From: Jeff King <peff@peff.net>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Stefan Beller" <sbeller@google.com>, git <git@vger.kernel.org>,
"Junio C Hamano" <gitster@pobox.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Edward Thomson" <ethomson@edwardthomson.com>,
"brian m. carlson" <sandals@crustytoothpaste.net>,
"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
demerphq <demerphq@gmail.com>,
"Brandon Williams" <bmwill@google.com>,
"Derrick Stolee" <stolee@gmail.com>
Subject: Re: How is the ^{sha256} peel syntax supposed to work?
Date: Wed, 29 Aug 2018 19:45:24 -0400 [thread overview]
Message-ID: <20180829234524.GA15802@sigill.intra.peff.net> (raw)
In-Reply-To: <20180829204623.GD7547@aiede.svl.corp.google.com>
On Wed, Aug 29, 2018 at 01:46:23PM -0700, Jonathan Nieder wrote:
> > Can you elaborate on that?
>
> What I'm saying is, regardless of the syntax used, as a user I *need*
> a way to look up $some_hash as a sha256-name, with zero risk of Git
> trying to outsmart me and treating $some_hash as a sha1-name instead.
>
> Any design without that capability is a non-starter.
Right, this is IMHO the only thing that makes sense for ^{hash} to do:
it disambiguates the sha1 that you just gave it. Nothing more, nothing
less.
> > I.e. if I'm using this in a script I'd need:
> >
> > if x = git rev-parse $some_hash^{sha256}^{commit}
> > hash = x
> > elsif x = git rev-parse $some_hash^{sha1}^{commit}
> > hash = x
> > endif
>
> Why wouldn't you use "git rev-parse $some_hash^{commit}" instead?
Yes, the sane rules seem to me to be:
# try any available hash for $some_hash
git rev-parse $some_hash
# look _only_ for $some_hash as a sha1
git rev-parse $some_hash^{sha1}
# ditto for sha256
git rev-parse $some_hash^{sha256}
# ditto, but then peel the result to a commit
git rev-parse $some_hash^{sha256}^{commit}
# this is nonsense, and should produce an error
git rev-parse $some_hash^{commit}^{sha256}
For convenience of scripts, we may also want:
git rev-parse --input-hash=sha256 $some_hash
to pretend as if "^{sha256}" was appended to each command-line hash we
try to resolve (e.g., consider a case where a script is feeding 0 or
more hashes).
-Peff
next prev parent reply other threads:[~2018-08-29 23:45 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-23 14:02 Questions about the hash function transition Ævar Arnfjörð Bjarmason
2018-08-23 14:27 ` Junio C Hamano
2018-08-23 15:20 ` Ævar Arnfjörð Bjarmason
2018-08-23 16:13 ` Junio C Hamano
2018-08-24 1:40 ` brian m. carlson
2018-08-24 1:54 ` Jonathan Nieder
2018-08-24 4:47 ` brian m. carlson
2018-08-24 4:52 ` Jonathan Nieder
2018-08-24 1:47 ` Jonathan Nieder
2018-08-28 12:04 ` Johannes Schindelin
2018-08-28 12:49 ` Derrick Stolee
2018-08-28 17:12 ` Jonathan Nieder
2018-08-28 17:11 ` Jonathan Nieder
2018-08-29 13:09 ` Johannes Schindelin
2018-08-29 13:27 ` Derrick Stolee
2018-08-29 14:43 ` Derrick Stolee
2018-08-29 9:13 ` How is the ^{sha256} peel syntax supposed to work? Ævar Arnfjörð Bjarmason
2018-08-29 17:51 ` Stefan Beller
2018-08-29 17:59 ` Jonathan Nieder
2018-08-29 18:34 ` Stefan Beller
2018-08-29 18:41 ` Ævar Arnfjörð Bjarmason
2018-08-29 19:12 ` Jonathan Nieder
2018-08-29 19:37 ` Ævar Arnfjörð Bjarmason
2018-08-29 20:46 ` Jonathan Nieder
2018-08-29 23:45 ` Jeff King [this message]
2018-08-29 20:53 ` Junio C Hamano
2018-08-29 21:01 ` Jonathan Nieder
2018-08-29 17:56 ` Jonathan Nieder
2018-08-24 2:51 ` Questions about the hash function transition Jonathan Nieder
2018-08-28 13:50 ` Ævar Arnfjörð Bjarmason
2018-08-28 14:15 ` Edward Thomson
2018-08-28 15:02 ` Ævar Arnfjörð Bjarmason
2018-08-28 15:45 ` Junio C Hamano
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