Re: [PATCH v4 7/8] update-ref: support multiple simultaneous updates

From: Brad King <brad.king@kitware.com>
Date: Sep 5, 2013, 23:44 UTC
Message-ID: <5229175A.4070203@kitware.com>
In-Reply-To: <xmqqk3ivgdxz.fsf@gitster.dls.corp.google.com>

On 9/5/2013 5:23 PM, Junio C Hamano wrote:

Show 6 quoted lines

> Brad King <brad.king@kitware.com> writes:
>> 	create SP <ref> NUL <newvalue> NUL
>> 	update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL
> 
> That SP in '-z' format looks strange.  Was there a reason why NUL
> was inappropriate?

The precedent I saw in the -z survey I posted is that NUL is used to terminate fields that can contain arbitrary text but otherwise SP or TAB is still used to terminate simple fields. I recall no cases that use NUL after fields that only contain simple values.

Show 8 quoted lines

>> option::
>> 	Specify an option to take effect for following commands.
> 
> This last one is somewhat peculiar, especially because it says
> "following command*s*".
> 
> How would I request to update refs HEAD and next in an all-or-none
> fashion, while applying 'no-deref' only to HEAD but not next?

You're right. It will be simpler for clients to generate each sequence of options followed by a <ref> command without worrying about options possibly generated for preceding <ref>s. So:

option::
	Modify behavior of the next command naming a <ref>.
	The only valid option is `no-deref` to avoid dereferencing
	a symbolic ref.

> When I said "create or update" in the message you are responding to,
> I did not mean that we should have two separate commands.

The nice thing about "create" is that it implies oldvalue=zero, just as "delete" implies newvalue=zero. The symmetry feels clean. Also, in -z mode we need to treat an empty string <oldvalue> as missing rather than zero. The only way to specify create with the "update" command is with literal 40 "0" as <oldvalue>.

> The regular command line does create-or-update; if it exists already,
> it is an update, and if it does not, it is a create.

The proposed update command can be used for create, update, delete, or verify with proper arguments and use of 40 "0". The other <ref> commands are for convenience, shorter input, and statement of intent.

> 	create-or-update-no-deref <ref> <newvalue> [<oldvalue>]
>         delete-no-deref <ref> [<oldvalue>]
> 
> Also how would one set the reflog message for the proposed update?

This is why I proposed a separate option command. It can be used both for no-deref and for other options we want to add later e.g.

  option SP message SP <reason> LF

and with -z:

  option SP message SP <reason> NUL

For now I think it is sufficient for the -m <reason> command-line option to set the same message for all updates. The option command leaves room to add a per-ref message later.

BTW, the reasons I propose message as an option rather than its own command are:

* It is simpler to document the reach of the one option command
  (affects next <ref>) in one place rather than separately for
  each option-like command.

* It reduces the number of commands that do not take a <ref>.

-Brad