/usr/lib/ghc-doc/hoogle/Diff.txt is in libghc-diff-doc 0.3.0-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-diff-doc/html/Diff.txt
/usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-diff-doc/html/Diff.txt