/usr/lib/ghc-doc/hoogle/libghc-cassava-doc.txt is in libghc-cassava-doc 0.4.4.0-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-cassava-doc/html/cassava.txt