Auto merge of #6034 - rail-rain:fix_fp_in_indexing_slicing, r=flip1995

Treat refs to arrays the same as owned arrays in `indexing_slicing` and `out_of_bounds_indexing`

Fixes #6021

...and remove `walk_ptrs_ty` in favour of `peel_refs`, which came in 2019.

---

changelog: Fix a false positive in `indexing_slicing` and `out_of_bounds_indexing` where references to arrays weren't treated as arrays.

clippy_lints/src/bytecount.rs

@@ -1,6 +1,5 @@
 use crate::utils::{
-    contains_name, get_pat_name, match_type, paths, single_segment_path, snippet_with_applicability,
+    contains_name, get_pat_name, match_type, paths, single_segment_path, snippet_with_applicability, span_lint_and_sugg,
-    span_lint_and_sugg, walk_ptrs_ty,
 };
 use if_chain::if_chain;
 use rustc_ast::ast::UintTy;
@@ -53,7 +52,7 @@ impl<'tcx> LateLintPass<'tcx> for ByteCount {
                     if let ExprKind::Binary(ref op, ref l, ref r) = body.value.kind;
                     if op.node == BinOpKind::Eq;
                     if match_type(cx,
-                               walk_ptrs_ty(cx.typeck_results().expr_ty(&filter_args[0])),
+                               cx.typeck_results().expr_ty(&filter_args[0]).peel_refs(),
                                &paths::SLICE_ITER);
                     then {
                         let needle = match get_path_name(l) {
@@ -63,7 +62,7 @@ impl<'tcx> LateLintPass<'tcx> for ByteCount {
                                 _ => { return; }
                             }
                         };
-                        if ty::Uint(UintTy::U8) != *walk_ptrs_ty(cx.typeck_results().expr_ty(needle)).kind() {
+                        if ty::Uint(UintTy::U8) != *cx.typeck_results().expr_ty(needle).peel_refs().kind() {
                             return;
                         }
                         let haystack = if let ExprKind::MethodCall(ref path, _, ref args, _) =

clippy_lints/src/duration_subsec.rs

@@ -7,7 +7,7 @@ use rustc_span::source_map::Spanned;
 
 use crate::consts::{constant, Constant};
 use crate::utils::paths;
-use crate::utils::{match_type, snippet_with_applicability, span_lint_and_sugg, walk_ptrs_ty};
+use crate::utils::{match_type, snippet_with_applicability, span_lint_and_sugg};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for calculation of subsecond microseconds or milliseconds
@@ -43,7 +43,7 @@ impl<'tcx> LateLintPass<'tcx> for DurationSubsec {
         if_chain! {
             if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, ref left, ref right) = expr.kind;
             if let ExprKind::MethodCall(ref method_path, _ , ref args, _) = left.kind;
-            if match_type(cx, walk_ptrs_ty(cx.typeck_results().expr_ty(&args[0])), &paths::DURATION);
+            if match_type(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), &paths::DURATION);
             if let Some((Constant::Int(divisor), _)) = constant(cx, cx.typeck_results(), right);
             then {
                 let suggested_fn = match (method_path.ident.as_str().as_ref(), divisor) {

clippy_lints/src/entry.rs

@@ -1,6 +1,6 @@
 use crate::utils::SpanlessEq;
 use crate::utils::{get_item_name, higher, is_type_diagnostic_item, match_type, paths, snippet, snippet_opt};
-use crate::utils::{snippet_with_applicability, span_lint_and_then, walk_ptrs_ty};
+use crate::utils::{snippet_with_applicability, span_lint_and_then};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
@@ -106,7 +106,7 @@ fn check_cond<'a>(cx: &LateContext<'_>, check: &'a Expr<'a>) -> Option<(&'static
         if let ExprKind::AddrOf(BorrowKind::Ref, _, ref key) = params[1].kind;
         then {
             let map = &params[0];
-            let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(map));
+            let obj_ty = cx.typeck_results().expr_ty(map).peel_refs();
 
             return if match_type(cx, obj_ty, &paths::BTREEMAP) {
                 Some(("BTreeMap", map, key))

clippy_lints/src/fallible_impl_from.rs

@@ -1,7 +1,5 @@
 use crate::utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT};
-use crate::utils::{
+use crate::utils::{is_expn_of, is_type_diagnostic_item, match_def_path, method_chain_args, span_lint_and_then};
-    is_expn_of, is_type_diagnostic_item, match_def_path, method_chain_args, span_lint_and_then, walk_ptrs_ty,
-};
 use if_chain::if_chain;
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
@@ -96,7 +94,7 @@ fn lint_impl_body<'tcx>(cx: &LateContext<'tcx>, impl_span: Span, impl_items: &[h
 
