Address missing local-provisioner scenario

[kevin-bates]

There have been a few instances of users reporting that they can't run kernels due to the local-provisioner not being available. However, this provisioner is registered in the current jupyter_client package, yet when the package searches for the default provisioner (i.e., local-provisioner) it is not found.

• https://discourse.jupyter.org/t/kernel-python-3-is-referencing-a-kernel-provisioner-local-provisioner-that-is-not-available-ensure-the-appropriate-package-has-been-installed-and-retry/10436
• Kernal provisioner not available anaconda/nb_conda_kernels#209

It turns out that in certain circumstances, which remain a mystery to me, there can be multiple dist-info directories present related to jupyter_client - one representing the previous release (6.x - which does not include kernel provisioning and local-provisioner) and the current release, which is obviously running since its looking for the local-provisioner. Since entrypoints uses the first distribution it finds, it locates the 6.x dist-info directory and deems local-provisioner as not available.

This pull request will detect this condition (i.e., local-provisioner is not available), issue a warning message alerting users to the situation instructing them what to do, but then constructs a local-provisioner entrypoint instance so that default behavior is experienced and kernels can be started.

Here's an example of the logged warning:
[W 10:08:17.848 NotebookApp] Kernel Provisioning: The 'local-provisioner' is not found. This is likely due to the presence of multiple jupyter_client distributions and a previous distribution is being used as the source for entrypoints - which does not include 'local-provisioner'. That distribution should be removed such that only the version-appropriate distribution remains (version >= 7). Until then, a 'local-provisioner' entrypoint will be automatically constructed and used.
The candidate distribution locations are: ['/opt/anaconda3/envs/elyra-dev/lib/python3.8/site-packages/jupyter_client-6.1.12.dist-info', '/opt/anaconda3/envs/elyra-dev/lib/python3.8/site-packages/jupyter_client-7.0.2.dist-info']

I think we should treat this as a HOTFIX since it appears to be occurring at a high enough frequency.

If anyone has ideas for what causes a previous distribution to remain, that would be helpful.

[meeseeksmachine]

This pull request has been mentioned on Jupyter Community Forum. There might be relevant details there:

https://discourse.jupyter.org/t/kernel-python-3-is-referencing-a-kernel-provisioner-local-provisioner-that-is-not-available-ensure-the-appropriate-package-has-been-installed-and-retry/10436/10

[blink1073]

Thank you!

[blink1073]

Releasing now

[kevin-bates]

Wow - thank you @blink1073!