data A = A { a :: {-# UNPACK #-} Maybe Int}

[1 of 1] Compiling Main             ( Temp.hs, Temp.o )

Temp.hs:1:19: error:
    • Unexpected strictness annotation: {-# UNPACK #-}Maybe
    • In the type ‘{-# UNPACK #-}Maybe Int’
      In the definition of data constructor ‘A’
      In the data declaration for ‘A’
  |
1 | data A = A { a :: {-# UNPACK #-} Maybe Int}
  |

The diagnostic is incorrect because it complains about an "unexpected strictness annotation" although the error is the opposite.

A quick glance at the relevant GHC code suggests that it's running into the wrong diagnostic from #7210 (closed). Verified on nightly-2018-01-29.