[darcs-devel] [issue772] bug in get_extra commuting patch

[David Roundy]

On Mon, Mar 31, 2008 at 02:40:48PM -0600, zooko wrote:
> >The key mistake you're making is that you seem to assume that we could
> >check this hash, but it's an uncheckable hash, because there's no reason
> >to believe we could ever again recreate that context.
> 
> This is what I meant by "theoretically could be used by a future  
> version of darcs".  It is theoretically possible that a future  
> version of darcs could get access to the context.

No, if a patch in this context is obliterated (and the file describing that
patch is deleted, or this copy of the repository is deleted), then there is
absolutely no way any possible future version of darcs (okay, maybe I
should add that the hard drive was thrown into a volcano) could reconstruct
that context.  Barring a search of all possible patch names that might have
ever been created.

> If in the future there were an extension to darcs to provide such  
> contexts, then darcs would gain the same provenance guarantee that  
> the other decentralized revision control tools offer without losing  
> its unique flexibility.

As mentioned above, there is no possible way such an extension could be
written.

> Perhaps such an extension is too difficult to implement, but perhaps  
> not.

No, it's not difficult.  It's impossible.

If we modified a future version of darcs to store all patches ever
recorded, and transmit all such patches to every other repository it comes
in contact with, then this hash could be useful for verification purposes.
But until we make that change, there's just no reason to store it except as
repeatable pseudorandom garbage.
-- 
David Roundy
Department of Physics
Oregon State University