Auto merge of #13543 - GnomedDev:symbol-comparisons, r=y21

Add internal lint to check for slow symbol comparisons

See the conversation on [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Checking.20a.20Symbol.20is.20equal.20to.20a.20string.20literal).

changelog: none

36 files changed, 200 insertions, 63 deletions

diff --git a/book/src/development/common_tools_writing_lints.md b/book/src/development/common_tools_writing_lints.md
index 09171d86a20..77910917963 100644
--- a/book/src/development/common_tools_writing_lints.md
+++ b/book/src/development/common_tools_writing_lints.md
@@ -68,7 +68,7 @@ impl<'tcx> LateLintPass<'tcx> for MyStructLint {
         // Check our expr is calling a method
         if let hir::ExprKind::MethodCall(path, _, _self_arg, ..) = &expr.kind
             // Check the name of this method is `some_method`
-            && path.ident.name == sym!(some_method)
+            && path.ident.name.as_str() == "some_method"
             // Optionally, check the type of the self argument.
             // - See "Checking for a specific type"
         {
@@ -167,7 +167,7 @@ impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
         // Check if item is a method/function
         if let ImplItemKind::Fn(ref signature, _) = impl_item.kind
             // Check the method is named `some_method`
-            && impl_item.ident.name == sym!(some_method)
+            && impl_item.ident.name.as_str() == "some_method"
             // We can also check it has a parameter `self`
             && signature.decl.implicit_self.has_implicit_self()
             // We can go further and even check if its return type is `String`
diff --git a/book/src/development/method_checking.md b/book/src/development/method_checking.md
index 56d1be37519..9c5d4b516db 100644
--- a/book/src/development/method_checking.md
+++ b/book/src/development/method_checking.md
@@ -3,8 +3,8 @@
 In some scenarios we might want to check for methods when developing
 a lint. There are two kinds of questions that we might be curious about:
 
-- Invocation: Does an expression call a specific method?
-- Definition: Does an `impl` define a method?
+-   Invocation: Does an expression call a specific method?
+-   Definition: Does an `impl` define a method?
 
 ## Checking if an `expr` is calling a specific method
 
@@ -23,7 +23,7 @@ impl<'tcx> LateLintPass<'tcx> for OurFancyMethodLint {
         // Check our expr is calling a method with pattern matching
         if let hir::ExprKind::MethodCall(path, _, [self_arg, ..]) = &expr.kind
             // Check if the name of this method is `our_fancy_method`
-            && path.ident.name == sym!(our_fancy_method)
+            && path.ident.name.as_str() == "our_fancy_method"
             // We can check the type of the self argument whenever necessary.
             // (It's necessary if we want to check that method is specifically belonging to a specific trait,
             // for example, a `map` method could belong to user-defined trait instead of to `Iterator`)
@@ -41,10 +41,6 @@ information on the pattern matching. As mentioned in [Define
 Lints](defining_lints.md#lint-types), the `methods` lint type is full of pattern
 matching with `MethodCall` in case the reader wishes to explore more.
 
-Additionally, we use the [`clippy_utils::sym!`][sym] macro to conveniently
-convert an input `our_fancy_method` into a `Symbol` and compare that symbol to
-the [`Ident`]'s name in the [`PathSegment`] in the [`MethodCall`].
-
 ## Checking if a `impl` block implements a method
 
 While sometimes we want to check whether a method is being called or not, other
@@ -71,7 +67,7 @@ impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
         // Check if item is a method/function
         if let ImplItemKind::Fn(ref signature, _) = impl_item.kind
             // Check the method is named `our_fancy_method`
-            && impl_item.ident.name == sym!(our_fancy_method)
+            && impl_item.ident.name.as_str() == "our_fancy_method"
             // We can also check it has a parameter `self`
             && signature.decl.implicit_self.has_implicit_self()
             // We can go even further and even check if its return type is `String`
@@ -85,9 +81,6 @@ impl<'tcx> LateLintPass<'tcx> for MyTypeImpl {
 
