---

yaml
---
r: 137622
b: refs/heads/master
c: 7a07f2a
h: refs/heads/master
v: v3

Author: nikomatsakis

[refs]

@@ -1,5 +1,5 @@
 ---
-refs/heads/master: 2bb0796ae27b3b1c0563f1779680e63b2ca322c3
+refs/heads/master: 7a07f2a78092b3381d44a86330eb2de364aafb95
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: 78a7676898d9f80ab540c6df5d4c9ce35bb50463
 refs/heads/try: cd53dac86b43e0b46f06ab265b71526242a2fc5e

trunk/src/librustc/middle/traits/select.rs

@@ -109,6 +109,7 @@ enum BuiltinBoundConditions {
     AmbiguousBuiltin
 }
 
+#[deriving(Show)]
 enum EvaluationResult {
     EvaluatedToOk,
     EvaluatedToErr,
@@ -246,7 +247,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                obligation.repr(self.tcx()));
 
         let stack = self.push_stack(previous_stack.map(|x| x), obligation);
-        self.evaluate_stack(&stack)
+        let result = self.evaluate_stack(&stack);
+        debug!("result: {}", result);
+        result
     }
 
     fn evaluate_stack(&mut self,
@@ -259,6 +262,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // that does provide an impl.
         let input_types = &stack.skol_trait_ref.substs.types;
         if input_types.iter().any(|&t| ty::type_is_skolemized(t)) {
+            debug!("evaluate_stack({}) --> unbound argument, must be ambiguous",
+                   stack.skol_trait_ref.repr(self.tcx()));
             return EvaluatedToAmbig;
         }
 
@@ -286,6 +291,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .skip(1) // skip top-most frame
             .any(|prev| stack.skol_trait_ref == prev.skol_trait_ref)
         {
+            debug!("evaluate_stack({}) --> recursive",
+                   stack.skol_trait_ref.repr(self.tcx()));
             return EvaluatedToOk;
         }