Re: [RFC PATCH] GIT-VERSION-GEN: set --abbrev=9 to match auto-scaling

[Junio C Hamano <gitster@pobox.com>]

Jeff King <peff@peff.net> writes:

> On Mon, Dec 05, 2016 at 10:01:19AM -0800, Junio C Hamano wrote:
>
>> > That said, I think the right patch may be to just drop --abbrev
>> > entirely.
>> > ...
>> > I think at that point it was a noop, as 7 should have been the default.
>> > And now we probably ought to drop it, so that we can use the
>> > auto-scaling default.
>> 
>> Yeah, I agree.
>> 
>> It does mean that snapshot binaries built out of the same commit in
>> the same repository before and after a repack have higher chances of
>> getting named differently, which may surprise people, but that
>> already is possible with a fixed length if the repacking involves
>> pruning (albeit with lower probabilities), and I do not think it is
>> a problem.
>
> I think that the number is already unstable, even with --abbrev, as it
> just specifies a minimum. So any operation that creates objects has a
> possibility of increasing the length. Or more likely, two people
> describing the same version may end up with different strings because
> they have different objects in their repositories (e.g., I used to
> carry's trast's git-notes archive of the mailing list which added quite
> a few objects).
>
> I agree that having it change over the course of a repack is slightly
> _more_ surprising than those cases, but ultimately the value just isn't
> stable.

Yup, that is what I meant to say with "that is already possible" and
we are on the same page.  As all three of us seem to be happy with
just dropping --abbrev and letting describe do its default thing (as
configured by whoever is doing the build), let's do so.

-- >8 --
From: Ramsay Jones <ramsay@ramsayjones.plus.com>
Date: Sun, 4 Dec 2016 20:45:59 +0000
Subject: [PATCH] GIT-VERSION-GEN: do not force abbreviation length used by 'describe'

The default version name for a Git binary is computed by running
"git describe" on the commit the binary is made out of, basing on a
tag whose name matches "v[0-9]*", e.g. v2.11.0-rc2-2-g7f1dc9.

In the very early days, with 9b88fcef7d ("Makefile: use git-describe
to mark the git version.", 2005-12-27), we used "--abbrev=4" to get
absolute minimum number of abbreviated commit object name.  This was
later changed to match the default minimum of 7 with bf505158d0
("Git 1.7.10.1", 2012-05-01).

These days, the "default minimum" scales automatically depending on
the size of the repository, and there is no point in specifying a
particular abbreviation length; all we wanted since Git 1.7.10.1
days was to get "something reasonable we would use by default".

Just drop "--abbrev=<number>" from the invocation of "git describe"
and let the command pick what it thinks is appropriate, taking the
end user's configuration and the repository contents into account.

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 GIT-VERSION-GEN | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/GIT-VERSION-GEN b/GIT-VERSION-GEN
index 556fbfc104..f95b04bb36 100755
--- a/GIT-VERSION-GEN
+++ b/GIT-VERSION-GEN
@@ -12,7 +12,7 @@ if test -f version
 then
 	VN=$(cat version) || VN="$DEF_VER"
 elif test -d ${GIT_DIR:-.git} -o -f .git &&
-	VN=$(git describe --match "v[0-9]*" --abbrev=7 HEAD 2>/dev/null) &&
+	VN=$(git describe --match "v[0-9]*" HEAD 2>/dev/null) &&
 	case "$VN" in
 	*$LF*) (exit 1) ;;
 	v[0-9]*)
-- 
2.11.0-263-gd89495280e