/usr/lib/ghc-doc/hoogle/monoid-subclasses.txt is in libghc-monoid-subclasses-doc 0.3.5-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-monoid-subclasses-doc/html/monoid-subclasses.txt