> where do i get the "OLD" one ?
The approach I suggested in the Lucene issue was to have some ant properties that determine the subversion tag url of the prior version. In trunk this would point to the prior release. We'd update it in trunk after each release is made. Then the ant build script would check this out in build/ if it didn't already exist there. We could (and should) permit this to be optimized, perhaps by permitting folks to override a property so that the prior version is stored somewhere more permanent than build/, and perhaps use 'svn switch; svn update' to make sure that the cached prior version contains what we expect.
> Does the user need to download and then pass the path to ant with -D option ?
I'd imagined that specifying -Djdiff.prior.dir would be optional, but would help performance a lot, but we could make it mandatory, and emit an error if it's not specified. That might reduce the load on subversion somewhat.