Timeline not displayed due to no '_mergesort' function

[ktkt2020]

It seems the _mergesort function in the rosbag.bag was replaced by heapq.merge (ros/ros_comm#2017).
But in the current version

rqt_bag/rqt_bag/src/rqt_bag/bag_timeline.py

Line 273 in b36db71

for entry, _ in bag._mergesort(bag_entries, key=lambda entry: entry.time):

and

rqt_bag/rqt_bag/src/rqt_bag/bag_timeline.py

Line 303 in b36db71

for entry, it in bag._mergesort(bag_entries, key=lambda entry: entry.time):

the old function was still called.
This might cause the timeline to show incorrectly.

[zgxsin]

I am facing the same issue here.

[BurryChen]

I have the same issue.

[ktkt2020]

Adding the original _mergesort function back to rosbag/bag.py could temporarily help to show the Timeline (root permission required for the apt-installed ROS). Perhaps an adaptation of heapq.merge might be required for ROS1's rqt_bag.

https://github.com/ros/ros_comm/blob/47ad91df5cf0a60f29140be21e78b1587d0adf98/tools/rosbag/src/rosbag/bag.py#L2906:L2968

[MichaelGrupp]

I created a pull request with a fix: #93