Tidy doesn't respect comment indentation at the end of a block

[wclr]

In this example I would like to comment where clause (maybe to uncomment it later):

fn x = x*x
  -- where
  -- res = x*x

After formatting, such indented commented lines lose indentation:

fn x = x*x
-- where
-- res = x*x

If to uncomment on them there will be no indentation, this seems to be minor, though I think it should not happen.

[natefaubion]

That's because these are technically leading comments for the next declaration, or trailing module comments. Tidy would have to have some heuristic for preserving some whitespace in comments.