Add var to BoundRegion. Add query to get bound vars for applicable items.

compiler/rustc_middle/src/ty/context.rs

@@ -810,7 +810,7 @@ impl CanonicalUserType<'tcx> {
                             ty::ReLateBound(debruijn, br) => {
                                 // We only allow a `ty::INNERMOST` index in substitutions.
                                 assert_eq!(*debruijn, ty::INNERMOST);
-                                cvar == br.assert_bound_var()
+                                cvar == br.var
                             }
                             _ => false,
                         },
@@ -2672,6 +2672,17 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn object_lifetime_defaults(self, id: HirId) -> Option<Vec<ObjectLifetimeDefault>> {
         self.object_lifetime_defaults_map(id.owner)
     }
+
+    pub fn late_bound_vars(self, id: HirId) -> &'tcx List<ty::BoundVariableKind> {
+        self.mk_bound_variable_kinds(
+            self.late_bound_vars_map(id.owner)
+                .and_then(|map| map.get(&id.local_id).cloned())
+                .unwrap_or_else(|| {
+                    bug!("No bound vars found for {:?} ({:?})", self.hir().node_to_string(id), id)
+                })
+                .iter(),
+        )
+    }
 }
 
 impl TyCtxtAt<'tcx> {