Add a redirect handler to open non-notebook files from the cli

[jtpio]

This makes it possible to open non-notebook files from the cli, for example:

jupyter nbclassic setup.py

open-files-edit.mp4

[jtpio]

Starting nbclassic with this PR and:

jupyter nbclassic LICENSE

Throws the following exception in jupyter_server:

$ jupyter nbclassic LICENSE
Traceback (most recent call last):
  File "/path/to/miniforge3/envs/nbclassic/bin/jupyter-nbclassic", line 33, in <module>
    sys.exit(load_entry_point('nbclassic', 'console_scripts', 'jupyter-nbclassic')())
  File "/path/to/miniforge3/envs/nbclassic/lib/python3.9/site-packages/jupyter_server/extension/application.py", line 500, in launch_instance
    subapp = _preparse_for_subcommand(cls, args)
  File "/path/to/miniforge3/envs/nbclassic/lib/python3.9/site-packages/jupyter_server/extension/application.py", line 42, in _preparse_for_subcommand
    if re.match(r'^\w(\-?\w)*$', subc) and subc in Application.subcommands:
TypeError: argument of type 'Dict' is not iterable

It looks like passing a file name without an extension like LICENSE makes the regex check truthy here and reveals the issue:

https://github.com/jupyter-server/jupyter_server/blob/9b9b311feddf1a6769ad16553357a87984e98085/jupyter_server/extension/application.py#L42

[jtpio]

Updated the regex to also handle files without an extension.

Tested locally with:

• LICENSE
• setup.py
• Untitled.ipynb

[Zsailer]

Thanks, @jtpio. I verified this works locally for me too.