Cache explorable root page on user object via PagePermissionPolicy

wagtail/admin/tests/pages/test_edit_page.py

@@ -1876,7 +1876,7 @@ class TestPageEdit(WagtailTestUtils, TestCase):
         # as when running it within the full test suite
         self.client.get(reverse("wagtailadmin_pages:edit", args=(self.event_page.id,)))
 
-        with self.assertNumQueries(39):
+        with self.assertNumQueries(35):
             self.client.get(
                 reverse("wagtailadmin_pages:edit", args=(self.event_page.id,))
             )

wagtail/admin/wagtail_hooks.py

@@ -918,7 +918,7 @@ class WorkflowReportMenuItem(MenuItem):
 
 class SiteHistoryReportMenuItem(MenuItem):
     def is_shown(self, request):
-        return UserPagePermissionsProxy(request.user).explorable_pages().exists()
+        return get_explorable_root_page(request.user) is not None
 
 
 class AgingPagesReportMenuItem(MenuItem):

wagtail/images/tests/test_admin_views.py

@@ -316,7 +316,7 @@ class TestImageIndexView(WagtailTestUtils, TestCase):
         self.get()
 
         # Initial number of queries.
-        with self.assertNumQueries(14):
+        with self.assertNumQueries(12):
             self.get()
 
         # Add 5 images.
@@ -326,11 +326,11 @@ class TestImageIndexView(WagtailTestUtils, TestCase):
                 file=get_test_image_file(size=(1, 1)),
             )
 
-        with self.assertNumQueries(34):
+        with self.assertNumQueries(32):
             # The renditions needed don't exist yet. We have 20 = 5 * 4 additional queries.
             self.get()
 
-        with self.assertNumQueries(14):
+        with self.assertNumQueries(12):
             # No extra additional queries since renditions exist and are saved in
             # the prefetched objects cache.
             self.get()

wagtail/permission_policies/pages.py

@@ -7,6 +7,7 @@ from wagtail.permission_policies.base import BasePermissionPolicy
 
 class PagePermissionPolicy(BasePermissionPolicy):
     permission_cache_name = "_page_permission_cache"
+    _explorable_root_instance_cache_name = "_explorable_root_page_cache"
 
     def __init__(self, model=Page):
         super().__init__(model=model)
@@ -163,6 +164,10 @@ class PagePermissionPolicy(BasePermissionPolicy):
             ]
 
     def explorable_root_instance(self, user):
+        # This method is used all around the admin via get_explorable_root_page,
+        # so cache the result on the user for the duration of the request
+        if hasattr(user, self._explorable_root_instance_cache_name):
+            return getattr(user, self._explorable_root_instance_cache_name)
         pages = self.instances_with_direct_explore_permission(user)
         try:
             root_page = Page.objects.first_common_ancestor_of(
@@ -170,6 +175,7 @@ class PagePermissionPolicy(BasePermissionPolicy):
             )
         except Page.DoesNotExist:
             root_page = None
+        setattr(user, self._explorable_root_instance_cache_name, root_page)
         return root_page
 
     def explorable_instances(self, user):