Enrich displayed python error message occuring while serving app

[tmoulignier]

Hello,

Between the versions 1.8.2 and 1.8.3, a behavior was changed in the error handler. If we serve a function that runs into a python error, the behavior goes from

1.8.2 : Error 505 appearing in the browser, full traceback in the console
to

1.8.3 : Simple error message in the browser, nothing in the console
The loss of traceback turns debugging into a nightmare.

The simple error message seem to come from this, whose code actually changed between the two versions:
https://github.com/holoviz/panel/blob/v1.8.3/panel/io/handlers.py#L369

I propose to replace the simple e put in the string by its traceback, and print it to have it in the console to benefit from IDE console features.

I propose a pull request with the associated changes.

Thanks,
Thibault

[holovizbot]

This pull request has been mentioned on HoloViz Discourse. There might be relevant details there:

https://discourse.holoviz.org/t/python-error-showing-in-browser/9114/4

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.04%. Comparing base (a222327) to head (7cd044d).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/io/handlers.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #8478       +/-   ##
===========================================
+ Coverage   70.44%   86.04%   +15.60%     
===========================================
  Files         348      349        +1     
  Lines       55047    55100       +53     
===========================================
+ Hits        38776    47411     +8635     
+ Misses      16271     7689     -8582     

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[philippjfr]

Thank you @tmoulignier! Test failure unrelated, will merge.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.