decl.output {
+                ty_contains_infer(ty)
+            } else {
+                false
+            }
+        },
+        &TyKind::Path(
+            QPath::TypeRelative(_, path)
+            | QPath::Resolved(
+                _,
+                Path {
+                    segments: [.., path], ..
+                },
+            ),
+        ) => {
+            if let Some(args) = path.args {
+                args.args.iter().any(|arg| {
+                    if let GenericArg::Type(ty) = arg {
+                        ty_contains_infer(ty)
+                    } else {
+                        false
+                    }
+                })
+            } else {
+                false
+            }
+        },
+        TyKind::Path(_) | TyKind::OpaqueDef(..) | TyKind::Infer | TyKind::Typeof(_) | TyKind::Err => true,
+        TyKind::Never | TyKind::TraitObject(..) => false,
+    }
+}
+
+// Checks whether a type is stable when switching to auto dereferencing,
+fn is_param_auto_deref_stable(ty: Ty<'_>) -> bool {
+    let (ty, count) = peel_mid_ty_refs(ty);
+    if count != 1 {
+        return false;
+    }
+
+    match ty.kind() {
+        ty::Bool
+        | ty::Char
+        | ty::Int(_)
+        | ty::Uint(_)
+        | ty::Float(_)
+        | ty::Foreign(_)
+        | ty::Str
+        | ty::Array(..)
+        | ty::Slice(..)
+        | ty::RawPtr(..)
+        | ty::FnDef(..)
+        | ty::FnPtr(_)
+        | ty::Closure(..)
+        | ty::Generator(..)
+        | ty::GeneratorWitness(..)
+        | ty::Never
+        | ty::Tuple(_)
+        | ty::Ref(..)
+        | ty::Projection(_) => true,
+        ty::Infer(_)
+        | ty::Error(_)
+        | ty::Param(_)
+        | ty::Bound(..)
+        | ty::Opaque(..)
+        | ty::Placeholder(_)
+        | ty::Dynamic(..) => false,
+        ty::Adt(..) => !(ty.has_placeholders() || ty.has_param_types_or_consts()),
+    }
+}
+
 #[expect(clippy::needless_pass_by_value)]
-fn report<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>, state: State, data: StateData) {
+fn report<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, state: State, data: StateData) {
     match state {
         State::DerefMethod {
             ty_changed_count,
@@ -663,6 +937,29 @@ fn report<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>, state: State, data: S
                 diag.span_suggestion(data.span, "change this to", sugg, app);
             });
         },
+        State::ExplicitDeref {
+            deref_span,
+            deref_hir_id,
+        } => {
+            let (span, hir_id) = if cx.typeck_results().expr_ty(expr).is_ref() {
+                (data.span, data.hir_id)
+            } else {
+                (deref_span, deref_hir_id)
+            };
+            span_lint_hir_and_then(
+                cx,
+                EXPLICIT_AUTO_DEREF,
+                hir_id,
+                span,
+                "deref which would be done by auto-deref",
+                |diag| {
+                    let mut app = Applicability::MachineApplicable;
+                    let snip = snippet_with_context(cx, expr.span, span.ctxt(), "..", &mut app).0;
+                    diag.span_suggestion(span, "try this", snip.into_owned(), app);
+                },
+            );
+        },
+        State::Borrow => (),
     }
 }
 

clippy_lints/src/lib.register_all.rs

@@ -44,6 +44,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(crate_in_macro_def::CRATE_IN_MACRO_DEF),
     LintId::of(default::FIELD_REASSIGN_WITH_DEFAULT),
     LintId::of(default_instead_of_iter_empty::DEFAULT_INSTEAD_OF_ITER_EMPTY),
+    LintId::of(dereference::EXPLICIT_AUTO_DEREF),
     LintId::of(dereference::NEEDLESS_BORROW),
     LintId::of(derivable_impls::DERIVABLE_IMPLS),
     LintId::of(derive::DERIVE_HASH_XOR_EQ),

clippy_lints/src/lib.register_complexity.rs

@@ -9,6 +9,7 @@ store.register_group(true, "clippy::complexity", Some("clippy_complexity"), vec!
     LintId::of(bytes_count_to_len::BYTES_COUNT_TO_LEN),
     LintId::of(casts::CHAR_LIT_AS_U8),
     LintId::of(casts::UNNECESSARY_CAST),
+    LintId::of(dereference::EXPLICIT_AUTO_DEREF),
     LintId::of(derivable_impls::DERIVABLE_IMPLS),
     LintId::of(double_comparison::DOUBLE_COMPARISONS),
     LintId::of(double_parens::DOUBLE_PARENS),

