From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 20 Jul 2016 19:26:44 GMT
Subject: Re: Git and SHA-1 security (again)
Message-ID: <xmqq1t2odsaz.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <CAGZ79kYzhPayXKq5LrddKTuO7d5=7_AZVvr7rJ4ztAzBFv-7eg@mail.gmail.com>

Stefan Beller <sbeller@google.com> writes:

>> to follow the above, in my view, interaction with sha1 repos go
>> through some conversion bridges like what we have with hg and svn. I
>> don't know if we are going this route. It's certainly simpler and
>> people already have experiences (from previous migration) to prepare
>> for it.
>
> When treating the SHA1 version as a foreign dvcs and the SHA256
> as the real deal, we could introduce "pointer objects", and during the
> conversion
> create a 4e55ed3 pointer that points to the SHA256 commit of (add:
> add --chmod=+x / --chmod=-x options, 2016-05-31).

Hmmm.  If you are designing this "pointer objects" to be extensible
enough to cover other foreign vcs (i.e.e.g. you make it to be
capable of mapping Subversion's r24323 to a matching commit in the
converted result), I would think it may be a very useful thing to
have, but I think it is pretty much orthogonal to the discussion in
this topic.  IOW, that can happen with or without change of the hash
function.

And looking at it that way, I am not sure if such a mapping feature
should require adding a new type of "object".