Re: [BUG?] fetch into shallow sends a large number of objects

[Jeff King <peff@peff.net>]

On Fri, Mar 11, 2016 at 07:47:34AM +0700, Duy Nguyen wrote:

> Well, assume again that F and G are ref heads, and their respective
> distance to C and D are the same (like the below graph), then "fetch
> --deptch=<distance>" can mark C and D as shallow cut points because
> --depth traverses from refs until the distance is met, it does not do
> total exclusion ^C like rev-list.
> 
>        --- B ---- C ---- H ---- F
>           /      /
>      --- D ---- E ---- G

Right, so I think we would only apply the "use existing cutoffs as
bounds" thing when we were not otherwise given a --depth. Because it can
definitely cause us to override the depth (and there's no need to; the
point is to avoid linking in all of history, and --depth already solves
that). So we probably do want the client to ask "I'm not giving you a
depth, but please use my existing shallows as cutoffs".

I think a more interesting case here is when we have C as a cutoff, and
somebody fetches "E" directly. They are part of the truncated history.
So we should exclude them from a fetch of "G", but if the user asked for
them directly, that probably needs to override the existing shallow
cutoff.

We probably want to compute the --boundary of "E ^C", but then omit from
that any items that are directly in want_obj. IOW, it is OK to truncate
at depth=1 due to an existing cutoff, but not at depth=0. :)

That does mean we would then fetch all of the history leading up to E,
but I think that's OK. If the user didn't specify --depth and they are
fetching from behind the shallow-cutoff point, we don't have any real
way of knowing how much they wanted (though I guess it would also be
sensible to just apply depth=1 in such a case).

-Peff