/usr/lib/ghc-doc/hoogle/libghc-stm-chans-doc.txt is in libghc-stm-chans-doc 3.0.0.4-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-stm-chans-doc/html/stm-chans.txt