/usr/lib/ghc-doc/hoogle/libghc-gnuidn-doc.txt is in libghc-gnuidn-doc 0.2.1-4build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-gnuidn-doc/html/gnuidn.txt