+ -- Just [t1..tn] for data instance T t1..tn = ...
+ -- in this case tcdTyVars = fv( tcdTyPats )
+ -- Nothing for everything else
+
+ tcdKindSig:: Maybe Kind, -- Optional kind sig
+ -- (Just k) for a
+ -- (a) GADT-style 'data', or 'data instance' decl
+ -- with explicit kind sig
+ -- (b) 'data family' decl, whether or not
+ -- there is an explicit kind sig
+ -- (this is how we distinguish a data family decl)