1 files changed, 31 insertions, 0 deletions
diff --git a/libraries/base/tests/T19288.hs b/libraries/base/tests/T19288.hs
new file mode 100644
index 0000000000..7bb5fd2616
--- /dev/null
+++ b/libraries/base/tests/T19288.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE DataKinds, PolyKinds, TypeOperators, Safe, TypeFamilies #-}
+
+module Main where
+
+import Data.Maybe
+import Data.Proxy
+import Type.Reflection
+import GHC.TypeLits
+
+data Dat (x :: Proxy 1) = MkD1
+
+evil :: Maybe (Nat :~~: Symbol)
+evil = eqTypeRep (case (typeRepKind (typeRep :: TypeRep Dat)) of
+                          (Fun (App _ x) _) -> typeRepKind x)
+                 (typeRep :: TypeRep Symbol)
+
+
+data family Cast k l r
+newtype instance Cast Nat l r = CastNat { runCastNat :: l }
+newtype instance Cast Symbol l r = CastSymbol { runCastSymbol :: r }
+
+{-# NOINLINE castHelper #-}
+castHelper :: Maybe (a :~~: b) -> Cast a l r -> Cast b l r
+castHelper (Just HRefl) = id
+castHelper Nothing      = error "No more bug!"
+
+cast :: a -> b
+cast = runCastSymbol . castHelper evil . CastNat
+
+main :: IO ()
+main = print (cast 'a' :: Int)