drive-by nits and debug

Co-authored-by: Tyler Mandry <[email protected]>

Author: nikomatsakis

src/librustc/traits/select.rs

@@ -1237,6 +1237,11 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         let mut candidates: Vec<EvaluatedCandidate> =
             candidates?.into_iter().filter_map(|c| c).collect();
 
+        debug!("winnowed to {} candidates for {:?}: {:?}",
+               candidates.len(),
+               stack,
+               candidates);
+
         // If there are STILL multiple candidate, we can further
         // reduce the list by dropping duplicates -- including
         // resolving specializations.

src/librustc/ty/mod.rs

@@ -2862,8 +2862,8 @@ fn param_env<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     }
     // Compute the bounds on Self and the type parameters.
 
-    let bounds = tcx.predicates_of(def_id).instantiate_identity(tcx);
-    let predicates = bounds.predicates;
+    let InstantiatedPredicates { predicates } =
+        tcx.predicates_of(def_id).instantiate_identity(tcx);
 
     // Finally, we have to normalize the bounds in the environment, in
     // case they contain any associated type projections. This process