Simplify and "fix" render_old_messages management command.

The command to render old messages now looks for all messages
not matching the bugdown version, and it no longer directly calls
into model code.  We should still be extremely cautious about
using this code.

zerver/lib/message.py

@@ -213,3 +213,19 @@ class MessageDict(object):
 
         return obj
 
+def re_render_content_for_management_command(message):
+    # type: (Message) -> None
+
+    '''
+    Please avoid using this function, as its only used in a management command that
+    is somewhat deprecated.
+    '''
+    assert Message.need_to_render_content(message.rendered_content,
+                                          message.rendered_content_version,
+                                          bugdown.version)
+
+    rendered_content = message.render_markdown(message.content)
+    message.rendered_content = rendered_content
+    message.rendered_content_version = bugdown.version
+    message.save_rendered_content()
+

zerver/models.py

@@ -878,22 +878,6 @@ class Message(ModelReprMixin, models.Model):
         # type: () -> None
         self.save(update_fields=["rendered_content", "rendered_content_version"])
 
-    def maybe_render_content(self, domain, save = False):
-        # type: (Optional[text_type], bool) -> bool
-        """Render the markdown if there is no existing rendered_content"""
-        # TODO: see #1379 to eliminate bugdown dependencies
-        global bugdown
-        if bugdown is None:
-            import zerver.lib.bugdown as bugdown
-            # 'from zerver.lib import bugdown' gives mypy error in python 3 mode.
-
-        if Message.need_to_render_content(self.rendered_content,
-                                          self.rendered_content_version,
-                                          bugdown.version):
-            return self.set_rendered_content(self.render_markdown(self.content, domain), save)
-        else:
-            return True
-
     @staticmethod
     def need_to_render_content(rendered_content, rendered_content_version, bugdown_version):
         # type: (Optional[text_type], int, int) -> bool

zilencer/management/commands/render_old_messages.py

@@ -5,6 +5,8 @@ from typing import Any
 
 from django.core.management.base import BaseCommand
 
+import zerver.lib.bugdown as bugdown
+from zerver.lib.message import re_render_content_for_management_command
 from zerver.models import Message
 import datetime
 import time
@@ -18,11 +20,11 @@ Usage: python manage.py render_old_messages"""
         # type: (*Any, **Any) -> None
         total_rendered = 0
         while True:
-            messages = Message.objects.filter(rendered_content_version=None)[0:100]
+            messages = Message.objects.exclude(rendered_content_version=bugdown.version)[0:100]
             if len(messages) == 0:
                 break
             for message in messages:
-                message.maybe_render_content(None, save=True)
+                re_render_content_for_management_command(message)
             total_rendered += len(messages)
             print(datetime.datetime.now(), total_rendered)
             # Put in some sleep so this can run safely on low resource machines