 [`check_impl_item`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html#method.check_impl_item
 [`ExprKind`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html
-[`Ident`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_span/symbol/struct.Ident.html
 [`ImplItem`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_hir/hir/struct.ImplItem.html
 [`LateLintPass`]: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/trait.LateLintPass.html
 [`MethodCall`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/enum.ExprKind.html#variant.MethodCall
-[`PathSegment`]: https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/hir/struct.PathSegment.html
-[sym]: https://doc.rust-lang.org/stable/nightly-rustc/clippy_utils/macro.sym.html
diff --git a/clippy_lints/src/casts/cast_ptr_alignment.rs b/clippy_lints/src/casts/cast_ptr_alignment.rs
index b11b967f8bc..205357afd84 100644
--- a/clippy_lints/src/casts/cast_ptr_alignment.rs
+++ b/clippy_lints/src/casts/cast_ptr_alignment.rs
@@ -20,7 +20,7 @@ pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
         );
         lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
     } else if let ExprKind::MethodCall(method_path, self_arg, [], _) = &expr.kind {
-        if method_path.ident.name == sym!(cast)
+        if method_path.ident.name.as_str() == "cast"
             && let Some(generic_args) = method_path.args
             && let [GenericArg::Type(cast_to)] = generic_args.args
             // There probably is no obvious reason to do this, just to be consistent with `as` cases.
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index 3c4e75df8ab..d8918d37afa 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -28,6 +28,8 @@ pub static LINTS: &[&crate::LintInfo] = &[
     #[cfg(feature = "internal")]
     crate::utils::internal_lints::produce_ice::PRODUCE_ICE_INFO,
     #[cfg(feature = "internal")]
+    crate::utils::internal_lints::slow_symbol_comparisons::SLOW_SYMBOL_COMPARISONS_INFO,
+    #[cfg(feature = "internal")]
     crate::utils::internal_lints::unnecessary_def_path::UNNECESSARY_DEF_PATH_INFO,
     #[cfg(feature = "internal")]
     crate::utils::internal_lints::unsorted_clippy_utils_paths::UNSORTED_CLIPPY_UTILS_PATHS_INFO,
diff --git a/clippy_lints/src/explicit_write.rs b/clippy_lints/src/explicit_write.rs
index 4e4434ec7d1..0550c22761a 100644
--- a/clippy_lints/src/explicit_write.rs
+++ b/clippy_lints/src/explicit_write.rs
@@ -58,7 +58,7 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
             // match call to write_fmt
             && let ExprKind::MethodCall(write_fun, write_recv, [write_arg], _) = *look_in_block(cx, &write_call.kind)
             && let ExprKind::Call(write_recv_path, []) = write_recv.kind
-            && write_fun.ident.name == sym!(write_fmt)
+            && write_fun.ident.name.as_str() == "write_fmt"
             && let Some(def_id) = path_def_id(cx, write_recv_path)
         {
             // match calls to std::io::stdout() / std::io::stderr ()
diff --git a/clippy_lints/src/from_raw_with_void_ptr.rs b/clippy_lints/src/from_raw_with_void_ptr.rs
index d62d008d480..c8828c93615 100644
--- a/clippy_lints/src/from_raw_with_void_ptr.rs
+++ b/clippy_lints/src/from_raw_with_void_ptr.rs
@@ -41,7 +41,7 @@ impl LateLintPass<'_> for FromRawWithVoidPtr {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
         if let ExprKind::Call(box_from_raw, [arg]) = expr.kind
             && let ExprKind::Path(QPath::TypeRelative(ty, seg)) = box_from_raw.kind
-            && seg.ident.name == sym!(from_raw)
+            && seg.ident.name.as_str() == "from_raw"
             && let Some(type_str) = path_def_id(cx, ty).and_then(|id| def_id_matches_type(cx, id))
             && let arg_kind = cx.typeck_results().expr_ty(arg).kind()
             && let ty::RawPtr(ty, _) = arg_kind
diff --git a/clippy_lints/src/implicit_hasher.rs b/clippy_lints/src/implicit_hasher.rs
index 4c5375730b8..c370f206c8f 100644
--- a/clippy_lints/src/implicit_hasher.rs
+++ b/clippy_lints/src/implicit_hasher.rs
@@ -340,7 +340,7 @@ impl<'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'_, '_, 'tcx> {
             if self.cx.tcx.is_diagnostic_item(sym::HashMap, ty_did) {
                 if method.ident.name == sym::new {
                     self.suggestions.insert(e.span, "HashMap::default()".to_string());
-                } else if method.ident.name == sym!(with_capacity) {
+                } else if method.ident.name.as_str() == "with_capacity" {
                     self.suggestions.insert(
                         e.span,
                         format!(
@@ -352,7 +352,7 @@ impl<'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'_, '_, 'tcx> {
             } else if self.cx.tcx.is_diagnostic_item(sym::HashSet, ty_did) {
                 if method.ident.name == sym::new {
                     self.suggestions.insert(e.span, "HashSet::default()".to_string());
-                } else if method.ident.name == sym!(with_capacity) {
+                } else if method.ident.name.as_str() == "with_capacity" {
                     self.suggestions.insert(
                         e.span,
                         format!(
diff --git a/clippy_lints/src/infinite_iter.rs b/clippy_lints/src/infinite_iter.rs
index 71c317552ee..48874d6064b 100644
--- a/clippy_lints/src/infinite_iter.rs
+++ b/clippy_lints/src/infinite_iter.rs
@@ -157,7 +157,7 @@ fn is_infinite(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
                     .and(cap);
                 }
             }
-            if method.ident.name == sym!(flat_map) && args.len() == 1 {
+            if method.ident.name.as_str() == "flat_map" && args.len() == 1 {
                 if let ExprKind::Closure(&Closure { body, .. }) = args[0].kind {
                     let body = cx.tcx.hir().body(body);
                     return is_infinite(cx, body.value);
@@ -224,7 +224,7 @@ fn complete_infinite_iter(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
                     return MaybeInfinite.and(is_infinite(cx, receiver));
                 }
             }
-            if method.ident.name == sym!(last) && args.is_empty() {
+            if method.ident.name.as_str() == "last" && args.is_empty() {
                 let not_double_ended = cx
                     .tcx
                     .get_diagnostic_item(sym::DoubleEndedIterator)
@@ -234,7 +234,7 @@ fn complete_infinite_iter(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
                 if not_double_ended {
                     return is_infinite(cx, receiver);
                 }
-            } else if method.ident.name == sym!(collect) {
+            } else if method.ident.name.as_str() == "collect" {
                 let ty = cx.typeck_results().expr_ty(expr);
                 if matches!(
                     get_type_diagnostic_name(cx, ty),
diff --git a/clippy_lints/src/iter_without_into_iter.rs b/clippy_lints/src/iter_without_into_iter.rs
index 1e6404190d3..36e94593e6f 100644
--- a/clippy_lints/src/iter_without_into_iter.rs
+++ b/clippy_lints/src/iter_without_into_iter.rs
@@ -142,7 +142,7 @@ impl LateLintPass<'_> for IterWithoutIntoIter {
                 ty.peel_refs().is_slice() || get_adt_inherent_method(cx, ty, expected_method_name).is_some()
             })
             && let Some(iter_assoc_span) = imp.items.iter().find_map(|item| {
-                if item.ident.name == sym!(IntoIter) {
+                if item.ident.name.as_str() == "IntoIter" {
                     Some(cx.tcx.hir().impl_item(item.id).expect_type().span)
                 } else {
                     None
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 6e29dde2211..a0ff8316d5c 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -603,6 +603,7 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
         store.register_late_pass(|_| {
             Box::new(utils::internal_lints::almost_standard_lint_formulation::AlmostStandardFormulation::new())
         });
+        store.register_late_pass(|_| Box::new(utils::internal_lints::slow_symbol_comparisons::SlowSymbolComparisons));
     }
 
