Subject: Re: Plumbing version of 'git branch --contains' ?

From: Jeff King <[email-masked]>
Date: Thu, 23 Oct 2014 10:19:22 -0700

On Wed, Oct 22, 2014 at 08:19:07PM +0000, Crabtree, Andrew wrote:

> I need to get a list of refs that can reach a certain SHA in in a script.
> 
> git branch --contains SHA 
> 
> would be great (runs in ~2 seconds), but not my preferred option for scripting.
> 
> I tried
>  
> for br in $(git for-each-ref --format='%(refname:short)' refs/heads/)
> do
>     git merge-base --is-ancestor $1 ${br}
>     if [ $? -eq 0 ]
>     then
>             echo "${br}"
>     fi
> done
> 
> Which gives me perfect output, but takes 82 seconds to run in my environment.

Right. There's some setup work that happens in `git branch --contains`
that we end up repeating.

> Is there an alternative I'm missing to give me the run time
> performance of 'git branch --contains' but with stable output suitable
> for parsing?

Sadly, no, there isn't currently. The right tool would be `git
for-each-ref --contains`, but it doesn't exist yet. I was working
towards it, but got stopped on factoring out a `--contains` traversal
suitable for both `git tag` and `git branch` (they currently are
different and make performance tradeoffs based on the expected depth of
the merge bases, which is usually different between tags and
branches)[1].  That's work I'd love to resume, but I haven't gotten
around to it yet.

-Peff

[1] http://thread.gmane.org/gmane.comp.version-control.git/252472