Should decorate completer node to reduce CSS selector complexity

[krassowski]

Since #949 we no longer override the completer handler and do not have access to widget, hence we set the a data attribute on body and use a selector like body[data-lsp-completer-layout] .jp-Completer; this is somewhat wasteful as the browser needs to traverse the DOM tree up until body to check if the element of given class should be decorated.

In jupyterlab/jupyterlab#9763 I proposed to allow to add a class in renderer upstream; if the completion renderer had createWidgetNode() method we could add the data attributes (or classes directly), reducing the CSS selector complexity.

• jupyterlab-lsp 5.0-alpha.0
• jupyterlab 4.0.5

[krassowski]

This is low priority because as of today the completer gets attache directly to the body, which means that the distance to traverse is tiny.