clippy_lints/src/lib.register_lints.rs

@@ -110,6 +110,7 @@ store.register_lints(&[
     default_instead_of_iter_empty::DEFAULT_INSTEAD_OF_ITER_EMPTY,
     default_numeric_fallback::DEFAULT_NUMERIC_FALLBACK,
     default_union_representation::DEFAULT_UNION_REPRESENTATION,
+    dereference::EXPLICIT_AUTO_DEREF,
     dereference::EXPLICIT_DEREF_METHODS,
     dereference::NEEDLESS_BORROW,
     dereference::REF_BINDING_TO_REFERENCE,

clippy_lints/src/matches/match_str_case_mismatch.rs

@@ -118,7 +118,7 @@ fn lint(cx: &LateContext<'_>, case_method: &CaseMethod, bad_case_span: Span, bad
         MATCH_STR_CASE_MISMATCH,
         bad_case_span,
         "this `match` arm has a differing case than its expression",
-        &*format!("consider changing the case of this arm to respect `{}`", method_str),
+        &format!("consider changing the case of this arm to respect `{}`", method_str),
         format!("\"{}\"", suggestion),
         Applicability::MachineApplicable,
     );

clippy_lints/src/non_expressive_names.rs

@@ -326,7 +326,7 @@ impl<'a, 'tcx> Visitor<'tcx> for SimilarNamesLocalVisitor<'a, 'tcx> {
         // add the pattern after the expression because the bindings aren't available
         // yet in the init
         // expression
-        SimilarNamesNameVisitor(self).visit_pat(&*local.pat);
+        SimilarNamesNameVisitor(self).visit_pat(&local.pat);
     }
     fn visit_block(&mut self, blk: &'tcx Block) {
         self.single_char_names.push(vec![]);

clippy_lints/src/ptr.rs

@@ -574,14 +574,13 @@ fn check_ptr_arg_usage<'tcx>(cx: &LateContext<'tcx>, body: &'tcx Body<'_>, args:
                 Some((Node::Expr(e), child_id)) => match e.kind {
                     ExprKind::Call(f, expr_args) => {
                         let i = expr_args.iter().position(|arg| arg.hir_id == child_id).unwrap_or(0);
-                        if expr_sig(self.cx, f)
-                            .map(|sig| sig.input(i).skip_binder().peel_refs())
-                            .map_or(true, |ty| match *ty.kind() {
+                        if expr_sig(self.cx, f).and_then(|sig| sig.input(i)).map_or(true, |ty| {
+                            match *ty.skip_binder().peel_refs().kind() {
                                 ty::Param(_) => true,
                                 ty::Adt(def, _) => def.did() == args.ty_did,
                                 _ => false,
-                            })
-                        {
+                            }
+                        }) {
                             // Passed to a function taking the non-dereferenced type.
                             set_skip_flag();
                         }

clippy_lints/src/redundant_static_lifetimes.rs

@@ -87,7 +87,7 @@ impl RedundantStaticLifetimes {
                         _ => {},
                     }
                 }
-                self.visit_type(&*borrow_type.ty, cx, reason);
+                self.visit_type(&borrow_type.ty, cx, reason);
             },
             _ => {},
         }

clippy_utils/src/lib.rs

@@ -2058,6 +2058,21 @@ pub fn peel_hir_expr_refs<'a>(expr: &'a Expr<'a>) -> (&'a Expr<'a>, usize) {
     (e, count)
 }
 
+/// Peels off all references on the type. Returns the underlying type and the number of references
+/// removed.
+pub fn peel_hir_ty_refs<'a>(mut ty: &'a hir::Ty<'a>) -> (&'a hir::Ty<'a>, usize) {
+    let mut count = 0;
+    loop {
+        match &ty.kind {
+            TyKind::Rptr(_, ref_ty) => {
+                ty = ref_ty.ty;
+                count += 1;
+            },
+            _ => break (ty, count),
+        }
+    }
+}
+
 /// Removes `AddrOf` operators (`&`) or deref operators (`*`), but only if a reference type is
 /// dereferenced. An overloaded deref such as `Vec` to slice would not be removed.
 pub fn peel_ref_operators<'hir>(cx: &LateContext<'_>, mut expr: &'hir Expr<'hir>) -> &'hir Expr<'hir> {
@@ -2110,7 +2125,7 @@ fn with_test_item_names<'tcx>(tcx: TyCtxt<'tcx>, module: LocalDefId, f: impl Fn(
                 }
             }
             names.sort_unstable();
-            f(&*entry.insert(names))
+            f(entry.insert(names))
         },
     }
 }
@@ -2168,6 +2183,57 @@ pub fn is_test_module_or_function(tcx: TyCtxt<'_>, item: &Item<'_>) -> bool {
             && item.ident.name.as_str().split('_').any(|a| a == "test" || a == "tests")
 }
 