     store.register_late_pass(move |_| Box::new(operators::arithmetic_side_effects::ArithmeticSideEffects::new(conf)));
diff --git a/clippy_lints/src/manual_hash_one.rs b/clippy_lints/src/manual_hash_one.rs
index c62bd65bea6..7a9c9963742 100644
--- a/clippy_lints/src/manual_hash_one.rs
+++ b/clippy_lints/src/manual_hash_one.rs
@@ -68,7 +68,7 @@ impl LateLintPass<'_> for ManualHashOne {
             && let Some(init) = local.init
             && !init.span.from_expansion()
             && let ExprKind::MethodCall(seg, build_hasher, [], _) = init.kind
-            && seg.ident.name == sym!(build_hasher)
+            && seg.ident.name.as_str() == "build_hasher"
 
             && let Node::Stmt(local_stmt) = cx.tcx.parent_hir_node(local.hir_id)
             && let Node::Block(block) = cx.tcx.parent_hir_node(local_stmt.hir_id)
@@ -96,7 +96,7 @@ impl LateLintPass<'_> for ManualHashOne {
             && let Node::Expr(finish_expr) = cx.tcx.parent_hir_node(path_expr.hir_id)
             && !finish_expr.span.from_expansion()
             && let ExprKind::MethodCall(seg, _, [], _) = finish_expr.kind
-            && seg.ident.name == sym!(finish)
+            && seg.ident.name.as_str() == "finish"
 
             && self.msrv.meets(msrvs::BUILD_HASHER_HASH_ONE)
         {
diff --git a/clippy_lints/src/manual_is_ascii_check.rs b/clippy_lints/src/manual_is_ascii_check.rs
index 24207705743..dec8c5d85de 100644
--- a/clippy_lints/src/manual_is_ascii_check.rs
+++ b/clippy_lints/src/manual_is_ascii_check.rs
@@ -105,7 +105,7 @@ impl<'tcx> LateLintPass<'tcx> for ManualIsAsciiCheck {
                 check_is_ascii(cx, macro_call.span, recv, &range, None);
             }
         } else if let ExprKind::MethodCall(path, receiver, [arg], ..) = expr.kind
-            && path.ident.name == sym!(contains)
+            && path.ident.name.as_str() == "contains"
             && let Some(higher::Range {
                 start: Some(start),
                 end: Some(end),
diff --git a/clippy_lints/src/matches/redundant_guards.rs b/clippy_lints/src/matches/redundant_guards.rs
index 564c598a334..051a4eceab8 100644
--- a/clippy_lints/src/matches/redundant_guards.rs
+++ b/clippy_lints/src/matches/redundant_guards.rs
@@ -10,7 +10,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{Arm, BinOpKind, Expr, ExprKind, MatchSource, Node, PatKind, UnOp};
 use rustc_lint::LateContext;
 use rustc_span::symbol::Ident;
-use rustc_span::{Span, Symbol, sym};
+use rustc_span::{Span, sym};
 use std::borrow::Cow;
 use std::ops::ControlFlow;
 
@@ -95,7 +95,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'tcx>], msrv:
         } else if let ExprKind::MethodCall(path, recv, args, ..) = guard.kind
             && let Some(binding) = get_pat_binding(cx, recv, outer_arm)
         {
-            check_method_calls(cx, outer_arm, path.ident.name, recv, args, guard, &binding);
+            check_method_calls(cx, outer_arm, path.ident.name.as_str(), recv, args, guard, &binding);
         }
     }
 }
@@ -103,7 +103,7 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, arms: &'tcx [Arm<'tcx>], msrv:
 fn check_method_calls<'tcx>(
     cx: &LateContext<'tcx>,
     arm: &Arm<'tcx>,
-    method: Symbol,
+    method: &str,
     recv: &Expr<'_>,
     args: &[Expr<'_>],
     if_expr: &Expr<'_>,
@@ -112,7 +112,7 @@ fn check_method_calls<'tcx>(
     let ty = cx.typeck_results().expr_ty(recv).peel_refs();
     let slice_like = ty.is_slice() || ty.is_array();
 
-    let sugg = if method == sym!(is_empty) {
+    let sugg = if method == "is_empty" {
         // `s if s.is_empty()` becomes ""
         // `arr if arr.is_empty()` becomes []
 
