roachpb: improve RangeDescriptor.Validate

Make sure there isn't more than one replica per store.

Release note: None

pkg/roachpb/metadata.go

@@ -220,6 +220,7 @@ func (r *RangeDescriptor) Validate() error {
 		return errors.Errorf("NextReplicaID must be non-zero")
 	}
 	seen := map[ReplicaID]struct{}{}
+	stores := map[StoreID]struct{}{}
 	for i, rep := range r.Replicas().All() {
 		if err := rep.Validate(); err != nil {
 			return errors.Errorf("replica %d is invalid: %s", i, err)
@@ -232,6 +233,10 @@ func (r *RangeDescriptor) Validate() error {
 			return errors.Errorf("ReplicaID %d must be less than NextReplicaID %d",
 				rep.ReplicaID, r.NextReplicaID)
 		}
+		if _, ok := stores[rep.StoreID]; ok {
+			return errors.Errorf("StoreID %d was reused", rep.StoreID)
+		}
+		stores[rep.StoreID] = struct{}{}
 	}
 	return nil
 }