With the release of 3.0.0, function return types always start on a newline:

module X where

x ::
  (Int ->
  Int) ->
  Int
x f = f 1

It should print that in one line

module X where

x ::
  (Int -> Int) ->
  Int
x f = f 1

This is a bug that should be released as a hotfix as it's a pretty big regression.