[Grok-dev] [PSPS08] Salt - kills slugs!
optilude at gmx.net
Fri Feb 15 18:57:41 EST 2008
This is another Plone Strategic Planning Summit follow-up. This wasn't
directly a focus area since iet's so small, but I feel it's important
I'm also CC'ing the Grok list, since I know they've worked on something
similar (but not quite the same - see below) and may have some
I think Wichert and Hanno have already done some work on this. With
luck, we can get this for Plone 3.2, or as an add-on earlier.
The proposal text is below.
Salt - Kills Slugs!
ZCML slugs are a pain and frequent source of confusion. For pluggable
systems such as Plone, we generally want to load the ZCML configuration
for every package that broadcasts that it is a Plone package. Buildout's
concept of a working set of eggs makes it relatively easy to predict
what will be installed.
User story - installing an egg-distributed package
The user edits buildout.cfg and adds a line to the 'eggs' option for a
package he wants to install. He runs ./bin/buildout and the package is
installed. It is found at Zope startup and all ZCML is loaded properly.
User story - installing an development egg
The user adds a new develop egg to buildout.cfg and runs ./bin/buildout.
Its ZCML is loaded on startup without having to explicitly register slugs.
A new package, 'plone.salt', provides the facility for packages to use
an entry point that points at a ZCML file. The entry point comes in
variants for configure.zcml, meta.zcml and overrides.zcml, and includes
an identifier (e.g. 'plone') and optionally a version specification that
make it clear which platform the package is aimed at. For example, the
entry point may be:
configure:plone[>=3.0,<4dev] = my.package:configure.zcml
meta:plone = my.package:meta.zcml
Plone itself includes a single line of ZCML for each type of
configuration file (configure.zcml, meta.zcml and overrides.zcml) that
will include the relevant files in all registered packages. Inside
Products.CMFPlone, this may look like:
Behind the scenes, this will find all ZCML files registered for target
'plone' of type 'configure' which apply to version 3.0.4.
Note that this system is opt-in both for the packages and for the
pluggable system (Plone in this case). ZCML will not automatically be
loaded by other Zope 3 systems where the same egg happens to be on the
module path, and Plone will not scan the module path looking for any and
all packages that it could install. It is possible for a package to
broadcast its configuration for multiple systems that subscribe to
different identifiers than "plone".
The Grok project have created a system that can load all ZCML for
packages listed as dependencies (install_requires) of a given package in
its setup.py. This approach is complementary. For example, an add-on
product may use this mechanism to ensure that its dependencies are
automatically loaded, but would still use plone.salt to ensure that it
was easy to install for Plone. It may be desirable to put both of these
types of functionality in the same package, however.
Author of `Professional Plone Development`, a book for developers who
want to work with Plone. See http://martinaspeli.net/plone-book
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