ENH: Highlight some kernels in the UI while allowing access to more kernels

[andreas-h]

When on the Notebook interface I click on "New"; I see a dropdown-list
of all installed kernelspecs. Is there any way I can hide all
kernelspecs except for a list of "favorite" kernels? I'm thinking of
just seeing the 'favorite' kernels in the dropdown list, which should
also include a "More ..." entry, which again opens a sub-dropdown
listing all installed kernels.

The motivation is that I would like to provide to our cluster users
(we're using Jupyterhub) frequent updates on default Python
environments, which would make the list of all installed kernelspecs
long. However, users should be able to still use older kernelspecs if
they really want to.

@takluyver said the following about this:

You can whitelist some of the installed kernels by configuring
KernelSpecManager.whitelist , but this will completely disable any that
aren't on the whitelist. I don't think there's currently any way to
highlight certain kernels in the UI while still making others available.
There's no reason we couldn't add that, though.

[Carreau]

I don't see any obvious ways to do it right now.
I guess a way to "sort" kernels in the UI would be nice If you have a lot of kernels I guess a top-10 kernel and See All kernels would make sens, but that will have to be changed in the codebase.

Do you want to try and make a PR ? OR even just a shot as to what the user experience should look like ?

[andreas-h]

In a very crude approach, the kernelspec JSON (is it JSON? I forgot ...) could get an additional boolean parameter hide_in_drawer. Then the New dropdown in the Notebook could group all those kernels which have hide_in_drawer set to True into a sub-menu More kernels ..., while all those kernelspecs with hide_in_drawer missing or set to False being displayed as is currently the case.

From a user perspective, I believe this should be independent of the ordering of the kernels (or, rather, if a sort order is specified, then the hidden_in_drawer and "normal" kernels should be ordered separately, see #2513 ).