storage: sort InternalReplicas before comparing

Fixes an issue where the in-memory copy of RangeDescriptor is
out-of-sync with the copy in kv.

Release note: None

pkg/storage/replica_command.go

@@ -1160,6 +1160,22 @@ func conditionalGetDescValueFromDB(
 			return nil, errors.Wrap(err, "decoding current range descriptor value")
 		}
 	}
+	// TODO(jeffreyxiao): This hacky fix ensures that we don't fail the
+	// conditional get because of the ordering of InternalReplicas. Calling
+	// Replicas() will sort the list of InternalReplicas as a side-effect. The
+	// invariant of having InternalReplicas sorted is not maintained in 19.1.
+	// Additionally, in 19.2, it's possible for the in-memory copy of
+	// RangeDescriptor to become sorted from a call to Replicas() without
+	// updating the copy in kv. These two factors makes it possible for the
+	// in-memory copy to be out of sync from the copy in kv. The sorted invariant
+	// of InternalReplicas is used by ReplicaDescriptors.Voters() and
+	// ReplicaDescriptors.Learners().
+	if existingDesc != nil {
+		existingDesc.Replicas() // for sorting side-effect
+	}
+	if expectation != nil {
+		expectation.Replicas() // for sorting side-effect
+	}
 	if !existingDesc.Equal(expectation) {
 		return nil, &roachpb.ConditionFailedError{ActualValue: existingDescKV.Value}
 	}