             // check for `unwrap`
             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
-                let reciever_ty = walk_ptrs_ty(self.typeck_results.expr_ty(&arglists[0][0]));
+                let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
                 if is_type_diagnostic_item(self.lcx, reciever_ty, sym!(option_type))
                     || is_type_diagnostic_item(self.lcx, reciever_ty, sym!(result_type))
                 {

clippy_lints/src/format.rs

@@ -1,7 +1,7 @@
 use crate::utils::paths;
 use crate::utils::{
     is_expn_of, is_type_diagnostic_item, last_path_segment, match_def_path, match_function_call, snippet,
-    span_lint_and_then, walk_ptrs_ty,
+    span_lint_and_then,
 };
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
@@ -90,7 +90,7 @@ fn on_argumentv1_new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, arms: &
         if let PatKind::Tuple(ref pats, None) = arms[0].pat.kind;
         if pats.len() == 1;
         then {
-            let ty = walk_ptrs_ty(cx.typeck_results().pat_ty(&pats[0]));
+            let ty = cx.typeck_results().pat_ty(&pats[0]).peel_refs();
             if *ty.kind() != rustc_middle::ty::Str && !is_type_diagnostic_item(cx, ty, sym!(string_type)) {
                 return None;
             }

clippy_lints/src/indexing_slicing.rs

@@ -88,7 +88,7 @@ declare_lint_pass!(IndexingSlicing => [INDEXING_SLICING, OUT_OF_BOUNDS_INDEXING]
 impl<'tcx> LateLintPass<'tcx> for IndexingSlicing {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::Index(ref array, ref index) = &expr.kind {
-            let ty = cx.typeck_results().expr_ty(array);
+            let ty = cx.typeck_results().expr_ty(array).peel_refs();
             if let Some(range) = higher::range(index) {
                 // Ranged indexes, i.e., &x[n..m], &x[n..], &x[..n] and &x[..]
                 if let ty::Array(_, s) = ty.kind() {

clippy_lints/src/inherent_to_string.rs

@@ -5,7 +5,7 @@ use rustc_session::{declare_lint_pass, declare_tool_lint};
 
 use crate::utils::{
     get_trait_def_id, implements_trait, is_type_diagnostic_item, paths, return_ty, span_lint_and_help,
-    trait_ref_of_method, walk_ptrs_ty,
+    trait_ref_of_method,
 };
 
 declare_clippy_lint! {
@@ -125,7 +125,7 @@ fn show_lint(cx: &LateContext<'_>, item: &ImplItem<'_>) {
     // Get the real type of 'self'
     let fn_def_id = cx.tcx.hir().local_def_id(item.hir_id);
     let self_type = cx.tcx.fn_sig(fn_def_id).input(0);
-    let self_type = walk_ptrs_ty(self_type.skip_binder());
+    let self_type = self_type.skip_binder().peel_refs();
 
     // Emit either a warning or an error
     if implements_trait(cx, self_type, display_trait_id, &[]) {

clippy_lints/src/len_zero.rs

@@ -1,4 +1,4 @@
-use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg, walk_ptrs_ty};
+use crate::utils::{get_item_name, snippet_with_applicability, span_lint, span_lint_and_sugg};
 use rustc_ast::ast::LitKind;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Applicability;
@@ -285,7 +285,7 @@ fn has_is_empty(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
         })
     }
 
