[Zope3-dev] Re: RFC: Known working sets

[Philipp von Weitershausen]

Wichert Akkerman wrote:
>> The only problem is that distributing grok-0.11.cfg is a bit tedious. 
>> How about if buildout could get it from the web?
> 
> How about making it available from an egg, through a hook in egg-info
> perhaps?

This is a very good point. So good in fact that I thought of it myself 
:) I was already writing the email when your message came in.


Martijn and I discussed the known working set problem over IRC this 
afternoon. He brought up a few good points which suggest that the 
version data could be associated with the egg:

The approach that I described in my original posting (and which actually 
works *today*, as I found out!) has some disadvantages. For instance, 
the discoverability and release mechanism of the known working set 
configuration file differs a lot from our normal packages. Releasing a 
package is a well-known routine by now. How and where would we release 
the working set configuration file? SVN?

Another problem are dependencies and how we'd like to depend on other 
working sets. Let's say we made a 'Zope' working set that contained the 
stable versions of the zope.* packages. It would make sense for grok to 
depend on this information. And packages using grok should depend on 
that. It'll be complicated to maintain such a chain in separate text 
files, especially across version updates. It only seems natural to use 
the egg dependency mechanism for this.

So, a possible solution is to associate the known working version info 
with an egg. More to the point, an egg could -- in addition to simply 
listing the names of its dependencies -- also specify which versions of 
those eggs it works best with. Wichert and I suggest that this could be 
put in a file in the EGG-INFO directory.

The only problem is that we usually don't version control egg-info 
directories. That means the information needs to be contained or at 
least referenced in setup.py and then written upon "setup.py egg_info". 
Here's what setup.py *could* look like::

   known_working_versions = {
     'ZODB3': '3.8.0',
     'zope.component': 3.4.0,
     ...
   }

   setup(
       name='grok',
       version='0.11',
       ...
       install_requires=known_working_versions.keys(),
       known_working_versions=known_working_versions
       )

When EGG-INFO is written, a custom writer will then take this 
information and generate 'known_working_versions.txt' or whatever in 
EGG-INFO. The only problem is that this custom writer needs to be 
installed when setup.py is called to create egg, in other words to 
generate the right kind of eggs you'd need to have something installed 
first. Not sure if this is better than maintaining .egg-info directories 
in SVN...


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