[Zope-CMF] [dev] CMFSetup add-on support: a rough proposal

[yuppie]

Hi!


Currently CMF has two machineries for setting up / configuring a site. 
While the new CMFSetup machinery has replaced the old way to set up 
complete sites, it doesn't allow to add configuration fragments needed 
by add-on products.

A while ago the problem was discussed in this thread:
http://mail.zope.org/pipermail/zope-cmf/2004-November/021476.html


AFAICS the following changes are necessary to add basic support for 
'profile fragments':

1.) extending the ProfileRegistry to allow specifying two different 
types of profiles: 'base' and 'add-on'

2.) not clearing _import_registry and _export_registry if add-on 
profiles are loaded

3.) distinguishing between registered and available import steps 
(registered export steps are always available)

4.) disabling purge mode for add-on profiles

5.) improving the 'skip purge' behavior, adding special merging 
instructions to the XML if necessary, e.g.:

     <skins-tool>
      <skin-path id="*">
       <layer name="zpt_calendar" before="zpt_content"/>
       <layer name="calendar"/>
      </skin-path>
     </skins-tool>

This would insert the layer 'zpt_calendar' before 'zpt_content' and 
'calendar' at the end of each skin path.


If there are no objections or better ideas, I'd like to work on this on 
HEAD and merge it into the 1.5 branch as soon as it is stable enough.


Cheers,

	Yuppie