Add autoreload option

[philippjfr]

Adds an --autoreload option to panel serve which reloads the application when a change in a script/notebook is detected.

out.mp4

[MarcSkovMadsen]

I want this so badly as it will speed up my workflow a lot.

Does it only reload one module or all modules that change?

[philippjfr]

Does it only reload one module or all modules that change?

Currently reloads the scripts you are serving but I'll be working on making that configurable.

[MarcSkovMadsen]

You should consider whether more advanced reloading is worth it. I know from Streamlit that reloading nested modules can be difficult. They never got it working 100% even though it was one of the first bugs I reported.

[philippjfr]

Can you clarify what you mean by "nested modules"?

[MarcSkovMadsen]

You can see a description of some of the problems here streamlit/streamlit#358

[philippjfr]

I've now borrowed some code from streamlit after trying a couple of different approaches but I suspect we'll have the same limitations as they do.

[codecov]

Codecov Report

Merging #1983 (3cad2bd) into master (bb8dbca) will decrease coverage by 0.19%.
The diff coverage is 59.77%.

@@            Coverage Diff             @@
##           master    #1983      +/-   ##
==========================================
- Coverage   84.90%   84.71%   -0.20%     
==========================================
  Files         160      162       +2     
  Lines       19522    19696     +174     
==========================================
+ Hits        16576    16686     +110     
- Misses       2946     3010      +64     

Impacted Files	Coverage Δ
panel/command/serve.py	17.54% <9.09%> (-0.05%)	⬇️
panel/io/server.py	62.28% <14.28%> (-6.55%)	⬇️
panel/io/reload.py	69.41% <69.41%> (ø)
panel/config.py	51.65% <100.00%> (+0.14%)	⬆️
panel/tests/io/test_reload.py	100.00% <100.00%> (ø)
panel/io/state.py	57.50% <0.00%> (+1.50%)	⬆️

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[MarcSkovMadsen]

Just testing out the autoreload feature. It seems to work really, really well. This will definitely speed up my development process.

And seeing errors show up in the browser instead of terminal is also just so nice.