Make {-# UNPACK #-} work for type/data family invocations

This fixes most of Trac #3990.  Consider
  data family D a
  data instance D Double = CD Int Int
  data T = T {-# UNPACK #-} !(D Double)
Then we want the (D Double unpacked).

To do this we need to construct a suitable coercion, and it's much
safer to record that coercion in the interface file, lest the in-scope
instances differ somehow.  That in turn means elaborating the HsBang
type to include a coercion.

To do that I moved HsBang from BasicTypes to DataCon, which caused
quite a few minor knock-on changes.

Interface-file format has changed!

Still to do: need to do knot-tying to allow instances to take effect
within the same module.

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/iface/MkIface.lhs b/compiler/iface/MkIface.lhs
index 217dad305a..50c775fc7f 100644
--- a/compiler/iface/MkIface.lhs
+++ b/compiler/iface/MkIface.lhs
@@ -1505,7 +1505,7 @@ tyConToIfaceDecl env tycon
                     ifConArgTys  = map (tidyToIfaceType env2) arg_tys,
                     ifConFields  = map getOccName 
                                        (dataConFieldLabels data_con),
-                    ifConStricts = dataConRepBangs data_con }
+                    ifConStricts = map (toIfaceBang env2) (dataConRepBangs data_con) }
         where
           (univ_tvs, ex_tvs, eq_spec, theta, arg_tys, _) = dataConFullSig data_con
 
@@ -1516,6 +1516,12 @@ tyConToIfaceDecl env tycon
           to_eq_spec spec = [ (getOccName (tidyTyVar env2 tv), tidyToIfaceType env2 ty) 
                             | (tv,ty) <- spec]
 
+toIfaceBang :: TidyEnv -> HsBang -> IfaceBang
+toIfaceBang _    HsNoBang            = IfNoBang
+toIfaceBang _   (HsUnpack Nothing)   = IfUnpack
+toIfaceBang env (HsUnpack (Just co)) = IfUnpackCo (coToIfaceType (tidyCo env co))
+toIfaceBang _   HsStrict             = IfStrict
+toIfaceBang _   (HsBang {})          = panic "toIfaceBang"
 
 classToIfaceDecl :: TidyEnv -> Class -> IfaceDecl
 classToIfaceDecl env clas