Fix parent position in RnNames.nubAvails

- `RnNames.nubAvails', which amalgamates AvailInfo items that belong to the
  same parent, needs to be careful that the parent name occurs first if it is
  in the list of subnames at all.  (Otherwise, we can get funny export items
  in ifaces.)
- I discovered this while debugging family import/exports, but I am pretty
  sure the bug would also have shown up without using families under the
  right circumstances.

diff --git a/compiler/rename/RnNames.lhs b/compiler/rename/RnNames.lhs
index 8661c0e..90cf81f 100644 (file)
--- a/compiler/rename/RnNames.lhs
+++ b/compiler/rename/RnNames.lhs
@@ -58,7 +58,7 @@ import BasicTypes     ( DeprecTxt )
 import DriverPhases    ( isHsBoot )
 import Util
 import ListSetOps
-import Data.List        ( partition, concatMap, (\\) )
+import Data.List        ( partition, concatMap, (\\), delete )
 import IO              ( openFile, IOMode(..) )
 import Monad           ( when )
 \end{code}
@@ -780,9 +780,18 @@ mkAvailEnv :: [AvailInfo] -> AvailEnv
        -- We want to combine these; addAvail does that
 mkAvailEnv avails = foldl addAvail emptyAvailEnv avails
 
+-- After combining the avails, we need to ensure that the parent name is the
+-- first entry in the list of subnames, if it is included at all.  (Subsequent
+-- functions rely on that.)
+normaliseAvail :: AvailInfo -> AvailInfo
+normaliseAvail avail@(Avail _)     = avail
+normaliseAvail (AvailTC name subs) = AvailTC name subs'
+  where
+    subs' = if name `elem` subs then name : (delete name subs) else subs
+
 -- | combines 'AvailInfo's from the same family
 nubAvails :: [AvailInfo] -> [AvailInfo]
-nubAvails avails = nameEnvElts (mkAvailEnv avails)
+nubAvails avails = map normaliseAvail . nameEnvElts . mkAvailEnv $ avails
 \end{code}
 
 
@@ -874,6 +883,7 @@ exports_from_avail Nothing rdr_env imports this_mod
 
 exports_from_avail (Just rdr_items) rdr_env imports this_mod
   = do (ie_names, _, exports) <- foldlM do_litem emptyExportAccum rdr_items
+
        return (Just ie_names, exports)
   where
     do_litem :: ExportAccum -> LIE RdrName -> RnM ExportAccum