Serialize visual custom code (R/Python script visual, Deneb, etc.) as standalone files when saving a report using the Power BI enhanced report format (PBIR)

Currently reports containing the R or Python script visual or a custom visual where the user provides their own code (such as Deneb), when being saved using the Power BI enhanced report format (PBIR), store the script/code embedded as JSON strings within the "visual.json" file for that visual, with new line characters and double quote marks in the code needing to be escaped with a backslash. For the R/Python script visual, the script code appears in a property called "source". For the Deneb custom visual, the code appears in properties called "jsonSpec" and "jsonConfig".

This custom code should instead be stored as one or more separate files that sit alongside the "visual.json" file. For the R/Python script visual, this could be a file called "source.R" or "source.py". For the Deneb custom visual, this could be files called "jsonSpec.json" and "jsonConfig.json". This solution would give report developers a better source control experience when modifying visual custom code, with the ability to easily modify code offline, and with clean diffs free of escape characters.

In the case of the R/Python script visual, Microsoft could implement this solution themselves in the PBIR serializer. In the case of custom visuals like Deneb, Microsoft should enhance the Power BI visual SDK so custom visual developers can specify that certain text-valued properties should be serialized as standalone files in PBIR mode, rather than being serialized as a string within the "visual.json" file.