Re: [PATCH 4/5] rebase -i: don't fork git checkout

[Philippe Blain <levraiphilippeblain@gmail.com>]

Hi Phillip,

Le 2021-09-08 à 09:41, Phillip Wood via GitGitGadget a écrit :
> From: Phillip Wood <phillip.wood@dunelm.org.uk>
> 
> The "apply" based rebase has avoided forking git checkout since
> ac7f467fef ("builtin/rebase: support running "git rebase <upstream>"",
> 2018-08-07). The code that handles the checkout was moved into libgit
> by b309a97108 ("reset: extract reset_head() from rebase", 2020-04-07)
> so lets start using it for the "merge" based rebase as well. This
> opens the way for us to stop calling the post-checkout hook in the
> future.
> 

While in general I think it's a good thing to avoid forking, this change
might result in behavioral differences. Any config that affects
'git checkout' but not the internal 'reset.c::reset_head' function might
play a role in the rebase UX.

One that immediately came to mind is 'submodule.recurse'. This initial 'onto'
checkout was pretty much the only part of 'git rebase' that did something useful
for submodules, so it's kind of sad to see it regress. [That is, until someone
takes the time to implement 'git rebase --recurse-submodules' and makes sure *all*
code paths that touch the working tree pay attention to this flag, and that will
probably necessitate 'git merge --recurse-submodules' first because of the 'merge'
backend... as far as I'm aware it's on Emily's list [1], it's also on mine but
I don't know when I'll get the time.]

Anyway, I'm not saying that we should not do what this patch is proposing, but
I think caveats such as that should be documented in the commit message, and maybe
an audit of other configs that might results in behavioural differences should be done.

Thanks,

Philippe.

[1] https://lore.kernel.org/git/YHofmWcIAidkvJiD@google.com/t/#m0229af9183a84c2367f21e82adfbd21f08aa4437