Handling unmergeable files -- a call to arms

[David Ingamells]

Hi all,

Martin Pool wrote:
>> My thinking is that we can have a short debate on the list, leading to a
>> group of people splitting off using some mechanism or other, so as to
>> come up with ideas and prototypes that can be submitted to the core team
>> for review.
>>     
>  * write a plugin that does the simplest thing that could possibly
> work (tm) - maybe keeping a list in ~/.bazaar/ of locked files, and
> sending mail when a lock is taken or released - or maybe committing to
> this list in a centralized branch
>
>   
Martin has implied here the most important issue with file locking in a 
DVCS, and maybe I'm stating here the bleeding obvious (tm)
but to state this issue explicitly:

With a DVSC where do you save the file's lock?
CVS and Subversion both have a central repository but the Bazaar model 
does not have any central location - and a branch may even be stored on 
a computer that is only very intermittently connected to the internet. 
How will the developer working on that computer (e.g. while riding in a 
bus) check/set a lock if he wants to edit such an unmergeable file?

I'm curious what other DVCS packages provide in this area.

David.