Re: [Monotone-devel] Re: [cdv-devel] more merging stuff (bit long...)

[Ross Cohen]

On Sun, Aug 07, 2005 at 01:06:50AM -0700, Nathaniel Smith wrote:
> Hmm, in traditional cdv tree-merging, all merges are marked the same
> -- if the name is totally new, it's a new change; if it has the same
> value as a parent, it's not.  _Because_ of this, it hits ambiguous
> clean in some simple cases, like the classic criss-cross:
>    |
>    a
>   / \
>  b*  c*
>  |\ /|    (marked like traditional cdv-merge would, IIUC)
>  | X |
>  |/ \|
>  b   c
> 
> Here *(b) is an ancestor of c, *(c) is an ancestor of b; you lose.
> 
> It's exactly that I mark the conflict resolutions as changed, that
> eliminates ambiguous clean merge.

Merging of the last c and c in this case gives a conflict, just as your
suggested algorithm does.

> (ambiguous clean merge is sufficiently annoying that I feel like I'm
> using too weak a verb there.  "annihilates"?  "obliterates"?
> 
> maybe I'm taking this too personally.)

I think you are. As should already be obvious, I don't consider the negative
conflict of the ambiguous case to be less valid than the affirmative conflict
mode which you are attempting to force everything into.

In addition, your proofs are nice, they demonstrate we understand the
behaviour of a very specific case. However, they are about an algorithm which
gets some common cases wrong. While your objection to designing around a
bunch of test cases is understandable, the test cases are still a necessary
condition for acceptance.

This is not to say the proofs server no purpose. We definitely need to build
up an approach to formal modeling in this area. And you did list a bunch of
very useful test cases. :)

Ross