git@vger.kernel.org mailing list mirror (one of many)
 help / color / mirror / code / Atom feed
From: Junio C Hamano <gitster@pobox.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, dstolee@microsoft.com,
	git@jeffhostetler.com, peff@peff.net, johannes.schindelin@gmx.de,
	jrnieder@gmail.com,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 19/20] abbrev: support relative abbrev values
Date: Tue, 12 Jun 2018 12:16:03 -0700	[thread overview]
Message-ID: <xmqqvaan95os.fsf@gitster-ct.c.googlers.com> (raw)
In-Reply-To: <20180608224136.20220-20-avarab@gmail.com> ("Ævar Arnfjörð Bjarmason"'s message of "Fri, 8 Jun 2018 22:41:35 +0000")

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

> Change the core.abbrev config variable and the corresponding --abbrev
> command-line option to support relative values such as +1 or -1.
>
> Before Linus's e6c587c733 ("abbrev: auto size the default
> abbreviation", 2016-09-30) git would default to abbreviating object
> names to 7-hexdigits, and only picking longer SHA-1s as needed if that
> was ambiguous.
>
> That change instead set the default length as a function of the
> estimated current count of objects:
>
>     Based on the expectation that we would see collision in a
>     repository with 2^(2N) objects when using object names shortened
>     to first N bits, use sufficient number of hexdigits to cover the
>     number of objects in the repository.  Each hexdigit (4-bits) we
>     add to the shortened name allows us to have four times (2-bits) as
>     many objects in the repository.
>
> By supporting relative values for core.abbrev we can allow users to
> consistently opt-in for either a higher or lower probability of
> collision, without needing to hardcode a given numeric value like
> "10", which would be overkill on some repositories, and far to small
> on others.

Nicely explained and calculated ;-)

>  test_expect_success 'describe core.abbrev=[-+]1 and --abbrev=[-+]1' '
> -	test_must_fail git -c core.abbrev=+1 describe | sed_g_tr_d_n >describe &&
> -	test_must_fail git -c core.abbrev=-1 describe | sed_g_tr_d_n >describe &&
> +	git -c core.abbrev=-1 describe | sed_g_tr_d_n >describe &&
> +	test_byte_count = 6 describe &&
> +
> +	git -c core.abbrev=+1 describe | sed_g_tr_d_n >describe &&
> +	test_byte_count = 8 describe &&

Even though I see the point of supporting absurdly small absolute
values like 4, I do not quite see the point of supporting negative
relative values here.  What's the expected use case?

>  	git log --abbrev=+1 --pretty=format:%h -1 | tr_d_n >log &&
> -	test_byte_count = 4 log &&
> +	test_byte_count = 8 log &&

This, together with many many others in the rest of the patch, is
cute but confusing in that the diff shows change from 4 to 8 due to
the redefinition of what abbrev=+1 means.  I have a feeling that it
may not be worth doing it "right", but if we were doing it "right",
we would probably have done it in multiple steps:

    - the earlier patches in this series that demonstrates
      --abbrev=+1 is --abbrev=1 and core.abbrev=+1 is an error.

    - ensure --abbrev=+1 is rejected as syntax error just like
      core.abbrev=+1 was, without introducing relative values

    - introduce relative value.

That way, the last step (which corresponds to this patch) would show
change from "log --abbrev=+1" failing due to syntax error to showing
abbreviated value that is slightly longer than the default.

But a I said, it may not be worth doing so.  "Is it worth supporting
negative relative length?" still stands, though.

  parent reply	other threads:[~2018-06-12 19:16 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-08 22:41 [PATCH 00/20] unconditional O(1) SHA-1 abbreviation Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 01/20] t/README: clarify the description of test_line_count Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 02/20] test library: add a test_byte_count Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 03/20] blame doc: explicitly note how --abbrev=40 gives 39 chars Ævar Arnfjörð Bjarmason
2018-06-12 18:10   ` Junio C Hamano
2018-06-08 22:41 ` [PATCH 04/20] abbrev tests: add tests for core.abbrev and --abbrev Ævar Arnfjörð Bjarmason
2018-06-12 18:31   ` Junio C Hamano
2018-06-08 22:41 ` [PATCH 05/20] abbrev tests: test "git-blame" behavior Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 06/20] blame: fix a bug, core.abbrev should work like --abbrev Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 07/20] abbrev tests: test "git branch" behavior Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 08/20] abbrev tests: test for "git-describe" behavior Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 09/20] abbrev tests: test for "git-log" behavior Ævar Arnfjörð Bjarmason
2018-06-09  8:43   ` Martin Ågren
2018-06-09  9:56     ` Ævar Arnfjörð Bjarmason
2018-06-09 13:56       ` Martin Ågren
2018-06-08 22:41 ` [PATCH 10/20] abbrev tests: test for "git-diff" behavior Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 11/20] abbrev tests: test for plumbing behavior Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 12/20] abbrev tests: test for --abbrev and core.abbrev=[+-]N Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 13/20] parse-options-cb.c: convert uses of 40 to GIT_SHA1_HEXSZ Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 14/20] config.c: use braces on multiple conditional arms Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 15/20] parse-options-cb.c: " Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 16/20] abbrev: unify the handling of non-numeric values Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 17/20] abbrev: unify the handling of empty values Ævar Arnfjörð Bjarmason
2018-06-09 14:24   ` Martin Ågren
2018-06-09 14:31     ` Martin Ågren
2018-06-08 22:41 ` [PATCH 18/20] abbrev parsing: use braces on multiple conditional arms Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 19/20] abbrev: support relative abbrev values Ævar Arnfjörð Bjarmason
2018-06-09 15:38   ` Martin Ågren
2018-06-12 19:16   ` Junio C Hamano [this message]
2018-06-13 22:22     ` Ævar Arnfjörð Bjarmason
2018-06-13 22:34       ` Junio C Hamano
2018-06-14  7:36         ` Ævar Arnfjörð Bjarmason
2018-06-14 15:50           ` Junio C Hamano
2018-06-14 19:07             ` Ævar Arnfjörð Bjarmason
2018-06-08 22:41 ` [PATCH 20/20] abbrev: add a core.validateAbbrev setting Ævar Arnfjörð Bjarmason
2018-06-09 15:47   ` Martin Ågren
2018-06-12 18:58     ` Junio C Hamano

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=xmqqvaan95os.fsf@gitster-ct.c.googlers.com \
    --to=gitster@pobox.com \
    --cc=avarab@gmail.com \
    --cc=dstolee@microsoft.com \
    --cc=git@jeffhostetler.com \
    --cc=git@vger.kernel.org \
    --cc=johannes.schindelin@gmx.de \
    --cc=jrnieder@gmail.com \
    --cc=peff@peff.net \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).