Ipywidget comm breaks when a new ipywidget is rendered

[govinda18]

Fixes #4088

This commit drops explicitly calling ipywidget.comm.open() as it causes a protocol version mismatch issue - reproducer in the referenced issue. When opening a new comm, as per the docs, we need to pass data and meta data. So the w.comm.open() call should be something like:

metadata = {"version": "2.0.0"}
data = {"state": w.get_state()}
w.comm.open(data=data, metadata=metadata)

This seems to fix the error but the widgets still do not update. This is because when we create a new comm, ipywidgets seems to create a new model reference. In my understanding, we need not explicitly open a comm to the frontend as the kernel will automatically reconstruct an existing comm. If for some reason we do want to open a comm, then ipywidgets bokeh needs to be updated so that the view uses the correct model.

[codecov]

Codecov Report

Merging #4091 (395a2b3) into master (a1fc86d) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4091      +/-   ##
==========================================
+ Coverage   83.58%   83.59%   +0.01%     
==========================================
  Files         223      223              
  Lines       33243    33231      -12     
==========================================
- Hits        27785    27780       -5     
+ Misses       5458     5451       -7     

Flag	Coverage Δ
ui-tests	37.57% <ø> (ø)
unitexamples-tests	74.67% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
panel/pane/ipywidget.py	50.00% <ø> (+1.11%)	⬆️
panel/io/state.py	69.65% <0.00%> (-0.35%)	⬇️
panel/tests/util.py	91.17% <0.00%> (-0.09%)	⬇️
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/tests/ui/widgets/test_tabulator.py	99.07% <0.00%> (+0.10%)	⬆️
panel/pane/idom.py	28.36% <0.00%> (+0.19%)	⬆️
panel/tests/conftest.py	88.79% <0.00%> (+0.38%)	⬆️
panel/io/callbacks.py	79.41% <0.00%> (+0.57%)	⬆️
panel/command/convert.py	32.35% <0.00%> (+0.92%)	⬆️
panel/tests/command/test_serve.py	83.95% <0.00%> (+1.02%)	⬆️

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[philippjfr]

Thanks @govinda18. Would love to sync with you some time to survey the current issues with ipywidgets + bokeh/panel and then make a plan for resolving them.

[govinda18]

Thanks @govinda18. Would love to sync with you sometime to survey the current issues with ipywidgets + bokeh/panel and then make a plan for resolving them.

Surely, feel free to send an invite to totla@deshaw.com.

[govinda18]

@philippjfr let me know whenever you are free to catch up. My colleague @mlucool would also love to join at udoff@deshaw.com.

Also, let me know if you have any feedback on the PR.

[philippjfr]

Together with bokeh/ipywidgets_bokeh#69 this fixes the issue.