From: Michael J Gruber <michaeljgruber+gmane@fastmail.fm>
Date: Fri, 27 Jun 2008 15:13:29 GMT
Subject: Re: Determining if two commits are on a separate branch
Message-ID: <g4302r$ms9$1@ger.gmane.org>
In-Reply-To: <308083c30806270755t4316be67u1f468b51bf475d28@mail.gmail.com>

Adr3nal D0S venit, vidit, dixit 27.06.2008 16:55:
> We are making extensive use of submodules at work and we have created
> a number of extra scripts to simplify our usage.  For example, there
> is git-rstatus, which recursively reports status of all submodules.
> 
> I am working on another script to check whether or not a change to any
> submodules jump branches.  If we have commits like this:
> 
> A--B--C
>    \--D
> 
> I don't care if a submodule moves from A to C or B to C, but I do care
> if a commit of the super-project would cause a jump from D to C or
> revert from C to B, effectively dropping previously committed code on
> the floor.
> 
> So, is there a "correct" or "best" way to determine if one commit's
> SHA follows directly from another's SHA in the commit history?

"Directly" as in "is child of", or as in "connected by the DAG"?

"git rev-list C..B" lists all commits which are not in C but in B. If 
this list is empty then B is "contained" in C. This is how you can test 
for being connected by the DAG. For the graph above, all of the 
following refspecs would return an empty list, indicating connectedness:

C..B
C..A
B..A
D..B
D..A

Are those the "good ones" in your case? Then you know how to test for 
the bad guys ;)

Michael