Auto merge of rust-lang#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

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`

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

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.

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,

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 ()

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

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!(

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),

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

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)));

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)
         {

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),

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;
 
@@ -95,15 +95,15 @@ 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);
         }
     }
 }
 
 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;

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,

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));

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)

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)
             {

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

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;

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)

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)
     {

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));
             }
         }

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,
                 }
         },