We currently only generate com.google.rpc classes that are used by GAPICs. In cases where handwritten libraries explicitly call other com.google.rpc classes via reflection, we've had to add configurations manually: googleapis/java-spanner#2617.

As pointed out in googleapis/java-spanner#2617 (comment), great care needs to be taken in order to ensure that such classes are covered through configurations if a library chooses to call them reflectively in the future. Generating configs for java-common-protos can mitigate the need for this but comes at a cost of extra configs being generate for the libraries.