Add ability to add custom CSS and JavaScript to the ZMI.

This requires using fanstatic resources in an event subscriber.

docs/ZMI.rst

@@ -28,3 +28,30 @@ value should be one of the names listed on `available icons`_.
 
 .. _`zmi.icons` : https://github.com/zopefoundation/zmi.icons
 .. _`available icons` : http://htmlpreview.github.io/?https://github.com/zopefoundation/zmi.icons/blob/master/zmi/icons/resources/demo.html
+
+Use custom icons
+++++++++++++++++
+
+To use custom icons (which are not part of `zmi.icons`), you need to subscribe
+to ``App.interfaces.IRenderZMIEvent`` to need your resources.
+
+Example from `Products.CMFCore/Products/CMFCore/zmi.py`::
+
+    import App.interfaces
+    import cmf.icons
+    import zope.component
+
+
+    @zope.component.adapter(App.interfaces.IRenderZMIEvent)
+    def load_assets(event):
+        """Load the CMS icons for the ZMI."""
+        cmf.icons.cmf_icons.need()
+
+The subscriber is registered in
+`Products.CMFCore/Products/CMFCore/event.zcml` like this::
+
+    <subscriber
+        handler=".zmi.load_assets" />
+
+You can can `need` arbitrary fanstatic resources in the event subscriber, not
+only icon fonts, but also custom CSS and JavaScript.

src/App/Management.py

@@ -18,13 +18,13 @@
 from AccessControl.class_init import InitializeClass
 from AccessControl.Permissions import view_management_screens
 from App.interfaces import INavigation
+from App.interfaces import RenderZMIEvent
 from App.special_dtml import DTMLFile
 from ExtensionClass import Base
 from six.moves.urllib.parse import quote, unquote
 from zExceptions import Redirect
 from zope.interface import implementer
-import js.bootstrap
-import zmi.icons
+import zope.event
 
 try:
     from html import escape
@@ -156,13 +156,11 @@ class Navigation(Base):
     manage_form_title._setFuncSignature(
         varnames=('form_title', 'help_product', 'help_topic'))
 
-
     _manage_page_header = DTMLFile('dtml/manage_page_header', globals())
     security.declareProtected(view_management_screens, 'manage_page_header')
     def manage_page_header(self, *args, **kw):
         """manage_page_header."""
-        js.bootstrap.bootstrap.need()
-        zmi.icons.zmi_icons.need()
+        zope.event.notify(RenderZMIEvent())
         return self._manage_page_header(*args, **kw)
 
     security.declarePublic('manage_zmi_logout')

src/App/interfaces.py

@@ -15,6 +15,7 @@
 
 from zope.interface import Attribute
 from zope.interface import Interface
+from zope.interface import implementer
 
 
 class INavigation(Interface):
@@ -30,3 +31,12 @@ def manage_zmi_logout(REQUEST, RESPONSE):
         """Logout current user"""
 
 INavigation.setTaggedValue('manage_page_style.css', Attribute(""" """))
+
+
+class IRenderZMIEvent(Interface):
+    """ZMI is rendered."""
+
+
+@implementer(IRenderZMIEvent)
+class RenderZMIEvent(object):
+    """Event fired when the ZMI is rendered."""

src/Zope2/App/configure.zcml

@@ -17,4 +17,7 @@
   <securityPolicy
       component="AccessControl.security.SecurityPolicy" />
 
+  <subscriber
+      handler=".zmi.load_assets" />
+
 </configure>

src/Zope2/App/zmi.py

@@ -0,0 +1,27 @@
+##############################################################################
+#
+# Copyright (c) 2018 Zope Foundation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+
+from __future__ import absolute_import
+
+import App.interfaces
+import js.bootstrap
+import zmi.icons
+import zope.component
+
+
+@zope.component.adapter(App.interfaces.IRenderZMIEvent)
+def load_assets(event):
+    """Load the static assets needed to render the ZMI."""
+    js.bootstrap.bootstrap.need()
+    zmi.icons.zmi_icons.need()