From: Junio C Hamano <email@example.com> To: Jeff King <firstname.lastname@example.org> Cc: "Ævar Arnfjörð Bjarmason" <email@example.com>, "Git Mailing List" <firstname.lastname@example.org> Subject: Re: [PATCH 2/4] peel_ref: do not return a null sha1 Date: Thu, 04 Oct 2012 11:32:13 -0700 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20121004080019.GB31325@sigill.intra.peff.net> (Jeff King's message of "Thu, 4 Oct 2012 04:00:19 -0400") Jeff King <firstname.lastname@example.org> writes: > The idea of the peel_ref function is to dereference tag > objects recursively until we hit a non-tag, and return the > sha1. Conceptually, it should return 0 if it is successful > (and fill in the sha1), or -1 if there was nothing to peel. > > However, the current behavior is much more confusing. For a > regular loose ref, the behavior is as described above. But > there is an optimization to reuse the peeled-ref value for a > ref that came from a packed-refs file. If we have such a > ref, we return its peeled value, even if that peeled value > is null (indicating that we know the ref definitely does > _not_ peel). > > It might seem like such information is useful to the caller, > who would then know not to bother loading and trying to peel > the object. Except that they should not bother loading and > trying to peel the object _anyway_, because that fallback is > already handled by peel_ref. In other words, the whole point > of calling this function is that it handles those details > internally, and you either get a sha1, or you know that it > is not peel-able. > > This patch catches the null sha1 case internally and > converts it into a -1 return value (i.e., there is nothing > to peel). This simplifies callers, which do not need to > bother checking themselves. > > Two callers are worth noting: > > - in pack-objects, a comment indicates that there is a > difference between non-peelable tags and unannotated > tags. But that is not the case (before or after this > patch). Whether you get a null sha1 has to do with > internal details of how peel_ref operated. Yeah, this is what I was wondering while reviewing [1/4]. We traditionally said both HEAD^0 and HEAD^0^0 peel to HEAD, but this at least at the internal API level redefines them to "these do not peel at all and is a failure". In other words, peel_ref(ref, sha1) that returns 0 is a way to see if ref points at a real tag object, and if the function returns non-zero, the caller cannot tell if the failure is because it was a valid commit or a corrupt object. The check !is_null_sha1(peeled) always looked fishy to me. Good riddance.
next prev parent reply other threads:[~2012-10-04 22:13 UTC|newest] Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-10-03 12:36 upload-pack is slow with lots of refs Ævar Arnfjörð Bjarmason 2012-10-03 13:06 ` Nguyen Thai Ngoc Duy 2012-10-03 18:03 ` Jeff King 2012-10-03 18:53 ` Junio C Hamano 2012-10-03 18:55 ` Jeff King 2012-10-03 19:41 ` Shawn Pearce 2012-10-03 20:13 ` Jeff King 2012-10-04 21:52 ` Sascha Cunz 2012-10-05 0:20 ` Jeff King 2012-10-05 6:24 ` Johannes Sixt 2012-10-05 16:57 ` Shawn Pearce 2012-10-08 15:05 ` Johannes Sixt 2012-10-09 6:46 ` Shawn Pearce 2012-10-09 20:30 ` Johannes Sixt 2012-10-09 20:46 ` Johannes Sixt 2012-10-03 20:16 ` Ævar Arnfjörð Bjarmason 2012-10-03 21:20 ` Jeff King 2012-10-03 22:15 ` Ævar Arnfjörð Bjarmason 2012-10-03 23:15 ` Jeff King 2012-10-03 23:54 ` Ævar Arnfjörð Bjarmason 2012-10-04 7:56 ` [PATCH 0/4] optimizing upload-pack ref peeling Jeff King 2012-10-04 7:58 ` [PATCH 1/4] peel_ref: use faster deref_tag_noverify Jeff King 2012-10-04 18:24 ` Junio C Hamano 2012-10-04 8:00 ` [PATCH 2/4] peel_ref: do not return a null sha1 Jeff King 2012-10-04 18:32 ` Junio C Hamano [this message] 2012-10-04 8:02 ` [PATCH 3/4] peel_ref: check object type before loading Jeff King 2012-10-04 19:06 ` Junio C Hamano 2012-10-04 19:41 ` Jeff King 2012-10-04 20:41 ` Junio C Hamano 2012-10-04 21:59 ` Jeff King 2012-10-04 8:03 ` [PATCH 4/4] upload-pack: use peel_ref for ref advertisements Jeff King 2012-10-04 8:04 ` [PATCH 0/4] optimizing upload-pack ref peeling Jeff King 2012-10-04 9:01 ` Ævar Arnfjörð Bjarmason 2012-10-04 12:14 ` Nazri Ramliy 2012-10-03 22:32 ` upload-pack is slow with lots of refs Ævar Arnfjörð Bjarmason 2012-10-03 23:21 ` Jeff King 2012-10-03 23:47 ` Ævar Arnfjörð Bjarmason 2012-10-03 19:13 ` Junio C Hamano
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