[Monotone-devel] Re: Mark merge for existence

[Graydon Hoare]

Matt Johnston wrote:
> On Thu, Nov 15, 2007 at 09:57:50AM +0100, Markus Schiltknecht wrote:
> > You've read and understand *-merge? Best sources here [1].  Can you 
> > expand on you concept of 'existince marks'?
>
> Existence marks already exist for attrs don't they - the
> difference being that attrs aren't deleted that often so we
> don't care about their ghosts hanging round forever?

I would not worry, in general, about the persistence of ghosts or 
trimming their marks from the roster. I don't think people will be 
killing and resurrecting buckets of files. Maybe make a super-duper-kill 
command that drops a node forever, relegating it to die-die-die, 
irrespective of "existence" state. Use the "existence" mark for an 
undoable-kill, and make that the default for UI actions like "drop". You 
can work out a UI for reviving dead ghosts sometime later :)

A point you have to be sure to address throughout the tool is that you 
have to modify things that detect conflicting nodes by path, since paths 
can only have a unique *live* occupant. Change it such that eg. 
a/b/foo.txt and a/b/foo.txt only conflict if neither of those foo.txt 
nodes is a ghost. And likewise, when we write out files and directories, 
we need to skip the ghosts.

It's a little weird that, given this change, mtn may occasionally find 
itself merging content, filename and attribute state on ghosts, but 
probably harmless. I bet it will never happen. You could even warn the 
user when it does: someone thinks they're editing a living file, but 
they're talking to a ghost!

I'm curious to see how it turns out, though. Please test extensively and 
make the absolute *most conservative* form of this change you can. 
Fiddling the merge algorithm is ... probably the most destabilizing 
thing you can do to this program.

-Graydon