Re: Question about pre-merge and git merge octopus strategy

>
> Elijah Newren <newren@gmail.com> 于2022年5月13日周五 13:16写道：
> >
> > On Thu, May 12, 2022 at 8:39 AM Junio C Hamano <gitster@pobox.com> wrote:
> > >
> > > Elijah Newren <newren@gmail.com> writes:
> > >
> > > >     Merge with strategy octopus failed.
> > > >
> > > > Also, if we check `git status`:
> > > >
> > > >     $ git status
> > > >     On branch main
> > > >     Unmerged paths:
> > > >       (use "git restore --staged <file>..." to unstage)
> > > >       (use "git add <file>..." to mark resolution)
> > > >     both modified:   base
> > > >
> > > >     no changes added to commit (use "git add" and/or "git commit -a")
> > > >
> > > > And in git-merge-octopus.sh we see:
> > > >
> > > >     case "$OCTOPUS_FAILURE" in
> > > >     1)
> > > >     # We allow only last one to have a hand-resolvable
> > > >     # conflicts.  Last round failed and we still had
> > > >     # a head to merge.
> > > >     gettextln "Automated merge did not work."
> > > >     gettextln "Should not be doing an octopus."
> > > >     exit 2
> > > >     esac
> > > >
> > > > and in builtin/merge.c, we see:
> > > >
> > > >     /*
> > > >      * The backend exits with 1 when conflicts are
> > > >      * left to be resolved, with 2 when it does not
> > > >      * handle the given merge at all.
> > > >      */
> > > >
> > > > Which means git-merge-octopus.sh is claiming it can't handle this type
> > > > of merge, and some other merge strategy should be tried, and
> > > > implicitly that it didn't leave any conflicts to be resolved because
> > > > it can't handle this merge.
> > >
> > > Correct.  Near the beginning of the loop you found the above
> > > comment, there is this code:
> > >
> > >         if (use_strategies_nr == 1 ||
> > >             /*
> > >              * Stash away the local changes so that we can try more than one.
> > >              */
> > >             save_state(&stash))
> > >                 oidclr(&stash);
> > >
> > >         for (i = 0; !merge_was_ok && i < use_strategies_nr; i++) {
> > >                 int ret, cnt;
> > >                 if (i) {
> > >                         printf(_("Rewinding the tree to pristine...\n"));
> > >                         restore_state(&head_commit->object.oid, &stash);
> > >                 }
> >
> > Side-comment, which becomes important below: The save/restore code in
> > builtin/merge.c appears to be broken to me.  As noted in the code
> > above, stash will be set to null_oid() if save_state() returns
> > non-zero (which happens when "stash create" has no output, which
> > happens if there is _initially_ no state to save, i.e. if there are no
> > local changes before the merge started).  restore_state() is a no-op
> > whenever stash is the null_oid, meaning in that case it won't actually
> > rewind the tree to a pristine state to undo the changes of the
> > previous merge attempt.  So, if:
> >
> > * The user had no local changes before starting the merge
> > * Multiple merge strategies are applicable
> > * The first merge strategy makes index/working-tree changes, but
> > returns with exit status 2
> >
> > Then the restore_state() called before the second merge strategy will
> > do nothing, and the second merge strategy will be working on an index
> > and working tree with garbage leftover from the first merge strategy.
> > While this may have never been triggered (in what case do we have
> > multiple merge strategies that all return an exit status of 2?), I
> > suspect we want to fix this problem with something like this:
> >
> > diff --git a/builtin/merge.c b/builtin/merge.c
> > index f178f5a3ee..7f3650fb09 100644
> > --- a/builtin/merge.c
> > +++ b/builtin/merge.c
> > @@ -378,11 +378,11 @@ static void restore_state(const struct object_id *head,
> >         struct strbuf sb = STRBUF_INIT;
> >         const char *args[] = { "stash", "apply", NULL, NULL };
> >
> > +       reset_hard(head, 1);
> > +
> >         if (is_null_oid(stash))
> >                 return;
> >
> > -       reset_hard(head, 1);
> > -
> >         args[2] = oid_to_hex(stash);
> >
> >         /*
> >
>
> It looks like this code can go back to the old state now?
>
> I think if we can handle it as special case when:
>
> 1. Use octopus merge without other strategies (no friend).
> 2. Merge failed, so we don't have the best strategy.
>
> Then we force restore the original state?