Respect subscriptions in the executor

After the last commit there were a few places needed to be adjusted to
support subscriptions. This is done and a test case is added.

It is important to implement subscriptions now, because they require
changes to the library API, and they are a big missing part to finish
the executor. When the executor is finished, we can start to provide
more stable API without breaking everything every release. Validation
and introspection shouldn't require much changes to the API; AST would
require some changes to report good errors after the validation - this
is one thing I can think of.

Fixes #5.

docs/tutorial/tutorial.lhs

@@ -5,7 +5,7 @@ title: GraphQL Haskell Tutorial
 
 == Getting started ==
 
-Welcome to graphql-haskell!
+Welcome to GraphQL!
 
 We have written a small tutorial to help you (and ourselves) understand the
 graphql package.
@@ -39,16 +39,18 @@ Now, as our first example, we are going to look at the example from
 First we build a GraphQL schema.
 
 > schema1 :: Schema IO
-> schema1 = Schema queryType Nothing
+> schema1 = Schema
+>   { query = queryType , mutation = Nothing , subscription = Nothing }
 >
 > queryType :: ObjectType IO
 > queryType = ObjectType "Query" Nothing []
->   $ HashMap.singleton "hello" helloField
+>   $ HashMap.singleton "hello"
+>   $ ValueResolver helloField hello
 >
 > helloField :: Field IO
-> helloField = Field Nothing (Out.NamedScalarType string) mempty hello
+> helloField = Field Nothing (Out.NamedScalarType string) mempty
 >
-> hello :: ResolverT IO Value
+> hello :: Resolve IO
 > hello = pure $ String "it's me"
 
 This defines a simple schema with one type and one field, that resolves to a
@@ -74,16 +76,18 @@ This runs the query by fetching the one field defined, returning
 For this example, we're going to be using time.
 
