avoid some Symbol to String conversions

Author: TaKO8Ki

clippy_lints/src/format.rs

@@ -82,7 +82,7 @@ impl<'tcx> LateLintPass<'tcx> for UselessFormat {
                 then {
                     let is_new_string = match value.kind {
                         ExprKind::Binary(..) => true,
-                        ExprKind::MethodCall(path, ..) => path.ident.name.as_str() == "to_string",
+                        ExprKind::MethodCall(path, ..) => path.ident.name == sym::to_string,
                         _ => false,
                     };
                     let sugg = if format_args.format_string_span.contains(value.span) {

clippy_lints/src/inherent_to_string.rs

@@ -98,7 +98,7 @@ impl<'tcx> LateLintPass<'tcx> for InherentToString {
         if_chain! {
             // Check if item is a method, called to_string and has a parameter 'self'
             if let ImplItemKind::Fn(ref signature, _) = impl_item.kind;
-            if impl_item.ident.name.as_str() == "to_string";
+            if impl_item.ident.name == sym::to_string;
             let decl = &signature.decl;
             if decl.implicit_self.has_implicit_self();
             if decl.inputs.len() == 1;

clippy_lints/src/methods/unnecessary_to_owned.rs

@@ -427,5 +427,5 @@ fn is_cow_into_owned(cx: &LateContext<'_>, method_name: Symbol, method_def_id: D
 
 /// Returns true if the named method is `ToString::to_string`.
 fn is_to_string(cx: &LateContext<'_>, method_name: Symbol, method_def_id: DefId) -> bool {
-    method_name.as_str() == "to_string" && is_diag_trait_item(cx, method_def_id, sym::ToString)
+    method_name == sym::to_string && is_diag_trait_item(cx, method_def_id, sym::ToString)
 }