Re: tags sorted by their depth, *committerdate, and taggerdate

[clime <clime7@gmail.com>]

On Thu, 7 May 2020 at 21:42, Jeff King <peff@peff.net> wrote:
>
> On Wed, May 06, 2020 at 08:16:35PM +0200, clime wrote:
>
> > I have some very specific requirements to get annotated tags sorted in
> > a certain way. I would like them to be sorted:
> > - primarily by their depth (i.e. how far they are from current HEAD
> > and if they are not reachable then they should not be displayed).
> > - secondarily by committerdate of the commit they are associated with
> > - ternarily by taggerdate
>
> There's no way to compute the depth with for-each-ref or similar. In
> fact, I'm not even sure of a way to do it for all tags with a single
> command. So I'd probably script something like:
>
>   git for-each-ref \
>     --format='%(*committerdate:unix) %(taggerdate:unix) %(refname)' \
>     refs/tags |
>   while read cdate tdate ref; do
>     depth=$(git rev-list --count --ancestry-path $ref..HEAD)
>
>     # if depth is 0, then either $ref isn't an ancestor of HEAD, or $ref
>     # points to the same commit as HEAD. Not sure if you want to salvage
>     # the latter case, but you could compare rev-parse output on the
>     # two.
>     if test "$depth" = 0; then
>       continue
>     fi
>
>     echo "$depth $cdate $tdate $ref"
>   done |
>   sort -k 3rn -k 2rn -k 1n
>
> But it's kind of expensive (we'd walk over the history near HEAD
> multiple times, once per tag).
>
> It seems like git-describe should be able to do a better job of the
> traversal, but I had trouble convincing it to do so.
>
> > Is something like that possible?
> > Is something like that possible even with git 1.7.1?
>
> You'd need v1.7.2 for --ancestry-path. You could just use "$ref..HEAD"
> without it, and instead do:
>
>   git merge-base --is-ancestor $ref HEAD
>
> to cover the case where they aren't reachable from HEAD. But of course
> that's an extra traversal per tag.
>
> I'm not sure why you need to use such an antique version of Git.
>
> > If this isn't possible, I am thinking I could write some simple
> > utility in C to do it but can I rely on certain binary format of
> > commit and tag objects? Has the format changed at some point since git
> > 1.7.1? Is there a git library I could use for it? Or is the format
> > documented somewhere?
>
> Doing better would require a custom traversal of the commits. You could
> look something with libgit2 (which is in C, but has bindings to some
> other languages).

Thank you, Jeff. I didn't actually expect somebody would respond to my
crazy demand.

I probably could drop support for that version, it is in centos:6 but
that is soon going to be eoled.

Thank you also for the scripts. I would like to be the operation as
fast as possible so I am actually considering libgit2 now.

Thank you very much again for your advice
clime

>
> -Peff