From: Ian Lynagh <igloo@earth.li>
Date: Sat, 27 Feb 2010 17:39:51 +0000 (+0000)
Subject: Fix trac #2578
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=09d2b3b2e1f9d0a4c4b938dc6ff6a0b068138445

Fix trac #2578
We define empty datatypes as not being enumerations, which means the
empty blocks aren't generated.
---

diff --git a/compiler/iface/BuildTyCl.lhs b/compiler/iface/BuildTyCl.lhs
index ba383d8..54adfdf 100644
--- a/compiler/iface/BuildTyCl.lhs
+++ b/compiler/iface/BuildTyCl.lhs
@@ -118,7 +118,13 @@ mkOpenDataTyConRhs = OpenTyCon Nothing
 
 mkDataTyConRhs :: [DataCon] -> AlgTyConRhs
 mkDataTyConRhs cons
-  = DataTyCon { data_cons = cons, is_enum = all isNullarySrcDataCon cons }
+  = DataTyCon {
+        data_cons = cons,
+        is_enum = -- We define datatypes with no constructors to not be
+                  -- enumerations; this fixes trac #2578
+                  not (null cons) &&
+                  all isNullarySrcDataCon cons
+    }
 
 mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
 -- Monadic because it makes a Name for the coercion TyCon