Re: [PATCH v1 3/5] list-objects-filter: implement composite filters

> On Tue, May 28, 2019 at 10:59:31AM -0700, Junio C Hamano wrote:
>> Jeff Hostetler <git@jeffhostetler.com> writes:
>>
>>> In the RFC version, there was discussion [2] of the wire format
>>> and the need to be backwards compatible with existing servers and
>>> so use the "combine:" syntax so that we only have a single filter
>>> line on the wire.  Would it be better to have compliant servers
>>> advertise a "filters" (plural) capability in addition to the
> 
> This is a good idea and I hadn't considered it. It does seem to make the
> repeated filter lines a safer bet than I though.
> 
>>> existing "filter" (singular) capability?  Then the client would
>>> know that it could send a series of filter lines using the existing
>>> syntax.  Likewise, if the "filters" capability was omitted, the
>>> client could error out without the extra round-trip.
>>
>> All good ideas.
> 
> After hacking the code halfway together to make the above idea work, and
> learning quite a lot in the process, I saw set_git_option in transport.c and
> realized that all existing transport options are assumed to be ? (0 or 1) rather
> than * (0 or more). So "filter" would be the first transport option that is
> repeated.
> 
> Even though multiple reviewers have weighed in supporting repeated filter lines,
> I'm still conflicted about it. It seems the drawback to the + syntax is the
> requirement for encoding the individual filters, but this encoding is no longer
> required since the sparse:path=... filter no longer has to be supported. And the
> URL encoding, if it is ever reintroduced, is just boilerplate and is unlikely to
> change later or cause a significant maintainance burden.

> 
> The essence of the repeated filter line is that we need additional high-level
> machinery just for the sake of making the lower-level machinery... marginally
> simpler, hopefully? And if we ever need to add new filter combinations (like OR
> or XOR rather than AND) this repeated filter line thing will be a legacy
> annoyance (users will wonder why does repeated "filter" mean AND rather than
> one of the other supported combination methods?). Repeating filter lines seems
> like a leaky abstraction to me.
> 
> I would be helped if someone re-iterated why the repeated filter lines are a
> good idea in light of the fact that URL escaping is no longer required to make
> it work.
>