Haddock comments needs to be separated by semi-colons when explicit layout is used

[anonymous]

Haddock comments are parsed as separate declarations so we need to insert a ';' when using them with explicit layout:

module NoLayout where {
  -- | the class 'C'
  ;
  g :: Int;
  g = undefined
 }

This should be fixed in the GHC parser, hence the 2.3.0 milestone.