Hi Elijah, On Sat, 4 Dec 2021, Elijah Newren via GitGitGadget wrote: > Range-diff vs v1: > > 1: 50812ed6fdf ! 1: 5d068486f9f name-rev: prefer shorter names over following merges > @@ Commit message > the printed name over fewer total parent traversals performed to get the > answer. > > + == Side-note on tie-breakers == > + > + When there are the same number of segments for two different names, we > + actually use the name of an ancestor commit as a tie-breaker as well. > + For example, for the commit cbdca289fb in the git.git repository, we > + prefer the name v2.33.0-rc0~112^2~1 over v2.33.0-rc0~57^2~5. This is > + because: > + > + * cbdca289fb is the parent of 25e65b6dd5, which implies the name for > + cbdca289fb should be the first parent of the preferred name for > + 25e65b6dd5 > + * 25e65b6dd5 could be named either v2.33.0-rc0~112^2 or > + v2.33.0-rc0~57^2~4, but the former is preferred over the latter due > + to fewer segments > + * combine the two previous facts, and the name we get for cbdca289fb > + is "v2.33.0-rc0~112^2~1" rather than "v2.33.0-rc0~57^2~5". > + > + Technically, we get this for free out of the implementation since we > + only keep track of one name for each commit as we walk history (and > + re-add parents to the queue if we find a better name for those parents), > + but the first bullet point above ensures users get results that feel > + more consistent. > + > + == Alternative Ideas and Meanings Discussed == > + > + One suggestion that came up during review was that shortest > + string-length might be easiest for users to consume. However, such a > + scheme would be rather computationally expensive (we'd have to track all > + names for each commit as we traversed the graph) and would additionally > + come with the possibly perplexing result that on a linear segment of > + history we could rapidly swap back and forth on names: > + MYTAG~3^2 would be preferred over MYTAG~9998 > + MYTAG~3^2~1 would NOT be preferred over MYTAG~9999 > + MYTAG~3^2~2 might be preferred over MYTAG~10000 > + > + Another item that came up was possible auxiliary semantic meanings for > + name-rev results either before or after this patch. The basic answer > + was that the previous implementation had no known useful auxiliary > + semantics, but that for many repositories (most in my experience), the > + new scheme does. In particular, the new name-rev output can often be > + used to answer the question, "How or when did this commit get merged?" > + Since that usefulness depends on how merges happen within the repository > + and thus isn't universally applicable, details are omitted here but you > + can see them at [1]. > + > + [1] https://lore.kernel.org/git/CABPp-BEeUM+3NLKDVdak90_UUeNghYCx=Dgir6=8ixvYmvyq3Q@xxxxxxxxxxxxxx/ > + > + Finally, it was noted that the algorithm could be improved by just > + explicitly tracking the number of segments and using both it and > + distance in the comparison, instead of giving a magic number that tries > + to blend the two (and which therefore might give suboptimal results in > + repositories with really huge numbers of commits that periodically merge > + older code). However, "[this patch] seems to give us a much better > + results than the current code, so let's take it and leave further > + futzing outside the scope." > + > Signed-off-by: Elijah Newren <newren@xxxxxxxxx> Very nice addition! And obviously, I am still in favor of moving this patch along in the direction of `main`. Thank you, Dscho
