Installation instructions have you installing mismatched versions

Description

pip install --upgrade jupyterlab jupyterlab-git installs backend version 0.23.3

jupyter labextension install @jupyterlab/git installs frontend version 0.30.0b1

When you install the two extensions this way and then open JupyterLab you get a message telling you that the two versions are not the same and to run pip install --upgrade jupyterlab-git to fix it:

But the pip install --upgrade jupyterlab-git command also installs the 0.23.3 version. So this isn’t a viable solution. The only way for me to get matching versions was to run pip install jupyterlab-git==0.30.0b1 (and I’m assuming we regular users don’t want to be running beta versions, right? I couldn’t figure out how to install the 0.23.3 frontend version, so I’m stuck using both beta versions for now).

Reproduce

After running pip install --upgrade jupyterlab jupyterlab-git you can then run pip list to check the version of the backend version (and in this case see that it is version 0.23.3).

After running jupyter labextension install @jupyterlab/git you can then run jupyter labextension list to check the frontend version (and in this case see that it is version 0.30.0b1).

Expected behavior

When I ran those initial commands to install the extensions I expected both versions to match and to not have to troubleshoot why my versions weren’t matching.

Context

Not sure additional context is needed, but happy to provide if so!

[fcollonval]

Ok the error is due to the jupyterlab version. No release has been done for JupyterLab 3 (see #779).

So you should either install the beta version for JLab 3 or stick with JLab2 for now.

To install the beta version, you need to execute:

pip install --pre jupyterlab-git==0.30.0b1

And nothing else, JLab3 introduces a way to load directly the extension in the frontend.

[fcollonval]

For now, using pip (there should not be any trouble with conda), you can either install the stable version on JupyterLab 2 (requires nodejs):

pip install jupyterlab~=2.2.9 jupyterlab-git
jupyter lab build

To check the version:

jupyter serverextension list
jupyter labextension list

Or try the beta version on JupyterLab 3:

pip install jupyterlab~=3.0
pip install --pre jupyterlab-git==0.30.0b1

To check the version:

jupyter server extension list
jupyter labextension list

There is a space between server and extension for JupyterLab 3 as the server changed.

If you mixed up version, best is to remove the environment you created. If this is not possible, run jupyter lab clean --all, remove the packages and install them again.