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From: Junio C Hamano <gitster@pobox.com>
To: Johan Herland <johan@herland.net>
Cc: git@vger.kernel.org
Subject: Re: [RFD] Making "git push [--force/--delete]" safer?
Date: Wed, 03 Jul 2013 01:49:56 -0700	[thread overview]
Message-ID: <7vli5ogh8r.fsf@alter.siamese.dyndns.org> (raw)
In-Reply-To: <CALKQrgdovWTd50LVDnNR+BhurWgSCKkhr88wCo01VZF3sd5PNg@mail.gmail.com> (Johan Herland's message of "Wed, 3 Jul 2013 08:34:25 +0200")

Johan Herland <johan@herland.net> writes:

> Overnight, it occured to me that --force-if-expected could be
> simplified by leveraging the existing --force option; for the above
> two examples, respectively:
>
>   $ git push --force --expect
>   # validate foo @ origin == @{upstream} before pushing
>
> and
>
>   $ git push --force --expect=refs/original/foo my_remote HEAD:foo
>   # validate foo @ my_remote == refs/original/foo before pushing

First, on the name.

I do not think either "--validate" or "--expect" is particularly a
good one.  The former lets this feature squat on a good name that
covers a much broader spectrum, forbidding people from adding other
kinds of validation later.  "--expect" is slightly less bad in that
sense; saying "we expect this" does imply "otherwise it is an
unexpected situation and we would fail", but the name still does not
feel ideal.

What is the essense of compare-and-swap?  Perhaps we can find a good
word by thinking that question through.  

To me, it is a way to implement a "lock" on the remote ref without
actually taking a lock (which would leave us open for a stale lock),
and this "lock"-ness is what we want in order to guarantee safety.

So we could perhaps call it "--lockref"?

I'll leave the name open but tentatively use this name in the
following, primarily to see how well it sits on the command line
examples.

Then on the semantics/substance.

I had quite a similar thought as you had while reading your initial
response.  In the most generic form, we would want to be able to
pass necessary information fully via the option, i.e.

	--lockref=theirRefName:expectedValue

but when the option is spelled without details, we could fill in the
default values by making a reasonable guess of what the user could
have meant.  If we only have --lockref without refname nor value,
then we will enable the safety for _all_ refs that we are going to
update during this push.  If we have --lockref=theirRefName without
the expected value for that ref, we will enable the safety only for
the ref (you can give more than one --lockref=theirRefName), and
guess what value we should expect.  If we have a fully specified
option, we do not have to guess the value.

And for the expected value, when we have a tracking branch for the
branch at the remote we are trying to update, its value is a very
good guess of what the user meant.

Note, however, that this is very different from @{upstream}.

You could be pushing a branch "frotz", that is configured to
integrate with "master" taken from "origin", but

 (1) to a branch different from "master" of "origin", e.g.

	$ git push --lockref origin frotz:nitfol
	$ git push --lockref origin :nitfol	;# deleting

 (2) even to a branch of a remote that is different from "origin",
     e.g.

	$ git push --lockref xyzzy frotz:nitfol
	$ git push --lockref xyzzy :nitfol	;# deleting

Even in these case, if you have a remote tracking branch for the
destination (i.e. you have refs/remotes/origin/nitfol in case (1) or
refs/remotes/xyzzy/nitfol in case (2) to be updated by fetching from
origin or xyzzy), we can and should use that value as the default.

There is no room for frotz@{upstream} (or @{upstream} of the current
branch) to get in the picture.

