fix non nullable nested object marked as nullable (#368)

* fix non nullable nested object marked as nullable

* update federated schema nested test expected result

* fix lint issues

* return same type when GraphqlNonNull passed to wrapInNonNull

Author: de55

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

@@ -157,7 +157,7 @@ class FederatedSchemaGeneratorTest {
             type SelfReferenceObject {
               description: String
               id: Int!
-              nextObject: [SelfReferenceObject]
+              nextObject: [SelfReferenceObject]!
             }
 
             type _Service {

graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/exceptions/NestingNonNullTypeException.kt

@@ -47,12 +47,12 @@ internal open class TypeBuilder constructor(protected val generator: SchemaGener
 
         // Do not call the hook on GraphQLTypeReference as we have not generated the type yet
         val unwrappedType = GraphQLTypeUtil.unwrapType(graphQLType).lastElement()
+        val typeWithNullability = graphQLType.wrapInNonNull(type)
         if (unwrappedType !is GraphQLTypeReference) {
-            val typeWithNullability = graphQLType.wrapInNonNull(type)
             return config.hooks.didGenerateGraphQLType(type, typeWithNullability)
         }
 
-        return graphQLType
+        return typeWithNullability
     }
 
     private fun objectFromReflection(type: KType, inputType: Boolean): GraphQLType {

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

@@ -17,7 +17,6 @@
 package com.expediagroup.graphql.generator.extensions
 
 import com.expediagroup.graphql.exceptions.CouldNotCastGraphQLType
-import com.expediagroup.graphql.exceptions.NestingNonNullTypeException
 import graphql.schema.GraphQLDirective
 import graphql.schema.GraphQLDirectiveContainer
 import graphql.schema.GraphQLFieldDefinition
@@ -27,11 +26,10 @@ import kotlin.reflect.KType
 
 /**
  * Map null and non-null types.
- * Throws an exception on wrapping a non-null graphql type twice.
+ * Returns same type when wrapping a non-null graphql type twice.
  */
-@Throws(NestingNonNullTypeException::class)
 internal fun GraphQLType.wrapInNonNull(type: KType): GraphQLType = when {
-    this is GraphQLNonNull -> throw NestingNonNullTypeException(this, type)
+    this is GraphQLNonNull -> this
     type.isMarkedNullable -> this
     else -> GraphQLNonNull.nonNull(this)
 }

graphql-kotlin-schema-generator/src/main/kotlin/com/expediagroup/graphql/generator/extensions/graphQLExtensions.kt

@@ -17,7 +17,6 @@
 package com.expediagroup.graphql.generator.extensions
 
 import com.expediagroup.graphql.exceptions.CouldNotCastGraphQLType
-import com.expediagroup.graphql.exceptions.NestingNonNullTypeException
 import graphql.schema.GraphQLArgument
 import graphql.schema.GraphQLDirective
 import graphql.schema.GraphQLDirectiveContainer
@@ -52,13 +51,10 @@ internal class GraphQLExtensionsTest {
     private val mockDirective: GraphQLDirective = mockk()
 
     @Test
-    fun `wrapInNonNull twice throws exception`() {
+    fun `wrapInNonNull twice returns object`() {
         val nonNull = GraphQLNonNull(basicType)
         val mockKType: KType = mockk()
-
-        assertFailsWith(NestingNonNullTypeException::class) {
-            nonNull.wrapInNonNull(mockKType)
-        }
+        assertEquals(nonNull, nonNull.wrapInNonNull(mockKType))
     }
 
     @Test

graphql-kotlin-schema-generator/src/test/kotlin/com/expediagroup/graphql/generator/extensions/GraphQLExtensionsTest.kt

@@ -54,10 +54,12 @@ internal class FunctionBuilderTest : TypeTestHelper() {
 
     internal interface MyInterface {
         fun printMessage(message: String): String
+        fun nestedReturnType(): MyImplementation
     }
 
     internal class MyImplementation : MyInterface {
         override fun printMessage(message: String): String = "message=$message"
+        override fun nestedReturnType(): MyImplementation = MyImplementation()
     }
 
     @GraphQLDirective(locations = [Introspection.DirectiveLocation.FIELD_DEFINITION])
@@ -282,4 +284,15 @@ internal class FunctionBuilderTest : TypeTestHelper() {
         val stringType = GraphQLTypeUtil.unwrapNonNull(result.type)
         assertEquals("String", stringType.name)
     }
+
+    @Test
+    fun `Nested Self referencing object returns non null`() {
+        val kInterfaceFunction = MyInterface::nestedReturnType
+        val kInterfaceResult = builder.function(fn = kInterfaceFunction, parentName = "Query", target = null, abstract = false)
+        val kImplFunction = MyImplementation::nestedReturnType
+        val implResult = builder.function(fn = kImplFunction, parentName = "Query", target = null, abstract = false)
+
+        assertTrue(implResult.type is GraphQLNonNull)
+        assertEquals(kInterfaceResult.type, implResult.type)
+    }
 }