Make default_trait_impls private and add accessor

src/librustc/middle/traits/select.rs

@@ -1149,7 +1149,7 @@ fn assemble_candidates_from_impls(&mut self,
             });
         }
 
-        if self.tcx().default_trait_impls.borrow().contains(&def_id) {
+        if ty::trait_has_default_impl(self.tcx(), def_id) {
             candidates.vec.push(DefaultTraitCandidate(def_id.clone()))
         }
 

src/librustc/middle/ty.rs

@@ -758,7 +758,7 @@ pub struct ctxt<'tcx> {
     pub trait_impls: RefCell<DefIdMap<Rc<RefCell<Vec<ast::DefId>>>>>,
 
     /// Maps a trait onto a list of *default* trait implementations
-    pub default_trait_impls: RefCell<DefIdSet>,
+    default_trait_impls: RefCell<DefIdSet>,
 
     /// Maps a DefId of a type to a list of its inherent impls.
     /// Contains implementations of methods that are inherent to a type.
@@ -5999,6 +5999,10 @@ pub fn item_variances(tcx: &ctxt, item_id: ast::DefId) -> Rc<ItemVariances> {
         || Rc::new(csearch::get_item_variances(&tcx.sess.cstore, item_id)))
 }
 
+pub fn trait_has_default_impl(tcx: &ctxt, trait_def_id: DefId) -> bool {
+    tcx.default_trait_impls.borrow().contains(&trait_def_id)
+}
+
 /// Records a trait-to-implementation mapping.
 pub fn record_default_trait_implementation(tcx: &ctxt, trait_def_id: DefId) {