+/// Walks the HIR tree from the given expression, up to the node where the value produced by the
+/// expression is consumed. Calls the function for every node encountered this way until it returns
+/// `Some`.
+///
+/// This allows walking through `if`, `match`, `break`, block expressions to find where the value
+/// produced by the expression is consumed.
+pub fn walk_to_expr_usage<'tcx, T>(
+    cx: &LateContext<'tcx>,
+    e: &Expr<'tcx>,
+    mut f: impl FnMut(Node<'tcx>, HirId) -> Option<T>,
+) -> Option<T> {
+    let map = cx.tcx.hir();
+    let mut iter = map.parent_iter(e.hir_id);
+    let mut child_id = e.hir_id;
+
+    while let Some((parent_id, parent)) = iter.next() {
+        if let Some(x) = f(parent, child_id) {
+            return Some(x);
+        }
+        let parent = match parent {
+            Node::Expr(e) => e,
+            Node::Block(Block { expr: Some(body), .. }) | Node::Arm(Arm { body, .. }) if body.hir_id == child_id => {
+                child_id = parent_id;
+                continue;
+            },
+            Node::Arm(a) if a.body.hir_id == child_id => {
+                child_id = parent_id;
+                continue;
+            },
+            _ => return None,
+        };
+        match parent.kind {
+            ExprKind::If(child, ..) | ExprKind::Match(child, ..) if child.hir_id != child_id => {
+                child_id = parent_id;
+                continue;
+            },
+            ExprKind::Break(Destination { target_id: Ok(id), .. }, _) => {
+                child_id = id;
+                iter = map.parent_iter(id);
+                continue;
+            },
+            ExprKind::Block(..) => {
+                child_id = parent_id;
+                continue;
+            },
+            _ => return None,
+        }
+    }
+    None
+}
+
 macro_rules! op_utils {
     ($($name:ident $assign:ident)*) => {
         /// Binary operation traits like `LangItem::Add`

clippy_utils/src/ty.rs

@@ -6,16 +6,16 @@ use core::ops::ControlFlow;
 use rustc_ast::ast::Mutability;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir as hir;
-use rustc_hir::def::{CtorKind, DefKind, Res};
+use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
 use rustc_hir::def_id::DefId;
-use rustc_hir::{Expr, LangItem, TyKind, Unsafety};
+use rustc_hir::{Expr, FnDecl, LangItem, TyKind, Unsafety};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::LateContext;
 use rustc_middle::mir::interpret::{ConstValue, Scalar};
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
 use rustc_middle::ty::{
-    self, AdtDef, Binder, BoundRegion, FnSig, IntTy, ParamEnv, Predicate, PredicateKind, ProjectionTy, Region,
-    RegionKind, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitor, UintTy, VariantDiscr,
+    self, AdtDef, Binder, BoundRegion, DefIdTree, FnSig, IntTy, ParamEnv, Predicate, PredicateKind, ProjectionTy,
+    Region, RegionKind, Ty, TyCtxt, TypeFoldable, TypeSuperFoldable, TypeVisitor, UintTy, VariantDef, VariantDiscr,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::{sym, Span, Symbol, DUMMY_SP};
@@ -502,16 +502,46 @@ pub fn all_predicates_of(tcx: TyCtxt<'_>, id: DefId) -> impl Iterator<Item = &(P
 #[derive(Clone, Copy)]
 pub enum ExprFnSig<'tcx> {
     Sig(Binder<'tcx, FnSig<'tcx>>),
-    Closure(Binder<'tcx, FnSig<'tcx>>),
+    Closure(Option<&'tcx FnDecl<'tcx>>, Binder<'tcx, FnSig<'tcx>>),
     Trait(Binder<'tcx, Ty<'tcx>>, Option<Binder<'tcx, Ty<'tcx>>>),
 }
 impl<'tcx> ExprFnSig<'tcx> {
-    /// Gets the argument type at the given offset.
-    pub fn input(self, i: usize) -> Binder<'tcx, Ty<'tcx>> {
+    /// Gets the argument type at the given offset. This will return `None` when the index is out of
+    /// bounds only for variadic functions, otherwise this will panic.
+    pub fn input(self, i: usize) -> Option<Binder<'tcx, Ty<'tcx>>> {
         match self {
-            Self::Sig(sig) => sig.input(i),
-            Self::Closure(sig) => sig.input(0).map_bound(|ty| ty.tuple_fields()[i]),
-            Self::Trait(inputs, _) => inputs.map_bound(|ty| ty.tuple_fields()[i]),
+            Self::Sig(sig) => {
+                if sig.c_variadic() {
+                    sig.inputs().map_bound(|inputs| inputs.get(i).copied()).transpose()
+                } else {
+                    Some(sig.input(i))
+                }
+            },
+            Self::Closure(_, sig) => Some(sig.input(0).map_bound(|ty| ty.tuple_fields()[i])),
+            Self::Trait(inputs, _) => Some(inputs.map_bound(|ty| ty.tuple_fields()[i])),
+        }
+    }
+
+    /// Gets the argument type at the given offset. For closures this will also get the type as
+    /// written. This will return `None` when the index is out of bounds only for variadic
+    /// functions, otherwise this will panic.
+    pub fn input_with_hir(self, i: usize) -> Option<(Option<&'tcx hir::Ty<'tcx>>, Binder<'tcx, Ty<'tcx>>)> {
+        match self {
+            Self::Sig(sig) => {
+                if sig.c_variadic() {
+                    sig.inputs()
+                        .map_bound(|inputs| inputs.get(i).copied())
+                        .transpose()
+                        .map(|arg| (None, arg))
+                } else {
+                    Some((None, sig.input(i)))
+                }
+            },
+            Self::Closure(decl, sig) => Some((
+                decl.and_then(|decl| decl.inputs.get(i)),
+                sig.input(0).map_bound(|ty| ty.tuple_fields()[i]),
+            )),
+            Self::Trait(inputs, _) => Some((None, inputs.map_bound(|ty| ty.tuple_fields()[i]))),
         }
     }
 
