better debug dumping with inference variables

src/librustc/infer/mod.rs

@@ -643,6 +643,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                             -> T::Lifted
         where T: TypeFoldable<'tcx> + ty::Lift<'gcx>
     {
+        debug!("drain_fulfillment_cx_or_panic()");
+
         let when = "resolving bounds after type-checking";
         let v = match self.drain_fulfillment_cx(fulfill_cx, result) {
             Ok(v) => v,
@@ -817,6 +819,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     fn start_snapshot(&self) -> CombinedSnapshot {
+        debug!("start_snapshot()");
+
         let obligations_in_snapshot = self.obligations_in_snapshot.get();
         self.obligations_in_snapshot.set(false);
 
@@ -854,7 +858,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     }
 
     fn commit_from(&self, snapshot: CombinedSnapshot) {
-        debug!("commit_from!");
+        debug!("commit_from()");
         let CombinedSnapshot { type_snapshot,
                                int_snapshot,
                                float_snapshot,

src/librustc/infer/type_variable.rs

@@ -178,7 +178,9 @@ impl<'tcx> TypeVariableTable<'tcx> {
             value: Bounded { relations: vec![], default: default },
             diverging: diverging
         });
-        ty::TyVid { index: index as u32 }
+        let v = ty::TyVid { index: index as u32 };
+        debug!("new_var() -> {:?}", v);
+        v
     }
 
     pub fn root_var(&mut self, vid: ty::TyVid) -> ty::TyVid {
@@ -219,6 +221,17 @@ impl<'tcx> TypeVariableTable<'tcx> {
     }
 
     pub fn rollback_to(&mut self, s: Snapshot) {
+        debug!("rollback_to{:?}", {
+            for action in self.values.actions_since_snapshot(&s.snapshot) {
+                match *action {
+                    sv::UndoLog::NewElem(index) => {
+                        debug!("inference variable _#{}t popped", index)
+                    }
+                    _ => { }
+                }
+            }
+        });
+
         self.values.rollback_to(s.snapshot);
         self.eq_relations.rollback_to(s.eq_snapshot);
     }