@@ -137,9 +137,9 @@ fn check_method_calls<'tcx>(
 
         if needles.is_empty() {
             sugg.insert_str(1, "..");
-        } else if method == sym!(starts_with) {
+        } else if method == "starts_with" {
             sugg.insert_str(sugg.len() - 1, ", ..");
-        } else if method == sym!(ends_with) {
+        } else if method == "ends_with" {
             sugg.insert_str(1, ".., ");
         } else {
             return;
diff --git a/clippy_lints/src/methods/filter_map.rs b/clippy_lints/src/methods/filter_map.rs
index 06482a743dd..c181e944fff 100644
--- a/clippy_lints/src/methods/filter_map.rs
+++ b/clippy_lints/src/methods/filter_map.rs
@@ -234,12 +234,12 @@ impl<'tcx> OffendingFilterExpr<'tcx> {
             // the latter only calls `effect` once
             let side_effect_expr_span = receiver.can_have_side_effects().then_some(receiver.span);
 
-            if cx.tcx.is_diagnostic_item(sym::Option, recv_ty.did()) && path.ident.name == sym!(is_some) {
+            if cx.tcx.is_diagnostic_item(sym::Option, recv_ty.did()) && path.ident.name.as_str() == "is_some" {
                 Some(Self::IsSome {
                     receiver,
                     side_effect_expr_span,
                 })
-            } else if cx.tcx.is_diagnostic_item(sym::Result, recv_ty.did()) && path.ident.name == sym!(is_ok) {
+            } else if cx.tcx.is_diagnostic_item(sym::Result, recv_ty.did()) && path.ident.name.as_str() == "is_ok" {
                 Some(Self::IsOk {
                     receiver,
                     side_effect_expr_span,
diff --git a/clippy_lints/src/methods/needless_collect.rs b/clippy_lints/src/methods/needless_collect.rs
index 96a31812ca4..055107068ae 100644
--- a/clippy_lints/src/methods/needless_collect.rs
+++ b/clippy_lints/src/methods/needless_collect.rs
@@ -322,7 +322,7 @@ impl<'tcx> Visitor<'tcx> for IterFunctionVisitor<'_, 'tcx> {
         // Check function calls on our collection
         if let ExprKind::MethodCall(method_name, recv, args, _) = &expr.kind {
             if args.is_empty()
-                && method_name.ident.name == sym!(collect)
+                && method_name.ident.name.as_str() == "collect"
                 && is_trait_method(self.cx, expr, sym::Iterator)
             {
                 self.current_mutably_captured_ids = get_captured_ids(self.cx, self.cx.typeck_results().expr_ty(recv));
diff --git a/clippy_lints/src/methods/read_line_without_trim.rs b/clippy_lints/src/methods/read_line_without_trim.rs
index 65e545ed03a..db2b9d4d92f 100644
--- a/clippy_lints/src/methods/read_line_without_trim.rs
+++ b/clippy_lints/src/methods/read_line_without_trim.rs
@@ -44,7 +44,7 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
             if let Some(parent) = get_parent_expr(cx, expr) {
                 let data = if let ExprKind::MethodCall(segment, recv, args, span) = parent.kind {
                     if args.is_empty()
-                        && segment.ident.name == sym!(parse)
+                        && segment.ident.name.as_str() == "parse"
                         && let parse_result_ty = cx.typeck_results().expr_ty(parent)
                         && is_type_diagnostic_item(cx, parse_result_ty, sym::Result)
                         && let ty::Adt(_, substs) = parse_result_ty.kind()
@@ -58,7 +58,7 @@ pub fn check(cx: &LateContext<'_>, call: &Expr<'_>, recv: &Expr<'_>, arg: &Expr<
                             "calling `.parse()` on a string without trimming the trailing newline character",
                             "checking",
                         ))
-                    } else if segment.ident.name == sym!(ends_with)
+                    } else if segment.ident.name.as_str() == "ends_with"
                         && recv.span == expr.span
                         && let [arg] = args
                         && expr_is_string_literal_without_trailing_newline(arg)
diff --git a/clippy_lints/src/methods/unnecessary_filter_map.rs b/clippy_lints/src/methods/unnecessary_filter_map.rs
index ca46da81fa0..1cbb1bcc663 100644
--- a/clippy_lints/src/methods/unnecessary_filter_map.rs
+++ b/clippy_lints/src/methods/unnecessary_filter_map.rs
@@ -78,7 +78,7 @@ fn check_expression<'tcx>(cx: &LateContext<'tcx>, arg_id: hir::HirId, expr: &'tc
             (true, true)
         },
         hir::ExprKind::MethodCall(segment, recv, [arg], _) => {
-            if segment.ident.name == sym!(then_some)
+            if segment.ident.name.as_str() == "then_some"
                 && cx.typeck_results().expr_ty(recv).is_bool()
                 && path_to_local_id(arg, arg_id)
             {
diff --git a/clippy_lints/src/minmax.rs b/clippy_lints/src/minmax.rs
index e95864c6db8..ed89b3b3438 100644
--- a/clippy_lints/src/minmax.rs
+++ b/clippy_lints/src/minmax.rs
@@ -79,9 +79,9 @@ fn min_max<'a, 'tcx>(cx: &LateContext<'tcx>, expr: &'a Expr<'a>) -> Option<(MinM
         },
         ExprKind::MethodCall(path, receiver, args @ [_], _) => {
             if cx.typeck_results().expr_ty(receiver).is_floating_point() || is_trait_method(cx, expr, sym::Ord) {
-                if path.ident.name == sym!(max) {
+                if path.ident.name.as_str() == "max" {
                     fetch_const(cx, Some(receiver), args, MinMax::Max)
-                } else if path.ident.name == sym!(min) {
+                } else if path.ident.name.as_str() == "min" {
                     fetch_const(cx, Some(receiver), args, MinMax::Min)
                 } else {
                     None
diff --git a/clippy_lints/src/missing_fields_in_debug.rs b/clippy_lints/src/missing_fields_in_debug.rs
index fc01b6753f1..f28b431ab99 100644
--- a/clippy_lints/src/missing_fields_in_debug.rs
+++ b/clippy_lints/src/missing_fields_in_debug.rs
@@ -116,7 +116,7 @@ fn should_lint<'tcx>(
 
