Make a debug check more refined

diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs
index d697fb3..097ecd2 100644 (file)
--- a/compiler/simplCore/SimplUtils.lhs
+++ b/compiler/simplCore/SimplUtils.lhs
@@ -1438,9 +1438,9 @@ prepareDefault _ _ case_bndr (Just (tycon, inst_tys)) imposs_cons (Just deflt_rh
 
        _ -> return [(DEFAULT, [], deflt_rhs)]
 
-  | debugIsOn, isAlgTyCon tycon, [] <- tyConDataCons tycon
+  | debugIsOn, isAlgTyCon tycon, not (isOpenTyCon tycon), null (tyConDataCons tycon)
+       -- This can legitimately happen for type families, so don't report that
   = pprTrace "prepareDefault" (ppr case_bndr <+> ppr tycon)
-       -- This can legitimately happen for type families
         $ return [(DEFAULT, [], deflt_rhs)]
 
 --------- Catch-all cases -----------