Re: [PATCH] notes: Use get_sha1_committish instead of read_ref in init_notes()

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 17, 2015, 03:17 UTC
Message-ID: <xmqq1thb58i8.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1434503731-26414-1-git-send-email-mh@glandium.org>

Mike Hommey <mh@glandium.org> writes:

> init_notes() is essentially the only point of entry to the notes API.
> It is an arbitrary restriction that all it allows as input is a strict
> ref name, when callers may want to give an arbitrary committish.

While it may be a good idea to allow reading from any note-shaped tree-ish, not just what is at the tip of a ref, I suspect that the use of read_ref() is not an arbitrary restriction, but is an effective way to achieve safety against callers that update notes.

That is, you can feed refs/notes/commit@{4.days.ago} to the machinery and show you notes from 4 days ago, but you cannot update that as if it were a ref.

Hence, if you are loosening the safety at init_notes() site, you would at least need to add a similar safety in the write codepath, I would think.

One thing you would need to be careful about is that you would give users a crappy experience, if an operation reads notes, does its own thing, and then tries to write updated notes (think: rebase that transplants notes from original to rewritten commits), and you fail the operation only at the very last phase of updating. In order to prevent that, "in the write codepath" above has to be "reject any non-ref note, e.g. --notes=refs/notes/commit@{4.days.ago} upfront, if the operation will write updated notes".