Friends

As part of the reinstallable base project I'm adding an extension "ImplicitKnownKeyNames" to GHC.  But if I put "NoImplicitKnownKeyNames" in base.cabal.in I get the error

Warning: [unknown-extension] Unknown extensions: NoImplicitKnownKeyNames

when building the base library.  I think this comes from cabal.

How can I tell cabal about the new extension?

Thanks

Simon