revlog: don't consider nullrev when choosing delta base In the most complex case, we try using the incoming delta base, then we try both parents, and then we try the previous revlog entry. If none of these result in a good delta, we natually use the null revision as base. However, we sometimes consider the nullrev before we have exhausted our other options. Specifically, when both parents are null, we use the nullrev as delta base if it produces a good delta (according to _isgooddelta()), and we fail to try the previous revlog entry as delta base. After 20a9226bdc8a (addrevision: use general delta when the incoming base delta is bad, 2015-12-01), it can also happen for non-merge commits when the incoming delta is not good. The Firefox repo (from many months back) shrinks a tiny bit with this patch: from 1.855GB to 1.830GB (1.4%). The hg repo itself shrinks even less: by less than 0.1%. There may be repos that get larger instead. This undoes the unexplained test change in 20a9226bdc8a.