             if path.ident.name == sym::debug_struct && is_type_diagnostic_item(cx, recv_ty, sym::Formatter) {
                 has_debug_struct = true;
-            } else if path.ident.name == sym!(finish_non_exhaustive)
+            } else if path.ident.name.as_str() == "finish_non_exhaustive"
                 && is_type_diagnostic_item(cx, recv_ty, sym::DebugStruct)
             {
                 has_finish_non_exhaustive = true;
diff --git a/clippy_lints/src/non_octal_unix_permissions.rs b/clippy_lints/src/non_octal_unix_permissions.rs
index 3f156aa5510..0caa19cd844 100644
--- a/clippy_lints/src/non_octal_unix_permissions.rs
+++ b/clippy_lints/src/non_octal_unix_permissions.rs
@@ -43,12 +43,12 @@ impl<'tcx> LateLintPass<'tcx> for NonOctalUnixPermissions {
         match &expr.kind {
             ExprKind::MethodCall(path, func, [param], _) => {
                 if let Some(adt) = cx.typeck_results().expr_ty(func).peel_refs().ty_adt_def()
-                    && ((path.ident.name == sym!(mode)
+                    && ((path.ident.name.as_str() == "mode"
                         && matches!(
                             cx.tcx.get_diagnostic_name(adt.did()),
                             Some(sym::FsOpenOptions | sym::DirBuilder)
                         ))
-                        || (path.ident.name == sym!(set_mode)
+                        || (path.ident.name.as_str() == "set_mode"
                             && cx.tcx.is_diagnostic_item(sym::FsPermissions, adt.did())))
                     && let ExprKind::Lit(_) = param.kind
                     && param.span.eq_ctxt(expr.span)
diff --git a/clippy_lints/src/operators/float_cmp.rs b/clippy_lints/src/operators/float_cmp.rs
index 8e394944c21..ab5f91c1d67 100644
--- a/clippy_lints/src/operators/float_cmp.rs
+++ b/clippy_lints/src/operators/float_cmp.rs
@@ -107,7 +107,7 @@ fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     }
 
     if let ExprKind::MethodCall(method_name, self_arg, [], _) = expr.kind
-        && sym!(signum) == method_name.ident.name
+        && method_name.ident.name.as_str() == "signum"
     // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
     // the method call)
     {
diff --git a/clippy_lints/src/ptr_offset_with_cast.rs b/clippy_lints/src/ptr_offset_with_cast.rs
index 56d07aeae17..808a7e005c6 100644
--- a/clippy_lints/src/ptr_offset_with_cast.rs
+++ b/clippy_lints/src/ptr_offset_with_cast.rs
@@ -96,7 +96,7 @@ fn expr_as_ptr_offset_call<'tcx>(
             if path_segment.ident.name == sym::offset {
                 return Some((arg_0, arg_1, Method::Offset));
             }
-            if path_segment.ident.name == sym!(wrapping_offset) {
+            if path_segment.ident.name.as_str() == "wrapping_offset" {
                 return Some((arg_0, arg_1, Method::WrappingOffset));
             }
         }
diff --git a/clippy_lints/src/question_mark.rs b/clippy_lints/src/question_mark.rs
index 9344cb41993..28968866e1f 100644
--- a/clippy_lints/src/question_mark.rs
+++ b/clippy_lints/src/question_mark.rs
@@ -163,8 +163,8 @@ fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_
             is_type_diagnostic_item(cx, caller_ty, smbl)
                 && expr_return_none_or_err(smbl, cx, if_then, caller, None)
                 && match smbl {
-                    sym::Option => call_sym == sym!(is_none),
-                    sym::Result => call_sym == sym!(is_err),
+                    sym::Option => call_sym.as_str() == "is_none",
+                    sym::Result => call_sym.as_str() == "is_err",
                     _ => false,
                 }
         },
diff --git a/clippy_lints/src/slow_vector_initialization.rs b/clippy_lints/src/slow_vector_initialization.rs
index ec6e45256d1..8c8f11569c8 100644
--- a/clippy_lints/src/slow_vector_initialization.rs
+++ b/clippy_lints/src/slow_vector_initialization.rs
@@ -235,7 +235,7 @@ impl<'tcx> VectorInitializationVisitor<'_, 'tcx> {
         if self.initialization_found
             && let ExprKind::MethodCall(path, self_arg, [extend_arg], _) = expr.kind
             && path_to_local_id(self_arg, self.vec_alloc.local_id)
-            && path.ident.name == sym!(extend)
+            && path.ident.name.as_str() == "extend"
             && self.is_repeat_take(extend_arg)
         {
             self.slow_expression = Some(InitializationType::Extend(expr));
@@ -247,7 +247,7 @@ impl<'tcx> VectorInitializationVisitor<'_, 'tcx> {
         if self.initialization_found
             && let ExprKind::MethodCall(path, self_arg, [len_arg, fill_arg], _) = expr.kind
             && path_to_local_id(self_arg, self.vec_alloc.local_id)
-            && path.ident.name == sym!(resize)
+            && path.ident.name.as_str() == "resize"
             // Check that is filled with 0
             && is_integer_literal(fill_arg, 0)
         {
@@ -269,7 +269,7 @@ impl<'tcx> VectorInitializationVisitor<'_, 'tcx> {
     /// Returns `true` if give expression is `repeat(0).take(...)`
     fn is_repeat_take(&mut self, expr: &'tcx Expr<'tcx>) -> bool {
         if let ExprKind::MethodCall(take_path, recv, [len_arg], _) = expr.kind
-            && take_path.ident.name == sym!(take)
+            && take_path.ident.name.as_str() == "take"
             // Check that take is applied to `repeat(0)`
             && self.is_repeat_zero(recv)
         {
diff --git a/clippy_lints/src/strings.rs b/clippy_lints/src/strings.rs
index bf49bb60162..e09c0706006 100644
--- a/clippy_lints/src/strings.rs
+++ b/clippy_lints/src/strings.rs
@@ -286,7 +286,7 @@ impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
 
