Define DsUtils.mkCastDs and use it

This change avoids a spurious WARNing from mkCast.  In the output of
the desugarer (only, I think) we can have a cast where the type of the
expression and cast don't syntactically match, because of an enclosing
type-let binding.

1 files changed, 3 insertions, 3 deletions

diff --git a/compiler/deSugar/DsCCall.hs b/compiler/deSugar/DsCCall.hs
index 19ac062ce9..26551b58fa 100644
--- a/compiler/deSugar/DsCCall.hs
+++ b/compiler/deSugar/DsCCall.hs
@@ -21,7 +21,7 @@ module DsCCall
 import CoreSyn
 
 import DsMonad
-
+import DsUtils( mkCastDs )
 import CoreUtils
 import MkCore
 import Var
@@ -138,7 +138,7 @@ unboxArg arg
 
   -- Recursive newtypes
   | Just(co, _rep_ty) <- topNormaliseNewType_maybe arg_ty
-  = unboxArg (mkCast arg co)
+  = unboxArg (mkCastDs arg co)
 
   -- Booleans
   | Just tc <- tyConAppTyCon_maybe arg_ty,
@@ -338,7 +338,7 @@ resultWrapper result_ty
   -- Newtypes
   | Just (co, rep_ty) <- topNormaliseNewType_maybe result_ty
   = do (maybe_ty, wrapper) <- resultWrapper rep_ty
-       return (maybe_ty, \e -> mkCast (wrapper e) (mkSymCo co))
+       return (maybe_ty, \e -> mkCastDs (wrapper e) (mkSymCo co))
 
   -- The type might contain foralls (eg. for dummy type arguments,
   -- referring to 'Ptr a' is legal).