Add a generalized git-file? to Guix?

[Christopher Allan Webber <cwebber@dustycloud.org>]

Thompson, David writes:

> Hi Christopher and Jan,
>
> On Tue, Jan 10, 2017 at 11:28 AM, Christopher Allan Webber
> <cwebber@dustycloud.org> wrote:
>> Jan Nieuwenhuizen writes:
>>
>>> Christopher Allan Webber writes:
>>>
>>>> Thanks!
>>>>
>>>> The file is updated, and even nicer now, since I'm using a hack from
>>>> guile-sdl2 which allows you to set the source to the whole checkout.
>>>
>>> Ohh!  That needs to go in the Guix manual... could git-file? be added
>>> to guix/utils?
>>
>> Maybe!  I think David knows more about the provenance?
>
> I took this code from Ludovic.  See make-git-predicate in
> gnu/packages/package-management.scm in the Guix source tree.
>
>> I agree it would be nice to have in Guix itself.
>
> Agreed.  A generalized and publicly available procedure would be great.
>
> - Dave

Hello!  See the above conversation... 8sync now uses `git-file?' in its
guix.scm, a predicate check which allows for checking out the whole
local directory as a "source" for testing a package.  I borrowed it from
Dave who originally adapted it from some code in Guix itself.  See:

  http://git.savannah.gnu.org/cgit/8sync.git/tree/guix.scm#n62

This is pretty handy; probably other projects would like to make use of
it.  What do we think of making it a generally available utility?

 - Chris