History horizons: how hard can they be ?

[Martin Pool]

2009/11/16 Robert Collins <robertc at robertcollins.net>:
> On Sun, 2009-11-15 at 18:54 +0100, Jelmer Vernooij wrote:
>> As far as I can tell the only things required to support history
>> horizons properly are:
>>
>>  * have a --horizon X option to 'bzr branch' that limits the revisions
>> to fetch
>>  * have a branch.conf option that limits the revisions to fetch
>>  * support ghosts on the mainline well (there are some open bugs in this
>> area)
>>
>> Am I missing anything important?
>
> Yes, stopping fetch ever grabbing those revisions again: history
> horizons are _not_ the same thing as 'just download a bit less'. They
> are intended as a 'hard stop' on history - the history behind the
> horizon is forever inaccessible.

I think this is just a confusion of terminology, and Jelmer is talking
about what has previously been called 'shallow branches'.  In that
case I think his list is pretty much correct - and personally I would
leave out the second until I had some experience with it.

There is another issue that may come up though and that's whether you
care about revnos being different between the shallow and non-shallow
copies of the branch.  it might be nice to at least avoid people
thinking they're confusable when they have what should otherwise be a
mirror.  That may be too hard for dotted revnos or when the cutoff of
the local branch is 'ragged'.

It would be very cool.
-- 
Martin <http://launchpad.net/~mbp/>