"Format on save" using vscode-purty discards pending changes

[megamaddu]

Saving a file with VSCode's "Format on save" option enabled discards my pending file changes, sends the on-disk version of the file through purty and then saves that. Ideally the in-buffer file would get streamed to purty and the result saved to disk, but it might also be ok to save unformatted and then run purty on that updated file (not sure how the VSCode API works).