Except when you happen to be pushing with "push.default = upstream",
that is.  But that is a natural consequence of the more generic
check with "our remote tracking branch of the branch we are updating
at the remote" rule.

  reply	other threads:[~2013-07-03  8:52 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-02 20:57 [RFD] Making "git push [--force/--delete]" safer? Junio C Hamano
2013-07-02 22:55 ` Johan Herland
2013-07-03  6:34   ` Johan Herland
2013-07-03  8:49     ` Junio C Hamano [this message]
2013-07-03 10:00       ` Johan Herland
2013-07-03 10:06         ` Jonathan del Strother
2013-07-03 10:11           ` Johan Herland
2013-07-03 10:50             ` Michael Haggerty
2013-07-03 12:06               ` Johannes Sixt
2013-07-03 19:53                 ` Junio C Hamano
2013-07-04  5:37                   ` Johannes Sixt
2013-07-04  5:46                     ` Junio C Hamano
2013-07-03 19:50           ` Junio C Hamano
2013-07-03 20:18             ` Junio C Hamano
2013-07-03 19:48         ` Junio C Hamano
2013-07-09 19:53 ` [PATCH 0/7] safer "push --force" with compare-and-swap Junio C Hamano
2013-07-09 19:53   ` [PATCH 1/7] cache.h: move remote/connect API out of it Junio C Hamano
2013-07-09 19:53   ` [PATCH 2/7] builtin/push.c: use OPT_BOOL, not OPT_BOOLEAN Junio C Hamano
2013-07-09 19:53   ` [PATCH 3/7] push: beginning of compare-and-swap "force/delete safety" Junio C Hamano
2013-07-09 19:53   ` [PATCH 4/7] remote.c: add command line option parser for --lockref Junio C Hamano
2013-07-16 22:13     ` John Keeping
2013-07-17 17:06       ` Junio C Hamano
2013-07-17 17:09       ` Junio C Hamano
2013-07-09 19:53   ` [PATCH 5/7] push --lockref: implement logic to populate old_sha1_expect[] Junio C Hamano
2013-07-09 19:53   ` [PATCH 6/7] t5533: test "push --lockref" Junio C Hamano
2013-07-09 19:53   ` [PATCH 7/7] push: document --lockref Junio C Hamano
2013-07-09 20:17     ` Aaron Schrab
2013-07-09 20:39       ` Junio C Hamano
2013-07-09 20:24     ` Johannes Sixt
2013-07-09 20:37       ` Junio C Hamano
2013-07-09 20:55         ` Johannes Sixt
2013-07-09 22:09           ` Junio C Hamano
2013-07-09 23:08             ` Junio C Hamano
2013-07-11 21:10               ` Johannes Sixt
2013-07-11 21:57                 ` Junio C Hamano
2013-07-11 22:14                 ` Junio C Hamano
2013-07-12 17:21                   ` Johannes Sixt
2013-07-12 17:40                     ` Junio C Hamano
2013-07-12 20:00                       ` Johannes Sixt
2013-07-12 21:19                         ` Junio C Hamano
2013-07-13  6:52                           ` Johannes Sixt
2013-07-13 18:14                             ` Junio C Hamano
2013-07-13 20:08                               ` Junio C Hamano
2013-07-13 21:11                                 ` Johannes Sixt
2013-07-14 14:28                                 ` John Keeping
2013-07-13 20:17                               ` Johannes Sixt
2013-07-14 19:17                                 ` Junio C Hamano
2013-07-14 20:21                                   ` Johannes Sixt
2013-07-14 20:34                                     ` Jonathan Nieder
2013-07-14 20:49                                       ` Jonathan Nieder
2013-07-14 20:59                                       ` Johannes Sixt
2013-07-14 21:28                                         ` Jonathan Nieder
2013-07-15  4:10                                           ` Junio C Hamano
2013-07-15  4:44                                             ` Jonathan Nieder
2013-07-15 15:37                                               ` Junio C Hamano
2013-07-15 20:30                                         ` Johannes Sixt
2013-07-15  3:50                                     ` Junio C Hamano
2013-07-15 15:47                                       ` Default expectation of --lockref Junio C Hamano
2013-07-15 20:27                                       ` [PATCH 7/7] push: document --lockref Johannes Sixt
2013-07-09 21:37         ` Marc Branchaud
2013-07-09 20:27     ` Michael Haggerty
2013-07-09 20:42       ` Junio C Hamano

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