[commit: ghc] master: Add role-checking ASSERT to mkCast (3ac1539)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/3ac1539cfa1745ef5133fc5747095deb0c1d795d/ghc

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

commit 3ac1539cfa1745ef5133fc5747095deb0c1d795d
Author: Joachim Breitner <mail at joachim-breitner.de>
Date:   Wed Nov 27 10:33:56 2013 +0000

    Add role-checking ASSERT to mkCast


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

3ac1539cfa1745ef5133fc5747095deb0c1d795d
 compiler/coreSyn/CoreUtils.lhs |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs
index 8f7b777..91f68a2 100644
--- a/compiler/coreSyn/CoreUtils.lhs
+++ b/compiler/coreSyn/CoreUtils.lhs
@@ -190,7 +190,9 @@ applyTypeToArgs e op_ty args
 -- | Wrap the given expression in the coercion safely, dropping
 -- identity coercions and coalescing nested coercions
 mkCast :: CoreExpr -> Coercion -> CoreExpr
-mkCast e co | isReflCo co = e
+mkCast e co | ASSERT2 ( coercionRole co == Representational
+                      , ptext (sLit "coercion") <+> ppr co <+> ptext (sLit "passed to mkCast") <+> ppr e <+> ptext (sLit "has wrong role") <+> ppr (coercionRole co) )
+              isReflCo co = e
 
 mkCast (Coercion e_co) co 
   | isCoVarType (pSnd (coercionKind co))