Re: [PATCH 2/2] pretty: add merge and exclude options to %(describe)

On Sun, Feb 14, 2021 at 11:10:57AM +0100, René Scharfe. wrote:

Allow restricting the tags used by the placeholder %(describe) with the
options match and exclude.  E.g. the following command describes the
current commit using official version tags, without those for release
candidates:

   $ git log -1 --format='%(describe:match=v[0-9]*,exclude=*rc*)'

An interesting side effect of this series is that it allows remote users
asking for archives to fill in this data, too (by using export-subst
placeholders). That includes servers allowing "git archive --remote",
but also services like GitHub that will run git-archive on behalf of
clients.

I wonder what avenues for mischief this provides. Certainly using extra
CPU to run git-describe. But I guess also probing at otherwise hidden
refs using the match/exclude system (though since it's limited to
refs/tags/, that's pretty unlikely).

I present this mostly as an observation, not an objection. Certainly we
already have %D which can look at hidden refs. And I strongly suspect
that the server-side git-upload-archive does not respect hidden refs
when resolving object names in the first place.

Kind of an interesting thought as we extend the formatting language,
though. I generally think of them as something that is always under
control of caller, but export-subst's $Format$ will come from the repo
contents.

-Peff