@@ -519,7 +549,7 @@ impl<'tcx> ExprFnSig<'tcx> {
     /// specified.
     pub fn output(self) -> Option<Binder<'tcx, Ty<'tcx>>> {
         match self {
-            Self::Sig(sig) | Self::Closure(sig) => Some(sig.output()),
+            Self::Sig(sig) | Self::Closure(_, sig) => Some(sig.output()),
             Self::Trait(_, output) => output,
         }
     }
@@ -536,7 +566,12 @@ pub fn expr_sig<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<ExprFnS
 
 fn ty_sig<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<ExprFnSig<'tcx>> {
     match *ty.kind() {
-        ty::Closure(_, subs) => Some(ExprFnSig::Closure(subs.as_closure().sig())),
+        ty::Closure(id, subs) => {
+            let decl = id
+                .as_local()
+                .and_then(|id| cx.tcx.hir().fn_decl_by_hir_id(cx.tcx.hir().local_def_id_to_hir_id(id)));
+            Some(ExprFnSig::Closure(decl, subs.as_closure().sig()))
+        },
         ty::FnDef(id, subs) => Some(ExprFnSig::Sig(cx.tcx.bound_fn_sig(id).subst(cx.tcx, subs))),
         ty::FnPtr(sig) => Some(ExprFnSig::Sig(sig)),
         ty::Dynamic(bounds, _) => {
@@ -739,3 +774,17 @@ pub fn for_each_top_level_late_bound_region<B>(
     }
     ty.visit_with(&mut V { index: 0, f })
 }
+
+pub fn variant_of_res<'tcx>(cx: &LateContext<'tcx>, res: Res) -> Option<&'tcx VariantDef> {
+    match res {
+        Res::Def(DefKind::Struct, id) => Some(cx.tcx.adt_def(id).non_enum_variant()),
+        Res::Def(DefKind::Variant, id) => Some(cx.tcx.adt_def(cx.tcx.parent(id)).variant_with_id(id)),
+        Res::Def(DefKind::Ctor(CtorOf::Struct, _), id) => Some(cx.tcx.adt_def(cx.tcx.parent(id)).non_enum_variant()),
+        Res::Def(DefKind::Ctor(CtorOf::Variant, _), id) => {
+            let var_id = cx.tcx.parent(id);
+            Some(cx.tcx.adt_def(cx.tcx.parent(var_id)).variant_with_id(var_id))
+        },
+        Res::SelfCtor(id) => Some(cx.tcx.type_of(id).ty_adt_def().unwrap().non_enum_variant()),
+        _ => None,
+    }
+}

tests/ui/borrow_deref_ref_unfixable.rs

@@ -1,4 +1,4 @@
-#![allow(dead_code, unused_variables)]
+#![allow(dead_code, unused_variables, clippy::explicit_auto_deref)]
 
