Unable to use Headers with UVerb

[brendanhay]

Given the terminal instance for response Headers:

servant-swagger/src/Servant/Swagger/Internal.hs

Lines 245 to 247 in 1909e44

	instance {-# OVERLAPPABLE #-} (ToSchema a, AllAccept cs, AllToResponseHeader hs, KnownNat status, SwaggerMethod method)
	=> HasSwagger (Verb method status cs (Headers hs a)) where
	toSwagger = mkEndpoint "/"

And the singular instance for UVerb introduced in #127:

servant-swagger/src/Servant/Swagger/Internal.hs

Lines 191 to 236 in 1909e44

	-- | @since <TODO>
	instance
	{-# OVERLAPPABLE #-}
	( ToSchema a,
	HasStatus a,
	AllAccept cs,
	SwaggerMethod method,
	HasSwagger (UVerb method cs as)
	) =>
	HasSwagger (UVerb method cs (a ': as))
	where
	toSwagger _ =
	toSwagger (Proxy :: Proxy (Verb method (StatusOf a) cs a))
	`combineSwagger` toSwagger (Proxy :: Proxy (UVerb method cs as))
	where
	-- workaround for https://github.com/GetShopTV/swagger2/issues/218
	-- We'd like to juse use (<>) but the instances are wrong
	combinePathItem :: PathItem -> PathItem -> PathItem
	combinePathItem s t = PathItem
	{ _pathItemGet = _pathItemGet s <> _pathItemGet t
	, _pathItemPut = _pathItemPut s <> _pathItemPut t
	, _pathItemPost = _pathItemPost s <> _pathItemPost t
	, _pathItemDelete = _pathItemDelete s <> _pathItemDelete t
	, _pathItemOptions = _pathItemOptions s <> _pathItemOptions t
	, _pathItemHead = _pathItemHead s <> _pathItemHead t
	, _pathItemPatch = _pathItemPatch s <> _pathItemPatch t
	, _pathItemParameters = _pathItemParameters s <> _pathItemParameters t
	}
	combineSwagger :: Swagger -> Swagger -> Swagger
	combineSwagger s t = Swagger
	{ _swaggerInfo = _swaggerInfo s <> _swaggerInfo t
	, _swaggerHost = _swaggerHost s <|> _swaggerHost t
	, _swaggerBasePath = _swaggerBasePath s <|> _swaggerBasePath t
	, _swaggerSchemes = _swaggerSchemes s <> _swaggerSchemes t
	, _swaggerConsumes = _swaggerConsumes s <> _swaggerConsumes t
	, _swaggerProduces = _swaggerProduces s <> _swaggerProduces t
	, _swaggerPaths = InsOrdHashMap.unionWith combinePathItem (_swaggerPaths s) (_swaggerPaths t)
	, _swaggerDefinitions = _swaggerDefinitions s <> _swaggerDefinitions t
	, _swaggerParameters = _swaggerParameters s <> _swaggerParameters t
	, _swaggerResponses = _swaggerResponses s <> _swaggerResponses t
	, _swaggerSecurityDefinitions = _swaggerSecurityDefinitions s <> _swaggerSecurityDefinitions t
	, _swaggerSecurity = _swaggerSecurity s <> _swaggerSecurity t
	, _swaggerTags = _swaggerTags s <> _swaggerTags t
	, _swaggerExternalDocs = _swaggerExternalDocs s <|> _swaggerExternalDocs t
	}

I'm not certain it's possible to declare an endpoint of the form:

type Redirect = Headers '[Header "Content-Location" Text] ()

type API = UVerb 'POST '[JSON] '[WithStatus 202 Redirect]

 • No instance for (Data.Swagger.Internal.Schema.ToSchema (Servant.WithStatus 202 Redirect)

Due to the instance's ToSchema a constraint and recursion via:

toSwagger (Proxy :: Proxy (Verb method (StatusOf a) cs a))

Am I missing something obvious?

[akhesaCaro]

Hi,
Servant-swagger will be moved into the main Servant repo (see : haskell-servant/servant#1475)
If this issue is still relevant, would it be possible for you to summit it there? : https://github.com/haskell-servant/servant/issues

Thanks in advance!