git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: Erin Dahlgren <eedahlgren@gmail.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v2] Simplify handling of setup_git_directory_gently() failure cases.
Date: Tue, 18 Dec 2018 12:54:02 -0800	[thread overview]
Message-ID: <CAP_Smy14j4WK-mkqdKTKue=j7YoNjfaZVCBA-7S8xwNqX2rKhQ@mail.gmail.com> (raw)
In-Reply-To: <20181218175418.GB31070@sigill.intra.peff.net>

Hi Peff,

On Tue, Dec 18, 2018 at 9:54 AM Jeff King <peff@peff.net> wrote:
>
> On Sat, Dec 15, 2018 at 05:05:08PM -0800, Erin Dahlgren wrote:
>
> > setup_git_directory_gently() expects two types of failures to
> > discover a git directory (e.g. .git/):
> > [...]
>
> When I read your subject line, I'll admit to having a funny feeling in
> the pit of my stomach. This setup code has historically been full of
> subtle corner cases, and I expected a very tricky review.
>
> However, your explanation was so well-written that it was a pleasure to
> read. :)

Thanks :)

>
> > Before this change are two misleading additional behaviors:
> >
> >   - GIT_DIR_HIT_CEILING: setup_nongit() changes to the cwd for no
> >       apparent reason. We never had the chance to change directories
> >       up to this point so chdir(current cwd) is pointless.
>
> That makes sense. I think this is a holdover from when we used to walk
> backwards via chdir(), prior to ce9b8aab5d (setup_git_directory_1():
> avoid changing global state, 2017-03-13). Back then, we needed to
> restore the state at this point, but now we don't.
>
> >   - GIT_DIR_HIT_MOUNT_POINT: strbuf_release() frees the buffer
> >       of a static struct strbuf (cwd). This is unnecessary because the
> >       struct is static so its buffer is always reachable. This is also
> >       misleading because nowhere else in the function is this buffer
> >       released.
>
> Makes sense.
>
> I do have one question, though:
>
> >       case GIT_DIR_HIT_CEILING:
> > -             prefix = setup_nongit(cwd.buf, nongit_ok);
> > -             break;
> > +             if (!nongit_ok)
> > +                     die(_("not a git repository (or any of the parent directories): %s"),
> >a +                                    DEFAULT_GIT_DIR_ENVIRONMENT);
> > +             *nongit_ok = 1;
> > +             strbuf_release(&dir);
> > +             return NULL;
>
> This case used to break out of the switch, and now returns early.
>
> So we do not execute the later code which clears GIT_PREFIX_ENVIRONMENT,
> and zeroes the fields in startup_info. Those probably don't matter in
> most cases, but I wonder if there are some obscure ones where it might.
>
> Might it make sense to make GIT_DIR_HIT_MOUNT_POINT more like
> GIT_DIR_HIT_CEILING currently is, rather than the other way around?
> I.e., something like:
>
>   case GIT_DIR_HIT_CEILING:
>         if (!nongit_ok)
>                 die(...);
>         *nongit_ok = 1;
>         prefix = NULL;
>         break;
>   case GIT_DIR_HIT_MOUNT_POINT:
>         if (!nongit_ok)
>                 die(...);
>         *nongit_ok = 1;
>         prefix = NULL;
>         break;
>
> ?

After some digging, there seems to be a documented guarantee that
"`GIT_PREFIX` is set as returned by running 'git rev-parse
--show-prefix'". See Documentation/config/alias.txt. If the
environment variable GIT_PREFIX is already set to something and we
don't clear it when prefix is NULL, then the two can be out of sync.
So that's a problem with my patch and the current handling of
GIT_DIR_HIT_MOUNT_POINT. I'm not sure how important of a guarantee it
is, but we should respect what's documented.

Side note: One of the secondary goals of my patch was to make it
really obvious that neither the GIT_DIR_HIT_CEILING nor the
GIT_DIR_HIT_MOUNT_POINT case can get us into the block protected by
(startup_info->have_repository || getenv(GIT_DIR_ENVIRONMENT)). With
your suggestion (and it's a fair one) I don't think that's feasible
without more significant refactoring. Should I just settle with a
comment that explains this?

Thanks,
Erin

>
> -Peff

  reply	other threads:[~2018-12-18 20:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-13 17:30 [PATCH] " Erin Dahlgren
2018-12-14 10:32 ` Johannes Schindelin
2018-12-16  1:05   ` Erin Dahlgren
2018-12-16  1:05 ` [PATCH v2] " Erin Dahlgren
2018-12-18 12:35   ` Johannes Schindelin
2018-12-18 19:50     ` Erin Dahlgren
2018-12-18 17:54   ` Jeff King
2018-12-18 20:54     ` Erin Dahlgren [this message]
2018-12-19 15:59       ` Jeff King
2018-12-26 22:22         ` Junio C Hamano
2018-12-27 16:24           ` Jeff King
2018-12-27 23:46             ` Erin Dahlgren
2019-01-03  4:54               ` Jeff King
2018-12-27 23:36   ` [PATCH v3] " Erin Dahlgren
2019-01-03  5:14     ` Jeff King
2019-01-03 18:09       ` Junio C Hamano
2019-01-04  8:25         ` Jeff King
2019-01-05 16:57           ` Erin Dahlgren
2019-01-06  6:22             ` Jeff King

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='CAP_Smy14j4WK-mkqdKTKue=j7YoNjfaZVCBA-7S8xwNqX2rKhQ@mail.gmail.com' \
    --to=eedahlgren@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=johannes.schindelin@gmx.de \
    --cc=peff@peff.net \
    --subject='Re: [PATCH v2] Simplify handling of setup_git_directory_gently() failure cases.' \
    /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

git@vger.kernel.org list mirror (unofficial, one of many)

This inbox may be cloned and mirrored by anyone:

	git clone --mirror https://public-inbox.org/git
	git clone --mirror http://ou63pmih66umazou.onion/git
	git clone --mirror http://czquwvybam4bgbro.onion/git
	git clone --mirror http://hjrcffqmbrq6wope.onion/git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V1 git git/ https://public-inbox.org/git \
		git@vger.kernel.org
	public-inbox-index git

Example config snippet for mirrors.
Newsgroups are available over NNTP:
	nntp://news.public-inbox.org/inbox.comp.version-control.git
	nntp://7fh6tueqddpjyxjmgtdiueylzoqt6pt7hec3pukyptlmohoowvhde4yd.onion/inbox.comp.version-control.git
	nntp://ie5yzdi7fg72h7s4sdcztq5evakq23rdt33mfyfcddc5u3ndnw24ogqd.onion/inbox.comp.version-control.git
	nntp://4uok3hntl7oi7b4uf4rtfwefqeexfzil2w6kgk2jn5z2f764irre7byd.onion/inbox.comp.version-control.git
	nntp://news.gmane.io/gmane.comp.version-control.git
 note: .onion URLs require Tor: https://www.torproject.org/

code repositories for project(s) associated with this inbox:

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

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git