/usr/lib/ghc-doc/hoogle/libghc-stmonadtrans-doc.txt is in libghc-stmonadtrans-doc 0.3.3-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-stmonadtrans-doc/html/STMonadTrans.txt