Re: [PATCH 0/9] git archive: use gzip again by default, document output stabilty

From: "Raymond E. Pasco" <ray@ameretat.dev>
To: phillip.wood@dunelm.org.uk,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>,
	"Eli Schwartz" <eschwartz93@gmail.com>,
	"René Scharfe" <l.s.r@web.de>,
	"brian m . carlson" <sandals@crustytoothpaste.net>,
	"Konstantin Ryabitsev" <konstantin@linuxfoundation.org>,
	"Michal Suchánek" <msuchanek@suse.de>,
	demerphq <demerphq@gmail.com>, "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH 0/9] git archive: use gzip again by default, document output stabilty
Date: Thu, 02 Feb 2023 19:23:46 +0000	[thread overview]
Message-ID: <de8f1e338e6ee99cd3ee06b16f1edbce@ameretat.dev> (raw)
In-Reply-To: <771a98ca-9540-ad4e-dfba-9d304e1dff09@dunelm.org.uk>

February 2, 2023 11:17 AM, "Phillip Wood" <phillip.wood123@gmail.com> wrote:
> Playing devil's advocate for a moment as we're not going to promise that the compressed output of
> "git archive" will be stable in the future perhaps we should use this breakage as an opportunity to
> highlight that to users and to advertize the config setting that allows them to use gzip for
> compressing archives. Reverting the change gives the misleading impression that we're making a
> commitment to keeping the output stable. The focus of this thread seems to be the problems relating
> to github which they have already addressed.
> 
> I think there is general agreement that it is not practical to promise that the compressed output
> of "git archive" is stable so maybe it is better to make that clear now while users can work around
> it in the short term with a config setting rather than waiting until we're faced with some security
> or other issue that forces a change to the output which users cannot work around so easily.

Reverting to the behavior of "use some arbitrary gzip from $PATH" would
be a poor decision whether or not git were willing to make some
commitment to gzip stability, because Git does not control arbitrary
gzips on the user's $PATH. If Git did want to promise gzip stability, it 
could only start from something like the current internal implementation
along with a vendored zlib; if it doesn't, as appears to be the case, 
then the internal implementation is superior for the other reasons 
already discussed.

If the user wants to depend on a particular gzip executable they supply, 
this configuration knob already exists for them.

Since there is no guarantee of stability, but there has been a popular 
misconception that there is some such guarantee (e.g., [1]), some kind 
of STABILITY section describing how there isn't any and suggesting ways
the user can attain more stability via configuration seems to be a good
idea.

[1]: https://lists.reproducible-builds.org/pipermail/rb-general/2021-October/002422.html