Remove str_to_string lint

Specialization makes all of the options equally efficient.

components/plugins/lib.rs

@@ -70,5 +70,4 @@ fn register_clippy(reg: &mut Registry) {
 }
 #[cfg(not(feature = "clippy"))]
 fn register_clippy(reg: &mut Registry) {
-    reg.register_late_lint_pass(box lints::str_to_string::StrToStringPass);
 }

components/plugins/lints/mod.rs

@@ -5,6 +5,5 @@
 pub mod ban;
 pub mod inheritance_integrity;
 pub mod privatize;
-pub mod str_to_string;
 pub mod transmute_type;
 pub mod unrooted_must_root;

components/plugins/lints/str_to_string.rs

@@ -1,48 +0,0 @@
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-use rustc::lint::{LateContext, LintPass, LintArray, LateLintPass, LintContext};
-use rustc::ty;
-use rustc_front::hir;
-
-declare_lint!(STR_TO_STRING, Deny,
-              "Warn when a String could use to_owned() instead of to_string()");
-
-/// Prefer str.to_owned() over str.to_string()
-///
-/// The latter creates a `Formatter` and is 5x slower than the former
-pub struct StrToStringPass;
-
-impl LintPass for StrToStringPass {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(STR_TO_STRING)
-    }
-}
-
-impl LateLintPass for StrToStringPass {
-    fn check_expr(&mut self, cx: &LateContext, expr: &hir::Expr) {
-        match expr.node {
-            hir::ExprMethodCall(ref method, _, ref args)
-                if method.node.as_str() == "to_string"
-                && is_str(cx, &*args[0]) => {
-                cx.span_lint(STR_TO_STRING, expr.span,
-                             "str.to_owned() is more efficient than str.to_string(), please use it instead");
-            },
-            _ => ()
-        }
-
-        fn is_str(cx: &LateContext, expr: &hir::Expr) -> bool {
-            fn walk_ty<'t>(ty: ty::Ty<'t>) -> ty::Ty<'t> {
-                match ty.sty {
-                    ty::TyRef(_, ref tm) | ty::TyRawPtr(ref tm) => walk_ty(tm.ty),
-                    _ => ty
-                }
-            }
-            match walk_ty(cx.tcx.expr_ty(expr)).sty {
-                ty::TyStr => true,
-                _ => false
-            }
-        }
-    }
-}

components/util/opts.rs

@@ -518,7 +518,6 @@ pub fn default_opts() -> Opts {
     }
 }
 
-#[allow(str_to_string)]
 pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     let (app_name, args) = args.split_first().unwrap();