-- Add catch-all default case unless the case is exhaustive
-- We do this explicitly so that we get a nice error message that
-- mentions this particular record selector
- deflt | length cons_w_field == length all_cons = []
+ deflt | not (any is_unused all_cons) = []
| otherwise = [mkSimpleMatch [nlWildPat]
(nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
(nlHsLit msg_lit))]
- unit_rhs = L loc $ ExplicitTuple [] Boxed
+ -- Do not add a default case unless there are unmatched
+ -- constructors. We must take account of GADTs, else we
+ -- get overlap warning messages from the pattern-match checker
+ is_unused con = not (con `elem` cons_w_field
+ || dataConCannotMatch inst_tys con)
+ inst_tys = tyConAppArgs data_ty
+
+ unit_rhs = mkLHsTupleExpr []
msg_lit = HsStringPrim $ mkFastString $
occNameString (getOccName sel_name)