 fn main() {}
 

tests/ui/explicit_auto_deref.fixed

@@ -0,0 +1,161 @@
+// run-rustfix
+
+#![warn(clippy::explicit_auto_deref)]
+#![allow(
+    dead_code,
+    unused_braces,
+    clippy::borrowed_box,
+    clippy::needless_borrow,
+    clippy::ptr_arg,
+    clippy::redundant_field_names,
+    clippy::too_many_arguments
+)]
+
+trait CallableStr {
+    type T: Fn(&str);
+    fn callable_str(&self) -> Self::T;
+}
+impl CallableStr for () {
+    type T = fn(&str);
+    fn callable_str(&self) -> Self::T {
+        fn f(_: &str) {}
+        f
+    }
+}
+impl CallableStr for i32 {
+    type T = <() as CallableStr>::T;
+    fn callable_str(&self) -> Self::T {
+        ().callable_str()
+    }
+}
+
+trait CallableT<U: ?Sized> {
+    type T: Fn(&U);
+    fn callable_t(&self) -> Self::T;
+}
+impl<U: ?Sized> CallableT<U> for () {
+    type T = fn(&U);
+    fn callable_t(&self) -> Self::T {
+        fn f<U: ?Sized>(_: &U) {}
+        f::<U>
+    }
+}
+impl<U: ?Sized> CallableT<U> for i32 {
+    type T = <() as CallableT<U>>::T;
+    fn callable_t(&self) -> Self::T {
+        ().callable_t()
+    }
+}
+
+fn f_str(_: &str) {}
+fn f_t<T>(_: T) {}
+fn f_ref_t<T: ?Sized>(_: &T) {}
+
+fn f_str_t<T>(_: &str, _: T) {}
+
+fn f_box_t<T>(_: &Box<T>) {}
+
+fn main() {
+    let s = String::new();
+
+    let _: &str = &s;
+    let _ = &*s; // Don't lint. Inferred type would change.
+    let _: &_ = &*s; // Don't lint. Inferred type would change.
+
+    f_str(&s);
+    f_t(&*s); // Don't lint. Inferred type would change.
+    f_ref_t(&*s); // Don't lint. Inferred type would change.
+
+    f_str_t(&s, &*s); // Don't lint second param.
+
+    let b = Box::new(Box::new(Box::new(5)));
+    let _: &Box<i32> = &b;
+    let _: &Box<_> = &**b; // Don't lint. Inferred type would change.
+
+    f_box_t(&**b); // Don't lint. Inferred type would change.
+
+    let c = |_x: &str| ();
+    c(&s);
+
+    let c = |_x| ();
+    c(&*s); // Don't lint. Inferred type would change.
+
+    fn _f(x: &String) -> &str {
+        x
+    }
+
+    fn _f1(x: &String) -> &str {
+        { x }
+    }
+
+    fn _f2(x: &String) -> &str {
+        { x }
+    }
+
+    fn _f3(x: &Box<Box<Box<i32>>>) -> &Box<i32> {
+        x
+    }
+
+    fn _f4(
+        x: String,
+        f1: impl Fn(&str),
+        f2: &dyn Fn(&str),
+        f3: fn(&str),
+        f4: impl CallableStr,
+        f5: <() as CallableStr>::T,
+        f6: <i32 as CallableStr>::T,
+        f7: &dyn CallableStr<T = fn(&str)>,
+        f8: impl CallableT<str>,
+        f9: <() as CallableT<str>>::T,
+        f10: <i32 as CallableT<str>>::T,
+        f11: &dyn CallableT<str, T = fn(&str)>,
+    ) {
+        f1(&x);
+        f2(&x);
+        f3(&x);
+        f4.callable_str()(&x);
+        f5(&x);
+        f6(&x);
+        f7.callable_str()(&x);
+        f8.callable_t()(&x);
+        f9(&x);
+        f10(&x);
+        f11.callable_t()(&x);
+    }
+
+    struct S1<'a>(&'a str);
+    let _ = S1(&s);
+
+    struct S2<'a> {
+        s: &'a str,
+    }
+    let _ = S2 { s: &s };
+
+    struct S3<'a, T: ?Sized>(&'a T);
+    let _ = S3(&*s); // Don't lint. Inferred type would change.
+
+    struct S4<'a, T: ?Sized> {
+        s: &'a T,
+    }
+    let _ = S4 { s: &*s }; // Don't lint. Inferred type would change.
+
+    enum E1<'a> {
+        S1(&'a str),
+        S2 { s: &'a str },
+    }
+    impl<'a> E1<'a> {
+        fn m1(s: &'a String) {
+            let _ = Self::S1(s);
+            let _ = Self::S2 { s: s };
+        }
+    }
+    let _ = E1::S1(&s);
+    let _ = E1::S2 { s: &s };
+
+    enum E2<'a, T: ?Sized> {
+        S1(&'a T),
+        S2 { s: &'a T },
+    }
+    let _ = E2::S1(&*s); // Don't lint. Inferred type would change.
+    let _ = E2::S2 { s: &*s }; // Don't lint. Inferred type would change.
+}

