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From:   Junio C Hamano <gitster@pobox.com>
To:     Han-Wen Nienhuys <hanwen@google.com>
Cc:     Han-Wen Nienhuys via GitGitGadget <gitgitgadget@gmail.com>,
        git <git@vger.kernel.org>, Han-Wen Nienhuys <hanwenn@gmail.com>,
        Michael Haggerty <mhagger@alum.mit.edu>,
        Jeff King <peff@peff.net>
Subject: Re: [PATCH v7 6/6] Reftable support for git-core
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Date:   Thu, 27 Feb 2020 08:23:05 -0800
In-Reply-To: <CAFQ2z_PGgQ19uyjaEaJ4XMuvbkzW5fvJng3r2vYHDz4Z6pT3Aw@mail.gmail.com>
        (Han-Wen Nienhuys's message of "Thu, 27 Feb 2020 17:03:51 +0100")
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Han-Wen Nienhuys <hanwen@google.com> writes:

> So, the ref backend should manage the HEAD ref, but iteration should
> not produce the HEAD ref.

Yeah, as there is a dedicated API function head_ref().

Things like ORIG_HEAD and MERGE_HEAD have always been curiosity
outside the official API, but IIRC read_ref() and friends are
prepared to read them [*1*], so the vocabulary may be unbounded [*2*].

These won't be listed in for_each_ref() iteration, either (think of
for_each_ref() as a filtered "ls -R .git/refs/" output).

Thanks.


[Footnotes]

*1* I do not offhand know if these *_HEAD pseudo-refs are written
via the refs API---it probably is the safest to arrange the ref
backends in such a way that they always go to the files backend,
even if HEAD and refs/* are managed by a backend different from the
files one.

*2* I vaguely recall that back when ref-backend infrastructure was
introduced, we had discussion on declaring that "^[A-Z_]*HEAD$"
directly under $GIT_DIR/ are these special refs (and nothing else
directly under $GIT_DIR/ is).  I do not recall what happend to the
discussion, though other folks may.