git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: ZheNing Hu <adlternative@gmail.com>
To: Elijah Newren <newren@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>,
	Christian Couder <christian.couder@gmail.com>,
	Git List <git@vger.kernel.org>,
	vascomalmeida@sapo.pt
Subject: Re: Question about pre-merge and git merge octopus strategy
Date: Thu, 19 May 2022 21:15:19 +0800	[thread overview]
Message-ID: <CAOLTT8TDomk9zUg49yrhpu1T776FKrnu7RGJ_bx9iaYKUEvvTg@mail.gmail.com> (raw)
In-Reply-To: <CABPp-BGOGLUPOn20yWzCrBYCykiet0=5UfbkuGC78f-QoWVvYg@mail.gmail.com>

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?

  parent reply	other threads:[~2022-05-19 13:15 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-06  8:14 ZheNing Hu
2022-05-06 17:23 ` Christian Couder
2022-05-07  4:09   ` Elijah Newren
2022-05-07 18:37     ` Junio C Hamano
2022-05-08 14:44     ` ZheNing Hu
2022-05-10  7:07       ` Elijah Newren
2022-05-11 11:21         ` ZheNing Hu
2022-05-12 15:04           ` Elijah Newren
2022-05-12 15:39             ` Junio C Hamano
2022-05-13  5:15               ` Elijah Newren
2022-05-13 12:56                 ` Junio C Hamano
2022-05-19 13:15                 ` ZheNing Hu [this message]
2022-05-19 14:46                   ` Elijah Newren
2022-05-08 14:13   ` ZheNing Hu
2022-05-08 15:01 ` Carlo Marcelo Arenas Belón

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAOLTT8TDomk9zUg49yrhpu1T776FKrnu7RGJ_bx9iaYKUEvvTg@mail.gmail.com \
    --to=adlternative@gmail.com \
    --cc=christian.couder@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=newren@gmail.com \
    --cc=vascomalmeida@sapo.pt \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this inbox:

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).