Cabal uses Haskell98 by default

[UnkindPartition]

Cabal passes -XHaskell98 to GHC by default. In practice this can be observed e.g. by getting warnings about pattern guards (which are H2010 but not H98).

Leaving this as a default forever would be at least strange.

Removing this default might break some old packages — how do we feel about that?

As a heuristic, we can enable Haskell98 when the package depends on the haskell98 package (and doesn't explicitly specify the language revision).

[UnkindPartition]

I just noticed that if I specify Cabal-Version: >= 1.10, it asks to give the default language for each component. I guess that's the correct behaviour.

[byorgey]

Note also that the latest cabal init sets Cabal-Version: >= 1.10, so new users will not run into this issue.