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Wednesday, December 31, 2014
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[logos] AttrDict instance has no key 'contacts'
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The online demo of :ref:`logos` had caused a traceback::

  AttrDict instance has no key 'contacts' (keys are languages, about, users, sessions, bibles, system, comments, lino, contenttypes, humanize, extjs, bootstrap3)

This revealed a subtle problem and inspired me to find a nice solution
to it.

The :mod:`lino.modlib.languages` is a small plugin which defines only
one menu item into the :menuselection:`Configuration` menu.

The subtle problem is: into which menu group should the `languages`
plugin integrate?  It makes no sense (and is irritating for the user)
if such a small plugin creates its own menu group.

I started to write :lino:`/dev/menu`. For example :ref:`menu.groups`.

When the ``languages`` plugin was written, I "spontaneously" imagined
that the `Languages` table fits into the `Contacts` menu group. Here
is who I wrote this::

    def setup_config_menu(site, ui, profile, m):
        m = m.add_menu('contacts', _("Contacts"))
        m.add_action(Languages)

A bit later (when Lino's plugin system was ready), I changed this to::

    def setup_config_menu(site, ui, profile, m):
        p = dd.plugins.contacts
        m = m.add_menu(p.app_label, p.verbose_name)
        m.add_action(Languages)

Now I discovered that this caused a problem in :ref:`logos`, because
:ref:`logos` has no :mod:`lino.modlib.contacts` installed.

The actual question is: How can the `languages` plugin know where I
want it to be in the menu tree?

The only realistic solution until now was to override
:meth:`setup_menu <lino.core.site.Site.setup_menu>` for both
applications.

I would like to avoid this in order to have the ``languages`` plugin
more "pluggable".

So I had this idea: I wrote a new plugin method :meth:`get_menu_group
<lino.core.plugin.Plugin.get_menu_group>` which looks at the
:attr:`lino.core.plugin.Plugin.needed_by` attribute.  And the
:mod:`lino.modlib.languages` plugin is the first usage example.
Firstly its :xfile:`models.py` specifies::

    def setup_config_menu(site, ui, profile, m):
        p = dd.plugins.languages.get_menu_group()
        m = m.add_menu(p.app_label, p.verbose_name)
        m.add_action('languages.Languages')

And secondly, I no longer explicitly yield this plugin in the
:meth:`get_installed_plugins
<lino.core.site.Site.get_installed_plugins>` method of
:ref:`welfare` and :ref:`logos`, but (thirdly) add it to the
:attr:`needs_plugins <lino.core.plugin.Plugin.needs_plugins>` attribute
of :mod:`lino.modlib.cv` and :mod:`lino_logos.apps.bibles`.

Cool!
Updated :ref:`demos` at :ref:`lf`.