/usr/lib/ghc-doc/hoogle/diagrams-lib.txt is in libghc-diagrams-lib-doc 0.7.1.1-1build2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-diagrams-lib-doc/html/diagrams-lib.txt