Subject: Re: [PATCH 3/4] Add 'promisor-remote' capability to protocol v2

From: Junio C Hamano <[email-masked]>
Date: Mon, 19 Aug 2024 13:00:11 -0700

Patrick Steinhardt <[email-masked]> writes:

>> +In this case, or if the client doesn't want to use any promisor remote
>> +the server advertised, the client should reply only "promisor-remote"
>> +without any value or "=" sign after it.
>
> Why does the client have to advertise anything if they don't want to use
> any of the promisor remotes?

Yeah, it is not very well justified why an empty capability needs to
be sent (from both sides).  My recommendation is to drop that part
of the design, but if there is a reason to keep, it should be done
by explaining how differently the other side should behave when the
capability is not sent at all and when the capability with no
promisor remote is sent.

>> +The "promisor.advertise" and "promisor.acceptFromServer" configuration
>> +options can be used on the server and client side respectively to
>> +control what they advertise or accept respectively. See the
>> +documentation of these configuration options for more information.
>
> One thing I'm not totally clear on is the consequence of this
> capability. What is the expected consequence if the client accepts one
> of the promisor remotes? What is the consequence if the client accepts
> none?

Yes, I also found the documentation lacking in that respect.  The
series talks about how the exchange can proceed, without saying much
(if anything) about what both sides want to exchange promisor-remote
for---what effect does it have on the behaviour of both sides to
send one.  I covered this point in one of my reviews a bit more.

  https://lore.kernel.org/git/[email-masked]/

> In the former case I'd expect that the server is free to omit objects,
> but that isn't made explicit anywhere, I think. Also, is there any
> mechanism that tells the client exactly which objects have been omitted?
> In the latter case I assume that the result will be a full clone, that
> is the server fetched any objects it didn't have from the promisor?
>
> Or does the server side continue to only honor whatever the client has
> provided as object filters, but signals to the client that it shall
> please contact somebody else when backfilling those promised objects?

Thanks.