"Open With > Vega" removes line breaks and indentation

[masonlr]

Describe the bug

The "Open With > Vega" feature removes line breaks and indentation from the source json file (making it difficult to develop vega json files using jupyter lab).

To Reproduce
Steps to reproduce the behavior:

1. Create a file called vega.json with example vega source:

   curl https://vega.github.io/vega/examples/bar-chart.vg.json > vega.json
   

2. Right click on the file in the jupyterlab file browser and go to "Open With > Vega" .

3. Line breaks and indentation will be removed.

Expected behavior
Original file formatting to be retained.

Screenshots

Desktop (please complete the following information):

• OS: macOS 10.12.6
• Browser: chrome 69.0
• JupyterLab: 0.34.10

[jasongrout]

Confirmed. Thanks for the easy and explicit instructions to reproduce!

My first question: why is the vega viewer saving the json? Shouldn't it be basically opening the file read-only?

[jasongrout]

I've also noticed sometimes opening csv files, it seems that the file shows as being dirty. Perhaps this is related? The CSV viewer also should be read-only.

[jasongrout]

Setting as a 1.0 issue so we can track down why the file is being saved - that seems really odd.

[JohnJohnsonIII]

Identified issue as being with the _changeCallback function in docregistry package's mimedocument.ts file. About to do a PR for the fix...