Re: A question about git-rev-list

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Jul 16, 2007, 20:05 UTC
Message-ID: <alpine.LFD.0.999.0707161258560.20061@woody.linux-foundation.org>
In-Reply-To: <86wsx0wwvs.fsf@lola.quinscape.zz>

On Mon, 16 Jul 2007, David Kastrup wrote:

Show 7 quoted lines

> 
> if I do
> 
> git-rev-list --remove-empty HEAD --not some-commit -- filename | tail -1
> 
> do I have any guarantee that the commit id I get (if any) is a direct
> descendant of some-commit?

No. You get the guarantee that

 - it's some kind of parent of HEAD
 - it's *not* a parent of some-commit

But the trivial case is a simple history like

	 /-B-\
	A     D
         \-C-/

(where "A" is the root commit, and "D" is the current HEAD, and there are two development lines from A to D).

If you now do

	git-rev-list HEAD --not C

you would generally see B on the list of commits, even though it's obviously not a direct descendant of C.

No amount of flags will change that. Of course, B might not show up for _other_ reasons (ie simply because it doesn't change "filename" at all), but generally you must always think of git-rev-list (and git log) as a _set_ operation.

There are no git operations that will look for "chain of commits from C to D" if that is what you want. No such chain necessarily even exists, and quite often it is ambiguous when it *does* exist (ie there is not a single chain from A to D, there are two chains).

You could add some kind of function that looks for the "shortest chain of commits from X to Y", but that would really be something fundamentally different from what git-rev-list gives you.

			Linus