Broken yaml code block syntax highlighting about jupyterlab-markup HOT 2 CLOSED

I can reproduce this, but I'm not initially sure what the cause is. jupyterlab-markup is receiving the highlight request, and passing it off to CM5, but I think something is going wrong thereafter.

from jupyterlab-markup.

This is actually the case for any mode which hasn't been loaded yet (a few are blessed, e.g. JSON, markdown, python). If it's loaded before the render occurs, it should work: for example, creating a .yml file and opening it with the editor, then re-opening a markdown file which has a yaml code block looks correct.

A quick look upstream suggests, after determining which mode is needed, we need to call await Mode.ensure(spec)... somewhere around here... which of course we can't have, directly, because asynchrony.

from jupyterlab-markup.