Error found:
in module Main
at tests/purs/failing/NewtypeInstance2.purs:8:1 - 8:54 (line 8, column 1 - line 8, column 54)

  Cannot derive newtype instance for
                         
    Data.Show.Show (X a0)
                         
  Make sure this is a newtype.

in value declaration showX

where a0 is a rigid type variable
        bound at (line 0, column 0 - line 0, column 0)

See https://github.com/purescript/documentation/blob/master/errors/InvalidNewtypeInstance.md for more information,
or to contribute content related to this error.