public_inbox: Handle missing parent is __get_thread_root()

A message can have an In-Reply-To header but the message it points to
might not be available for some reason.

In such a case, the Message.parent_id() method will return a proper
value, but __fetch_thread_root() on that message might not and would
return None.

Let's handle that case by returning the latest message we found as the
root message.

Signed-off-by: Maxime Ripard <[email protected]>

did/plugins/public_inbox.py

@@ -145,7 +145,7 @@ def __fetch_thread_root(self, msg: Message) -> typing.Optional[Message]:
         log.warn("Couldn't find message root")
         return None
 
-    def __get_thread_root(self, msg: Message) -> typing.Optional[Message]:
+    def __get_thread_root(self, msg: Message) -> Message:
         log.debug("Looking for thread root of message %s" % msg.id())
         if msg.is_thread_root():
             log.debug("Message is thread root already. Returning.")
@@ -154,6 +154,10 @@ def __get_thread_root(self, msg: Message) -> typing.Optional[Message]:
         parent_id = msg.parent_id()
         if parent_id not in self.messages_cache:
             root = self.__fetch_thread_root(msg)
+            if root is None:
+                log.debug("Can't retrieve the thread root, returning.")
+                return msg
+
             log.debug("Found root message %s for message %s" % (root.id(), msg.id()))
             return root
 
@@ -167,7 +171,11 @@ def __get_thread_root(self, msg: Message) -> typing.Optional[Message]:
 
             parent_id = parent.parent_id()
             if parent_id not in self.messages_cache:
-                root = self.__fetch_thread_root(msg)
+                root = self.__fetch_thread_root(parent)
+                if root is None:
+                    log.debug("Can't retrieve the message parent, returning.")
+                    return parent
+
                 log.debug(
                     "Found root message %s for message %s" %
                     (root.id(), msg.id()))