Add an is_shown() method to allow globally-registered menu items to specify whether or not they should be shown on a given request

wagtail/wagtailadmin/menu.py

@@ -27,16 +27,24 @@ class MenuItem(object):
         else:
             self.attr_string = ""
 
+    def is_shown(self, request):
+        return True
+
     def render_html(self):
         return format_html(
             """<li class="menu-{0}"><a href="{1}" class="{2}"{3}>{4}</a></li>""",
             self.name, self.url, self.classnames, self.attr_string, self.label)
 
 
-_menu_items = None
-def get_menu_items():
-    global _menu_items
-    if _menu_items is None:
-        _menu_items = [fn() for fn in hooks.get_hooks('register_admin_menu_item')]
+_master_menu_item_list = None
+def get_master_menu_item_list():
+    """
+    Return the list of menu items registered with the 'register_admin_menu_item' hook.
+    This is the "master list" because the final admin menu may vary per request
+    according to the value of is_shown() and the construct_main_menu hook.
+    """
+    global _master_menu_item_list
+    if _master_menu_item_list is None:
+        _master_menu_item_list = [fn() for fn in hooks.get_hooks('register_admin_menu_item')]
 
-    return _menu_items
+    return _master_menu_item_list

wagtail/wagtailadmin/templatetags/wagtailadmin_tags.py

@@ -6,7 +6,7 @@ from django import template
 from wagtail.wagtailcore import hooks
 from wagtail.wagtailcore.models import get_navigation_menu_items, UserPagePermissionsProxy, PageViewRestriction
 from wagtail.wagtailcore.utils import camelcase_to_underscore
-from wagtail.wagtailadmin.menu import get_menu_items
+from wagtail.wagtailadmin.menu import get_master_menu_item_list
 
 
 register = template.Library()
@@ -28,9 +28,8 @@ def explorer_subnav(nodes):
 
 @register.inclusion_tag('wagtailadmin/shared/main_nav.html', takes_context=True)
 def main_nav(context):
-    menu_items = get_menu_items()[:]  # need to clone with [:] because the return value of get_menu_items is global, and construct_main_menu hooks will mutate it
-
     request = context['request']
+    menu_items = [item for item in get_master_menu_item_list() if item.is_shown(request)]
 
     for fn in hooks.get_hooks('construct_main_menu'):
         fn(request, menu_items)