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

Author: bors

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)));