We already have FieldInfo/s to record which fields were indexed; I
think we should make this public (experimental) to replace
Patch, tests pass. I think it's ready!
New patch; I fixed the composite readers to throw UOE from getFieldInfos, to match how I port to 4.0. I added ReaderUtil.getMergedFieldInfos(IR) as sugar to do the merging from the subs...
I think it's ready.
patch looks good to me!