Remove "silent superclass parameters"

We introduced silent superclass parameters as a way to avoid
superclass loops, but we now solve that problem a different
way ("derived" superclass constraints carry no evidence). So
they aren't needed any more.

Apart from being a needless complication, they broke DoCon.
Admittedly in a very obscure way, but still the result is
hard to explain. To see the details see Trac #5051, with
test case typecheck/should_compile/T5051.  (The test is
nice and small!)

4 files changed, 8 insertions, 11 deletions

diff --git a/compiler/iface/BinIface.hs b/compiler/iface/BinIface.hs
index 0fab2d28c8..1e24f34dd3 100644
--- a/compiler/iface/BinIface.hs
+++ b/compiler/iface/BinIface.hs
@@ -1173,7 +1173,7 @@ instance Binary IfaceBinding where
 instance Binary IfaceIdDetails where
     put_ bh IfVanillaId      = putByte bh 0
     put_ bh (IfRecSelId a b) = do { putByte bh 1; put_ bh a; put_ bh b }
-    put_ bh (IfDFunId n)     = do { putByte bh 2; put_ bh n }
+    put_ bh IfDFunId         = putByte bh 2
     get bh = do
 	    h <- getByte bh
 	    case h of
@@ -1181,7 +1181,7 @@ instance Binary IfaceIdDetails where
 	      1 -> do a <- get bh
 		      b <- get bh
 		      return (IfRecSelId a b)
-              _ -> do { n <- get bh; return (IfDFunId n) }
+              _ -> return IfDFunId
 
 instance Binary IfaceIdInfo where
     put_ bh NoInfo = putByte bh 0
@@ -1276,12 +1276,10 @@ instance Binary IfaceUnfolding where
 instance Binary (DFunArg IfaceExpr) where
     put_ bh (DFunPolyArg  e) = putByte bh 0 >> put_ bh e
     put_ bh (DFunConstArg e) = putByte bh 1 >> put_ bh e
-    put_ bh (DFunLamArg i)   = putByte bh 2 >> put_ bh i
     get bh = do { h <- getByte bh
                 ; case h of
                     0 -> do { a <- get bh; return (DFunPolyArg a) }
-                    1 -> do { a <- get bh; return (DFunConstArg a) }
-                    _ -> do { a <- get bh; return (DFunLamArg a) } }
+                    _ -> do { a <- get bh; return (DFunConstArg a) } }
 
 instance Binary IfaceNote where
     put_ bh (IfaceSCC aa) = do
diff --git a/compiler/iface/IfaceSyn.lhs b/compiler/iface/IfaceSyn.lhs
index 21783813f8..41732a9215 100644
--- a/compiler/iface/IfaceSyn.lhs
+++ b/compiler/iface/IfaceSyn.lhs
@@ -177,7 +177,7 @@ type IfaceAnnTarget = AnnTarget OccName
 data IfaceIdDetails
   = IfVanillaId
   | IfRecSelId IfaceTyCon Bool
-  | IfDFunId Int          -- Number of silent args
+  | IfDFunId 
 
 data IfaceIdInfo
   = NoInfo                      -- When writing interface file without -O
@@ -672,7 +672,7 @@ instance Outputable IfaceIdDetails where
   ppr IfVanillaId       = empty
   ppr (IfRecSelId tc b) = ptext (sLit "RecSel") <+> ppr tc
                           <+> if b then ptext (sLit "<naughty>") else empty
-  ppr (IfDFunId ns)     = ptext (sLit "DFunId") <> brackets (int ns)
+  ppr IfDFunId          = ptext (sLit "DFunId")
 
 instance Outputable IfaceIdInfo where
   ppr NoInfo       = empty
diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 2ec14e48cb..42a4278b4f 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -1498,7 +1498,7 @@ toIfaceLetBndr id  = IfLetBndr (occNameFS (getOccName id))
 --------------------------
 toIfaceIdDetails :: IdDetails -> IfaceIdDetails
 toIfaceIdDetails VanillaId 		        = IfVanillaId
-toIfaceIdDetails (DFunId ns _)                  = IfDFunId ns
+toIfaceIdDetails (DFunId {})                    = IfDFunId 
 toIfaceIdDetails (RecSelId { sel_naughty = n
 		 	   , sel_tycon = tc })  = IfRecSelId (toIfaceTyCon tc) n
 toIfaceIdDetails other	     		        = pprTrace "toIfaceIdDetails" (ppr other) 
diff --git a/compiler/iface/TcIface.lhs b/compiler/iface/TcIface.lhs
index ab28615c80..2187f03c61 100644
--- a/compiler/iface/TcIface.lhs
+++ b/compiler/iface/TcIface.lhs
@@ -1026,8 +1026,8 @@ do_one (IfaceRec pairs) thing_inside
 \begin{code}
 tcIdDetails :: Type -> IfaceIdDetails -> IfL IdDetails
 tcIdDetails _  IfVanillaId = return VanillaId
-tcIdDetails ty (IfDFunId ns)
-  = return (DFunId ns (isNewTyCon (classTyCon cls)))
+tcIdDetails ty IfDFunId
+  = return (DFunId (isNewTyCon (classTyCon cls)))
   where
     (_, _, cls, _) = tcSplitDFunTy ty
 
@@ -1099,7 +1099,6 @@ tcUnfolding name dfun_ty _ (IfDFunUnfold ops)
     doc = text "Class ops for dfun" <+> ppr name
     tc_arg (DFunPolyArg  e) = do { e' <- tcIfaceExpr e; return (DFunPolyArg e') }
     tc_arg (DFunConstArg e) = do { e' <- tcIfaceExpr e; return (DFunConstArg e') }
-    tc_arg (DFunLamArg i)   = return (DFunLamArg i)
 
 tcUnfolding name ty info (IfExtWrapper arity wkr)
   = tcIfaceWrapper name ty info arity (tcIfaceExtId wkr)