Postfix Haddock comments on unnamed constructor fields can be lost

Summary

The -- ^ comment here is lost from the parse tree:

data Foo
  = -- | Cons 1
    Cons
      Int -- ^ Field 1

ghc -haddock -fforce-recomp -ddump-parsed /tmp/z.hs
[1 of 1] Compiling Main             ( /tmp/z.hs, /tmp/z.o )

==================== Parser ====================
data Foo = " Cons 1" Cons Int

Notes

The comment is treated as a constructor Haddock if -- | Cons 1 is removed (this is also questionable behavior):

data Foo
  = Cons
      Int  -- ^ Field 1

==================== Parser ====================
data Foo = " Field 1" Cons Int

The comment is treated as a field Haddock if there is more than one field (this is the right behavior):

data Foo
  = Cons
      Int  -- ^ Field 1
      Bool -- ^ Field 2

==================== Parser ====================
data Foo = Cons Int " Field 1" Bool " Field 2"

Environment

• GHC version used: 8.9.0.20191031