Send filepath urls to JupyterLab instead of classic notebook

[SylvainCorlay]

Now that JupyterLab 3 has been out for some time, and most lab extensions have been updated to work well with that version, it might be a good time to make the switch from classic notebook to lab.

In this PR, I am changing the default redirect URL from tree to doc/tree to enable the JupyterLab "simple mode" that is the closest to the classic notebook user interface (doc).

• Obviously, it is still possible to opt out using the urlpath instead of a filepath.
• Also referencing the poll about defaulting to JupyterLab in JupyterHub on discourse.

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[SylvainCorlay]

We could eventually decide to start the jupyterlab server instead of using the server extension, but I am not doing this now so that users can opt out.

[manics]

I created an issue in repo2docker a few weeks ago to discuss the transition, I think we should keep repo2docker and binderhub in sync if possible:
jupyterhub/repo2docker#1026

[SylvainCorlay]

I created an issue in repo2docker a few weeks ago to discuss the transition, I think we should keep repo2docker and binderhub in sync if possible:
jupyterhub/repo2docker#1026

Thanks! I missed that one.

I think we should keep repo2docker and binderhub in sync if possible.

My understanding is that the main thing to change in repo2docker would be in the start_container function to start jupyter lab instead of jupyter notebook. (Would there be anything else?) However some users might prefer to keep the notebook command for a while to be able to opt out completely until any issue that arises is resolved.

[betatim]

Is it a ridiculous idea to modify the default URL generated by BinderHub (https://mybinder.org/v2/gh/binder-examples/requirements/HEAD?urlpath=doc/tree instead of https://mybinder.org/v2/gh/binder-examples/requirements/HEAD) to include the new URL path instead of changing the behaviour when no URL path is specified?

[manics]

As explained in jupyterhub/repo2docker#1026 (comment) this PR only changes the URLs generated for the filepath option, and therefore only affects new URLs, so I think it's fine to merge.

However perhaps we should hold off until our binder-examples are updated to JupyterLab 3.0? I just tried to check how /doc/tree appears with https://github.com/binder-examples/conda, then discovered it's still using a cached image with JupyterLab 2.

[minrk]

How long have we been building with jupyterlab 3? Maybe we should do an image cache clean of images older than that?

[manics]

jupyterhub/mybinder.org-deploy#1839 was merged on 18 Feb.

[SylvainCorlay]

Let me know if anything else is needed from me in this PR!

[SylvainCorlay]

It could be quite interesting to get this in, especially with lab 3.1 being out!

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[agitter]

I support migrating to JupyterLab, but I wanted to note that this change breaks some existing Binder links. I was teaching a workshop today and participants got a 404 error with the URL https://mybinder.org/v2/gh/carpentries-incubator/ml4bio-workshop/gh-pages?filepath=illustration.ipynb

It took some digging to find this pull request and change the URL to https://mybinder.org/v2/gh/carpentries-incubator/ml4bio-workshop/gh-pages?urlpath=tree/illustration.ipynb to revert to the previous behavior.