From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Marco Costalba" <mcostalba@gmail.com>
Subject: Re: Gitk feature - show nearby tags
Date: Sun, 4 Jun 2006 11:54:25 +0200
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Cc: "Paul Mackerras" <paulus@samba.org>, git@vger.kernel.org,
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To: "Junio C Hamano" <junkio@cox.net>
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On 6/4/06, Junio C Hamano <junkio@cox.net> wrote:
> "Marco Costalba" <mcostalba@gmail.com> writes:
>
> > As example given a selected revision with id <sha> is it possible to
> > do something like this to fond the ancestor?
> >
> > 1) get the tag list with git-peek-remote or something similar if tags
> > are not already loaded
> >
> > 2) given the tagList vector with n elements run
> >
> >    git-rev-list  --topo-order <sha> ^tagList[0]  ^tagList[1]   ....
> >  ^tagList[n-1]
> >
> > 3) take the last sha spit out by git-rev-list, be it <lastSha>.
> >
> > 4) Previous nearest tag is the parent of lastSha
>
> Sorry, I do not understand what you are doing here at all.
> Suppose you have this simple history.
>
>   (root)
>
>          a---b---d---e---f---g
>          t1   \ /        t3
>             ---c
>                t2
>
> and <sha1> in (2) is "e".  When tagList = (t1, t2, t3), the
> above rev-list would return empty.

This is enough!

Empty list is an useful and enough information.

It means:

1) Parent of current revision ("e" in our case) is a tag, indeed our seeked tag.
2) If previous point is not true then there are no previous tags.

In a less corner case, just to better explaing my idea, consider this:

          a---b---d---e---f---g---h
          t1   \ /              t3
             ---c
                t2

Where our sha1 is still "e", in this case

git-rev-list  --topo-order <e>  ^a  ^c   ^g

gives, as last revision in output list, "f"
Then parentOf(<f>) is <g> and our looked for tag is t3

   Marco