Plugin operates on saved file, not on buffer

If I don't :w my changes before I call the plugin, it will silently overwrite my buffer and lose recent changes.

You mentioned you might add an option to make it auto-save the buffer before it does its work.

I'd prefer that the plugin just validate the current buffer without even having a saved file or a filename, but you said that's difficult/impossible. Maybe we can investigate workarounds later. The solution you mentioned above would be sufficient.