cabal-install and ghc 7.10.1

Question

I just upgraded to ghc 7.10.1 and whenever I try use cabal-install I run into the following error:

ghc: ghc no longer supports single-file style package databases (dist/package.conf.inplace) use 'ghc-pkg init' to create the database with the correct format.

How do I fix this?

Answer 1

If you are on Mac OS X and are using homebrew it may be that you installed Cabal through haskell-platform package, which is outdated with no direct upgrade path.

You should uninstall haskell-platform and reinstall Cabal using the cabal-install package.

Answer 2

It could well be you have a newer cabal on your path but can't find it because the old one shadows it. So looking for where cabal may help you resolve that. Barring that, you can download a newer cabal binary from the cabal homepage.