Re: Gitk feature - show nearby tags

[Paul Mackerras <paulus@samba.org>]

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.  It doesn't actually
happen in the kernel repository, though, because the tags there form a
linear list (at least the tags in the upstream repository do).

Paul.