tests/ui/explicit_auto_deref.rs

@@ -0,0 +1,161 @@
+// run-rustfix
+
+#![warn(clippy::explicit_auto_deref)]
+#![allow(
+    dead_code,
+    unused_braces,
+    clippy::borrowed_box,
+    clippy::needless_borrow,
+    clippy::ptr_arg,
+    clippy::redundant_field_names,
+    clippy::too_many_arguments
+)]
+
+trait CallableStr {
+    type T: Fn(&str);
+    fn callable_str(&self) -> Self::T;
+}
+impl CallableStr for () {
+    type T = fn(&str);
+    fn callable_str(&self) -> Self::T {
+        fn f(_: &str) {}
+        f
+    }
+}
+impl CallableStr for i32 {
+    type T = <() as CallableStr>::T;
+    fn callable_str(&self) -> Self::T {
+        ().callable_str()
+    }
+}
+
+trait CallableT<U: ?Sized> {
+    type T: Fn(&U);
+    fn callable_t(&self) -> Self::T;
+}
+impl<U: ?Sized> CallableT<U> for () {
+    type T = fn(&U);
+    fn callable_t(&self) -> Self::T {
+        fn f<U: ?Sized>(_: &U) {}
+        f::<U>
+    }
+}
+impl<U: ?Sized> CallableT<U> for i32 {
+    type T = <() as CallableT<U>>::T;
+    fn callable_t(&self) -> Self::T {
+        ().callable_t()
+    }
+}
+
+fn f_str(_: &str) {}
+fn f_t<T>(_: T) {}
+fn f_ref_t<T: ?Sized>(_: &T) {}
+
+fn f_str_t<T>(_: &str, _: T) {}
+
+fn f_box_t<T>(_: &Box<T>) {}
+
+fn main() {
+    let s = String::new();
+
+    let _: &str = &*s;
+    let _ = &*s; // Don't lint. Inferred type would change.
+    let _: &_ = &*s; // Don't lint. Inferred type would change.
+
+    f_str(&*s);
+    f_t(&*s); // Don't lint. Inferred type would change.
+    f_ref_t(&*s); // Don't lint. Inferred type would change.
+
+    f_str_t(&*s, &*s); // Don't lint second param.
+
+    let b = Box::new(Box::new(Box::new(5)));
+    let _: &Box<i32> = &**b;
+    let _: &Box<_> = &**b; // Don't lint. Inferred type would change.
+
+    f_box_t(&**b); // Don't lint. Inferred type would change.
+
+    let c = |_x: &str| ();
+    c(&*s);
+
+    let c = |_x| ();
+    c(&*s); // Don't lint. Inferred type would change.
+
+    fn _f(x: &String) -> &str {
+        &**x
+    }
+
+    fn _f1(x: &String) -> &str {
+        { &**x }
+    }
+
+    fn _f2(x: &String) -> &str {
+        &**{ x }
+    }
+
+    fn _f3(x: &Box<Box<Box<i32>>>) -> &Box<i32> {
+        &***x
+    }
+
+    fn _f4(
+        x: String,
+        f1: impl Fn(&str),
+        f2: &dyn Fn(&str),
+        f3: fn(&str),
+        f4: impl CallableStr,
+        f5: <() as CallableStr>::T,
+        f6: <i32 as CallableStr>::T,
+        f7: &dyn CallableStr<T = fn(&str)>,
+        f8: impl CallableT<str>,
+        f9: <() as CallableT<str>>::T,
+        f10: <i32 as CallableT<str>>::T,
+        f11: &dyn CallableT<str, T = fn(&str)>,
+    ) {
+        f1(&*x);
+        f2(&*x);
+        f3(&*x);
+        f4.callable_str()(&*x);
+        f5(&*x);
+        f6(&*x);
+        f7.callable_str()(&*x);
+        f8.callable_t()(&*x);
+        f9(&*x);
+        f10(&*x);
+        f11.callable_t()(&*x);
+    }
+
+    struct S1<'a>(&'a str);
+    let _ = S1(&*s);
+
+    struct S2<'a> {
+        s: &'a str,
+    }
+    let _ = S2 { s: &*s };
+
+    struct S3<'a, T: ?Sized>(&'a T);
+    let _ = S3(&*s); // Don't lint. Inferred type would change.
+
+    struct S4<'a, T: ?Sized> {
+        s: &'a T,
+    }
+    let _ = S4 { s: &*s }; // Don't lint. Inferred type would change.
+
+    enum E1<'a> {
+        S1(&'a str),
+        S2 { s: &'a str },
+    }
+    impl<'a> E1<'a> {
+        fn m1(s: &'a String) {
+            let _ = Self::S1(&**s);
+            let _ = Self::S2 { s: &**s };
+        }
+    }
+    let _ = E1::S1(&*s);
+    let _ = E1::S2 { s: &*s };
+
+    enum E2<'a, T: ?Sized> {
+        S1(&'a T),
+        S2 { s: &'a T },
+    }
+    let _ = E2::S1(&*s); // Don't lint. Inferred type would change.
+    let _ = E2::S2 { s: &*s }; // Don't lint. Inferred type would change.
+}

