/usr/lib/ghc-doc/hoogle/happstack-server.txt is in libghc-happstack-server-doc 7.1.7-2build7.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-happstack-server-doc/html/happstack-server.txt