From: Linus Torvalds <torvalds@osdl.org>
Date: Wed, 27 Apr 2005 22:19:23 GMT
Subject: Re: Finding file revisions
Message-ID: <Pine.LNX.4.58.0504271506290.18901@ppc970.osdl.org>
In-Reply-To: <200504271423.37433.mason@suse.com>



On Wed, 27 Apr 2005, Chris Mason wrote:
> 
> So, new prog attached.  New usage:
> 
> file-changes [-c commit_id] [-s commit_id] file ...
> 
> -c is the commit where you want to start searching
> -s is the commit where you want to stop searching

Your script will do some funky stuff, because you incorrectly think that
the rev-list is sorted linearly. It's not. It's sorted in a rough
chronological order, but you really can't do the "last" vs "cur" thing
that you do, because two commits after each other in the rev-list listing
may well be from two totally different branches, so when you compare one
tree against the other, you're really doing something pretty nonsensical.

diff-tree will happily compare trees that aren't related, so it will 
"work" in a sense, but it doesn't actually do what you think it does ;)

So what you should do is basically something like

	open(RL, "rev-list $commit|") || die "rev-list failed";
	while(<RL>) {
		chomp;
		my $cur = $_;

(so far so good) but then you should look at the _parents_ of that 
commit, ie do (NOTE NOTE NOTE! I'm a total perl idiot, so I'm not going to 
do this right):

		open(PARENT, "cat-file commit $cur") || die "cat-file failed");
		while(<PARENT>) {
			chomp;
			my @words = split;
			if ($words[1] == "tree")
				continue;
			if ($words[1] != "parent")
				break;
			test_diff($cur, $words[2]);
		}
		close(PARENT);
	}
	close(RL);

and now your "test_diff()" thing can do the tree diff.

That way you actually do "tree-diff" on the thing you should do, and it 
will show you _which_ way it changed in a merge (ie if you hit a 
merge-point, it will do a tree-diff against both parents, and show you 
which one had the difference - then you'll obviously usually see that same 
difference later on when you dig down to the actual changeset that did it 
too).

Remember: time is not a nice linear stream.

		Linus