-    let ty = &walk_ptrs_ty(cx.typeck_results().expr_ty(expr));
+    let ty = &cx.typeck_results().expr_ty(expr).peel_refs();
     match ty.kind() {
         ty::Dynamic(ref tt, ..) => tt.principal().map_or(false, |principal| {
             cx.tcx

clippy_lints/src/match_on_vec_items.rs

@@ -1,4 +1,3 @@
-use crate::utils::walk_ptrs_ty;
 use crate::utils::{is_type_diagnostic_item, is_type_lang_item, snippet, span_lint_and_sugg};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
@@ -90,12 +89,12 @@ fn is_vec_indexing<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Opti
 
 fn is_vector(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     let ty = cx.typeck_results().expr_ty(expr);
-    let ty = walk_ptrs_ty(ty);
+    let ty = ty.peel_refs();
     is_type_diagnostic_item(cx, ty, sym!(vec_type))
 }
 
 fn is_full_range(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     let ty = cx.typeck_results().expr_ty(expr);
-    let ty = walk_ptrs_ty(ty);
+    let ty = ty.peel_refs();
     is_type_lang_item(cx, ty, LangItem::RangeFull)
 }

clippy_lints/src/matches.rs

@@ -6,7 +6,7 @@ use crate::utils::{
     expr_block, get_arg_name, get_parent_expr, in_macro, indent_of, is_allowed, is_expn_of, is_refutable,
     is_type_diagnostic_item, is_wild, match_qpath, match_type, match_var, multispan_sugg, remove_blocks, snippet,
     snippet_block, snippet_with_applicability, span_lint_and_help, span_lint_and_note, span_lint_and_sugg,
-    span_lint_and_then, walk_ptrs_ty,
+    span_lint_and_then,
 };
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
@@ -794,7 +794,7 @@ fn check_overlapping_arms<'tcx>(cx: &LateContext<'tcx>, ex: &'tcx Expr<'_>, arms
 }
 
 fn check_wild_err_arm(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
-    let ex_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(ex));
+    let ex_ty = cx.typeck_results().expr_ty(ex).peel_refs();
     if is_type_diagnostic_item(cx, ex_ty, sym!(result_type)) {
         for arm in arms {
             if let PatKind::TupleStruct(ref path, ref inner, _) = arm.pat.kind {

clippy_lints/src/methods/mod.rs

@@ -32,8 +32,8 @@ use crate::utils::{
     is_copy, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment, match_def_path, match_qpath,
     match_trait_method, match_type, match_var, method_calls, method_chain_args, paths, remove_blocks, return_ty,
     single_segment_path, snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint,
-    span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then, sugg, walk_ptrs_ty,
+    span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then, sugg, walk_ptrs_ty_depth,
-    walk_ptrs_ty_depth, SpanlessEq,
+    SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -1774,7 +1774,7 @@ fn lint_or_fun_call<'tcx>(
     ) {
         if let hir::ExprKind::MethodCall(ref path, _, ref args, _) = &arg.kind {
             if path.ident.as_str() == "len" {
-                let ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&args[0]));
+                let ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
 
                 match ty.kind() {
                     ty::Slice(_) | ty::Array(_, _) => return,
@@ -1881,7 +1881,7 @@ fn lint_expect_fun_call(
                         && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
                         && {
                             let arg_type = cx.typeck_results().expr_ty(&call_args[0]);
-                            let base_type = walk_ptrs_ty(arg_type);
+                            let base_type = arg_type.peel_refs();
                             *base_type.kind() == ty::Str || is_type_diagnostic_item(cx, base_type, sym!(string_type))
                         }
                     {
@@ -2142,7 +2142,7 @@ fn lint_clone_on_copy(cx: &LateContext<'_>, expr: &hir::Expr<'_>, arg: &hir::Exp
 }
 
 fn lint_clone_on_ref_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>, arg: &hir::Expr<'_>) {
-    let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(arg));
+    let obj_ty = cx.typeck_results().expr_ty(arg).peel_refs();
 
     if let ty::Adt(_, subst) = obj_ty.kind() {
         let caller_type = if is_type_diagnostic_item(cx, obj_ty, sym::Rc) {
@@ -2173,7 +2173,7 @@ fn lint_string_extend(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::E
     let arg = &args[1];
     if let Some(arglists) = method_chain_args(arg, &["chars"]) {
         let target = &arglists[0][0];
-        let self_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(target));
+        let self_ty = cx.typeck_results().expr_ty(target).peel_refs();
         let ref_str = if *self_ty.kind() == ty::Str {
             ""
         } else if is_type_diagnostic_item(cx, self_ty, sym!(string_type)) {
@@ -2201,7 +2201,7 @@ fn lint_string_extend(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::E
 }
 
 fn lint_extend(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
-    let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&args[0]));
+    let obj_ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
     if is_type_diagnostic_item(cx, obj_ty, sym!(string_type)) {
         lint_string_extend(cx, expr, args);
     }
@@ -2384,7 +2384,7 @@ fn lint_iter_next<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, iter_
         }
     } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(caller_expr), sym!(vec_type))
         || matches!(
-            &walk_ptrs_ty(cx.typeck_results().expr_ty(caller_expr)).kind(),
+            &cx.typeck_results().expr_ty(caller_expr).peel_refs().kind(),
             ty::Array(_, _)
         )
     {
@@ -2587,7 +2587,7 @@ fn derefs_to_slice<'tcx>(
 
