Re: [PATCH] [GSOC] cat-file: fix --batch report changed-type bug

From: Jeff King <peff@peff.net>
To: ZheNing Hu <adlternative@gmail.com>
Cc: ZheNing Hu via GitGitGadget <gitgitgadget@gmail.com>,
	Git List <git@vger.kernel.org>,
	Junio C Hamano <gitster@pobox.com>,
	Christian Couder <christian.couder@gmail.com>,
	Hariom Verma <hariom18599@gmail.com>
Subject: Re: [PATCH] [GSOC] cat-file: fix --batch report changed-type bug
Date: Mon, 31 May 2021 10:44:33 -0400	[thread overview]
Message-ID: <YLT2UfCZyQIXWIOv@coredump.intra.peff.net> (raw)
In-Reply-To: <CAOLTT8Q0zbxh8X03ZmgAzHadTbE4-Af+AB3POOUF2n22u8RExw@mail.gmail.com>

On Mon, May 31, 2021 at 09:20:34PM +0800, ZheNing Hu wrote:

> > But I think we'd want to solve it by swapping the two conditionals I
> > showed above, which restores the assumption made in print_object_or_die().
> 
> This method is correct. This will ensure that skip_object_info will not
> be set when print_contents is set.

OK, good, it sounds like we are on the same page. :)

> By the way, maybe we can merge this two "if (opt->all_objects)" block to one.
> [...]

Yes, I think that would make sense to do. It might be worth doing as a
separate patch on top of the bug-fix, though, to make it clear that it's
just cosmetic and separate from the bug-fix.

> > > +test_expect_success 'cat-file --batch="batman" with --batch-all-objects will work' '
> > > +     git -C all-two cat-file --batch-all-objects --batch="%(objectname)" | wc -l >expect &&
> > > +     git -C all-two cat-file --batch-all-objects --batch="batman" | wc -l >actual &&
> > > +     test_cmp expect actual
> > > +'
> >
> > Is it worth testing both of these? The %(objectname) one will fail in
> > the same way (because we do not need to run oid_object_info() to get the
> > oid, which we already have). I'm OK doing both for better coverage, but
> > it may be worth mentioning either in a comment or in the commit message
> > that we expect both to fail, and why.
> 
> Yes, these damages need to be pointed out in the commit message.

I think what confused me here is that you are using "%(objectname)" as
the "expect" output, but it also exhibits the bug. So I'd expect this
test to pass even before your patch (though I didn't try it).

Really, the symptom of the bug is that _neither_ of those cat-file
invocations will exit with a success code. But because they're on the
left-hand side of a pipe, we wouldn't even notice.

The simplest test is just:

  git -C all-two cat-file --batch-all-objects --batch="%(objectname)" >/dev/null

which will currently fail. It would be nice to verify that its output is
sensible, but I'm not sure how to easily do that (it will spew a bunch
of binary tree data, and it cannot even be parsed reliably since we
haven't output the sizes).

-Peff