[MERGE] Content filtering (EOL part 2 of 3)

[Ian Clatworthy]

Martin Pool wrote:
> bb: comment
> 
> Ian said he's only done some of the items Aaron pointed out so this might
> not be ready to merge yet, but since it's still in the queue I thought I'd
> read through it now.

There are two things missing compared to "it's really, truly done":

1. Tracking derived size and not just derived sha through the guts of
   dirstate (and maybe hashcache). I'm honestly struggling to see how
   best to do that without impacting performance quite a bit. I'd expect
   to see some corner case bugs now and then if we don't do this, i.e.
   my naive guess is that the current patch will be ok in practice.
   The corner cases are likely to fall over in other ways before they
   break on this particular wart if my hunch is correct. :-(

2. Adding lots more tests so we know how well content filtering works or
   otherwise on pretty much every command. That's a big job and it's
   struggling to get to the top of my list. If you're happy that the core
   tests are enough to land this, then I think the right way forward is
   to include this as an "experimental" feature in bzr.dev, get the EOL
   plugin available and to fix the problems as users encounter them.

What do you think?

Ian C.