haskell-cabal-mode is a major mode for editing
package description files and is automatically associated with files
having a .cabal extension.
For quickly locating and jumping to the nearest .cabal file from
a Haskell source buffer, you can use M-x haskell-cabal-visit-file;
with a prefix argument (i.e. C-u)
used to visit the .cabal file.
haskell-cabal-visit-file is bound to the key sequence C-c v c.