Re: [PATCH] doc: pull: fix rebase=false documentation

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: Jul 23, 2021, 18:29 UTC
Message-ID: <60fb0a916c9cc_defb208eb@natae.notmuch>
In-Reply-To: <xmqqwnphowdx.fsf@gitster.g>

Junio C Hamano wrote:

Show 26 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > So I feel compelled to say now that I do not think that changing the
> > order of parents for "git pull" is the obviously correct thing to do.
> > And likewise, in the one thread I do remember participating in, I
> > expressed something similar:
> >
> >   https://lore.kernel.org/git/20140502214817.GA10801@sigill.intra.peff.net/
> 
> Thanks for the link.  Many articles in the thread are repeating the
> same opinion over and over (and later even descend into ad-hominem
> attacks) and it is not worth anybody's time to read all of them, but
> I found that there still were some gems.
> 
> In an worldview where the first-parent chain is the trunk history,
> merging in the upstream where you push back to into your working
> repository where your new work is happening as the second parent
> before pushing it back would obviously make the history that used to
> be trunk to lose the first-parent-ness at that point.  And if you
> ask if I just said is correct, everybody would say it is.  So there
> is a concensus that the result of "git pull upstream main" becomes
> a wrong shape for people in one workflow.
> 
> But that does not necessarily mean swapping the parent order would
> produce the history of a right shape, either, even for those with
> the "first-parent chain is the trunk" worldview.

Why not? Everyone who saw a problem agreed it would.

Reversing the order of the parents creates a merge commit like so:

  Y---X-+
         \
  B---A---M  trunk

Most git experts work with topic branches, and when you do that, you get the same thing:

    topic
      |
      v
  Y---X-+
         \
  B---A---M  master

If you merge topic to master, the first parent of the merge commit is A.

If you do `git pull --reverse-parents` on a trunk-based workflow as above, you would get exactly the same shape of the history.

How is it not the right shape?

-- 
Felipe Contreras