Re: [PATCH v5 3/3] cat-file: add --follow-symlinks to --batch

From: Junio C Hamano <gitster@pobox.com>
Date: May 12, 2015, 20:22 UTC
Message-ID: <xmqqd225fsw8.fsf@gitster.dls.corp.google.com>
In-Reply-To: <xmqqlhgtftw0.fsf@gitster.dls.corp.google.com>

Junio C Hamano <gitster@pobox.com> writes:

Show 21 quoted lines

> Ahh, that would also give us "missing", so in that sense you are
> being consistent.
>
> But I do not think that consistency is useful.  Showing just
> "missing" instead is losing information and that is what bothers me.
>
> Showing "symlink 6 nosuch" to this "link points at a target that
> would be in-tree but there is no such object in the tree" symbolic
> link instead of "missing" would make it more useful, and I do not
> offhand think of a downside, but maybe I am missing something.
>
> For a link that points outside, the code already gives
>
>     $ ln -s ../outside outlink
>     $ git add outlink
>     $ echo "$(git write-tree):outlink" |
>       git cat-file --batch --follow-symlinks
>
> "symlink ../outside", so the script reading from the batch output
> already has to be prepared to handle "symlink" and understand it as
> saying "the link does not point an object that is inside the tree".

Having said all that, I think we can make readers' life easier by classifying various reasons why --follow-symlinks cannot pretend as if the in-tree pointee were given as its input and signal it differently:

 * A link points outside the original tree (or the index, once we
   support "cat-file :RelNotes").

   I think your "symlink <size> LF <target> LF" already does this.

 * A link points (directly or indirectly) at itself.

   This would be your "loop <size> LF <target> LF", which I think is
   good.

 * A link does not step outside the original tree, but the pointee
   does not exist in the original tree.

   I think you currently say "<object name for HEAD:link> missing",
   but I do not think it is useful.  That object does exist, but it
   merely cannot be dereferenced.  Perhaps introducing a new one,
   e.g. "dangling <size> LF <target> LF" similar to symlink/loop,
   would help the reader better?

Are there other cases? The only other case I think of is when the link resolves cleanly inside the tree, which you already handle.

Thanks.