/usr/lib/ghc-doc/hoogle/regex-compat.txt is in libghc-regex-compat-doc 0.95.1-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-regex-compat-doc/html/regex-compat.txt