'toExpression' function is removed in a plugin by Kibana core

[fbaligand]

Kibana version: 7.8.0

Describe the bug:
I develop a community visualization plugin: github.com/fbaligand/kibana-enhanced-table.
I noticed that 'toExpression' function declared in my visualization type is removed somewhere by Kibana core.
Unfortunately I can't figure out where exactly in Kibana core code.
The result is that 'build_pipeline.ts' don't find 'toExpression' function in vis type, and so, don't call it:
https://github.com/elastic/kibana/blob/7.8/src/plugins/visualizations/public/legacy/build_pipeline.ts#L528
I precise that this bug exist only since Kibana 7.8.0.
It works fine with earlier Kibana versions.

Steps to reproduce:

1. add a 'toExpression' function in any Kibana visualization plugin
2. start Kibana
3. notice that 'toExpression' is not called

Expected behavior:
'toExpression' function in vis type not removed by Kibana core

Any additional context:
Here's my 'toExpression' function declaration:
https://github.com/fbaligand/kibana-enhanced-table/blob/master/public/enhanced-table-vis.js#L136

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[ppisljar]

thanks @fbaligand i'll take a look

[fbaligand]

Thanks @ppisljar
Maybe, there is some vis type structure validation, and all non official fields are removed, and 'toExpression' is missing in all official fields?

This bug is blocking for my plugin. Despite a desperate workaround, the workaround is not called in several use cases :(

[ppisljar]

sorry, this slipped my mind. This should be fixed by now, please reopen if you still encounter it.

[fbaligand]

Yes, it is fixed since Kibana 7.10.

I recently understood that issue was because « toExpression » function was not copied in basic_vis_type.