 /// lint use of `unwrap()` for `Option`s and `Result`s
 fn lint_unwrap(cx: &LateContext<'_>, expr: &hir::Expr<'_>, unwrap_args: &[hir::Expr<'_>]) {
-    let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&unwrap_args[0]));
+    let obj_ty = cx.typeck_results().expr_ty(&unwrap_args[0]).peel_refs();
 
     let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
         Some((UNWRAP_USED, "an Option", "None"))
@@ -2615,7 +2615,7 @@ fn lint_unwrap(cx: &LateContext<'_>, expr: &hir::Expr<'_>, unwrap_args: &[hir::E
 
 /// lint use of `expect()` for `Option`s and `Result`s
 fn lint_expect(cx: &LateContext<'_>, expr: &hir::Expr<'_>, expect_args: &[hir::Expr<'_>]) {
-    let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&expect_args[0]));
+    let obj_ty = cx.typeck_results().expr_ty(&expect_args[0]).peel_refs();
 
     let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
         Some((EXPECT_USED, "an Option", "None"))
@@ -3134,7 +3134,7 @@ fn lint_chars_cmp(
         if segment.ident.name == sym!(Some);
         then {
             let mut applicability = Applicability::MachineApplicable;
-            let self_ty = walk_ptrs_ty(cx.typeck_results().expr_ty_adjusted(&args[0][0]));
+            let self_ty = cx.typeck_results().expr_ty_adjusted(&args[0][0]).peel_refs();
 
             if *self_ty.kind() != ty::Str {
                 return false;

clippy_lints/src/misc.rs

@@ -17,7 +17,7 @@ use crate::utils::sugg::Sugg;
 use crate::utils::{
     get_item_name, get_parent_expr, higher, implements_trait, in_constant, is_integer_const, iter_input_pats,
     last_path_segment, match_qpath, match_trait_method, paths, snippet, snippet_opt, span_lint, span_lint_and_sugg,
-    span_lint_and_then, span_lint_hir_and_then, walk_ptrs_ty, SpanlessEq,
+    span_lint_and_then, span_lint_hir_and_then, SpanlessEq,
 };
 
 declare_clippy_lint! {
@@ -561,7 +561,7 @@ fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 }
 
 fn is_float(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    let value = &walk_ptrs_ty(cx.typeck_results().expr_ty(expr)).kind();
+    let value = &cx.typeck_results().expr_ty(expr).peel_refs().kind();
 
     if let ty::Array(arr_ty, _) = value {
         return matches!(arr_ty.kind(), ty::Float(_));
@@ -571,7 +571,7 @@ fn is_float(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
 }
 
 fn is_array(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
-    matches!(&walk_ptrs_ty(cx.typeck_results().expr_ty(expr)).kind(), ty::Array(_, _))
+    matches!(&cx.typeck_results().expr_ty(expr).peel_refs().kind(), ty::Array(_, _))
 }
 
 fn check_to_owned(cx: &LateContext<'_>, expr: &Expr<'_>, other: &Expr<'_>, left: bool) {

clippy_lints/src/mut_key.rs

@@ -1,4 +1,4 @@
-use crate::utils::{match_def_path, paths, span_lint, trait_ref_of_method, walk_ptrs_ty};
+use crate::utils::{match_def_path, paths, span_lint, trait_ref_of_method};
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty::{Adt, Array, RawPtr, Ref, Slice, Tuple, Ty, TypeAndMut};
@@ -98,7 +98,7 @@ fn check_sig<'tcx>(cx: &LateContext<'tcx>, item_hir_id: hir::HirId, decl: &hir::
 // We want to lint 1. sets or maps with 2. not immutable key types and 3. no unerased
 // generics (because the compiler cannot ensure immutability for unknown types).
 fn check_ty<'tcx>(cx: &LateContext<'tcx>, span: Span, ty: Ty<'tcx>) {
-    let ty = walk_ptrs_ty(ty);
+    let ty = ty.peel_refs();
     if let Adt(def, substs) = ty.kind() {
         if [&paths::HASHMAP, &paths::BTREEMAP, &paths::HASHSET, &paths::BTREESET]
             .iter()

