Order of vocabulary-specific plugins is not configurable

[kouralex]

At the moment, global plugins are declared in a list (which is – by default – ordered). However, this is not the case for vocabulary-specific plugins, please see https://github.com/NatLibFi/Skosmos/wiki/Plugins#activating-plugins. This will cause trouble as I can not guarantee/change their respective execution order.

I think implementing this will request two kinds of changes to the code base:

1. Deprecate skosmos:usePlugin in favor of skosmos:usePlugins (the name can be different, that was just an example) that takes a list as a parameter
2. In case there are similarly named plugins in skosmos:usePlugins and skosmos:globalPlugins, use the order for them declared in skosmos:usePlugins. For a reasonable default order, it should be decided whether to append or prepend skosmos:globalPlugins plugins with skosmos:usePlugins in order to determine their respective execution order.

Alternatively, one could just add a specific skosmos:executionOrder/Priority value for each plugin. However, this would make it impossible to have plugins in different order in different vocabularies.

Regarding plugins: it would be better to require a true object relation instead of plain strings. This would enable us to mix parameterized plugins with 'normal' ones in the list. Actually, this way we could still use skosmos:usePlugin in the same clever way it is used in parameterized plugin and just shift its use from vocabulary level (deprecate it there) to plugin level.

[Vainonen]

The pull request #1201 fixes this issue only partly. PluginRegister class loads plugins in alphabetical order and changes the order made by vocabularyConfig class and defined by skosmos:vocabularyPlugins in Skosmos configuration.

The order in which the plugins are loaded is actually not the same in which they are rendered to a concept page. Several NatLibFi's Skosmos widgets render the widget content after concept-info element in the concept page. This means that the last element in order will be the first element visible after concept info and the order is reverse of skosmos:vocabularyPlugins. It needs more planning to decide how the rendering of plugins could be done in the order listed in skosmos:vocabularyPlugins.

As said in the original issue notes the configuration property skosmos:usePlugin should be deprecated in future since skosmos:vocabularyPlugins does the same, but in a shorter manner. However, skosmos:useParamPlugin needs skosmos:usePlugin to define the name of the plugin it uses.