tests/ui/explicit_auto_deref.stderr

@@ -0,0 +1,160 @@
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:61:20
+   |
+LL |     let _: &str = &*s;
+   |                    ^^ help: try this: `s`
+   |
+   = note: `-D clippy::explicit-auto-deref` implied by `-D warnings`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:65:12
+   |
+LL |     f_str(&*s);
+   |            ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:69:14
+   |
+LL |     f_str_t(&*s, &*s); // Don't lint second param.
+   |              ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:72:25
+   |
+LL |     let _: &Box<i32> = &**b;
+   |                         ^^^ help: try this: `b`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:78:8
+   |
+LL |     c(&*s);
+   |        ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:84:9
+   |
+LL |         &**x
+   |         ^^^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:88:11
+   |
+LL |         { &**x }
+   |           ^^^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:92:9
+   |
+LL |         &**{ x }
+   |         ^^^^^^^^ help: try this: `{ x }`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:96:9
+   |
+LL |         &***x
+   |         ^^^^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:113:13
+   |
+LL |         f1(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:114:13
+   |
+LL |         f2(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:115:13
+   |
+LL |         f3(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:116:28
+   |
+LL |         f4.callable_str()(&*x);
+   |                            ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:117:13
+   |
+LL |         f5(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:118:13
+   |
+LL |         f6(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:119:28
+   |
+LL |         f7.callable_str()(&*x);
+   |                            ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:120:26
+   |
+LL |         f8.callable_t()(&*x);
+   |                          ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:121:13
+   |
+LL |         f9(&*x);
+   |             ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:122:14
+   |
+LL |         f10(&*x);
+   |              ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:123:27
+   |
+LL |         f11.callable_t()(&*x);
+   |                           ^^ help: try this: `x`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:127:17
+   |
+LL |     let _ = S1(&*s);
+   |                 ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:132:22
+   |
+LL |     let _ = S2 { s: &*s };
+   |                      ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:148:30
+   |
+LL |             let _ = Self::S1(&**s);
+   |                              ^^^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:149:35
+   |
+LL |             let _ = Self::S2 { s: &**s };
+   |                                   ^^^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:152:21
+   |
+LL |     let _ = E1::S1(&*s);
+   |                     ^^ help: try this: `s`
+
+error: deref which would be done by auto-deref
+  --> $DIR/explicit_auto_deref.rs:153:26
+   |
+LL |     let _ = E1::S2 { s: &*s };
+   |                          ^^ help: try this: `s`
+
+error: aborting due to 26 previous errors
+

tests/ui/explicit_deref_methods.fixed

@@ -4,7 +4,8 @@
     unused_variables,
     clippy::clone_double_ref,
     clippy::needless_borrow,
-    clippy::borrow_deref_ref
+    clippy::borrow_deref_ref,
+    clippy::explicit_auto_deref
 )]
 #![warn(clippy::explicit_deref_methods)]
 

tests/ui/explicit_deref_methods.rs

@@ -4,7 +4,8 @@
     unused_variables,
     clippy::clone_double_ref,
     clippy::needless_borrow,
-    clippy::borrow_deref_ref
+    clippy::borrow_deref_ref,
+    clippy::explicit_auto_deref
 )]
 #![warn(clippy::explicit_deref_methods)]
 

tests/ui/explicit_deref_methods.stderr

@@ -1,5 +1,5 @@
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:35:19
+  --> $DIR/explicit_deref_methods.rs:36:19
    |
 LL |     let b: &str = a.deref();
    |                   ^^^^^^^^^ help: try this: `&*a`
@@ -7,67 +7,67 @@ LL |     let b: &str = a.deref();
    = note: `-D clippy::explicit-deref-methods` implied by `-D warnings`
 
 error: explicit `deref_mut` method call
-  --> $DIR/explicit_deref_methods.rs:37:23
+  --> $DIR/explicit_deref_methods.rs:38:23
    |
 LL |     let b: &mut str = a.deref_mut();
    |                       ^^^^^^^^^^^^^ help: try this: `&mut **a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:40:39
+  --> $DIR/explicit_deref_methods.rs:41:39
    |
 LL |     let b: String = format!("{}, {}", a.deref(), a.deref());
    |                                       ^^^^^^^^^ help: try this: `&*a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:40:50
+  --> $DIR/explicit_deref_methods.rs:41:50
    |
 LL |     let b: String = format!("{}, {}", a.deref(), a.deref());
    |                                                  ^^^^^^^^^ help: try this: `&*a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:42:20
+  --> $DIR/explicit_deref_methods.rs:43:20
    |
 LL |     println!("{}", a.deref());
    |                    ^^^^^^^^^ help: try this: `&*a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:45:11
+  --> $DIR/explicit_deref_methods.rs:46:11
    |
 LL |     match a.deref() {
    |           ^^^^^^^^^ help: try this: `&*a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:49:28
+  --> $DIR/explicit_deref_methods.rs:50:28
    |
 LL |     let b: String = concat(a.deref());
    |                            ^^^^^^^^^ help: try this: `&*a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:51:13
+  --> $DIR/explicit_deref_methods.rs:52:13
    |
 LL |     let b = just_return(a).deref();
    |             ^^^^^^^^^^^^^^^^^^^^^^ help: try this: `just_return(a)`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:53:28
+  --> $DIR/explicit_deref_methods.rs:54:28
    |
 LL |     let b: String = concat(just_return(a).deref());
    |                            ^^^^^^^^^^^^^^^^^^^^^^ help: try this: `just_return(a)`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:55:19
+  --> $DIR/explicit_deref_methods.rs:56:19
    |
 LL |     let b: &str = a.deref().deref();
    |                   ^^^^^^^^^^^^^^^^^ help: try this: `&**a`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:58:13
+  --> $DIR/explicit_deref_methods.rs:59:13
    |
 LL |     let b = opt_a.unwrap().deref();
    |             ^^^^^^^^^^^^^^^^^^^^^^ help: try this: `&*opt_a.unwrap()`
 
