add a clause to Canonicalize for (a :<|> b) :> c with the obvious definition

src/Servant/API.hs

@@ -91,7 +91,8 @@ import           Servant.Utils.Links      (HasLink (..), IsElem, IsElem',
 -- i.e distributing all ':>'-separated bits into the subsequent ':<|>'s.
 type family Canonicalize api :: * where
   -- requires UndecidableInstances
-  Canonicalize (a :> (b :<|> c)) = ((a :> Canonicalize b)  :<|>  (a :> Canonicalize c))
+  Canonicalize (a :> (b :<|> c)) = a :> Canonicalize b :<|> a :> Canonicalize c
+  Canonicalize ((a :<|> b) :> c) = a :> Canonicalize c :<|> b :> Canonicalize c
   Canonicalize (a :> b)          = Redex b (Canonicalize b) a
   Canonicalize (a :<|> b)        = Canonicalize a :<|> Canonicalize b
   Canonicalize a                 = a

src/Servant/API/ContentTypes.hs

@@ -55,6 +55,8 @@ module Servant.API.ContentTypes
     , AcceptHeader(..)
     , AllCTRender(..)
     , AllCTUnrender(..)
+    , AllMimeRender(..)
+    , AllMimeUnrender(..)
     , FromFormUrlEncoded(..)
     , ToFormUrlEncoded(..)
     , IsNonEmpty