Use TTG empty extensions to remove some `error`'s

None of these error cases should ever have been reachable, so this is
just a matter of leveraging the type system to assert this.

  * Use the `NoExtCon` and `noExtCon` to handle case matches for no
    extension constructors, instead of throwing an `error`.

  * Use the extension field of `HsSpliceTy` to ensure that this variant
    of `HsType` cannot exist in an `HsType DocNameI`.

1 files changed, 2 insertions, 1 deletions

diff --git a/haddock-api/src/Haddock/Types.hs b/haddock-api/src/Haddock/Types.hs
index 28e3caed..ec76fb72 100644
--- a/haddock-api/src/Haddock/Types.hs
+++ b/haddock-api/src/Haddock/Types.hs
@@ -35,6 +35,7 @@ import Control.Monad.IO.Class (MonadIO(..))
 import Data.Typeable (Typeable)
 import Data.Map (Map)
 import Data.Data (Data)
+import Data.Void (Void)
 import Documentation.Haddock.Types
 import BasicTypes (Fixity(..), PromotionFlag(..))
 
@@ -713,7 +714,7 @@ type instance XOpTy            DocNameI = NoExtField
 type instance XParTy           DocNameI = NoExtField
 type instance XIParamTy        DocNameI = NoExtField
 type instance XKindSig         DocNameI = NoExtField
-type instance XSpliceTy        DocNameI = NoExtField
+type instance XSpliceTy        DocNameI = Void       -- see `renameHsSpliceTy`
 type instance XDocTy           DocNameI = NoExtField
 type instance XBangTy          DocNameI = NoExtField
 type instance XRecTy           DocNameI = NoExtField