Extension shows up as both installed and uninstalled and doesn't work

JupyterLab
3

I encountered a similar problem here. I wanted to update the matplotlib widget but first uninstalled the extension. This got listed in the aforementioned json file. After reinstalling the matplotlib widget the state of jupyter lab look as follows:

JupyterLab v1.2.6
Known labextensions:
   app dir: C:\Miniconda3\envs\jupyter\share\jupyter\lab
        @jupyter-widgets/jupyterlab-manager v1.1.0 enabled  ok
        @jupyterlab/toc v1.0.1 enabled  ok
        @ryantam626/jupyterlab_code_formatter v1.1.0 enabled  ok
        jupyter-matplotlib v0.5.0 enabled  ok
        jupyterlab-flake8 v0.4.1 enabled  ok
        jupyterlab-jupytext v1.1.0 enabled  ok

Uninstalled core extensions:
    jupyter-matplotlib

The matplotlib widget failed to load, rebuilding or reinstallation did not change the situation. Manually deleting the .json file lead to jupyter recognizing that a rebuild is required.

JupyterLab v1.2.6
Known labextensions:
   app dir: C:\Miniconda3\envs\jupyter\share\jupyter\lab
        @jupyter-widgets/jupyterlab-manager v1.1.0 enabled  ok
        @jupyterlab/toc v1.0.1 enabled  ok
        @ryantam626/jupyterlab_code_formatter v1.1.0 enabled  ok
        jupyter-matplotlib v0.5.0 enabled  ok
        jupyterlab-flake8 v0.4.1 enabled  ok
        jupyterlab-jupytext v1.1.0 enabled  ok

Build recommended, please run `jupyter lab build`:
    jupyter-matplotlib needs to be included in build

After the rebuild everything worked again. So I think this is definitely a bug.

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