[Zope3-dev] Re: Autoconfiguring a site.zcml

[Martijn Faassen]

Hello,

Tres Seaver wrote:
> David Pratt wrote:
>> On the basis that eggs spell out dependencies, I am thinking the 
>> inclusion of packages and their dependencies should be enough to dictate 
>> the sequence of inclusion for package configuration (and creation of the 
>> site.zcml) for the app buidout recipe. This could be a option to the 
>> current manual configuration.
> 
> - -1.  Configuration is *policy*;  implicitly wiring in the default
> configuration for every egg on the path is not going to be an acceptable
> default.

In the path? David didn't say in the path, did we? What about in the 
buildout? Since my buildout already says explicitly it wants egg foo, 
and egg foo needs egg bar, it is a major pain to have to specify the 
ZCML for bar manually.

I don't think something being policy means it's automatically a bad 
candidate for automation. Information about the policy may after all be 
elsewhere in the system, for instance in a buildout.cfg.

>> Presumably, the reason folks would use this recipe is to configure one 
>> or more of the same app. I know attempting to do this manually is prone 
>> to errors if packages are not in the correct sequence or if you miss the 
>> configuration of a package. Any thoughts on this. Many thanks.
> 
> Not necessarily.  There are really two kinds of packages in play here:
> "libraryish" packages, which supply mechanisms, and "applicationish"
> packages, which use the mechanism according to some policy.  I would
> argue that the only things you can safely auto-include would be the
> 'meta.zcml', because it is policy-free.  Reusable packages need to avoid
> imposing policy (they may *suggest* it, but they shouldn't insist).

That's where we have the concept of overridable defaults. So the default 
should be to follow the suggestions, and there should be an option in 
the system to override this suggestion.

> I would cheer if somebody proposed writing a UI which introspcts
> packgaes for such suggestions, and allows the site manager to merge /
> override them to create an appropriate 'site.zcml'.  Until then, I don't
> want package authors dictating to site managers.

Who are these ZCML-using site managers you are speaking of? Anyway, are 
you saying you want some form of ZCML UI to be created before *any* 
automation can be implemented? Asking for the creation of a UI on the 
Zope 3 mailing list is paramount to waiting forever...

If you never automate policy, you'll be writing a lot of stuff by hand. 
That may be fine for you, but I myself would prefer to write less boring 
code and focus on more interesting problems.

Regards,

Martijn