         if !in_external_macro(cx.sess(), e.span)
             && let ExprKind::MethodCall(path, receiver, ..) = &e.kind
-            && path.ident.name == sym!(as_bytes)
+            && path.ident.name.as_str() == "as_bytes"
             && let ExprKind::Lit(lit) = &receiver.kind
             && let LitKind::Str(lit_content, _) = &lit.node
         {
@@ -332,7 +332,7 @@ impl<'tcx> LateLintPass<'tcx> for StringLitAsBytes {
         }
 
         if let ExprKind::MethodCall(path, recv, [], _) = &e.kind
-            && path.ident.name == sym!(into_bytes)
+            && path.ident.name.as_str() == "into_bytes"
             && let ExprKind::MethodCall(path, recv, [], _) = &recv.kind
             && matches!(path.ident.name.as_str(), "to_owned" | "to_string")
             && let ExprKind::Lit(lit) = &recv.kind
@@ -493,7 +493,7 @@ impl<'tcx> LateLintPass<'tcx> for TrimSplitWhitespace {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
         let tyckres = cx.typeck_results();
         if let ExprKind::MethodCall(path, split_recv, [], split_ws_span) = expr.kind
-            && path.ident.name == sym!(split_whitespace)
+            && path.ident.name.as_str() == "split_whitespace"
             && let Some(split_ws_def_id) = tyckres.type_dependent_def_id(expr.hir_id)
             && cx.tcx.is_diagnostic_item(sym::str_split_whitespace, split_ws_def_id)
             && let ExprKind::MethodCall(path, _trim_recv, [], trim_span) = split_recv.kind
diff --git a/clippy_lints/src/transmute/eager_transmute.rs b/clippy_lints/src/transmute/eager_transmute.rs
index 1dfc9f7091e..ca9daf2d2a0 100644
--- a/clippy_lints/src/transmute/eager_transmute.rs
+++ b/clippy_lints/src/transmute/eager_transmute.rs
@@ -43,7 +43,7 @@ fn binops_with_local(cx: &LateContext<'_>, local_expr: &Expr<'_>, expr: &Expr<'_
             binops_with_local(cx, local_expr, lhs) || binops_with_local(cx, local_expr, rhs)
         },
         ExprKind::MethodCall(path, receiver, [arg], _)
-            if path.ident.name == sym!(contains)
+            if path.ident.name.as_str() == "contains"
                 // ... `contains` called on some kind of range
                 && let Some(receiver_adt) = cx.typeck_results().expr_ty(receiver).peel_refs().ty_adt_def()
                 && let lang_items = cx.tcx.lang_items()
@@ -81,7 +81,7 @@ pub(super) fn check<'tcx>(
     if let Some(then_some_call) = peel_parent_unsafe_blocks(cx, expr)
         && let ExprKind::MethodCall(path, receiver, [arg], _) = then_some_call.kind
         && cx.typeck_results().expr_ty(receiver).is_bool()
-        && path.ident.name == sym!(then_some)
+        && path.ident.name.as_str() == "then_some"
         && is_local_with_projections(transmutable)
         && binops_with_local(cx, transmutable, receiver)
         && is_normalizable(cx, cx.param_env, from_ty)
diff --git a/clippy_lints/src/utils/internal_lints.rs b/clippy_lints/src/utils/internal_lints.rs
index f662c7651f6..deb983b6971 100644
--- a/clippy_lints/src/utils/internal_lints.rs
+++ b/clippy_lints/src/utils/internal_lints.rs
@@ -6,5 +6,6 @@ pub mod lint_without_lint_pass;
 pub mod msrv_attr_impl;
 pub mod outer_expn_data_pass;
 pub mod produce_ice;
+pub mod slow_symbol_comparisons;
 pub mod unnecessary_def_path;
 pub mod unsorted_clippy_utils_paths;
diff --git a/clippy_lints/src/utils/internal_lints/lint_without_lint_pass.rs b/clippy_lints/src/utils/internal_lints/lint_without_lint_pass.rs
index 51235de9f29..b067e88cead 100644
--- a/clippy_lints/src/utils/internal_lints/lint_without_lint_pass.rs
+++ b/clippy_lints/src/utils/internal_lints/lint_without_lint_pass.rs
@@ -218,9 +218,7 @@ pub(super) fn is_lint_ref_type(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> bool {
 
 fn check_invalid_clippy_version_attribute(cx: &LateContext<'_>, item: &'_ Item<'_>) {
     if let Some(value) = extract_clippy_version_value(cx, item) {
-        // The `sym!` macro doesn't work as it only expects a single token.
-        // It's better to keep it this way and have a direct `Symbol::intern` call here.
-        if value == Symbol::intern("pre 1.29.0") {
+        if value.as_str() == "pre 1.29.0" {
             return;
         }
 
