Re: Determining commit reachability

From: Jeff King <peff@peff.net>
Date: Sep 6, 2010, 03:17 UTC
Message-ID: <20100906031700.GA25012@sigill.intra.peff.net>
In-Reply-To: <4C83FEC3.3040101@gmail.com>

On Sun, Sep 05, 2010 at 10:34:11PM +0200, Artur Skawina wrote:

Show 5 quoted lines

> Given commit C, refs (branches) R, S and T what would be the best way
> to test whether 'C' is reachable from any of the heads?
> 
> Checking if `git rev-list -n1 O ^R ^S ^T` produces any output is what
> i came up with; is there a better (ie faster) solution?

I think that is about as fast as you will get. You could try something with git-merge-base, but it should be about the same speed.

Note that neither will tell you _which_ head the target was reachable from. For that, given the current interface you have to test each head individually. If you write some C code, you can do it all in a single traversal. See this thread for some discussion of how "git tag --contains" can be sped up:

  http://article.gmane.org/gmane.comp.version-control.git/150039

-Peff