Junio C Hamano venit, vidit, dixit 08.02.2017 23:55: > Ashutosh Bapat <ashutosh.bapat@xxxxxxxxxxxxxxxx> writes: > >> I have been using git rebase heavily these days and seem to have found a bug. >> >> If there are two commit messages which have same prefix e.g. >> yyyyyy This is prefix >> xxxxxx This is prefix and message >> >> xxxxxx comitted before yyyyyy >> >> Now I commit a fixup to yyyyyy using git commit --fixup yyyyyy >> zzzzzz fixup! This is prefix >> >> When I run git rebase -i --autosquash, the script it shows me looks like >> pick xxxxxx This is prefix and message >> fixup zzzzzz fixup! This is prefix >> pick yyyyyy This is prefix >> >> I think the correct order is >> pick xxxxxx This is prefix and message >> pick yyyyyy This is prefix >> fixup zzzzzz fixup! This is prefix >> >> Is that right? > > Because "commit" pretends as if it took the exact commit object name > to be fixed up (after all, it accepts "yyyyyy" that is a name of the > commit object), it would be nice if the fixup is applied to that > exact commit, even if you had many commits that share exactly the > same title (i.e. not just shared prefix). > > Unfortunately, "rebase -i --autosquash" reorders the entries by > identifying the commit by its title, and it goes with prefix match > so that fix-up commits created without using --fixup option but > manually records the title's prefix substring can also work. > > We could argue that the logic should notice that there is one exact > match and another non-exact prefix match and favor the former, and > certainly such a change would make your made-up example (you didn't > actually have a commit whose title is literally "This is prefix") > above work better. > > But I am not sure if adding such heuristics would really help in > general. It would not help those whose commits are mostly titled > ultra-vaguely, like "fix", "bugfix", "docfix", etc. > > Another possibility is to teach "commit --fixup" to cast exact > commit object name in stone. That certainly would solve your > immediate problem, but it has a grave negative impact when the user > rebases the same topic many times (which happens often). > > For example, I may have a series of commits A and B, notice that A > could be done a bit better and have "fixup A" on top, build a new > commit C on it, and then realize that the next step (i.e. D) would > need support from a newer codebase than where I started (i.e. A^). > > At that point, I would have a 4-commit series (A, B, "fixup A", and > C), and I would rebase them on top of something newer. I am > undecided if that "fixup A" is really an improvement or unnecessary, > when I do this, but I do know that I want to build the series on top > of a different commit. So I do rebase without --autosquash (I would > probably rebase without --interactive for this one). > > Then I keep working and add a new commit D on top. After all that, > I would have a more-or-less completed series and would be ready to > re-assess the whole series. I perhaps decide that "fixup A" is > really an improvement. And then I would "rebase -i" to squash the > fix-up into A. > > But notice that at this point, what we are calling A has different > object name than the original A the fixup was written for, because > we rebased once on top of a newer codebase. That commit can still > be identified by its title, but not with its original commit object > name. > > I think that is why "commit --fixup <commit>" turns the commit > object name (your "yyyyyy") into a string (your "This is prefix") > and that is a reasonable design decision [*1*]. > > So from that point of view, if we were to address your issue, it > should happen in "rebase -i --autosquash" side, not "commit --fixup" > side. > > Let's hear from some of those (Cc'ed) who were involved in an > earlier --autosquash thread. > > https://public-inbox.org/git/cover.1259934977.git.mhagger@xxxxxxxxxxxx/ > > > [Footnote] > > *1* "rebase -i --autosquash" does understand "fixup! yyyyyy", so if > you are willing to accept the consequence of not being able to > rebase twice, you could instead do > > $ git commit -m "fixup! yyyyyy" > > I would think. Doesn't this indicate that rebase is fine as is? How about: - introduce "git commit --fixup-fixed=<rev>" or the like which parses <rev> commits "-m fixup! <sha1>" - teach "git commit --fixup=<rev>" to check for duplicates (same prefix, maybe only in "recent" history) and make it issue a warning, say: prefix <prefix> matches the following commits: <sha1> <subject> Issue git commit --amend -m 'fixup! <sha1>' to fixup a specific commit. (Or git commit --amend --fixup-fixed=<rev> if that flies.) Additionally, we could teach commit --fixup-fixed to commit -m "fixup! <sha1> <prefix>" so that we have both uniqueness and verbosity in the rebase-i-editor. This would allow "rebase -i" to fall back to the old mode when "<sha1>" is not in the range it operates on. We could also try to rewrite <sha1>s when rebasing (without squashing) fixup!-commits, of course. Michael