From: Johannes Sixt <j.sixt@viscovery.net>
Date: Fri, 25 Jun 2010 06:02:00 GMT
Subject: Re: What's cooking in git.git (Jun 2010, #04; Wed, 23)
Message-ID: <4C244658.9020704@viscovery.net>
In-Reply-To: <7veifwchb6.fsf@alter.siamese.dyndns.org>

Am 6/24/2010 22:21, schrieb Junio C Hamano:
> Finn Arne Gangstad <finnag@pvv.org> writes:
>> If .gitattributes is different on the different sides, or if you
>> enable autocrlf, the current repo contents may change after
>> git-to-worktree and worktree-to-git again.
> 
> IOW, g2w-then-w2g may not be an identity function.
> 
> If we were to encourage use of this codepath to wider audiences, we may
> need to have a document for people who write smudge/clean filters.  In
> order for the result to be stable, applying g2w-then-w2g once again on top
> of the result of running g2w-then-w2g on anything should be no-op, no?

I think this is implicit to some degree in the documentation,
gitattributes(5):

  The content filtering is done to massage the content into a shape that
  is more convenient for the platform, filesystem, and the user to use.
  [...] the intent is that if someone unsets the filter driver
  definition, or does not have the appropriate filter program, the
  project should still be usable.

>From this I read that the content of the repository can only be in a
canonical shape; hence, the only thing that a clean filter can do is to
generate the canonical shape of the data. This is, by definition, an
idempotent operation (i.e., g2w(g2w(x)) == g2w(x)).

(I'm talking only about clean filters because any pair of smudge+clean
filters where the clean filter cannot undo the effect of the smudge filter
would be noticed immediately and be considered broken without being
mentioned explicitly in the documentation.)

-- Hannes