diff --git a/clippy_lints/src/utils/internal_lints/msrv_attr_impl.rs b/clippy_lints/src/utils/internal_lints/msrv_attr_impl.rs
index 63fcbd61528..68692246153 100644
--- a/clippy_lints/src/utils/internal_lints/msrv_attr_impl.rs
+++ b/clippy_lints/src/utils/internal_lints/msrv_attr_impl.rs
@@ -42,7 +42,7 @@ impl LateLintPass<'_> for MsrvAttrImpl {
                     .filter(|t| matches!(t.unpack(), GenericArgKind::Type(_)))
                     .any(|t| match_type(cx, t.expect_ty(), &paths::MSRV))
             })
-            && !items.iter().any(|item| item.ident.name == sym!(check_attributes))
+            && !items.iter().any(|item| item.ident.name.as_str() == "check_attributes")
         {
             let context = if is_late_pass { "LateContext" } else { "EarlyContext" };
             let lint_pass = if is_late_pass { "LateLintPass" } else { "EarlyLintPass" };
diff --git a/clippy_lints/src/utils/internal_lints/slow_symbol_comparisons.rs b/clippy_lints/src/utils/internal_lints/slow_symbol_comparisons.rs
new file mode 100644
index 00000000000..3742be0e103
--- /dev/null
+++ b/clippy_lints/src/utils/internal_lints/slow_symbol_comparisons.rs
@@ -0,0 +1,69 @@
+use clippy_utils::consts::{ConstEvalCtxt, Constant};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::ty::match_type;
+use clippy_utils::{match_function_call, paths};
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// Detects symbol comparision using `Symbol::intern`.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Comparision via `Symbol::as_str()` is faster if the interned symbols are not reused.
+    ///
+    /// ### Example
+    ///
+    /// None, see suggestion.
+    pub SLOW_SYMBOL_COMPARISONS,
+    internal,
+    "detects slow comparisions of symbol"
+}
+
+declare_lint_pass!(SlowSymbolComparisons => [SLOW_SYMBOL_COMPARISONS]);
+
+fn check_slow_comparison<'tcx>(
+    cx: &LateContext<'tcx>,
+    op1: &'tcx Expr<'tcx>,
+    op2: &'tcx Expr<'tcx>,
+) -> Option<(Span, String)> {
+    if match_type(cx, cx.typeck_results().expr_ty(op1), &paths::SYMBOL)
+        && let Some([symbol_name_expr]) = match_function_call(cx, op2, &paths::SYMBOL_INTERN)
+        && let Some(Constant::Str(symbol_name)) = ConstEvalCtxt::new(cx).eval_simple(symbol_name_expr)
+    {
+        Some((op1.span, symbol_name))
+    } else {
+        None
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for SlowSymbolComparisons {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
+        if let ExprKind::Binary(op, left, right) = expr.kind
+            && (op.node == BinOpKind::Eq || op.node == BinOpKind::Ne)
+            && let Some((symbol_span, symbol_name)) =
+                check_slow_comparison(cx, left, right).or_else(|| check_slow_comparison(cx, right, left))
+        {
+            let mut applicability = Applicability::MachineApplicable;
+            span_lint_and_sugg(
+                cx,
+                SLOW_SYMBOL_COMPARISONS,
+                expr.span,
+                "comparing `Symbol` via `Symbol::intern`",
+                "use `Symbol::as_str` and check the string instead",
+                format!(
+                    "{}.as_str() {} \"{symbol_name}\"",
+                    snippet_with_applicability(cx, symbol_span, "symbol", &mut applicability),
+                    op.node.as_str()
+                ),
+                applicability,
+            );
+        };
+    }
+}
diff --git a/tests/ui-internal/slow_symbol_comparisons.fixed b/tests/ui-internal/slow_symbol_comparisons.fixed
new file mode 100644
index 00000000000..2cbd646a0fd
--- /dev/null
+++ b/tests/ui-internal/slow_symbol_comparisons.fixed
@@ -0,0 +1,24 @@
+#![feature(rustc_private)]
+#![warn(clippy::slow_symbol_comparisons)]
+
+extern crate rustc_span;
+
+use clippy_utils::sym;
+use rustc_span::Symbol;
+
+fn main() {
+    let symbol = sym!(example);
+    let other_symbol = sym!(other_example);
+
+    // Should lint
+    let slow_comparison = symbol.as_str() == "example";
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+    let slow_comparison_macro = symbol.as_str() == "example";
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+    let slow_comparison_backwards = symbol.as_str() == "example";
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+
+    // Should not lint
+    let faster_comparison = symbol.as_str() == "other_example";
+    let preinterned_comparison = symbol == other_symbol;
+}
diff --git a/tests/ui-internal/slow_symbol_comparisons.rs b/tests/ui-internal/slow_symbol_comparisons.rs
new file mode 100644
index 00000000000..0cea3c3fcff
--- /dev/null
+++ b/tests/ui-internal/slow_symbol_comparisons.rs
@@ -0,0 +1,24 @@
+#![feature(rustc_private)]
+#![warn(clippy::slow_symbol_comparisons)]
+
+extern crate rustc_span;
+
+use clippy_utils::sym;
+use rustc_span::Symbol;
+
+fn main() {
+    let symbol = sym!(example);
+    let other_symbol = sym!(other_example);
+
+    // Should lint
+    let slow_comparison = symbol == Symbol::intern("example");
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+    let slow_comparison_macro = symbol == sym!(example);
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+    let slow_comparison_backwards = sym!(example) == symbol;
+    //~^ error: comparing `Symbol` via `Symbol::intern`
+
+    // Should not lint
+    let faster_comparison = symbol.as_str() == "other_example";
+    let preinterned_comparison = symbol == other_symbol;
+}
diff --git a/tests/ui-internal/slow_symbol_comparisons.stderr b/tests/ui-internal/slow_symbol_comparisons.stderr
new file mode 100644
index 00000000000..72cb20a7fed
--- /dev/null
+++ b/tests/ui-internal/slow_symbol_comparisons.stderr
@@ -0,0 +1,23 @@
+error: comparing `Symbol` via `Symbol::intern`
+  --> tests/ui-internal/slow_symbol_comparisons.rs:14:27
+   |
+LL |     let slow_comparison = symbol == Symbol::intern("example");
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `Symbol::as_str` and check the string instead: `symbol.as_str() == "example"`
+   |
+   = note: `-D clippy::slow-symbol-comparisons` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::slow_symbol_comparisons)]`
+
+error: comparing `Symbol` via `Symbol::intern`
+  --> tests/ui-internal/slow_symbol_comparisons.rs:16:33
+   |
+LL |     let slow_comparison_macro = symbol == sym!(example);
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^^ help: use `Symbol::as_str` and check the string instead: `symbol.as_str() == "example"`
+
+error: comparing `Symbol` via `Symbol::intern`
+  --> tests/ui-internal/slow_symbol_comparisons.rs:18:37
+   |
+LL |     let slow_comparison_backwards = sym!(example) == symbol;
+   |                                     ^^^^^^^^^^^^^^^^^^^^^^^ help: use `Symbol::as_str` and check the string instead: `symbol.as_str() == "example"`
+
+error: aborting due to 3 previous errors
+
diff --git a/tests/ui-internal/unnecessary_symbol_str.fixed b/tests/ui-internal/unnecessary_symbol_str.fixed
index eb79fdbc4b4..8e7f020c1f6 100644
--- a/tests/ui-internal/unnecessary_symbol_str.fixed
+++ b/tests/ui-internal/unnecessary_symbol_str.fixed
@@ -1,6 +1,7 @@
 #![feature(rustc_private)]
 #![deny(clippy::internal)]
 #![allow(
+    clippy::slow_symbol_comparisons,
     clippy::borrow_deref_ref,
     clippy::unnecessary_operation,
     unused_must_use,
diff --git a/tests/ui-internal/unnecessary_symbol_str.rs b/tests/ui-internal/unnecessary_symbol_str.rs
index bbea13af92a..9aeeb9aaf3a 100644
--- a/tests/ui-internal/unnecessary_symbol_str.rs
+++ b/tests/ui-internal/unnecessary_symbol_str.rs
@@ -1,6 +1,7 @@
 #![feature(rustc_private)]
 #![deny(clippy::internal)]
 #![allow(
+    clippy::slow_symbol_comparisons,
     clippy::borrow_deref_ref,
     clippy::unnecessary_operation,
     unused_must_use,
diff --git a/tests/ui-internal/unnecessary_symbol_str.stderr b/tests/ui-internal/unnecessary_symbol_str.stderr
index 551167a9ff5..668c11722f9 100644
--- a/tests/ui-internal/unnecessary_symbol_str.stderr
+++ b/tests/ui-internal/unnecessary_symbol_str.stderr
@@ -1,5 +1,5 @@
 error: unnecessary `Symbol` to string conversion
-  --> tests/ui-internal/unnecessary_symbol_str.rs:15:5
+  --> tests/ui-internal/unnecessary_symbol_str.rs:16:5
    |
 LL |     Symbol::intern("foo").as_str() == "clippy";
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Symbol::intern("foo") == rustc_span::sym::clippy`
@@ -12,25 +12,25 @@ LL | #![deny(clippy::internal)]
    = note: `#[deny(clippy::unnecessary_symbol_str)]` implied by `#[deny(clippy::internal)]`
 
