Fix Non-Blocking Entry Point in ConversationHandler (#3068)

telegram/ext/_conversationhandler.py

@@ -92,8 +92,9 @@ class PendingState:
 
     def resolve(self) -> object:
         """Returns the new state of the :class:`ConversationHandler` if available. If there was an
-        exception during the task execution, then return the old state. If the returned state was
-        :obj:`None`, then end the conversation.
+        exception during the task execution, then return the old state. If both the new and old
+        state are :obj:`None`, return `CH.END`. If only the new state is :obj:`None`, return the
+        old state.
 
         Raises:
             :exc:`RuntimeError`: If the current task has not yet finished.
@@ -106,13 +107,15 @@ class PendingState:
             _logger.exception(
                 "Task function raised exception. Falling back to old state %s",
                 self.old_state,
-                exc_info=exc,
             )
             return self.old_state
 
         res = self.task.result()
         if res is None and self.old_state is None:
             res = ConversationHandler.END
+        elif res is None:
+            # returning None from a callback means that we want to stay in the old state
+            return self.old_state
 
         return res
 
@@ -708,6 +711,11 @@ class ConversationHandler(BaseHandler[Update, CCT]):
             # check if future is finished or not
             if state.done():
                 res = state.resolve()
+                # Special case if an error was raised in a non-blocking entry-point
+                if state.old_state is None and state.task.exception():
+                    self._conversations.pop(key, None)
+                    state = None
+                else:
                     self._update_state(res, key)
                     state = self._conversations.get(key)
 

tests/test_conversationhandler.py

@@ -1050,9 +1050,10 @@ class TestConversationHandler:
 
             await app.stop()
 
-    async def test_non_blocking_exception(self, app, bot, user1, caplog):
+    @pytest.mark.parametrize(argnames="test_type", argvalues=["none", "exception"])
+    async def test_non_blocking_exception_or_none(self, app, bot, user1, caplog, test_type):
         """Here we make sure that when a non-blocking handler raises an
-        exception, the state isn't changed.
+        exception or returns None, the state isn't changed.
         """
         error = Exception("task exception")
 
@@ -1060,6 +1061,8 @@ class TestConversationHandler:
             return 1
 
         async def raise_error(*a, **kw):
+            if test_type == "none":
+                return None
             raise error
 
         handler = ConversationHandler(
@@ -1092,12 +1095,57 @@ class TestConversationHandler:
             with caplog.at_level(logging.ERROR):
                 # This also makes sure that we're still in the same state
                 assert handler.check_update(Update(0, message=message))
+            if test_type == "exception":
                 assert len(caplog.records) == 1
                 assert (
                     caplog.records[0].message
                     == "Task function raised exception. Falling back to old state 1"
                 )
-            assert caplog.records[0].exc_info[1] is error
+                assert caplog.records[0].exc_info[1] is None
+            else:
+                assert len(caplog.records) == 0
+
+    async def test_non_blocking_entry_point_exception(self, app, bot, user1, caplog):
+        """Here we make sure that when a non-blocking entry point raises an
+        exception, the state isn't changed.
+        """
+        error = Exception("task exception")
+
+        async def raise_error(*a, **kw):
+            raise error
+
+        handler = ConversationHandler(
+            entry_points=[CommandHandler("start", raise_error, block=False)],
+            states={},
+            fallbacks=self.fallbacks,
+        )
+        app.add_handler(handler)
+
+        message = Message(
+            0,
+            None,
+            self.group,
+            from_user=user1,
+            text="/start",
+            entities=[
+                MessageEntity(type=MessageEntity.BOT_COMMAND, offset=0, length=len("/start"))
+            ],
+            bot=bot,
+        )
+        # start the conversation
+        async with app:
+            await app.process_update(Update(update_id=0, message=message))
+            await asyncio.sleep(0.1)
+            caplog.clear()
+            with caplog.at_level(logging.ERROR):
+                # This also makes sure that we're still in the same state
+                assert handler.check_update(Update(0, message=message))
+            assert len(caplog.records) == 1
+            assert (
+                caplog.records[0].message
+                == "Task function raised exception. Falling back to old state None"
+            )
+            assert caplog.records[0].exc_info[1] is None
 
     async def test_conversation_timeout(self, app, bot, user1):
         handler = ConversationHandler(