Debugger can't be enabled with ipykernel (6.5.1)

[JTL0506]

Description

I read in the documentation that debugging using the ipykernel should now be possible starting jupyterlab version 3.
I have currently installed jupyterlab (3.2.4) and ipykernel (6.5.1) but the debugging toggle is not active.

However, debugging works with the xeus-python kernel.

Reproduce

This is the case in a fresh conda environment.

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[kycutler]

I have seen this caused by the wrong kernelspec getting picked up (also using Anaconda).

If you run jupyter --paths you should see a few directories listed under the data: heading. These are where kernelspecs are searched for.

If you open each directory in order and check the kernel subdirectory for python3, the first one you find should be the one that Jupyter server is finding as well. If the kernel.json inside there doesn't have the metadata.debugger = true key as in the example below, that explains why it isn't enabled in JLab. There are a few ways to resolve this:

• Simply add the missing debugger key. However, depending on your setup this may cause problems when switching between Anaconda environments if the targeted ipykernel version doesn't support debugging.
• If there is another instance of the python3 kernel directory later on that does have the key, you can rename the first (or second) python3 directory to avoid the collision so that both are accessible. You can also change the display_name to help you determine which is which.

Here's the content of one of my debuggable kernel.json files for reference:

{
 "argv": [
  "python",
  "-m",
  "ipykernel_launcher",
  "-f",
  "{connection_file}"
 ],
 "display_name": "Python 3 (ipykernel)",
 "language": "python",
 "metadata": {
  "debugger": true
 }
}