Description

JupyerLab allows a user to open a .vl VegaLite file in a text editor and live render at the same time. Editing the text file will update the rendered visualization. However, each render, the text in the text editor gets overwritten, with no identation or formatting.

Expected behavior

Rendered visualization should not mutate the model in the document case.

Root cause

The issue is that the VegaLite MIME renderer calls setData to update the image/png after the visualization is rendered. The MIMEDocument has a handler that is called that triggers the underlying text file to be overwritten. A new argument to setData should be added that causes the mutations to not be persisted to the file. We need to verify that the data is saved in the notebook output case.