Add an illustrative test demonstrating single question mark result

servant-docs/test/Servant/DocsSpec.hs

@@ -22,8 +22,6 @@ import           Control.Monad
 import           Control.Monad.Trans.Writer
                  (Writer, runWriter, tell)
 import           Data.Aeson
-import           Data.Data
-                 (Data)
 import           Data.List
                  (isInfixOf)
 import           Data.Proxy
@@ -161,7 +159,7 @@ spec = describe "Servant.Docs" $ do
 
 data Datatype1 = Datatype1 { dt1field1 :: String
                            , dt1field2 :: Int
-                           } deriving (Eq, Show, Data, Generic)
+                           } deriving (Eq, Show, Generic)
 
 instance ToJSON Datatype1
 instance ToForm Datatype1

servant-server/src/Servant/Server/Internal.hs

@@ -607,7 +607,7 @@ instance
             mev :: Maybe (Either T.Text a)
             mev = case B.length rawQS of
               0 -> Nothing
-              _ -> Just $ urlDecodeAsForm (BL.drop 1 . BL.fromStrict $ rawQS)
+              _ -> Just $ urlDecodeAsForm $ BL.drop 1 $ BL.fromStrict rawQS
 
             errReq = delayedFailFatal err400
               { errBody = "Query parameter form is required"

servant-server/test/Servant/ServerSpec.hs

@@ -514,6 +514,15 @@ queryParamFormSpec = do
            }
           liftIO $ do
             decode' (simpleBody response1) `shouldBe` (Just $ Animal { species = "bimac", numberOfLegs = 7})
+      it "Just a question mark will match but return a Left" $
+        (flip runSession) (serve queryParamFormApi qpFormServer) $ do
+          let paramsQ = "?"
+          response1 <- Network.Wai.Test.request defaultRequest{
+            rawQueryString = paramsQ,
+            queryString = parseQuery paramsQ
+           }
+          liftIO $ do
+            decode' (simpleBody response1) `shouldBe` (Just $ Animal { species = "broken", numberOfLegs = 0})
       it "allows no query params at all" $
         (flip runSession) (serve queryParamFormApi qpFormServer) $ do
           response1 <- Network.Wai.Test.request defaultRequest