Re: [PATCH v5 03/19] builtin/diff-tree: convert to struct object_id

[Junio C Hamano <gitster@pobox.com>]

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> Convert most leaf functions to struct object_id.  Change several
> hardcoded numbers to uses of parse_oid_hex.  In doing so, verify that we
> when we want two trees, we have exactly two trees.
>
> Finally, in stdin_diff_commit, avoid accessing the byte after the NUL.
> This will be a NUL as well, since the first NUL was a newline we
> overwrote.  However, with parse_oid_hex, we no longer need to increment
> the pointer directly, and can simply increment it as part of our check
> for the space character.

After reading the pre- and post-image twice, I think I convinced
myself that this is a faithful conersion and they do the same thing.

What the function does appears somewhat iffy in the modern world.
We are relying on the fact that while Git is operating in this mode
of reading a tuple of commits per line and doing log-tree, that Git
itself will not do the history traversal (instead, another instance
of Git that feeds us via our standard input is walking the history)
for this piece of code to work correctly.  

Of course, the "diff-tree --stdin" command was meant to sit on the
downstream of "rev-list --parents", so the assumption the code makes
(i.e. the parents field of the in-core commit objects do not have to
be usable for history traversal) may be reasonable, but still...