[Zope-dev] Re: zcml entry points

[Ross Patterson]

Martin Aspeli <optilude at gmx.net> writes:

> Fred Drake wrote:
>> On 10/17/07, Martin Aspeli <optilude at gmx.net> wrote:
>>> The main win, IMHO, is to avoid the requirement for people to install
>>> slugs for third party products. Slugs suck - they are confusing to
>>> explain and people forget them all the time. Buildout makes it a bit
>>> easier, but it's still not a terribly good solution.
>>
>> Slugs are evil; agreed.  We never use them.  They were an accident of
>> the "instance" tree inherited from older versions of Zope, and how
>> that tree was re-interpreted for Zope 3.  They never worked well, and
>> did no one any favors.
>
> Glad we all agree.
>
>>> For example, say you want to install oi.plum. You need to add the line
>>> 'oi.plum' twice - once under 'eggs' and once under 'zcml' in your
>>> buildout.cfg. Forget the latter, and the package doesn't work properly
>>> (or at all).
>>
>> I actually really like this; I don't get the configuration for a
>> package unless I ask for it.  It's not unusual to want only the code
>> and not the default configuration for a package.
>
> Right - but you're building an application, and you're pretty
> experienced with Zope. A lot of Plone users just want to install a
> plug-in (a product), basically. Before, they just dropped it into a
> directory. Now, they declare it twice in a file (presuming there's a
> cheese shop release). That's a (small) step backwards
> (duplication). Declaring it once would be a step forwards (no manual
> download)
>
>>> If we had entry points, we could just load the egg. Internally, oi.plum
>>> may use <include /> as much as necessary to load *its* dependencies, but
>>> that's not something the user of the package needs to worry about.
>>
>> Requiring a package doesn't say anything about how it's going to be
>> used; making an assumption about that is really bad.
>
> Maybe. I agree there should be an option not to do this, and many eggs
> may choose *not* to use an entry point. For things like Plone add-on
> products, though, it makes much more sense to have it be automatic. To
> generalise further - if what you're installing is a high level,
> cohesive product, with a UI and an install method and all the rest of
> it, having installation be as simple as possible is a big win. For the
> components further down the stack (e.g. the things that these high
> level products are depending on!), having the processing be explicit
> (via <include /> directives) makes more sense.
>
>>> If Zope loaded entry-point ZCML automatically (maybe with an on/off
>>> switch in zope.conf for those who need more fine grained control) that'd
>>> be a pretty nice solution.
>>
>> I suspect I'd always want it off.  Picking up configuration
>> willy-nilly is too dangerous.
>
> Maybe it's off by default, then, but I *know* this would make the
> add-on products story in Plone easier: I've seen people struggle with
> slugs, editing site.zcml is far tto scary, and you don't always have a
> package that you own to include other things from.
>
> I suspect entry points would make life simpler for other systems that
> used a similar mechanism for plug-ins/add-ons. However, I agree that
> they're not appropriate for more fundamental libraries.

I'm new to eggs, but maybe both sides could be satisfied with an
approach like extra_requires?  You could list "oi.plum [zope.zcml]" when
you require oi.plum *and* its ZCML and then it's ZCML would get loaded.
Is this easily possible with eggs and/or buildout?  If not, maybe it's
a worthwhile extension.  I guess the abstracted idea would be some way
to pass configuration directives to eggs as a part of requiring them.

Ross