break up lints.rs into separate files

components/plugins/lints/str_to_string.rs

@@ -0,0 +1,48 @@
+/* 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 syntax::ast;
+use rustc::lint::{Context, LintPass, LintArray};
+use rustc::middle::ty::expr_ty;
+use rustc::middle::ty;
+use rustc::middle::typeck::astconv::AstConv;
+
+declare_lint!(STR_TO_STRING, Deny,
+              "Warn when a String could use into_string() instead of to_string()")
+
+/// Prefer str.into_string() 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)
+    }
+
+    fn check_expr(&mut self, cx: &Context, expr: &ast::Expr) {
+        match expr.node {
+            ast::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.into_string() is more efficient than str.to_string(), please use it instead");
+            },
+            _ => ()
+        }
+
+        fn is_str(cx: &Context, expr: &ast::Expr) -> bool {
+            fn walk_ty<'t>(ty: ty::t) -> ty::t {
+                match ty::get(ty).sty {
+                    ty::ty_ptr(ref tm) | ty::ty_rptr(_, ref tm) => walk_ty(tm.ty),
+                    _ => ty
+                }
+            }
+            match ty::get(walk_ty(expr_ty(cx.tcx, expr))).sty {
+                ty::ty_str => true,
+                _ => false
+            }
+        }
+    }
+}