Re: [PATCH 3/3] bisect: make diff-tree output prettier

From: Jeff King <peff@peff.net>
Date: Feb 23, 2019, 13:44 UTC
Message-ID: <20190223134452.GE22403@sigill.intra.peff.net>
In-Reply-To: <xmqqsgwfr9vr.fsf@gitster-ct.c.googlers.com>

On Fri, Feb 22, 2019 at 09:49:44AM -0800, Junio C Hamano wrote:

Show 9 quoted lines

> > Even though bisect might be driven by scripts, there's no reason to
> > consider this part of the output as machine-readable (if anything, the
> > initial "$hash is the first bad commit" might be parsed, but we won't
> > touch that here). Let's make it prettier and more informative for a
> > human reading the output.
> 
> Sounds very sensible.  One potential point that makes me worried is
> this move might tempt people to make the output even larger (e.g. a
> full diff with "--patch" is overkill if done unconditionally).

Yeah, I agree that would be overkill. What I have here isn't actually much bigger. It mostly trades one line of --raw for one line of --stat. The big change is that we actually bother to recurse, but I think the old behavior was just buggy.

At any rate, I think we can discuss such a patch if and when it comes up.

Show 16 quoted lines

> > If we do care about the change in exit code from bisect, then it
> > probably does make sense to go with an external process. Then it can
> > happily die on the corruption, while bisect continues with the rest of
> > the high-level operation. I'm not sure it really matters much, though.
> > Once your repository is corrupted, all bets are off. It's nice that we
> > can bisect in such a state at all.
> 
> This is about showing the very final message after finding which one
> is the culprit.  Is there any other "clean-up" action we need to do
> after showing the message?  I do not care too much about the exit
> code from the bisection, but if dying from diff-tree can interfere
> with such a clean-up, that would bother me a lot more, and at that
> point, given especially that this is not a performance sensitive
> thing at all (it is not even invoked log(n) times---just once at the
> end), moving to external process may make it a lot simpler and
> cleaner.

Thanks, I had a vague feeling along these lines, but you nicely put it into words. As far as I can tell, no, we're not missing any important cleanup in that process; it looks like the only call to show_diff_tree() then calls exit(10) immediately after.

However, that does change our exit code, which git-bisect.sh then propagates instead of writing the entry into the BISECT_LOG.

I'm still not convinced this is really worth caring about, as it implies a corrupt repo. But if we did want to fix it, then I think the external diff-tree would still be the right thing (since it's hard for git-bisect.sh to tell the different between this death and another one).

-Peff