Fix nested federation (ExpediaGroup#316)

Fixes ExpediaGroup#310

While I don't think it is possible to have an input type extended we should still be able to have nested types that are not part of the federated entities be generated properly. This can happen when there are lists of nullalbes or double wrapped elements

Author: smyrick

examples/federation/base-app/src/main/kotlin/com/expedia/graphql/sample/Application.kt

@@ -29,7 +29,7 @@ class Application {
     private val logger = LoggerFactory.getLogger(Application::class.java)
 
     @Bean
-    fun hooks() = FederatedSchemaGeneratorHooks(FederatedTypeRegistry(emptyMap()))
+    fun hooks() = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
 
     @Bean
     fun dataFetcherFactoryProvider(springDataFetcherFactory: SpringDataFetcherFactory, hooks: SchemaGeneratorHooks) =

examples/federation/base-app/src/main/kotlin/com/expedia/graphql/sample/query/NestedQuery.kt

@@ -0,0 +1,15 @@
+package com.expedia.graphql.sample.query
+
+import org.springframework.stereotype.Component
+import kotlin.random.Random
+
+@Component
+class NestedQuery : Query {
+    fun getSimpleNestedObject(): List<SelfReferenceObject?> = listOf(SelfReferenceObject())
+}
+
+class SelfReferenceObject {
+    val description: String? = "SelfReferenceObject"
+    val id = Random.nextInt()
+    fun nextObject(): List<SelfReferenceObject?> = listOf(SelfReferenceObject())
+}

graphql-kotlin-federation/src/main/kotlin/com/expedia/graphql/federation/execution/FederatedTypeRegistry.kt

@@ -3,7 +3,7 @@ package com.expedia.graphql.federation.execution
 /**
  * Simple registry that holds mapping of all registered federated GraphQL types and their corresponding resolvers.
  */
-class FederatedTypeRegistry(private val federatedTypeResolvers: Map<String, FederatedTypeResolver<*>>) {
+class FederatedTypeRegistry(private val federatedTypeResolvers: Map<String, FederatedTypeResolver<*>> = emptyMap()) {
 
     /**
      * Retrieve target federated resolver for the specified GraphQL type.

graphql-kotlin-federation/src/test/kotlin/com/expedia/graphql/federation/FederatedSchemaGeneratorTest.kt

@@ -6,6 +6,7 @@ import com.expedia.graphql.federation.execution.FederatedTypeRegistry
 import graphql.schema.GraphQLUnionType
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
+import test.data.queries.simple.NestedQuery
 import test.data.queries.simple.SimpleQuery
 import kotlin.test.assertNotNull
 import kotlin.test.assertTrue
@@ -85,7 +86,7 @@ class FederatedSchemaGeneratorTest {
     fun `verify can generate federated schema`() {
         val config = FederatedSchemaGeneratorConfig(
             supportedPackages = listOf("test.data.queries.federated"),
-            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry(emptyMap()))
+            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
         )
 
         val schema = toFederatedSchema(config)
@@ -118,10 +119,42 @@ class FederatedSchemaGeneratorTest {
 
         val config = FederatedSchemaGeneratorConfig(
             supportedPackages = listOf("test.data.queries.simple"),
-            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry(emptyMap()))
+            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
         )
 
         val schema = toFederatedSchema(config, listOf(TopLevelObject(SimpleQuery())))
         assertEquals(expectedSchema, schema.print(includeDirectives = false).trim())
     }
+
+    @Test
+    fun `verify a nested federated schema still works`() {
+        val expectedSchema = """
+            schema {
+              query: Query
+            }
+
+            type Query {
+              _service: _Service
+              getSimpleNestedObject: [SelfReferenceObject]!
+            }
+
+            type SelfReferenceObject {
+              description: String
+              id: Int!
+              nextObject: [SelfReferenceObject]
+            }
+
+            type _Service {
+              sdl: String!
+            }
+        """.trimIndent()
+
+        val config = FederatedSchemaGeneratorConfig(
+            supportedPackages = listOf("test.data.queries.simple"),
+            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
+        )
+
+        val schema = toFederatedSchema(config, listOf(TopLevelObject(NestedQuery())))
+        assertEquals(expectedSchema, schema.print(includeDirectives = false).trim())
+    }
 }

graphql-kotlin-federation/src/test/kotlin/com/expedia/graphql/federation/execution/EntityQueryResolverTest.kt

@@ -43,7 +43,7 @@ class EntityQueryResolverTest {
 
     @Test
     fun `verify federated entity resolver returns GraphQLError if __typename cannot be resolved`() {
-        val resolver = EntityResolver(FederatedTypeRegistry(emptyMap()))
+        val resolver = EntityResolver(FederatedTypeRegistry())
         val representations = listOf(mapOf<String, Any>("__typename" to "User", "userId" to 123, "name" to "testName"))
         val env = mockk<DataFetchingEnvironment> {
             every { getArgument<Any>(any()) } returns representations

graphql-kotlin-federation/src/test/kotlin/com/expedia/graphql/federation/execution/ServiceQueryResolverTest.kt

@@ -40,7 +40,7 @@ class ServiceQueryResolverTest {
     fun `verify can retrieve SDL using _service query`() {
         val config = FederatedSchemaGeneratorConfig(
             supportedPackages = listOf("test.data.queries.federated"),
-            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry(emptyMap()))
+            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
         )
 
         val schema = toFederatedSchema(config)

graphql-kotlin-federation/src/test/kotlin/test/data/queries/simple/NestedQuery.kt

@@ -0,0 +1,13 @@
+package test.data.queries.simple
+
+import kotlin.random.Random
+
+class NestedQuery {
+    fun getSimpleNestedObject(): List<SelfReferenceObject?> = listOf(SelfReferenceObject())
+}
+
+class SelfReferenceObject {
+    val description: String? = "SelfReferenceObject"
+    val id = Random.nextInt()
+    fun nextObject(): List<SelfReferenceObject?> = listOf(SelfReferenceObject())
+}

graphql-kotlin-schema-generator/src/main/kotlin/com/expedia/graphql/generator/TypeBuilder.kt

@@ -30,7 +30,7 @@ internal open class TypeBuilder constructor(protected val generator: SchemaGener
             ?: objectFromReflection(type, inputType)
 
         // Do not call the hook on GraphQLTypeReference as we have not generated the type yet
-        val unwrappedType = GraphQLTypeUtil.unwrapNonNull(graphQLType)
+        val unwrappedType = GraphQLTypeUtil.unwrapType(graphQLType).lastElement()
         if (unwrappedType !is GraphQLTypeReference) {
             val typeWithNullability = graphQLType.wrapInNonNull(type)
             return config.hooks.didGenerateGraphQLType(type, typeWithNullability)

graphql-kotlin-schema-generator/src/test/kotlin/com/expedia/graphql/test/integration/NodeGraphTest.kt

@@ -36,7 +36,7 @@ data class Node(
     val id: Int,
     val value: String,
     val parent: Node? = null,
-    var children: List<Node> = emptyList()
+    var children: List<Node?> = emptyList()
 )
 
 class NodeQuery {