Recast converts all tabs to 4 spaces. It would be better to detect whether file uses tabs and then tell Recast to also use tabs. Similarly to what we did with LF/CRLF line terminators.
There's also a related issue in Recast: benjamn/recast#185
I tried to implement it using useTabs option of Recast, but it doesn't seem to work quite like advertised. Filed a bug to Recast: benjamn/recast#315