[darcs-users] Re: current status of darcs

[Simon Marlow]

zooko at zooko.com wrote:
>> The trouble is that, unless I misunderstand, darcs simply does not support
>> this scenario, at least not for projects as big as GHC.  Step 4 doesn't 
>> work, and there is no viable work-around.
> 
> One of us must be misunderstanding something, because I do things like this all
> the time.  The threat of a lockup is a hassle, but it doesn't strike that often
> and it can be worked around.

Sometimes you don't get a lockup, you get a crash (see some of the bug reports 
in the darcs bug tracker that Simon or I have submitted, for example).  On 
branches with more than just a few small changes, it's been our experience that 
a merge is very likely to either crash or lock up.

There's no good workaround.  To perform the merge you essentially have to 
re-record all the patches, starting from the first patch that causes a lockup or 
crash, on a fresh head repo.  This is possible (we've done it several times now, 
and are getting quite good at it), but it's not a workaround in general because 
the old branch repo is now defunct; any developer that was using the old branch 
has to start using the new merged repo.  Furthermore it's a very time-consuming 
workaround - the last branch I merged in this way took me nearly a day to sort 
out, and it was just a branch that I'd been developing on alone.

I don't want all this to sound like criticism, but I do feel we need to counter 
the perceived wisdom that the bug doesn't strike all that often.  For the GHC 
project, it seems to strike whenever we try to merge any non-trivial branch.

Cheers,
	Simon