Pass a Symbol to check_name, emit_feature_err, and related functions.

src/librustc_plugin/build.rs

@@ -1,6 +1,7 @@
 //! Used by `rustc` when compiling a plugin crate.
 
 use syntax::attr;
+use syntax::symbol::sym;
 use syntax_pos::Span;
 use rustc::hir::itemlikevisit::ItemLikeVisitor;
 use rustc::hir;
@@ -15,8 +16,7 @@ struct RegistrarFinder {
 impl<'v> ItemLikeVisitor<'v> for RegistrarFinder {
     fn visit_item(&mut self, item: &hir::Item) {
         if let hir::ItemKind::Fn(..) = item.node {
-            if attr::contains_name(&item.attrs,
-                                   "plugin_registrar") {
+            if attr::contains_name(&item.attrs, sym::plugin_registrar) {
                 self.registrars.push((item.hir_id, item.span));
             }
         }

src/librustc_plugin/load.rs

@@ -11,6 +11,7 @@ use std::mem;
 use std::path::PathBuf;
 use syntax::ast;
 use syntax::span_err;
+use syntax::symbol::sym;
 use syntax_pos::{Span, DUMMY_SP};
 
 /// Pointer to a registrar function.
@@ -45,7 +46,7 @@ pub fn load_plugins(sess: &Session,
     // the feature enabled will result in an error later...
     if sess.features_untracked().plugin {
         for attr in &krate.attrs {
-            if !attr.check_name("plugin") {
+            if !attr.check_name(sym::plugin) {
                 continue;
             }
 

src/librustc_plugin/registry.rs

@@ -49,7 +49,7 @@ pub struct Registry<'a> {
     pub llvm_passes: Vec<String>,
 
     #[doc(hidden)]
-    pub attributes: Vec<(String, AttributeType)>,
+    pub attributes: Vec<(Symbol, AttributeType)>,
 }
 
 impl<'a> Registry<'a> {
@@ -169,7 +169,7 @@ impl<'a> Registry<'a> {
     /// Registered attributes will bypass the `custom_attribute` feature gate.
     /// `Whitelisted` attributes will additionally not trigger the `unused_attribute`
     /// lint. `CrateLevel` attributes will not be allowed on anything other than a crate.
-    pub fn register_attribute(&mut self, name: String, ty: AttributeType) {
+    pub fn register_attribute(&mut self, name: Symbol, ty: AttributeType) {
         self.attributes.push((name, ty));
     }
 }