clippy_lints/src/open_options.rs

@@ -1,4 +1,4 @@
-use crate::utils::{match_type, paths, span_lint, walk_ptrs_ty};
+use crate::utils::{match_type, paths, span_lint};
 use rustc_ast::ast::LitKind;
 use rustc_hir::{Expr, ExprKind};
 use rustc_lint::{LateContext, LateLintPass};
@@ -30,7 +30,7 @@ declare_lint_pass!(OpenOptions => [NONSENSICAL_OPEN_OPTIONS]);
 impl<'tcx> LateLintPass<'tcx> for OpenOptions {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
         if let ExprKind::MethodCall(ref path, _, ref arguments, _) = e.kind {
-            let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&arguments[0]));
+            let obj_ty = cx.typeck_results().expr_ty(&arguments[0]).peel_refs();
             if path.ident.name == sym!(open) && match_type(cx, obj_ty, &paths::OPEN_OPTIONS) {
                 let mut options = Vec::new();
                 get_open_options(cx, &arguments[0], &mut options);
@@ -58,7 +58,7 @@ enum OpenOption {
 
 fn get_open_options(cx: &LateContext<'_>, argument: &Expr<'_>, options: &mut Vec<(OpenOption, Argument)>) {
     if let ExprKind::MethodCall(ref path, _, ref arguments, _) = argument.kind {
-        let obj_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&arguments[0]));
+        let obj_ty = cx.typeck_results().expr_ty(&arguments[0]).peel_refs();
 
         // Only proceed if this is a call on some object of type std::fs::OpenOptions
         if match_type(cx, obj_ty, &paths::OPEN_OPTIONS) && arguments.len() >= 2 {

clippy_lints/src/path_buf_push_overwrite.rs

@@ -1,4 +1,4 @@
-use crate::utils::{match_type, paths, span_lint_and_sugg, walk_ptrs_ty};
+use crate::utils::{match_type, paths, span_lint_and_sugg};
 use if_chain::if_chain;
 use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
@@ -46,7 +46,7 @@ impl<'tcx> LateLintPass<'tcx> for PathBufPushOverwrite {
             if let ExprKind::MethodCall(ref path, _, ref args, _) = expr.kind;
             if path.ident.name == sym!(push);
             if args.len() == 2;
-            if match_type(cx, walk_ptrs_ty(cx.typeck_results().expr_ty(&args[0])), &paths::PATH_BUF);
+            if match_type(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), &paths::PATH_BUF);
             if let Some(get_index_arg) = args.get(1);
             if let ExprKind::Lit(ref lit) = get_index_arg.kind;
             if let LitKind::Str(ref path_lit, _) = lit.node;

clippy_lints/src/repeat_once.rs

@@ -1,5 +1,5 @@
 use crate::consts::{constant_context, Constant};
-use crate::utils::{in_macro, is_type_diagnostic_item, snippet, span_lint_and_sugg, walk_ptrs_ty};
+use crate::utils::{in_macro, is_type_diagnostic_item, snippet, span_lint_and_sugg};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind};
@@ -44,7 +44,7 @@ impl<'tcx> LateLintPass<'tcx> for RepeatOnce {
             if let Some(Constant::Int(1)) = constant_context(cx, cx.typeck_results()).expr(&count);
             if !in_macro(receiver.span);
             then {
-                let ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&receiver));
+                let ty = cx.typeck_results().expr_ty(&receiver).peel_refs();
                 if ty.is_str() {
                     span_lint_and_sugg(
                         cx,

clippy_lints/src/strings.rs

@@ -8,7 +8,7 @@ use rustc_span::source_map::Spanned;
 use if_chain::if_chain;
 
 use crate::utils::SpanlessEq;
-use crate::utils::{get_parent_expr, is_allowed, is_type_diagnostic_item, span_lint, span_lint_and_sugg, walk_ptrs_ty};
+use crate::utils::{get_parent_expr, is_allowed, is_type_diagnostic_item, span_lint, span_lint_and_sugg};
 
