From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 04 Jun 2006 07:08:24 GMT
Subject: Re: Gitk feature - show nearby tags
Message-ID: <e5bfff550606040008m4dbf02bdga4f4e6bc2d2fe9d@mail.gmail.com>
In-Reply-To: <17538.16015.53244.876090@cargo.ozlabs.ibm.com>

On 6/4/06, Paul Mackerras <paulus@samba.org> wrote:
> Marco Costalba writes:
>
> > If I have understood correctly the patch runs a 'git rev-list --all
> > --topo-order --parents'
> > and then does a tree walking.
>
> Yes, that's right.  It means that gitk can show the nearest tags even
> if they aren't included in the current view.
>
> > I am wandering if there exist any native git way to found the previous tag.
>
> I don't know of any.  Doing the tree walking in Tcl turned out to be
> not too much of an overhead, though; it does the whole kernel
> repository in 1.5 seconds on my G5.
>
> > 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
> >
> > I've missed something?
>
> I'm not sure exactly what that would do, but gitk can show more than
> one tag (the term "nearest tag" is only a shorthand approximation for
> what it does).  For example, if you have two tagged commits where
> neither is an ancestor of the other, and do a merge of the two, gitk
> will show both tags when you select the merge.

What you suggest we need it's a kind of history of tags.

Currently we can run

git-rev-list --top-order --parents HEAD -- foo.c

and we get an history of file foo.c *with modified parents*

Junio, could be possible have something like

git-rev-list --top-order --parents --tags

with the history of tags ?

And, according to Paul suggestions, not only tags, but merge revisions
between tags.

A more general and IMHO very powerful tool could be something like

git-rev-list --top-order --parents --selected-only HEAD -- <sha 1>
<sha 2> .....  <sha n>

Where git rev list gives the history, with modified parents, of the
given revisions _only_ plus the merging revisions among them.

This could be used for tags (got from git-peek-remote), for branches
and in general for a given set of interesting revisions.

Once we have the history of tags, perhaps requested once at startup,
we can get the previous tags of a given revision, our original
problem, with

git-rev-list  --topo-order <sha> ^tagList[0]  ^tagList[1]   ....
^tagList[n-1] ^merge[0] ... ^merge[k]

And have one or more tags according if results is a rev in tagList or
mergeList. Having the tag history it's easy to look up _all_ the tag
ancestors.

       Marco

P.S: another use of

git-rev-list --top-order --parents --selected-only HEAD -- <sha 1>
<sha 2> .....  <sha n>

could be this:

Currently both qgit and gitk can filter revisions with a given set of
filter rules, but the results are shown together with the other
revisions or as a list of matching revisions with no useful graph
information.
We could feed git-rev-list --top-order --parents --selected-only with
the list of matching revisions and have a pretty and sensible graph
too.