+toIfaceIdDetails :: IdDetails -> IfaceIdDetails
+toIfaceIdDetails VanillaId = IfVanillaId
+toIfaceIdDetails DFunId = IfVanillaId
+toIfaceIdDetails (RecSelId { sel_naughty = n }) = IfRecSelId n
+toIfaceIdDetails other = pprTrace "toIfaceIdDetails" (ppr other)
+ IfVanillaId -- Unexpected
+