 declare_clippy_lint! {
     /// **What it does:** Checks for string appends of the form `x = x + y` (without
@@ -134,7 +134,7 @@ impl<'tcx> LateLintPass<'tcx> for StringAdd {
 }
 
 fn is_string(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
-    is_type_diagnostic_item(cx, walk_ptrs_ty(cx.typeck_results().expr_ty(e)), sym!(string_type))
+    is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(e).peel_refs(), sym!(string_type))
 }
 
 fn is_add(cx: &LateContext<'_>, src: &Expr<'_>, target: &Expr<'_>) -> bool {

clippy_lints/src/swap.rs

@@ -1,7 +1,6 @@
 use crate::utils::sugg::Sugg;
 use crate::utils::{
     differing_macro_contexts, eq_expr_value, is_type_diagnostic_item, snippet_with_applicability, span_lint_and_then,
-    walk_ptrs_ty,
 };
 use if_chain::if_chain;
 use rustc_errors::Applicability;
@@ -194,7 +193,7 @@ fn check_for_slice<'a>(cx: &LateContext<'_>, lhs1: &'a Expr<'_>, lhs2: &'a Expr<
     if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.kind {
         if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.kind {
             if eq_expr_value(cx, lhs1, lhs2) {
-                let ty = walk_ptrs_ty(cx.typeck_results().expr_ty(lhs1));
+                let ty = cx.typeck_results().expr_ty(lhs1).peel_refs();
 
                 if matches!(ty.kind(), ty::Slice(_))
                     || matches!(ty.kind(), ty::Array(_, _))

clippy_lints/src/unwrap_in_result.rs

@@ -1,4 +1,4 @@
-use crate::utils::{is_type_diagnostic_item, method_chain_args, return_ty, span_lint_and_then, walk_ptrs_ty};
+use crate::utils::{is_type_diagnostic_item, method_chain_args, return_ty, span_lint_and_then};
 use if_chain::if_chain;
 use rustc_hir as hir;
 use rustc_lint::{LateContext, LateLintPass};
@@ -81,7 +81,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindExpectUnwrap<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
         // check for `expect`
         if let Some(arglists) = method_chain_args(expr, &["expect"]) {
-            let reciever_ty = walk_ptrs_ty(self.typeck_results.expr_ty(&arglists[0][0]));
+            let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
             if is_type_diagnostic_item(self.lcx, reciever_ty, sym!(option_type))
                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym!(result_type))
             {
@@ -91,7 +91,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindExpectUnwrap<'a, 'tcx> {
 
         // check for `unwrap`
         if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
-            let reciever_ty = walk_ptrs_ty(self.typeck_results.expr_ty(&arglists[0][0]));
+            let reciever_ty = self.typeck_results.expr_ty(&arglists[0][0]).peel_refs();
             if is_type_diagnostic_item(self.lcx, reciever_ty, sym!(option_type))
                 || is_type_diagnostic_item(self.lcx, reciever_ty, sym!(result_type))
             {

clippy_lints/src/utils/internal_lints.rs

@@ -1,6 +1,6 @@
 use crate::utils::{
     is_expn_of, match_def_path, match_qpath, match_type, method_calls, path_to_res, paths, qpath_res, run_lints,
-    snippet, span_lint, span_lint_and_help, span_lint_and_sugg, walk_ptrs_ty, SpanlessEq,
+    snippet, span_lint, span_lint_and_help, span_lint_and_sugg, SpanlessEq,
 };
 use if_chain::if_chain;
 use rustc_ast::ast::{Crate as AstCrate, ItemKind, LitKind, NodeId};
@@ -427,7 +427,7 @@ impl<'tcx> LateLintPass<'tcx> for CompilerLintFunctions {
             if let ExprKind::MethodCall(ref path, _, ref args, _) = expr.kind;
             let fn_name = path.ident;
             if let Some(sugg) = self.map.get(&*fn_name.as_str());
-            let ty = walk_ptrs_ty(cx.typeck_results().expr_ty(&args[0]));
+            let ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
             if match_type(cx, ty, &paths::EARLY_CONTEXT)
                 || match_type(cx, ty, &paths::LATE_CONTEXT);
             then {
@@ -460,7 +460,7 @@ impl<'tcx> LateLintPass<'tcx> for OuterExpnDataPass {
             let args = arg_lists[1];
             if args.len() == 1;
             let self_arg = &args[0];
-            let self_ty = walk_ptrs_ty(cx.typeck_results().expr_ty(self_arg));
+            let self_ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
             if match_type(cx, self_ty, &paths::SYNTAX_CONTEXT);
             then {
                 span_lint_and_sugg(

clippy_lints/src/utils/mod.rs

@@ -754,14 +754,6 @@ pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
     }
 }
 
