Hi Ævar, On Tue, Mar 26, 2019 at 09:35:48PM +0100, Ævar Arnfjörð Bjarmason wrote: > > On Tue, Mar 26 2019, Denton Liu wrote: > > > Hi Ævar, > > > > On Tue, Mar 26, 2019 at 03:35:34PM +0100, Ævar Arnfjörð Bjarmason wrote: > >> > >> On Sat, Mar 23 2019, Denton Liu wrote: > >> > >> > This series teaches rebase the --keep-base option. > >> > > >> > 'git rebase --keep-base <upstream>' is equivalent to > >> > 'git rebase --onto <upstream>... <upstream>' or > >> > 'git rebase --onto $(git merge-base <upstream> HEAD) <upstream>' . > >> > > >> > This seems to be a common case that people (including myself!) run into; I was > >> > able to find these StackOverflow posts about this use case: > >> > > >> > * https://stackoverflow.com/questions/53234798/can-i-rebase-on-a-branchs-fork-point-without-explicitly-specifying-the-parent > >> > * https://stackoverflow.com/questions/41529128/how-do-you-rebase-only-changes-between-two-branches-into-another-branch > >> > * https://stackoverflow.com/a/4207357 > >> > >> Like with another series of yours I think this would be best squashed > >> into one patch. > > > > Will do. > > > >> > >> Maybe I've misunderstood this but isn't this like --fork-point except > >> with just plain "git merge-base" instead of "git merge-base > >> --fork-point", but then again 2/3 shows multiple base aren't supported, > >> but merge-base supports that. > >> > > > > --fork-point gets used to determine the _set of_ commits which are to be > > rebased, whereas --keep-base (and --onto) determine the base where that > > set of commits will be spliced. As a result, these two options cover > > orthogonal use-cases. > > Right. After playing with this a bit more though --fork-point is mostly > there, it it does find the same fork point, as evidenced all your tests > (that aren't asserting incompatibility with other options) passing with > this: > > diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh > index 9c2548423b..ab2d50e69a 100755 > --- a/t/t3416-rebase-onto-threedots.sh > +++ b/t/t3416-rebase-onto-threedots.sh > @@ -116,7 +116,7 @@ test_expect_success 'rebase --keep-base master from topic' ' > git checkout topic && > git reset --hard G && > > - git rebase --keep-base master && > + git rebase $(git merge-base --fork-point master HEAD) && > git rev-parse C >base.expect && > git merge-base master HEAD >base.actual && > test_cmp base.expect base.actual && > @@ -140,7 +140,7 @@ test_expect_success 'rebase -i --keep-base master from topic' ' > git reset --hard G && > > set_fake_editor && > - EXPECT_COUNT=2 git rebase -i --keep-base master && > + EXPECT_COUNT=2 git rebase -i $(git merge-base --fork-point master HEAD) && > git rev-parse C >base.expect && > git merge-base master HEAD >base.actual && > test_cmp base.expect base.actual && > > I've poked at some of this recently in > https://public-inbox.org/git/20190221214059.9195-3-avarab@xxxxxxxxx/ as > noted in the feedback there (I haven't gotten around to v2 yet) it's > entirely possible that I haven't understood this at all :) > > But it seems to me that this patch/implementation conflates two > unrelated things. > > Once is that we use --fork-point to mean that we're going to find the > divergence point with "merge-base --fork-point". This gets you halfway > to where you want to be, i.e. AFAICT the --keep-base and --fork-point > will always find the same commit for "git rebase" and "git rebase > --keep-base". See the "options.restrict_revision = get_fork_point(...)" > part of the code. I don't think this is true. The code that --keep-base uses to find the merge base is get_oid_mb, see the relevant snippet if (strstr(options.onto_name, "...")) { if (get_oid_mb(options.onto_name, &merge_base) < 0) whereas the --fork-point code uses get_fork_point, as you mentioned above. As a result, they don't necessarily refer to the same commit in the case where upstream is rewound. > > The other, which you want to disable, is that --fork-point *also* says > "OK, once we've found the divergence point, let's then rebase it on the > latest upstream. Or in the example above the "master" part of "git > merge-base --fork-point master HEAD". Correct, I guess in essence this is what I'm doing. > > Shouldn't --keep-base just be implemented in terms of skipping *that* > part, i.e. we find the fork point using the upstream info, but then > don't rebase *on* upstream. > > The reason the distinction matters is because with your patch these two > act differently: > > git rebase --keep-base > git rebase $(git merge-base @{u} HEAD) > > The latter will skip work ("Current branch master is up to date"), but > --keep-base will always re-rebase things. There's some cases where > --fork-point does that, which I was trying to address with my linked WIP > patch above. I believe this is desired behaviour. Suppose we have this (modified) graph from the git-merge-base docs, where B3 was formerly part of origin/master but it was then rewound: ---o---o---B2--o---o---o---B (origin/master) \ B3 \ Derived (local master) If we run "git rebase --keep-base", we'll get the following graph: ---o---o---B2--o---o---o---B (origin/master) \ Derived (local master) which I believe is the desired behaviour (we're abandoning B3 since upstream abandoned it). I hope I'm understanding you correctly. Please let me know if I've misinterpreted anything you've said or if anything I've said is unclear. Thanks, Denton > > Whereas the thing you actually want to work is: > > git rebase -i --keep-base > git rebase -i $(git merge-base @{u} HEAD) > > I.e. to have both of those allow you to re-arrange/fixup whatever and > still rebase on the same divergence point with @{u}, and won't run > rebase when there's no work to do unless you give it --force-rebase. > > > reason that --onto already disallows multiple bases. If we have multiple > > bases, how do we determine which one is the "true base" to use? It makes > > more sense to error out and let the user manually specify it. > > Ah, makes sense. > > >> I'd find something like the "DISCUSSION ON FORK-POINT MODE" in > >> git-merge-base helpful with examples of what we'd pick in the various > >> scenarios, and also if whatever commit this picks was something you > >> could have "git merge-base" spew out, so you could get what rebase would > >> do here from other tooling (which maybe is possible, but I'm confused by > >> the "no multiple bases"...). > > > > If I'm understanding you correctly then yes, this could be done with > > other tooling. See the 0/3 for equivalent commands. > > > > Perhaps I should update the rebase documentation to mention that > > --fork-point and --keep-base are orthogonal because it's unclear for > > you, it's probably unclear for other users as well. > > > > Thanks, > > > > Denton