 error: explicit `deref` method call
-  --> $DIR/explicit_deref_methods.rs:84:31
+  --> $DIR/explicit_deref_methods.rs:85:31
    |
 LL |     let b: &str = expr_deref!(a.deref());
    |                               ^^^^^^^^^ help: try this: `&*a`

tests/ui/useless_asref.fixed

@@ -1,6 +1,7 @@
 // run-rustfix
 
 #![deny(clippy::useless_asref)]
+#![allow(clippy::explicit_auto_deref)]
 
 use std::fmt::Debug;
 

tests/ui/useless_asref.rs

@@ -1,6 +1,7 @@
 // run-rustfix
 
 #![deny(clippy::useless_asref)]
+#![allow(clippy::explicit_auto_deref)]
 
 use std::fmt::Debug;
 

tests/ui/useless_asref.stderr

@@ -1,5 +1,5 @@
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:43:18
+  --> $DIR/useless_asref.rs:44:18
    |
 LL |         foo_rstr(rstr.as_ref());
    |                  ^^^^^^^^^^^^^ help: try this: `rstr`
@@ -11,61 +11,61 @@ LL | #![deny(clippy::useless_asref)]
    |         ^^^^^^^^^^^^^^^^^^^^^
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:45:20
+  --> $DIR/useless_asref.rs:46:20
    |
 LL |         foo_rslice(rslice.as_ref());
    |                    ^^^^^^^^^^^^^^^ help: try this: `rslice`
 
 error: this call to `as_mut` does nothing
-  --> $DIR/useless_asref.rs:49:21
+  --> $DIR/useless_asref.rs:50:21
    |
 LL |         foo_mrslice(mrslice.as_mut());
    |                     ^^^^^^^^^^^^^^^^ help: try this: `mrslice`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:51:20
+  --> $DIR/useless_asref.rs:52:20
    |
 LL |         foo_rslice(mrslice.as_ref());
    |                    ^^^^^^^^^^^^^^^^ help: try this: `mrslice`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:58:20
+  --> $DIR/useless_asref.rs:59:20
    |
 LL |         foo_rslice(rrrrrslice.as_ref());
    |                    ^^^^^^^^^^^^^^^^^^^ help: try this: `rrrrrslice`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:60:18
+  --> $DIR/useless_asref.rs:61:18
    |
 LL |         foo_rstr(rrrrrstr.as_ref());
    |                  ^^^^^^^^^^^^^^^^^ help: try this: `rrrrrstr`
 
 error: this call to `as_mut` does nothing
-  --> $DIR/useless_asref.rs:65:21
+  --> $DIR/useless_asref.rs:66:21
    |
 LL |         foo_mrslice(mrrrrrslice.as_mut());
    |                     ^^^^^^^^^^^^^^^^^^^^ help: try this: `mrrrrrslice`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:67:20
+  --> $DIR/useless_asref.rs:68:20
    |
 LL |         foo_rslice(mrrrrrslice.as_ref());
    |                    ^^^^^^^^^^^^^^^^^^^^ help: try this: `mrrrrrslice`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:71:16
+  --> $DIR/useless_asref.rs:72:16
    |
 LL |     foo_rrrrmr((&&&&MoreRef).as_ref());
    |                ^^^^^^^^^^^^^^^^^^^^^^ help: try this: `(&&&&MoreRef)`
 
 error: this call to `as_mut` does nothing
-  --> $DIR/useless_asref.rs:121:13
+  --> $DIR/useless_asref.rs:122:13
    |
 LL |     foo_mrt(mrt.as_mut());
    |             ^^^^^^^^^^^^ help: try this: `mrt`
 
 error: this call to `as_ref` does nothing
-  --> $DIR/useless_asref.rs:123:12
+  --> $DIR/useless_asref.rs:124:12
    |
 LL |     foo_rt(mrt.as_ref());
    |            ^^^^^^^^^^^^ help: try this: `mrt`