Allow addition of extra body classes via multiple ``IBodyClassAdapter…

…`` adapter registrations without the need to overload the ILayoutPolicy view.

CHANGES.rst

@@ -10,7 +10,8 @@ Breaking changes:
 
 New features:
 
-- *add item here*
+- Allow addition of extra body classes via multiple IBodyClassAdapter adapter registrations without the need to overload the ILayoutPolicy view.
+  [thet, jensens, agitator]
 
 Bug fixes:
 

plone/app/layout/globals/interfaces.py

@@ -275,6 +275,11 @@ class IViewView(Interface):
     """
 
 
+class IBodyClassAdapter(Interface):
+    """Adapter interface for retrieving extra body classes.
+    """
+
+
 class IPatternsSettingsRenderer(Interface):
     """ Interface for the adapter that renders the settings for patterns
     """

plone/app/layout/globals/layout.py

@@ -5,6 +5,7 @@
 from Products.CMFPlone.interfaces.controlpanel import ISiteSchema
 from Products.Five.browser.metaconfigure import ViewMixinForTemplates
 from Products.Five.browser.pagetemplatefile import ViewPageTemplateFile
+from plone.app.layout.globals.interfaces import IBodyClassAdapter
 from plone.app.layout.globals.interfaces import ILayoutPolicy
 from plone.app.layout.globals.interfaces import IViewView
 from plone.app.layout.icons.interfaces import IContentIcon
@@ -16,12 +17,15 @@
 from zope.browserpage.viewpagetemplatefile import (
     ViewPageTemplateFile as ZopeViewPageTemplateFile
 )
+from zope.component import adapter
+from zope.component import getAdapters
 from zope.component import getMultiAdapter
 from zope.component import getUtility
 from zope.component import queryMultiAdapter
 from zope.component import queryUtility
 from zope.interface import alsoProvides
 from zope.interface import implements
+from zope.interface import Interface
 from zope.publisher.browser import BrowserView
 
 
@@ -268,4 +272,30 @@ def bodyClass(self, template, view):
         if msl or elonw:
             body_classes.append('pat-markspeciallinks')
 
+        # Add externally defined extra body classes
+        body_class_adapters = getAdapters(
+            (self.context, self.request),
+            IBodyClassAdapter
+        )
+        for name, body_class_adapter in body_class_adapters:
+            extra_classes = body_class_adapter.get_classes() or []
+            if isinstance(extra_classes, basestring):
+                extra_classes = extra_classes.split(' ')
+            body_classes.extend(extra_classes)
+
         return ' '.join(body_classes)
+
+
+@adapter(Interface)
+class DefaultBodyClasses(object):
+
+    implements(IBodyClassAdapter)
+
+    def __init__(self, context, request):
+        self.context = context
+        self.request = request
+
+    def get_classes(self):
+        """Default body classes adapter.
+        """
+        return []