Martin Aspeli wrote:
We believe that these recent changes have introduced implicit magic
into a standard Zope3 api to fit Zope2 acquisition. There should be
an explicit separate api if we want acquisition wrapped context-aware
utilities. As an example of a symptom caused by the implicit
implementation, KSS (which was developed as a pure zope 3 component)
breaks when used with Plone, even though it is a perfectly valid z3
component. Once we return to using getToolByName for tool lookup, the
KSS/Plone3 issue disappears, because the magic wrapping of things
stops. This KSS/Plone3 issue arises because the five.lsm acquisition
breaks down when you add in non five.lsm component registries. If you
need Zope2 acquisition, you should use an accessor api to get things
wrapped.
In addition, getToolByName is the most fundamental and widely used api
in all of CMF, and we're going to be issuing hundreds of deprecating
warnings for every single cmf application extant.
As a solution, we propose
* The five.localsitemanager code should *NOT* be dealing with
acquisition, it should be restricted to setting up a bases chain for
persistent components that does parent lookup.
* getToolByName deprecation should be reverted. Its internal
mechanisms should be kept the same as in the current CMF 2.1 release,
using getUtility, *AND* it should be the one doing acquisition wrapping.
So instead of doing implicit magic in the getUtility call stack, let's
be explicit, while still allowing the flexibility that registered
components provide. Which in turn results in an untouched zope3
getUtility execution path for looking up utilities.
getToolByName should return acquisition wrapped utilities via name
mapping, and become un-deprecated. Context for wrapping would be the
context passed as an argument to getToolByName, as it always has been.
It would issue deprecation warnings when it has to lookup a tool via
aq_get instead of getUtility. The mechanism for registering tool
names would raise an error when anyone tries to register a component
which does not support Acquisition.
The getToolByInterfaceName method would no longer be necessary as
getToolByName can be called from restricted code. However if needed
it could remain and use the result of getSite() as the context for
wrapping the tool resulting from the utility lookup.
+1
The one thing I don't see here explicitly is the forward migration path.
Make tools not depend on acquisition and you get can start looking them
up using getUtility. This will take time, so I'd be ok if for now we
can't use getUtility right away (unless you're willing to do manual
__of__ing)
I think it would be worthwhile to work towards a future where we have no
tools or other programmer-support-mechanisms in content space.
At least new stuff can be Zope 3-style already.
I suspect
that all context-less tools today could be rewritten to be regular
global utilities,
Absolutely.
and all persitence-needing tools could be changed to
be standard local utilities that if needed did getUtility(ISiteRoot) to
get hold of the site root and acquire things from there (except, how
does the site root then get an acquisition context? Maybe it doesn't
need to?).
Well, ideally we'll be able to model containment relationships using
__parent__ in Zope 2 as well...
However, if we still promote and use getToolByName() then people will
not start using getUtility() and importing interfaces and we will find
it more difficult to deprecate (eventually) and then move to a world
where we can have real utilities (where possible/sensible).
I can say from personal experience that deprecating less in more time is
easier on the people and on yourself :).
Going back to square one, the reason why we (and I'm very guilty in
this) pushed for something at the framework level (spawning five.lsm)
was that originally we ended up with calling code needing to do:
>>> from Products.CMFCore.interfaces import IWorkflowTool
>>> from zope.component import getUtility
>>> wftool = getUtility(IWorkflowTool).__of__(context)
Such explicit wrapping is black magic voodoo to most people and would
probably lead to lots of hard-to-debug errors.
(Welcome to Acquisition!)
Requiring people to know
*when* to wrap and when it's not necessary is tantamount to requiring
them to know the implementation details of each tool.
getToolByName sounds like a sensible abstraction, don't you think?
We don't mean to belittle the hard work that anyone has put into this
so far, and we hope this is received in the spirit that it is
intended. We are willing to implement this if we can reach some
consensus that this is the right thing to do.
This is the part of the email I like the most :)
It's a bit scary to have to revert the hundreds of changes that have
been made to the Plone 3.0 codebase and probably hundreds more to the
CMF codebase to move to getUtility, though.
Why, you guys have tests, dontcha? :)
--
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