 > schema2 :: Schema IO
-> schema2 = Schema queryType2 Nothing
+> schema2 = Schema
+>   { query = queryType2, mutation = Nothing, subscription = Nothing }
 >
 > queryType2 :: ObjectType IO
 > queryType2 = ObjectType "Query" Nothing []
->   $ HashMap.singleton "time" timeField
+>   $ HashMap.singleton "time"
+>   $ ValueResolver timeField time
 >
 > timeField :: Field IO
-> timeField = Field Nothing (Out.NamedScalarType string) mempty time
+> timeField = Field Nothing (Out.NamedScalarType string) mempty
 >
-> time :: ResolverT IO Value
+> time :: Resolve IO
 > time = do
 >   t <- liftIO getCurrentTime
 >   pure $ String $ Text.pack $ show t
@@ -104,42 +108,18 @@ This runs the query, returning the current time
 ```{"data": {"time":"2016-03-08 23:28:14.546899 UTC"}}```
 
 
-=== Errors ===
-
-Errors are handled according to the spec, with fields that cause erros being
-resolved to `null`, and an error being added to the error list.
-
-An example of this is the following query:
-
-> queryShouldFail :: Text
-> queryShouldFail = "{ boyhowdy }"
-
-Since there is no `boyhowdy` field in our schema, it will not resolve, and the
-query will fail, as we can see in the following example.
-
-> mainShouldFail :: IO ()
-> mainShouldFail = do
->   failure <- graphql schema1 queryShouldFail
->   putStrLn $ encode failure
-
-This outputs:
-
-```
-{"data": {"boyhowdy": null}, "errors":[{"message": "the field boyhowdy did not resolve."}]}
-```
-
-
 === Combining resolvers ===
 
 Now that we have two resolvers, we can define a schema which uses them both.
 
 > schema3 :: Schema IO
-> schema3 = Schema queryType3 Nothing
+> schema3 = Schema
+>   { query = queryType3, mutation = Nothing, subscription = Nothing }
 >
 > queryType3 :: ObjectType IO
 > queryType3 = ObjectType "Query" Nothing [] $ HashMap.fromList
->   [ ("hello", helloField)
+>   [ ("hello", ValueResolver helloField hello)
->   , ("time", timeField)
+>   , ("time", ValueResolver timeField time)
 >   ]
 >
 > query3 :: Text
@@ -166,4 +146,4 @@ directory, in the [Test.StarWars](../../tests/Test/StarWars) module. This
 includes a more complex schema, and more complex queries.
 
 > main :: IO ()
-> main = main1 >> main2 >> mainShouldFail >> main3
+> main = main1 >> main2 >> main3

src/Language/GraphQL/Execute/Execution.hs

@@ -107,7 +107,13 @@ executeField :: (Monad m, Serialize a)
     -> Type.Value
     -> NonEmpty (Transform.Field m)
     -> CollectErrsT m a
-executeField (Out.ValueResolver fieldDefinition resolver) prev fields = do
+executeField fieldResolver prev fields
+    | Out.ValueResolver fieldDefinition resolver <- fieldResolver =
+        executeField' fieldDefinition resolver
+    | Out.EventStreamResolver fieldDefinition resolver _ <- fieldResolver =
+        executeField' fieldDefinition resolver
+  where
+    executeField' fieldDefinition resolver = do
         let Out.Field _ fieldType argumentDefinitions = fieldDefinition
         let (Transform.Field _ _ arguments' _ :| []) = fields
         case coerceArgumentValues argumentDefinitions arguments' of
@@ -117,7 +123,6 @@ executeField (Out.ValueResolver fieldDefinition resolver) prev fields = do
                 case answer of
                     Right result -> completeValue fieldType fields result
                     Left errorMessage -> addErrMsg errorMessage
-executeField _ _ _ = addErrMsg "No field value resolver specified."
 
 completeValue :: (Monad m, Serialize a)
     => Out.Type m

src/Language/GraphQL/Execute/Transform.hs

@@ -239,6 +239,10 @@ document schema operationName subs ast = do
             | Just mutationType <- mutation schema ->
                 pure $ Document referencedTypes mutationType
                     $ operation chosenOperation replacement
+        OperationDefinition Full.Subscription _ _ _ _
+            | Just subscriptionType <- subscription schema ->
+                pure $ Document referencedTypes subscriptionType
+                    $ operation chosenOperation replacement
         _ -> Left UnsupportedRootOperation
 
 defragment

src/Language/GraphQL/Type/Schema.hs

@@ -29,4 +29,5 @@ data Type m
 data Schema m = Schema
     { query :: Out.ObjectType m
     , mutation :: Maybe (Out.ObjectType m)
+    , subscription :: Maybe (Out.ObjectType m)
     }

tests/Language/GraphQL/ExecuteSpec.hs

@@ -1,3 +1,7 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
 {-# LANGUAGE OverloadedStrings #-}
 module Language.GraphQL.ExecuteSpec
     ( spec
@@ -5,6 +9,7 @@ module Language.GraphQL.ExecuteSpec
 
 import Data.Aeson ((.=))
 import qualified Data.Aeson as Aeson
+import Data.Conduit
 import Data.Either (fromRight)
 import Data.Functor.Identity (Identity(..))
 import Data.HashMap.Strict (HashMap)
@@ -15,11 +20,15 @@ import Language.GraphQL.Error
 import Language.GraphQL.Execute
