_get_comm_info() is needed for jupyter-widget set_state() but nteract doesn't have it implemented yet.

[kjcho-msft]

Looking for a way to add the functionality to save/restore ipywidget state using nteract widget manager.

See the following implementation of set_state() in jupyter-widget and it needs _get_comm_info() but _get_comm_info() is not implemented in nteract.

My question is, can nteract add _get_comm_info implementation?

<set_state() in jupyter-widget>
set_state(state: IManagerState): Promise<WidgetModel[]> {
// Check to make sure that it's the same version we are parsing.
if (!(state.version_major && state.version_major <= 2)) {
throw 'Unsupported widget state format';
}
const models = state.state as any;
// Recreate all the widget models for the given widget manager state.
const all_models = this._get_comm_info().then((live_comms) => {
/* Note: It is currently safe to just loop over the models in any order,
given that the following holds (does at the time of writing):
1: any call to new_model with state registers the model promise (e.g. with register_model)
synchronously (before it's first await statement).
2: any calls to a model constructor or the set_state method on a model,
happens asynchronously (in a then clause, or after an await statement).
Without these assumptions, one risks trying to set model state with a reference
to another model that doesn't exist yet!
*/

<_get_comm_info() in nteract>
_get_comm_info(): Promise<{}> {
throw new Error("_get_comm_info is not implemented!");
}

[captainsafia]

This felt oddly familiar so I took a look at this and noticed we had previously filed nteract/nteract#4675.

It looks like the lack of a __get_comm_info implementation was intentional based on the previous design and the way that that the ipywidgets implementation interacts with the state.

Was there a particular motivation for filing this issue?

cc: @miduncan

[kjcho-msft]

I found _get_comm_info implementation is needed for restoring ipywidget state feature based on set_state() API in jupyter-widget manager-base.

You said you didn't add it intentionally. Does it mean there is a way to get the feature enabled without implementing get_comm_info?

@captainsafia, please provide some guidance on what would be right way to add support for restoring ipywidget state using nteract.