---

yaml
---
r: 273157
b: refs/heads/beta
c: 1726c1b
h: refs/heads/master
i:
  273155: 141e97b

Author: aturon

[refs]

@@ -23,7 +23,7 @@ refs/tags/0.9: 36870b185fc5f5486636d4515f0e22677493f225
 refs/tags/0.10: ac33f2b15782272ae348dbd7b14b8257b2148b5a
 refs/tags/0.11.0: e1247cb1d0d681be034adb4b558b5a0c0d5720f9
 refs/tags/0.12.0: f0c419429ef30723ceaf6b42f9b5a2aeb5d2e2d1
-refs/heads/beta: eaf2f909561c3b2c26ee8d40ac7a95e89c5034d9
+refs/heads/beta: 1726c1b54a12b9f499affdc3ef0b769f3de15a23
 refs/tags/1.0.0-alpha: e42bd6d93a1d3433c486200587f8f9e12590a4d7
 refs/heads/tmp: e06d2ad9fcd5027bcaac5b08fc9aa39a49d0ecd3
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f

branches/beta/src/librustc/middle/traits/specialize/specialization_graph.rs

@@ -65,6 +65,8 @@ impl Graph {
         let trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
         let trait_def_id = trait_ref.def_id;
 
+        debug!("inserting TraitRef {:?} into specialization graph", trait_ref);
+
         // if the reference itself contains an earlier error (e.g., due to a
         // resolution failure), then we just insert the impl at the top level of
         // the graph and claim that there's no overlap (in order to supress
@@ -99,10 +101,16 @@ impl Graph {
                     let ge = specializes(tcx, possible_sibling, impl_def_id);
 
                     if le && !ge {
+                        let parent_trait_ref = tcx.impl_trait_ref(possible_sibling).unwrap();
+                        debug!("descending as child of TraitRef {:?}", parent_trait_ref);
+
                         // the impl specializes possible_sibling
                         parent = possible_sibling;
                         continue 'descend;
                     } else if ge && !le {
+                        let child_trait_ref = tcx.impl_trait_ref(possible_sibling).unwrap();
+                        debug!("placing as parent of TraitRef {:?}", child_trait_ref);
+
                         // possible_sibling specializes the impl
                         *slot = impl_def_id;
                         self.parent.insert(impl_def_id, parent);
@@ -123,6 +131,7 @@ impl Graph {
             }
 
             // no overlap with any potential siblings, so add as a new sibling
+            debug!("placing as new sibling");
             self.parent.insert(impl_def_id, parent);
             possible_siblings.push(impl_def_id);
             return Ok(());