Resolve type variables in resolver return types

src/main/kotlin/graphql/kickstart/tools/resolver/MethodFieldResolver.kt

@@ -130,9 +130,9 @@ internal class MethodFieldResolver(
         }
 
         // the class the return type unwraps to, so a value that happens to implement Future isn't mistaken for a wrapper.
-        // Object (e.g. for a union) can't tell them apart, so then every future of a method declared to return Future is checked
+        // Object (e.g. for a union) can't tell them apart, so then every future of a method whose return type is Future is checked
         val valueClass = (TypeUtils.getRawType(getResolvedReturnType(), null) ?: Any::class.java)
-            .takeUnless { it == Any::class.java && TypeUtils.getRawType(getReturnType(), null) == Future::class.java }
+            .takeUnless { it == Any::class.java && TypeUtils.getRawType(returnType, null) == Future::class.java }
 
         return if (numberOfParameters > 0 || isSuspendFunction) {
             // requires arguments and environment or is a suspend function
@@ -180,15 +180,18 @@ internal class MethodFieldResolver(
             ?.let { TypeUtils.parameterize(Publisher::class.java, it) }
             ?: this
 
-    private fun getReturnType(): JavaType =
-        try {
+    // the declared return type with type variables resolved, e.g. Future<Item> for get(): T in a subclass of Base<Future<Item>>
+    private val returnType: JavaType by lazy {
+        val declaredType = try {
             method.kotlinFunction?.returnType?.javaType ?: method.genericReturnType
         } catch (e: InternalError) {
             method.genericReturnType
         }
+        typeResolver.resolveTypeVariables(declaredType)
+    }
 
     private fun getResolvedReturnType(): JavaType =
-        getReturnType().let { typeResolver.resolve(if (search.isSubscription) it.asPublisher() else it) }
+        typeResolver.resolve(if (search.isSubscription) returnType.asPublisher() else returnType)
 
     private fun getIndexOffset(): Int {
         return if (resolverInfo is DataClassTypeResolverInfo && !method.declaringClass.isAssignableFrom(resolverInfo.dataClassType)) {

src/test/kotlin/graphql/kickstart/tools/ReactiveTest.kt

@@ -127,6 +127,7 @@ class ReactiveTest {
                     item: Item
                     boxedItem: Item
                     search: SearchResult
+                    inheritedSearch: SearchResult
                 }
 
                 union SearchResult = Item
@@ -151,16 +152,21 @@ class ReactiveTest {
                 search {
                     ... on Item { id }
                 }
+                inheritedSearch {
+                    ... on Item { id }
+                }
             }
             """)
 
-        assertEquals(result.getData(), mapOf("item" to null, "boxedItem" to null, "search" to null))
+        assertEquals(result.getData(), mapOf("item" to null, "boxedItem" to null, "search" to null, "inheritedSearch" to null))
         assertEquals(result.errorMessagesByPath(), mapOf(
             "item" to "Resolver method '${ItemQuery::class.java.name}.item' resolved to a java.util.concurrent.FutureTask, " +
                 "which graphql-java can't wait on. Return a CompletionStage, such as a CompletableFuture, from the method or its generic wrapper transformer instead.",
             "boxedItem" to "Resolver method '${FutureItemQuery::class.java.name}.boxedItem' resolved to a java.util.concurrent.FutureTask, " +
                 "which graphql-java can't wait on. Return a CompletionStage, such as a CompletableFuture, from the method or its generic wrapper transformer instead.",
             "search" to "Resolver method '${FutureItemQuery::class.java.name}.search' resolved to a java.util.concurrent.FutureTask, " +
+                "which graphql-java can't wait on. Return a CompletionStage, such as a CompletableFuture, from the method or its generic wrapper transformer instead.",
+            "inheritedSearch" to "Resolver method '${ItemQuery::class.java.name}.inheritedSearch' resolved to a java.util.concurrent.FutureTask, " +
                 "which graphql-java can't wait on. Return a CompletionStage, such as a CompletableFuture, from the method or its generic wrapper transformer instead."
         ))
     }
@@ -232,11 +238,15 @@ class ReactiveTest {
         fun nullItem(): Future<Item?> = FutureTask<Item?> { null }.also { it.run() }
     }
 
-    open class ItemQuery<R>(private val item: () -> R) {
+    open class ItemQuery<R, S>(private val item: () -> R, private val search: () -> S) {
         fun item(): R = item.invoke()
+        fun inheritedSearch(): S = search.invoke()
     }
 
-    private class FutureItemQuery : ItemQuery<Future<Item>>({ FutureTask { Item(1) }.also { it.run() } }), GraphQLQueryResolver {
+    private class FutureItemQuery : ItemQuery<Future<Item>, Future<Any>>(
+        { FutureTask { Item(1) }.also { it.run() } },
+        { FutureTask<Any> { Item(4) }.also { it.run() } }
+    ), GraphQLQueryResolver {
         fun boxedItem(): Box<Item> = Box(Item(2))
         fun search(): Future<Any> = FutureTask<Any> { Item(3) }.also { it.run() }
     }

src/test/kotlin/graphql/kickstart/tools/SchemaParserTest.kt

@@ -1297,7 +1297,7 @@ class SchemaParserTest {
 
     @Test
     fun `parser should accept subscription resolvers returning publisher subtypes`() {
-        class Subscription : OverriddenPublisherSubscription {
+        class Subscription : InheritedPublisherSubscription<SingleEventPublisher>(SingleEventPublisher("onInheritedPublisher")), OverriddenPublisherSubscription {
             fun onCustomPublisher(): EventPublisher<Event> = SingleEventPublisher("onCustomPublisher")
             fun onConcretePublisher() = SingleEventPublisher("onConcretePublisher")
             override fun onOverriddenPublisher() = SingleEventPublisher("onOverriddenPublisher")
@@ -1314,6 +1314,7 @@ class SchemaParserTest {
                     onCustomPublisher: Event!
                     onConcretePublisher: Event!
                     onOverriddenPublisher: Event!
+                    onInheritedPublisher: Event!
                 }
 
                 type Event {
@@ -1330,7 +1331,7 @@ class SchemaParserTest {
             .assertEveryFieldResolves()
         val gql = GraphQL.newGraphQL(schema).build()
 
-        listOf("onCustomPublisher", "onConcretePublisher", "onOverriddenPublisher").forEach { field ->
+        listOf("onCustomPublisher", "onConcretePublisher", "onOverriddenPublisher", "onInheritedPublisher").forEach { field ->
             assertEquals(gql.firstSubscriptionEvent("subscription { $field { name } }"), mapOf(field to mapOf("name" to field)))
         }
     }
@@ -1435,4 +1436,8 @@ class SchemaParserTest {
     interface OverriddenPublisherSubscription : GraphQLSubscriptionResolver {
         fun onOverriddenPublisher(): Publisher<Event>
     }
+
+    open class InheritedPublisherSubscription<P>(private val publisher: P) {
+        fun onInheritedPublisher(): P = publisher
+    }
 }