On Wed, Jun 23, 2021 at 10:53:25AM +0100, Phillip Wood wrote: > > Thanks for figuring that out. I agree that the output after the patch > > you showed is correct, in the sense that the common lines show up in the > > base now. It does feel like it's working against the point of zdiff3, > > though, which is to reduce the number of common lines shown in the > > "ours" and "theirs" hunks. > > I agree - the output is longer rather than shorter. As we only want to trim > the common prefix and suffix from the conflicts I wonder if it would be > better to special case zdiff3 rather than piggy backing on the existing > XDL_MERGE_ZEALOUS implementation. We can trim the common lines by looping > over the begging and end of the hunk comparing the lines with xdl_recmatch() > without going to the trouble of diffing them as XDL_MERGE_ZEALOUS does. I > don't think we need to worry about coalescing adjacent conflicts for zdiff3. > It makes sense to coalesce in the XDL_MERGE_ZEALOUS case as it can > potentially split a N line conflict hunk into N/2 single line conflict > hunks but zdiff3 does not split conflict hunks. That matches my intuition of a reasonable path forward (but I confess to not being too well-versed in the details of the XDL_MERGE internals). > Yes, I think the heuristic for coalescing conflict hunks could be improved. > It would be fairly simple to only join two hunks if the conflicts are longer > that the context between them and the existing XDL_MERGE_ZEALOUS_ALNUM logic > allows conflicts with more context between them to be coalesced if the > context lines are uninteresting. I think XDL_MERGE_ZEALOUS_ALNUM is only > used by `git merge-file` at the moment, with everything else going through > ll_merge() which uses XDL_MERGE_ZEALOUS I don't recall much discussion around using ALNUM versus not, nor could I find much in the archive. It looks like merge-file was converted to show off ALNUM when it was added in ee95ec5d58 (xdl_merge(): introduce XDL_MERGE_ZEALOUS_ALNUM, 2008-02-17), and it never really progressed from there. It might be an interesting exercise to re-run a bunch of merges and see if ALNUM produces better (or worse) results on the whole. -Peff
