i18n: Optimize get_language_list().

compilemessages command now does all the heavy lifting by creating a
language_name_map.json file under locale directory. This file is used
by get_language_list to retrieve the require information.

Fixes: #6486

static/.gitignore

@@ -9,4 +9,5 @@
 /generated/github-contributors.json
 /locale/en
 /locale/language_options.json
+/locale/language_name_map.json
 /third/emoji-data

zerver/lib/i18n.py

@@ -5,6 +5,7 @@ import operator
 from django.conf import settings
 from django.utils import translation
 from django.utils.translation import ugettext as _
+from django.utils.lru_cache import lru_cache
 
 from six.moves import urllib, zip_longest, zip, range
 from typing import Any, List, Dict, Optional, Text
@@ -14,24 +15,23 @@ import ujson
 
 def with_language(string, language):
     # type: (Text, Text) -> Text
+    """
+    This is an expensive function. If you are using it in a loop, it will
+    make your code slow.
+    """
     old_language = translation.get_language()
     translation.activate(language)
     result = _(string)
     translation.activate(old_language)
     return result
 
+@lru_cache()
 def get_language_list():
     # type: () -> List[Dict[str, Any]]
-    path = os.path.join(settings.STATIC_ROOT, 'locale', 'language_options.json')
+    path = os.path.join(settings.STATIC_ROOT, 'locale', 'language_name_map.json')
     with open(path, 'r') as reader:
         languages = ujson.load(reader)
-        lang_list = []
-        for lang_info in languages['languages']:
-            name = lang_info['name']
-            lang_info['name'] = with_language(name, lang_info['code'])
-            lang_list.append(lang_info)
-
-        return sorted(lang_list, key=lambda i: i['name'])
+        return languages['name_map']
 
 def get_language_list_for_templates(default_language):
     # type: (Text) -> List[Dict[str, Dict[str, str]]]

zerver/management/commands/compilemessages.py

@@ -11,6 +11,8 @@ from django.conf import settings
 
 import polib
 
+from zerver.lib.i18n import with_language
+
 class Command(compilemessages.Command):
 
     def handle(self, *args, **options):
@@ -24,6 +26,27 @@ class Command(compilemessages.Command):
             settings.LOCALE_PATHS = (os.path.join(settings.DEPLOY_ROOT, 'static/locale'),)
         super(Command, self).handle(*args, **options)
         self.extract_language_options()
+        self.create_language_name_map()
+
+    def create_language_name_map(self):
+        # type: () -> None
+        join = os.path.join
+        static_root = settings.STATIC_ROOT
+        path = join(static_root, 'locale', 'language_options.json')
+        output_path = join(static_root, 'locale', 'language_name_map.json')
+
+        with open(path, 'r') as reader:
+            languages = ujson.load(reader)
+            lang_list = []
+            for lang_info in languages['languages']:
+                name = lang_info['name']
+                lang_info['name'] = with_language(name, lang_info['code'])
+                lang_list.append(lang_info)
+
+            lang_list.sort(key=lambda lang: lang['name'])
+
+        with open(output_path, 'w') as output_file:
+            ujson.dump({'name_map': lang_list}, output_file, indent=4)
 
     def get_po_filename(self, locale_path, locale):
         # type: (Text, Text) -> Text