Do not send parsed JSON5 setting data as JSON

[jasongrout]

Description

The server produces invalid json for a settings get request if the raw setting text includes a value allowed by JSON5, but not by JSON (such as Infinity)

Reproduce

Add a user-level setting, such as Notebook.numberCellsToRenderDirectly, and set it to Infinity. This is a value that is allowed by JSON5, but is not allowed by JSON. Then start JupyterLab and note the many errors in the console about not being able to parse the results of the settings request.

Basically, this line adds converts the JSON5 raw setting to JSON:

jupyterlab_server/jupyterlab_server/settings_utils.py

Line 89 in f286ddf

settings = json5.loads(raw)

It does a pretty good job of stripping comments, etc, but it leaves in the Infinity. Python can serialize Infinity just fine, but the browser chokes on the response, giving an error like JSON.parse: unexpected character at line 1 column 25047 of the JSON data

Since we've standardized on JSON5, I think perhaps we should not try to include a parsed version of the setting. Instead, just send the raw text over and do a json5 conversion in the browser.

Expected behavior

Infinity to be properly recognized by the setting system.

Context

• Operating System and version: macOS Catalina
• Browser and version: Firefox 92
• JupyterLab version: 3.2 unreleased master

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[fcollonval]

The parsing to blame is the one in the connector: https://github.com/jupyterlab/jupyterlab/blob/master/packages/services/src/setting/index.ts#L63

[jasongrout]

The parsing to blame is the one in the connector: https://github.com/jupyterlab/jupyterlab/blob/master/packages/services/src/setting/index.ts#L63

I responded on the PR, but copying it here too. I think it would be better if the server did not send nonstandard JSON at all (for example, it could send the setting just as raw text to be interpreted as JSON5 on the frontend). If we send nonstandard JSON in response to a settings request, it breaks the expectation of the rest api that the response is valid JSON.