Switch to the multi-ghc-travis configuration
(https://github.com/hvr/multi-ghc-travis). With that we have a
way to update alex/happy as well (which was the source of the issue
with the haskell-src-extra's build).
Thank you very much this will be a great help checking everything works in different configurations, a test is failing in travis but obviously it has nothing to do with your changes.
Switch to the multi-ghc-travis configuration (https://github.com/hvr/multi-ghc-travis). With that we have a way to update alex/happy as well (which was the source of the issue with the haskell-src-extra's build).