`breakpoint()` not working

Commencez par reproduire le problème dans l’environnement conda minimal décrit, en comparant breakpoint() avec import pdb; pdb.set_trace() dans une cellule de notebook. Suivez ensuite la manière dont ipykernel gère ces points d’entrée du débogueur. Le travail est terminé lorsque breakpoint() invoque pdb dans l’environnement JupyterLab signalé et que le comportement existant est couvert contre les régressions.

Using a fresh install of Jupyter Lab my usual breakpoint() to invoke the debugger in a Notebook is skipped (see screenshot). Using import pdb; pdb.set_trace() instead invokes pdb as expected.

I was expecting (am I wrong?) that a call to breakpoint() in a cell would invoke pdb.

This is using a fresh conda install of Jupyter Lab this morning, no reconfiguration of the environment has occurred.

Description

Reproduce

I've created a fresh minimal environment:

$ conda create -n tmp_env python=3.8 jupyterlab

$ jupyter --version
jupyter core     : 4.7.1
jupyter-notebook : 6.4.3
qtconsole        : not installed
ipython          : 7.27.0
ipykernel        : 6.3.1
jupyter client   : 7.0.2
jupyter lab      : 3.1.10
nbconvert        : 6.1.0
ipywidgets       : not installed
nbformat         : 5.1.3
traitlets        : 5.1.0

and then I run jupyter lab and try to call breakpoint() as noted in the screenshot above.

I used jupyter lab --debug and scanned the output, nothing looked amiss (but there's a lot and I'm not sure what to look for) - I can attach a copy if needed?

I noticed this originally in a second more complex environment (also built today, making me think this is a library update issue somewhere) and I made the above simple environment to try to narrow things down, but the issue remains.

Environment

Linux Cinnamon using Anaconda with Firefox, the OS is all up to date.

$ inxi -b
System:    Host: ian-XPS-15-9550 Kernel: 5.4.0-77-generic x86_64 bits: 64 Desktop: Cinnamon 4.8.6 
           Distro: Linux Mint 20.1 Ulyssa 
Machine:   Type: Laptop System: Dell product: XPS 15 9550 v: N/A serial: <superuser/root required> 
           Mobo: Dell model: 0N7TVV v: A00 serial: <superuser/root required> UEFI [Legacy]: Dell v: 1.9.0 date: 10/11/2018

originally posted by @ianozsvald on https://github.com/jupyterlab/jupyterlab/issues/10996