hindent changes the meaning of the formatted code

[facundominguez]

Problem

hindent changes the meaning of the formatted code, which would make unattended formatting rather dangerous.

• I checked the issue tracker for existing issues about this problem.
• I'm using the latest version of hindent.

$ cat test.hs
{-# LANGUAGE CPP #-}
main = print (g && f1)
  where
        f1 = h
          where
            h = True
#ifdef C1
g = g1
  where
    g1 = g2
      where
        g2 = False
#else
        g = True
#endif

#ifndef C1
g = False
#endif

$ runhaskell test.hs
True

$ hindent --version
hindent 5.2.7

$ hindent test.hs

$ runhaskell test.hs
False

Actual output haskell

{-# LANGUAGE CPP #-}

main = print (g && f1)
  where
    f1 = h
      where
        h = True
#ifdef C1
g = g1
  where
    g1 = g2
      where
        g2 = False
#else
        g = True
#endif

#ifndef C1
g = False
#endif

Perhaps there should be a way to disable parsing of CPP directives to reject this program.