/usr/lib/ghc-doc/hoogle/libghc-case-insensitive-doc.txt is in libghc-case-insensitive-doc 1.2.0.5-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-case-insensitive-doc/html/case-insensitive.txt