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. 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". 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. 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
