Record default implementations in a separate step

src/librustc/middle/traits/select.rs

@@ -847,6 +847,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         self.assemble_candidates_from_projected_tys(obligation, &mut candidates);
         try!(self.assemble_candidates_from_caller_bounds(stack, &mut candidates));
+        // Default implementations have lower priority, so we only
+        // consider triggering a default if there is no other impl that can apply.
+        if candidates.vec.len() == 0 {
+            try!(self.assemble_candidates_from_default_impls(obligation, &mut candidates));
+        }
         debug!("candidate list size: {}", candidates.vec.len());
         Ok(candidates)
     }
@@ -1142,6 +1147,20 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             });
         }
 
+        Ok(())
+    }
+
+    fn assemble_candidates_from_default_impls(&mut self,
+                                              obligation: &TraitObligation<'tcx>,
+                                              candidates: &mut SelectionCandidateSet<'tcx>)
+                                              -> Result<(), SelectionError<'tcx>>
+    {
+
+        let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
+        debug!("assemble_candidates_from_default_impls(self_ty={})", self_ty.repr(self.tcx()));
+
+        let def_id = obligation.predicate.def_id();
+
         if ty::trait_has_default_impl(self.tcx(), def_id) {
             match self_ty.sty {
                 ty::ty_trait(..) |
@@ -1323,7 +1342,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             }
             (&DefaultImplCandidate(_), _) => {
                 // Prefer other candidates over default implementations.
-                true
+                self.tcx().sess.bug(
+                    "default implementations shouldn't be recorded \
+                     when there are other valid candidates");
             }
             (&ProjectionCandidate, &ParamCandidate(_)) => {
                 // FIXME(#20297) -- this gives where clauses precedent

src/libtest/stats.rs

@@ -332,6 +332,7 @@ pub fn winsorize<T: Float + FromPrimitive>(samples: &mut [T], pct: T) {
 
 /// Returns a HashMap with the number of occurrences of every element in the
 /// sequence that the iterator exposes.
+#[cfg(not(stage0))]
 pub fn freq_count<T, U>(iter: T) -> hash_map::HashMap<U, uint>
   where T: Iterator<Item=U>, U: Eq + Clone + Hash
 {

src/test/compile-fail/coherence-default-trait-impl.rs

@@ -12,7 +12,9 @@
 
 #![feature(optin_builtin_traits)]
 
-trait MyTrait {}
+use std::marker::MarkerTrait;
+
+trait MyTrait: MarkerTrait {}
 
 impl MyTrait for .. {}
 

src/test/compile-fail/typeck-default-trait-impl-constituent-types-2.rs

@@ -10,7 +10,9 @@
 
 #![feature(optin_builtin_traits)]
 
-trait MyTrait {}
+use std::marker::MarkerTrait;
+
+trait MyTrait: MarkerTrait {}
 
 impl MyTrait for .. {}
 

src/test/compile-fail/typeck-default-trait-impl-constituent-types.rs

@@ -10,7 +10,9 @@
 
 #![feature(optin_builtin_traits)]
 
-trait MyTrait {}
+use std::marker::MarkerTrait;
+
+trait MyTrait: MarkerTrait {}
 
 impl MyTrait for .. {}
 impl<T> !MyTrait for *mut T {}
@@ -30,7 +32,4 @@ fn main() {
 
     is_mytrait::<MyS2>();
     //~^ ERROR the trait `MyTrait` is not implemented for the type `MyS2`
-
-    is_mytrait::<Vec<MyS3>>();
-    //~^ ERROR the trait `MyTrait` is not implemented for the type `*mut MyS3`
 }

src/test/compile-fail/typeck-default-trait-impl-negation.rs

@@ -10,11 +10,13 @@
 
 #![feature(optin_builtin_traits)]
 
-trait MyTrait {}
+use std::marker::MarkerTrait;
+
+trait MyTrait: MarkerTrait {}
 
 impl MyTrait for .. {}
 
-unsafe trait MyUnsafeTrait {}
+unsafe trait MyUnsafeTrait: MarkerTrait {}
 
 unsafe impl MyUnsafeTrait for .. {}
 

src/test/compile-fail/typeck-default-trait-impl-supertrait.rs

@@ -13,7 +13,9 @@
 
 #![feature(optin_builtin_traits)]
 
-trait NotImplemented { }
+use std::marker::MarkerTrait;
+
+trait NotImplemented: MarkerTrait { }
 
 trait MyTrait : NotImplemented {}
 

src/test/compile-fail/typeck-default-trait-impl-trait-where-clause.rs

@@ -15,9 +15,11 @@
 
 #![feature(optin_builtin_traits)]
 
-trait NotImplemented { }
+use std::marker::MarkerTrait;
 
-trait MyTrait
+trait NotImplemented: MarkerTrait { }
+
+trait MyTrait: MarkerTrait
     where Option<Self> : NotImplemented
 {}