docs: public Diff toProto() {
      ApiDiffProto.Diff.Builder builder = ApiDiffProto.Diff.newBuilder();
      for (String className : unsupportedClasses()) {
        builder.addClassDiff(
            ApiDiffProto.ClassDiff.newBuilder()
                .setEverythingDiff(ApiDiffProto.EverythingDiff.newBuilder().setClassName(className)));
      }
      for (String className : unsupportedMembersByClass().keySet()) {
        ApiDiffProto.MemberDiff.Builder memberDiff =
            ApiDiffProto.MemberDiff.newBuilder().setClassName(className);
        for (ClassMemberKey member : unsupportedMembersByClass().get(className)) {
          memberDiff.addMember(
              ApiDiffProto.ClassMember.newBuilder()
                  .setIdentifier(member.identifier())
                  .setMemberDescriptor(member.descriptor()));
        }
        builder.addClassDiff(ApiDiffProto.ClassDiff.newBuilder().setMemberDiff(memberDiff));
      }
      return builder.build();
    }