From f47a4ae1d3d09d81d4afd50c503e1e4134b0718f Mon Sep 17 00:00:00 2001
From: Dan Braghis <dan.braghis@torchbox.com>
Date: Thu, 13 Jan 2022 20:15:51 +0000
Subject: [PATCH] Improve locale_label_from_id caching

---
 .../admin/templatetags/wagtailadmin_tags.py    | 18 ++++--------------
 wagtail/admin/tests/test_templatetags.py       | 11 +++--------
 wagtail/core/signal_handlers.py                | 10 +++++++++-
 wagtail/core/utils.py                          | 14 ++++++++++++++
 4 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/wagtail/admin/templatetags/wagtailadmin_tags.py b/wagtail/admin/templatetags/wagtailadmin_tags.py
index 66bebbf0ed..815a0c4581 100644
--- a/wagtail/admin/templatetags/wagtailadmin_tags.py
+++ b/wagtail/admin/templatetags/wagtailadmin_tags.py
@@ -40,7 +40,7 @@ from wagtail.core.models import (
 from wagtail.core.telepath import JSContext
 from wagtail.core.utils import camelcase_to_underscore
 from wagtail.core.utils import cautious_slugify as _cautious_slugify
-from wagtail.core.utils import escape_script, get_content_type_label
+from wagtail.core.utils import escape_script, get_content_type_label, get_locales_display_names
 from wagtail.users.utils import get_gravatar_url
 
 
@@ -766,22 +766,12 @@ def locales():
     ])
 
 
-@register.simple_tag(takes_context=True)
-def locale_label_from_id(context, locale_id):
+@register.simple_tag
+def locale_label_from_id(locale_id):
     """
     Returns the Locale display name given its id.
     """
-    request = context['request']
-
-    # Cache the locale id -> locale display name mapping on the request
-    if not hasattr(request, '_wagtail_locales'):
-        locales_map = {}
-        for locale in Locale.objects.all():
-            locales_map[locale.pk] = locale.get_display_name()
-        setattr(request, '_wagtail_locales', locales_map)
-        context['request'] = request
-
-    return context['request']._wagtail_locales.get(locale_id)
+    return get_locales_display_names().get(locale_id)
 
 
 @register.simple_tag()
diff --git a/wagtail/admin/tests/test_templatetags.py b/wagtail/admin/tests/test_templatetags.py
index ee0fa6ccf4..9b968db404 100644
--- a/wagtail/admin/tests/test_templatetags.py
+++ b/wagtail/admin/tests/test_templatetags.py
@@ -4,7 +4,6 @@ from datetime import timedelta
 from unittest import mock
 
 from django.conf import settings
-from django.http import HttpRequest
 from django.template import Context, Template
 from django.test import TestCase
 from django.test.utils import override_settings
@@ -196,16 +195,12 @@ class TestInternationalisationTags(TestCase):
         )
 
     def test_locale_label_from_id(self):
-        context = {
-            "request": HttpRequest()
-        }
-
         with self.assertNumQueries(1):
-            self.assertEqual(locale_label_from_id(context, self.locale_ids[0]), "English")
+            self.assertEqual(locale_label_from_id(self.locale_ids[0]), "English")
 
         with self.assertNumQueries(0):
-            self.assertEqual(locale_label_from_id(context, self.locale_ids[1]), "French")
+            self.assertEqual(locale_label_from_id(self.locale_ids[1]), "French")
 
         # check with an invalid id
         with self.assertNumQueries(0):
-            self.assertIsNone(locale_label_from_id(context, self.locale_ids[-1] + 100), None)
+            self.assertIsNone(locale_label_from_id(self.locale_ids[-1] + 100), None)
diff --git a/wagtail/core/signal_handlers.py b/wagtail/core/signal_handlers.py
index d8f7c94d4f..e9f79225ea 100644
--- a/wagtail/core/signal_handlers.py
+++ b/wagtail/core/signal_handlers.py
@@ -3,7 +3,8 @@ import logging
 from django.core.cache import cache
 from django.db.models.signals import post_delete, post_save, pre_delete
 
-from wagtail.core.models import Page, Site
+from wagtail.core.models import Locale, Page, Site
+from wagtail.core.utils import get_locales_display_names
 
 
 logger = logging.getLogger('wagtail.core')
@@ -29,9 +30,16 @@ def post_delete_page_log_deletion(sender, instance, **kwargs):
     logger.info("Page deleted: \"%s\" id=%d", instance.title, instance.id)
 
 
+def reset_locales_display_names_cache(sender, instance, **kwargs):
+    get_locales_display_names.cache_clear()
+
+
 def register_signal_handlers():
     post_save.connect(post_save_site_signal_handler, sender=Site)
     post_delete.connect(post_delete_site_signal_handler, sender=Site)
 
     pre_delete.connect(pre_delete_page_unpublish, sender=Page)
     post_delete.connect(post_delete_page_log_deletion, sender=Page)
+
+    post_save.connect(reset_locales_display_names_cache, sender=Locale)
+    post_delete.connect(reset_locales_display_names_cache, sender=Locale)
diff --git a/wagtail/core/utils.py b/wagtail/core/utils.py
index a74eeeb59e..712cebbc68 100644
--- a/wagtail/core/utils.py
+++ b/wagtail/core/utils.py
@@ -309,6 +309,20 @@ def get_supported_content_language_variant(lang_code, strict=False):
     raise LookupError(lang_code)
 
 
+@functools.lru_cache()
+def get_locales_display_names() -> dict:
+    """
+    Cache of the locale id -> locale display name mapping
+    """
+    from wagtail.core.models import Locale  # inlined to avoid circular imports
+
+    locales_map = {
+        locale.pk: locale.get_display_name()
+        for locale in Locale.objects.all()
+    }
+    return locales_map
+
+
 @receiver(setting_changed)
 def reset_cache(**kwargs):
     """