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From:   Junio C Hamano <gitster@pobox.com>
To:     Derrick Stolee <derrickstolee@github.com>
Cc:     Patrick Steinhardt <ps@pks.im>,
        Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>,
        git@vger.kernel.org, me@ttaylorr.com, abhishekkumar8222@gmail.com
Subject: Re: [PATCH 3/7] commit-graph: start parsing generation v2 (again)
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Date:   Wed, 02 Mar 2022 14:42:30 -0800
In-Reply-To: <1651a34e-38c1-fb8a-df59-1dcd8a8389b5@github.com> (Derrick
        Stolee's message of "Wed, 2 Mar 2022 13:46:43 -0500")
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Derrick Stolee <derrickstolee@github.com> writes:

>> I am wondering if there is some notion of "if you do not understand
>> what this chunk is, you are incapable of handling this file
>> correctly, so do not use it" kind of bit per chunks (similar to the
>> index extensions where ones that begin with [A-Z] are optional) that
>> may negatively affect this plan.
>
> The chunk IDs do not have this special casing rule. This is a
> bit unfortunate for certain cases like adding something that _must_
> be understood. Here, it works to our benefit that GDAT and GDOV are
> optional and can be safely ignored. Thus, clients with this patch
> will ignore GDAT and GDOV and continue using topological levels
> form the CDAT chunk. Older clients without this patch will ignore
> the new GDA2 and GDO2 chunks and continue using topological levels.
>
> For Git versions without this topic branch, this "continue using
> topological levels" means no change of behavior at all.

Excellent.  Thanks.