Re: looking for example of following code across files

From: Jeff King <peff@peff.net>
Date: Feb 16, 2008, 17:54 UTC
Message-ID: <20080216175445.GA19506@sigill.intra.peff.net>
In-Reply-To: <44F74AD0-CD8E-4715-BA88-4355F4513AB0@gmail.com>

On Sat, Feb 16, 2008 at 12:10:11PM -0500, Rhodes, Kate wrote:

> In order to find the original commit of each block is the system looking 
> up the commit for each block via it's SHA1, then following its parent 
> commits until it finds another commit that affected the same block or runs 
> out of commits?

Not exactly. You don't have a sha1 for each block, you have a sha1 for the whole file. So you walk the parent tree looking for the first time a particular chunk showed up. The basic idea is sketched out here:

http://article.gmane.org/gmane.comp.version-control.git/28826

> I'm thinking that while this would be possible to do manually it would  
> way too many lookups to be practical. Or, is there a simpler way to do it 
> on the command line?

You could do it manually, but it would be horribly slow. An overly simplified version of the algorithm is:

  1. Assume I'm interesed in a line that says "int foo() {"
  2. Check whether my parent has that line
     2a. If yes, then pass blame to parent, starting at '1'.
     2b. If no, then I introduced the line. Accept blame.

[When you talk about content movement, it gets a little trickier. See Junio's original explanation for more details.]

So you would end up pass blame for some lines through many commits that didn't touch those lines. I don't think you would want to do that by hand.

-Peff