feat: when a widget fails, show a fallback error widget

[maartenbreddels]

Fixes #657
Consider this code:

import ipywidgets as widgets
from traitlets import Unicode

class BadWidget(widgets.DOMWidget):
    _model_module = Unicode('badwidget').tag(sync=True)
    _view_module = Unicode('badwidget').tag(sync=True)
    _view_name = Unicode('DoesNotExist').tag(sync=True)
bad_widget = BadWidget()
widgets.HBox([bad_widget, widgets.Button(description='Hi')])

This would now render to:

If the semver is off:

import ipywidgets as widgets
from traitlets import Unicode

class BadVersion(widgets.Button):
    _model_module_version = Unicode('11.0').tag(sync=True)
bad_version = BadVersion()
widgets.HBox([bad_version, widgets.Button(description='Hi')])

You'd see this:

And if the widget model name is off:

import ipywidgets as widgets
import ipyvolume as ipv
from traitlets import Unicode

class BadName(ipv.Figure):
    _model_name = Unicode('Fig').tag(sync=True)
bad_name = BadName()
widgets.HBox([bad_name, widgets.Button(description='Hi')])

It renders:

So in all of these cases, something gets rendered. The only case that is not handled, is when the view_name is off (difficult to catch)

[SylvainCorlay]

cc @jasongrout

[maartenbreddels]

Me might want to have a troubleshoot link in the message. Maybe we should then also have a troubleshoot page at ipywidgets?

Another thing we should consider, is add two methods to the widget manager:

• loadViewClass (default implementation can call loadClass)
• loadModelClass (idem)

Since now we do not know when a Model or View needs to be loaded, we cannot create a fallback Model or View.

[maartenbreddels]

Code is simplified a bit (force pushed)

[maartenbreddels]

@SylvainCorlay I think we can merge this, the failure on Travis seems a fluke, and we cannot restart it 🤷

We might want to consider upstreaming this to core jupyter-widgets (working on it), but I think that will take a while.

[SylvainCorlay]

@maartenbreddels I just rebased your PR and translated the code to AnyScript so that it works with the new typescript codebase.

[trungleduc]

Hi @maartenbreddels, I'm working on testing Voila with different types of bugged widgets (#985) so I tried your PR and it works nicely. I think it will be super useful if it can be merged.

[maartenbreddels]

I think it would be better to work on the upstream version of this jupyter-widgets/ipywidgets#2960
Do you agree?

[martinRenou]

If we're fast enough, we can maybe squeeze it in ipywidgets 8.0

[trungleduc]

I think it would be better to work on the upstream version of this jupyter-widgets/ipywidgets#2960 Do you agree?

Indeed, it missed that part, I will try to push it into 8.0

[maartenbreddels]

That would be great!

[trungleduc]

This feature is added in ipywidgets 8.