[commit: ghc] wip/t11715: Use mkCastTy in subst_ty (07a1c1b)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : wip/t11715
Link       : http://ghc.haskell.org/trac/ghc/changeset/07a1c1b4d97e689a59b90b4095a977afe4638bbb/ghc

>---------------------------------------------------------------

commit 07a1c1b4d97e689a59b90b4095a977afe4638bbb
Author: Richard Eisenberg <rae at cs.brynmawr.edu>
Date:   Sun Jan 29 00:11:15 2017 -0500

    Use mkCastTy in subst_ty


>---------------------------------------------------------------

07a1c1b4d97e689a59b90b4095a977afe4638bbb
 compiler/types/TyCoRep.hs   | 6 ++++--
 compiler/types/Type.hs-boot | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/compiler/types/TyCoRep.hs b/compiler/types/TyCoRep.hs
index 85a1df8..696cd42 100644
--- a/compiler/types/TyCoRep.hs
+++ b/compiler/types/TyCoRep.hs
@@ -138,7 +138,7 @@ import {-# SOURCE #-} DataCon( dataConFullSig
                              , DataCon, filterEqSpec )
 import {-# SOURCE #-} Type( isPredTy, isCoercionTy, mkAppTy
                           , tyCoVarsOfTypesWellScoped
-                          , coreView, typeKind )
+                          , coreView, typeKind, mkCastTy )
    -- Transitively pulls in a LOT of stuff, better to break the loop
 
 import {-# SOURCE #-} Coercion
@@ -2180,7 +2180,9 @@ subst_ty subst ty
                                (ForAllTy $! ((TvBndr $! tv') vis)) $!
                                             (subst_ty subst' ty)
     go (LitTy n)         = LitTy $! n
-    go (CastTy ty co)    = (CastTy $! (go ty)) $! (subst_co subst co)
+    go (CastTy ty co)    = (mkCastTy $! (go ty)) $! (subst_co subst co)
+               -- NB: mkCastTy, not CastTy. The subst_co might make something
+               -- reflexive
     go (CoercionTy co)   = CoercionTy $! (subst_co subst co)
 
 substTyVar :: TCvSubst -> TyVar -> Type
diff --git a/compiler/types/Type.hs-boot b/compiler/types/Type.hs-boot
index 78c6681..39a4c80 100644
--- a/compiler/types/Type.hs-boot
+++ b/compiler/types/Type.hs-boot
@@ -1,12 +1,13 @@
 module Type where
 import TyCon
 import Var ( TyVar )
-import {-# SOURCE #-} TyCoRep( Type, Kind )
+import {-# SOURCE #-} TyCoRep( Type, Kind, Coercion )
 
 isPredTy     :: Type -> Bool
 isCoercionTy :: Type -> Bool
 
 mkAppTy :: Type -> Type -> Type
+mkCastTy :: Type -> Coercion -> Type
 piResultTy :: Type -> Type -> Type
 
 typeKind :: Type -> Kind