docs: public static ApiDiff fromProto(Diff diff) {
      ImmutableSet.Builder<String> unsupportedClasses = ImmutableSet.builder();
      ImmutableSetMultimap.Builder<String, ClassMemberKey> unsupportedMembersByClass =
          ImmutableSetMultimap.builder();
      for (ApiDiffProto.ClassDiff c : diff.getClassDiffList()) {
        switch (c.getDiffCase()) {
          case EVERYTHING_DIFF:
            unsupportedClasses.add(c.getEverythingDiff().getClassName());
            break;
          case MEMBER_DIFF:
            ApiDiffProto.MemberDiff memberDiff = c.getMemberDiff();
            for (ApiDiffProto.ClassMember member : memberDiff.getMemberList()) {
              unsupportedMembersByClass.put(
                  memberDiff.getClassName(),
                  ClassMemberKey.create(member.getIdentifier(), member.getMemberDescriptor()));
            }
            break;
          default:
            throw new AssertionError(c.getDiffCase());
        }
      }
      return new AutoValue_ApiDiff(unsupportedClasses.build(), unsupportedMembersByClass.build());
    }