 error: unnecessary `Symbol` to string conversion
-  --> tests/ui-internal/unnecessary_symbol_str.rs:16:5
+  --> tests/ui-internal/unnecessary_symbol_str.rs:17:5
    |
 LL |     Symbol::intern("foo").to_string() == "self";
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Symbol::intern("foo") == rustc_span::symbol::kw::SelfLower`
 
 error: unnecessary `Symbol` to string conversion
-  --> tests/ui-internal/unnecessary_symbol_str.rs:17:5
+  --> tests/ui-internal/unnecessary_symbol_str.rs:18:5
    |
 LL |     Symbol::intern("foo").to_ident_string() != "Self";
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Symbol::intern("foo") != rustc_span::symbol::kw::SelfUpper`
 
 error: unnecessary `Symbol` to string conversion
-  --> tests/ui-internal/unnecessary_symbol_str.rs:18:5
+  --> tests/ui-internal/unnecessary_symbol_str.rs:19:5
    |
 LL |     &*Ident::empty().as_str() == "clippy";
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Ident::empty().name == rustc_span::sym::clippy`
 
 error: unnecessary `Symbol` to string conversion
-  --> tests/ui-internal/unnecessary_symbol_str.rs:19:5
+  --> tests/ui-internal/unnecessary_symbol_str.rs:20:5
    |
 LL |     "clippy" == Ident::empty().to_string();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `rustc_span::sym::clippy == Ident::empty().name`