 import Language.GraphQL.Type as Type
 import Language.GraphQL.Type.Out as Out
-import Test.Hspec (Spec, describe, it, shouldBe)
+import Test.Hspec (Spec, context, describe, it, shouldBe)
 import Text.Megaparsec (parse)
 
 schema :: Schema Identity
-schema = Schema {query = queryType, mutation = Nothing}
+schema = Schema
+    { query = queryType
+    , mutation = Nothing
+    , subscription = Just subscriptionType
+    }
 
 queryType :: Out.ObjectType Identity
 queryType = Out.ObjectType "Query" Nothing []
@@ -45,9 +54,28 @@ philosopherType = Out.ObjectType "Philosopher" Nothing []
         = Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
     lastNameResolver = pure $ Type.String "Nietzsche"
 
+subscriptionType :: Out.ObjectType Identity
+subscriptionType = Out.ObjectType "Subscription" Nothing []
+    $ HashMap.singleton "newQuote"
+    $ EventStreamResolver quoteField (pure $ Type.Object mempty)
+    $ pure $ yield $ Type.Object mempty
+  where
+    quoteField =
+        Out.Field Nothing (Out.NonNullObjectType quoteType) HashMap.empty
+
+quoteType :: Out.ObjectType Identity
+quoteType = Out.ObjectType "Quote" Nothing []
+    $ HashMap.singleton "quote"
+    $ ValueResolver quoteField
+    $ pure "Naturam expelles furca, tamen usque recurret."
+  where
+    quoteField =
+        Out.Field Nothing (Out.NonNullScalarType string) HashMap.empty
+
 spec :: Spec
 spec =
     describe "execute" $ do
+        context "Query" $ do
             it "skips unknown fields" $
                 let data'' = Aeson.object
                         [ "philosopher" .= Aeson.object
@@ -75,3 +103,17 @@ spec =
                         $ either (pure . parseError) execute'
                         $ parse document "" "{ philosopher { firstName } philosopher { lastName } }"
                 in actual `shouldBe` expected
+        context "Subscription" $
+            it "subscribes" $
+                let data'' = Aeson.object
+                        [ "newQuote" .= Aeson.object
+                            [ "quote" .= ("Naturam expelles furca, tamen usque recurret." :: String)
+                            ]
+                        ]
+                    expected = Response data'' mempty
+                    execute' = execute schema Nothing (mempty :: HashMap Name Aeson.Value)
+                    Left stream = runIdentity
+                        $ either (pure . parseError) execute'
+                        $ parse document "" "subscription { newQuote { quote } }"
+                    Just actual = runConduitPure $ stream .| await
+                in actual `shouldBe` expected

tests/Test/DirectiveSpec.hs

@@ -1,3 +1,7 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}
 module Test.DirectiveSpec
@@ -14,7 +18,8 @@ import Test.Hspec (Spec, describe, it, shouldBe)
 import Text.RawString.QQ (r)
 
 experimentalResolver :: Schema IO
-experimentalResolver = Schema { query = queryType, mutation = Nothing }
+experimentalResolver = Schema
+    { query = queryType, mutation = Nothing, subscription = Nothing }
   where
     queryType = Out.ObjectType "Query" Nothing []
         $ HashMap.singleton "experimentalField"

tests/Test/FragmentSpec.hs

@@ -1,3 +1,7 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}
 module Test.FragmentSpec
@@ -76,7 +80,7 @@ sizeFieldType
 
 toSchema :: Text -> (Text, Value) -> Schema IO
 toSchema t (_, resolve) = Schema
-    { query = queryType, mutation = Nothing }
+    { query = queryType, mutation = Nothing, subscription = Nothing }
   where
     unionMember = if t == "Hat" then hatType else shirtType
     typeNameField = Out.Field Nothing (Out.NamedScalarType string) mempty

tests/Test/RootOperationSpec.hs

@@ -1,3 +1,7 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE QuasiQuotes #-}
 module Test.RootOperationSpec
@@ -20,8 +24,10 @@ hatType = Out.ObjectType "Hat" Nothing []
 
 schema :: Schema IO
 schema = Schema
-    (Out.ObjectType "Query" Nothing [] hatFieldResolver)
+    { query = Out.ObjectType "Query" Nothing [] hatFieldResolver
-    (Just $ Out.ObjectType "Mutation" Nothing [] incrementFieldResolver)
+    , mutation = Just $ Out.ObjectType "Mutation" Nothing [] incrementFieldResolver
+    , subscription = Nothing
+    }
   where
     garment = pure $ Object $ HashMap.fromList
         [ ("circumference", Int 60)

tests/Test/StarWars/Schema.hs

@@ -20,7 +20,11 @@ import Prelude hiding (id)
 -- See https://github.com/graphql/graphql-js/blob/master/src/__tests__/starWarsSchema.js
 
 schema :: Schema Identity
-schema = Schema { query = queryType, mutation = Nothing }
+schema = Schema
+    { query = queryType
+    , mutation = Nothing
+    , subscription = Nothing
+    }
   where
     queryType = Out.ObjectType "Query" Nothing [] $ HashMap.fromList
         [ ("hero", heroFieldResolver)