-/// Returns the base type for references and raw pointers.
-pub fn walk_ptrs_ty(ty: Ty<'_>) -> Ty<'_> {
-    match ty.kind() {
-        ty::Ref(_, ty, _) => walk_ptrs_ty(ty),
-        _ => ty,
-    }
-}
-
 /// Returns the base type for references and raw pointers, and count reference
 /// depth.
 pub fn walk_ptrs_ty_depth(ty: Ty<'_>) -> (Ty<'_>, usize) {

tests/ui/indexing_slicing_index.rs

@@ -15,7 +15,8 @@ fn main() {
     x[3]; // Ok, should not produce stderr.
 
     let y = &x;
-    y[0];
+    y[0]; // Ok, referencing shouldn't affect this lint. See the issue 6021
+    y[4]; // Ok, rustc will handle references too.
 
     let v = vec![0; 5];
     v[0];

tests/ui/indexing_slicing_index.stderr

@@ -8,15 +8,7 @@ LL |     x[index];
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:18:5
+  --> $DIR/indexing_slicing_index.rs:22:5
-   |
-LL |     y[0];
-   |     ^^^^
-   |
-   = help: Consider using `.get(n)` or `.get_mut(n)` instead
-
-error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:21:5
    |
 LL |     v[0];
    |     ^^^^
@@ -24,7 +16,7 @@ LL |     v[0];
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:22:5
+  --> $DIR/indexing_slicing_index.rs:23:5
    |
 LL |     v[10];
    |     ^^^^^
@@ -32,7 +24,7 @@ LL |     v[10];
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:23:5
+  --> $DIR/indexing_slicing_index.rs:24:5
    |
 LL |     v[1 << 3];
    |     ^^^^^^^^^
@@ -40,7 +32,7 @@ LL |     v[1 << 3];
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:29:5
+  --> $DIR/indexing_slicing_index.rs:30:5
    |
 LL |     v[N];
    |     ^^^^
@@ -48,12 +40,12 @@ LL |     v[N];
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
 error: indexing may panic.
-  --> $DIR/indexing_slicing_index.rs:30:5
+  --> $DIR/indexing_slicing_index.rs:31:5
    |
 LL |     v[M];
    |     ^^^^
    |
    = help: Consider using `.get(n)` or `.get_mut(n)` instead
 
-error: aborting due to 7 previous errors
+error: aborting due to 6 previous errors
 

tests/ui/indexing_slicing_slice.stderr

@@ -71,29 +71,17 @@ LL |     &x[1..][..5];
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
-error: slicing may panic.
+error: range is out of bounds
-  --> $DIR/indexing_slicing_slice.rs:24:6
+  --> $DIR/indexing_slicing_slice.rs:25:12
-   |
-LL |     &y[1..2];
-   |      ^^^^^^^
-   |
-   = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
-
-error: slicing may panic.
-  --> $DIR/indexing_slicing_slice.rs:25:6
    |
 LL |     &y[0..=4];
-   |      ^^^^^^^^
+   |            ^
-   |
-   = help: Consider using `.get(n..m)` or `.get_mut(n..m)` instead
 
-error: slicing may panic.
+error: range is out of bounds
-  --> $DIR/indexing_slicing_slice.rs:26:6
+  --> $DIR/indexing_slicing_slice.rs:26:11
    |
 LL |     &y[..=4];
-   |      ^^^^^^^
+   |           ^
-   |
-   = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
 error: slicing may panic.
   --> $DIR/indexing_slicing_slice.rs:31:6
@@ -133,5 +121,5 @@ LL |     &v[..100];
    |
    = help: Consider using `.get(..n)`or `.get_mut(..n)` instead
 
-error: aborting due to 17 previous errors
+error: aborting due to 16 previous errors