/usr/lib/haskell-packages/extra-packages/filestore-0.6.3.1 is in libghc-filestore-dev 0.6.3.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
libghc-filestore-data (>= 0.6.3.1)