---

yaml
---
r: 137555
b: refs/heads/snap-stage3
c: 7a07f2a
h: refs/heads/master
i:
  137553: a18d688
  137551: 62f89fa
v: v3

Author: nikomatsakis

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: 63fe80e1ffd036e99e1c707116774ac10203e2f1
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 2bb0796ae27b3b1c0563f1779680e63b2ca322c3
+refs/heads/snap-stage3: 7a07f2a78092b3381d44a86330eb2de364aafb95
 refs/heads/try: cd53dac86b43e0b46f06ab265b71526242a2fc5e
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/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;
         }