Re: [PATCH 1/2] pretty: add %(describe)

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Tue, Feb 16 2021, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> On Sun, Feb 14 2021, René Scharfe wrote:
>>
>>> Add a format placeholder for describe output.  Implement it by actually
>>> calling git describe, which is simple and guarantees correctness.  It's
>>> intended to be used with $Format:...$ in files with the attribute
>>> export-subst and git archive. 
>>
>> Does it really guarantee correctness though? In "builtin/describe.c" we
>> first walk over the refs and use that to format all N items we're asked
>> about.
>>
>> Under "git log" this is presumably in a race where refs added/deleted
>> during the run of "git log" will change the describe output to be
>> inconsistent with earlier lines.
>
> Yes, but it is not a news that the describe for a given commit will
> not stay the constant while you add more objects to the repository
> or you change the tags, whether the "describe" is driven internally
> by "git log" or by the end-user, so I am not sure how that becomes
> an issue.  If the output is inconsistent in a quiescent repository,
> that would be a problem, though.
>
> Puzzled.

Usually something shelling out has going for it is that even if it's
slow it's at least known to be bug-free, after all we use the command
like that already.

I just wanted to point out this edge case, for "git describe <commits>"
we do the ref list once at the beginning so our N list will be
consistent within itself.

Whereas one might expect "git log" to also format such a list, but due
to the internal implementation the semantics are different.