[federation] fix: SDL should be generated for non-federated schemas (#417)

Federated GraphQL gateway can contain number of services that are not exposing any of their types as federated types (i.e. without exposing any of them using @key directives). We were incorrectly generating SDL only if there were some federated types in the generated schema. Fix is to always generated the SDL.

Author: dariuszkuc

graphql-kotlin-federation/src/main/kotlin/com/expediagroup/graphql/federation/FederatedSchemaGeneratorHooks.kt

@@ -69,6 +69,25 @@ open class FederatedSchemaGeneratorHooks(private val federatedTypeRegistry: Fede
             .field(SERVICE_FIELD_DEFINITION)
             .withDirective(extendsDirectiveType)
 
+        /**
+         * SDL returned by _service query should NOT contain
+         * - default schema definition
+         * - empty Query type
+         * - any directive definitions
+         * - any custom directives
+         * - new federated scalars
+         */
+        val sdl = originalSchema.print(includeDefaultSchemaDefinition = false)
+            /**
+             * TODO: this can be simplified once this is solved: apollographql/apollo-server#3334
+             */
+            .replace(directiveDefinitionRegex, "")
+            .replace(scalarDefinitionRegex, "")
+            .replace(emptyQueryRegex, "")
+            .replace(customDirectivesRegex, "")
+            .trim()
+        federatedCodeRegistry.dataFetcher(FieldCoordinates.coordinates(originalQuery.name, SERVICE_FIELD_DEFINITION.name), DataFetcher { _Service(sdl) })
+
         val entityTypeNames = originalSchema.allTypesAsList
             .asSequence()
             .filterIsInstance<GraphQLObjectType>()
@@ -81,25 +100,6 @@ open class FederatedSchemaGeneratorHooks(private val federatedTypeRegistry: Fede
             val entityField = generateEntityFieldDefinition(entityTypeNames)
             federatedQuery.field(entityField)
 
-            /**
-             * SDL returned by _service query should NOT contain
-             * - default schema definition
-             * - empty Query type
-             * - any directive definitions
-             * - any custom directives
-             * - new federated scalars
-             */
-            val sdl = originalSchema.print(includeDefaultSchemaDefinition = false)
-                /**
-                 * TODO: this can be simplified once this is solved: apollographql/apollo-server#3334
-                 */
-                .replace(directiveDefinitionRegex, "")
-                .replace(scalarDefinitionRegex, "")
-                .replace(emptyQueryRegex, "")
-                .replace(customDirectivesRegex, "")
-                .trim()
-
-            federatedCodeRegistry.dataFetcher(FieldCoordinates.coordinates(originalQuery.name, SERVICE_FIELD_DEFINITION.name), DataFetcher { _Service(sdl) })
             federatedCodeRegistry.dataFetcher(FieldCoordinates.coordinates(originalQuery.name, entityField.name), EntityResolver(federatedTypeRegistry))
             federatedCodeRegistry.typeResolver("_Entity") { env: TypeResolutionEnvironment -> env.schema.getObjectType(env.getObjectName()) }
             federatedSchema.additionalType(ANY_SCALAR_TYPE)

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

@@ -16,12 +16,15 @@
 
 package com.expediagroup.graphql.federation.execution
 
+import com.expediagroup.graphql.TopLevelObject
 import com.expediagroup.graphql.federation.FederatedSchemaGeneratorConfig
 import com.expediagroup.graphql.federation.FederatedSchemaGeneratorHooks
 import com.expediagroup.graphql.federation.toFederatedSchema
 import graphql.ExecutionInput
 import graphql.GraphQL
 import org.junit.jupiter.api.Test
+import test.data.queries.simple.NestedQuery
+import test.data.queries.simple.SimpleQuery
 import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
 
@@ -51,6 +54,19 @@ type User @extends @key(fields : "userId") {
   userId: Int! @external
 }"""
 
+const val BASE_SERVICE_SDL = """
+type Query {
+  getSimpleNestedObject: [SelfReferenceObject]!
+  hello(name: String!): String!
+}
+
+type SelfReferenceObject {
+  description: String
+  id: Int!
+  nextObject: [SelfReferenceObject]!
+}
+"""
+
 class ServiceQueryResolverTest {
 
     @Test
@@ -81,4 +97,33 @@ class ServiceQueryResolverTest {
             }
         }
     }
+
+    @Test
+    fun `verify can retrieve SDL using _service query for non-federated schemas`() {
+        val config = FederatedSchemaGeneratorConfig(
+            supportedPackages = listOf("test.data.queries.simple"),
+            hooks = FederatedSchemaGeneratorHooks(FederatedTypeRegistry())
+        )
+
+        val schema = toFederatedSchema(config = config, queries = listOf(TopLevelObject(SimpleQuery()), TopLevelObject(NestedQuery())))
+        val query = """
+            query sdlQuery {
+              _service {
+                sdl
+              }
+            }
+        """.trimIndent()
+        val executionInput = ExecutionInput.newExecutionInput()
+            .query(query)
+            .build()
+        val graphQL = GraphQL.newGraphQL(schema).build()
+        val result = graphQL.executeAsync(executionInput).get().toSpecification()
+
+        assertNotNull(result["data"] as? Map<*, *>) { data ->
+            assertNotNull(data["_service"] as? Map<*, *>) { queryResult ->
+                val sdl = queryResult["sdl"] as? String
+                assertEquals(BASE_SERVICE_SDL.trim(), sdl)
+            }
+        }
+    }
 }