How can I add a ruler (vertical line) to CodeMirror editors in JupyterLab?

Question

I would like to add a ruler at 80 characters. I know that you can add rulers to CodeMirror, but I don't know if I'm supposed to place the corresponding javascript in a file somewhere, or in JupyterLab's Advanced Settings Editor > CodeMirror > User Overides section, or if I should do something else all together to get it working.

I'm using JupyterLab 0.31.8

Answer 1

The feature is available in the recently shipped JupyterLab 1.0.

The feature now is implemented in the current JupyterLab 1.0 alpha (see this PR).

Note: in addition to adding

{
    "codeCellConfig": {
        "rulers": [80]
    }
}

to the Notebook settings as shown above, you can also add

{
    "editorConfig": {
        "rulers": [80]
    }
}

to the Text Editor settings.