Warning police

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index 7a584cd..58db618 100644 (file)
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -381,6 +381,8 @@ deriveTyData (deriv_pred, L loc decl@(TyData { tcdLName = L _ tycon_name,
                -- The "deriv_pred" is a LHsType to take account of the fact that for
                -- newtype deriving we allow deriving (forall a. C [a]).
        ; mkEqnHelp DerivOrigin (tvs++deriv_tvs) cls cls_tys tc_app } }
+deriveTyData (deriv_pred, other_decl)
+  = panic "derivTyData"        -- Caller ensures that only TyData can happen
 
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 mkEqnHelp orig tvs cls cls_tys tc_app