Pavel Zůna wrote:
Since there weren't any comments on my proposal about plugin versioning and dependencies, I decided to make a first implementation, that shows what I had in mind.

Sorry, I had looked at it and never responded. Seeing an implementation does help though :-)

This patch adds two class variables to plugable.Plugin: VERSION and DEPENDENCIES. VERSION is supposed to be a tuple with 2 ints specifying the plugin major and minor version number. DEPENDENCIES is supposed to be a tuple of tuples. The inner tuples will contain the plugin class name (as a string) and a major version number.

The plugable.Registrar class has changed a bit. I decided to remove the 'override' keyword argument. It wasn't used anywhere. Overriding is now automatic based on the plugin class VERSION. Higher version overrides lower. This way, we can have several versions of the same plugin living in IPA directory (not in API!) at the same time. It allows higher versions to easily build on top (extend) older ones.

So to override a plugin you need to have a higher version? What if you want two separate plugins to extend a plugin, there can be only one? For example, you have one extension that adds some Samba attributes to a user and another that adds some Solaris-specific attributes. Not everyone would want both of these but some might, I think this would throw a DuplicateError.


There's also a new exception:
PluginMissingDependencyError: Plugin 'service' is missing dependency plugin 'host' (version 1)

Plugin dependencies are checked when all plugin have been loaded, that is when API is finalizing.

An example of what we can do with this approach:

Let's say a customer needs to extend users and groups by storing some additional computed information in the entries.

from ipalib.plugins.user import user, user_add
from import group, group_add

class user(user):
    VERSION = (2, 0)
    DEPENDENCIES = (('group', 2), )
    takes_params = user.takes_params + (
        # some new params here


class user_add(user_add):
    VERSION = (2, 0)
    def pre_callback( # I don't feel like writing all the args :)
         dn = super(user_add, self).pre_callback( # and again
         # do some new stuff here
         return dn


# same analogous thing for groups comes here...



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