Teach BodyTypes' to recurse through UVerb endpoints

Author: JackKelly-Bellroy

src/Servant/OpenApi/Internal/TypeLevel/API.hs

@@ -95,4 +95,17 @@ type family BodyTypes' c api :: [*] where
 #if MIN_VERSION_servant(0,19,0)
   BodyTypes' c (NamedRoutes api) = BodyTypes' c (ToServantApi api)
 #endif
+  -- Handle UVerb by recursively expanding it to BodyTypes' c (Verb ...)
+  -- Unwrap WithStatus explicitly to avoid trying to expand
+  -- `Verb .. (WithStatus n a)` later on.
+  BodyTypes' c (UVerb verb cs ((WithStatus n a) ': as)) =
+    AppendList (BodyTypes' c (Verb verb (StatusOf a) cs a)) (BodyTypes' c (UVerb verb cs as))
+  -- If we don't have a WithStatus wrapper, it might be 'NoContent' or
+  -- some other type with a `HasStatus` instance. The catch-all will
+  -- expand it to '[] if we can't extract a useful body type from it,
+  -- so that's fine.
+  BodyTypes' c (UVerb verb cs (a ': as)) =
+    AppendList (BodyTypes' c (Verb verb (StatusOf a) cs a)) (BodyTypes' c (UVerb verb cs as))
+  BodyTypes' c (UVerb verb cs '[]) = '[]
+
   BodyTypes' c api = '[]