Merge pull request #751 from phadej/regression-734

Add regression test for #734

servant/servant.cabal

@@ -112,6 +112,7 @@ test-suite spec
       Servant.API.ContentTypesSpec
       Servant.API.ResponseHeadersSpec
       Servant.Utils.LinksSpec
+      Servant.Utils.EnterSpec
   build-depends:
       base == 4.*
     , base-compat

servant/test/Servant/Utils/EnterSpec.hs

@@ -0,0 +1,32 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeOperators #-}
+module Servant.Utils.EnterSpec where
+
+import Test.Hspec (Spec)
+
+import Servant.API
+import Servant.Utils.Enter
+
+-------------------------------------------------------------------------------
+-- https://github.com/haskell-servant/servant/issues/734
+-------------------------------------------------------------------------------
+
+-- This didn't fail if executed in GHCi; cannot have as a doctest.
+
+data App a
+
+f :: App :~> App
+f = NT id
+
+server :: App Int :<|> (String -> App Bool)
+server = undefined
+
+server' :: App Int :<|> (String -> App Bool)
+server' = enter f server
+
+-------------------------------------------------------------------------------
+-- Spec
+-------------------------------------------------------------------------------
+
+spec :: Spec
+spec = return ()