Fix Trac #1981: seq on a type-family-typed expression

We were crashing when we saw
	case x of DEFAULT -> rhs
where x had a type-family type.  This patch fixes it.

MERGE to the 6.8 branch.

diff --git a/compiler/stgSyn/CoreToStg.lhs b/compiler/stgSyn/CoreToStg.lhs
index 91c9a20..40023bf 100644 (file)
--- a/compiler/stgSyn/CoreToStg.lhs
+++ b/compiler/stgSyn/CoreToStg.lhs
@@ -371,7 +371,7 @@ coreToStgExpr (Case scrut bndr _ alts)
                     (getLiveVars alts_lv_info)
                     bndr'
                     (mkSRT alts_lv_info)
-                    (mkStgAltType (idType bndr) alts)
+                    (mkStgAltType bndr alts)
                     alts2,
       scrut_fvs `unionFVInfo` alts_fvs_wo_bndr,
       alts_escs_wo_bndr `unionVarSet` getFVSet scrut_fvs
@@ -411,21 +411,27 @@ coreToStgExpr (Let bind body)
 \end{code}
 
 \begin{code}
-mkStgAltType scrut_ty alts
-  = case splitTyConApp_maybe (repType scrut_ty) of
+mkStgAltType bndr alts
+  = case splitTyConApp_maybe (repType (idType bndr)) of
        Just (tc,_) | isUnboxedTupleTyCon tc -> UbxTupAlt tc
                    | isUnLiftedTyCon tc     -> PrimAlt tc
                    | isHiBootTyCon tc       -> look_for_better_tycon
                    | isAlgTyCon tc          -> AlgAlt tc
-                   | isFunTyCon tc          -> PolyAlt
-                    | isPrimTyCon tc         -> PolyAlt -- for "Any"
-                   | otherwise              -> pprPanic "mkStgAlts" (ppr tc)
+                   | otherwise              -> ASSERT( _is_poly_alt_tycon tc )
+                                               PolyAlt
        Nothing                              -> PolyAlt
 
   where
-   -- Sometimes, the TyCon in the type of the scrutinee is an HiBootTyCon,
-   -- which may not have any constructors inside it.  If so, then we
-   -- can get a better TyCon by grabbing the one from a constructor alternative
+   _is_poly_alt_tycon tc
+       =  isFunTyCon tc
+        || isPrimTyCon tc   -- "Any" is lifted but primitive
+       || isOpenTyCon tc   -- Type family; e.g. arising from strict
+                           -- function application where argument has a
+                           -- type-family type
+
+   -- Sometimes, the TyCon is a HiBootTyCon which may not have any 
+   -- constructors inside it.  Then we can get a better TyCon by 
+   -- grabbing the one from a constructor alternative
    -- if one exists.
    look_for_better_tycon
        | ((DataAlt con, _, _) : _) <- data_alts =