fix: recursive interfaces (#143)

Fixes #141

Author: smyrick

src/main/kotlin/com/expedia/graphql/generator/types/InterfaceTypeBuilder.kt

@@ -1,11 +1,11 @@
 package com.expedia.graphql.generator.types
 
-import com.expedia.graphql.generator.extensions.getValidFunctions
-import com.expedia.graphql.generator.extensions.getValidProperties
-import com.expedia.graphql.generator.extensions.getGraphQLDescription
 import com.expedia.graphql.generator.SchemaGenerator
 import com.expedia.graphql.generator.TypeBuilder
+import com.expedia.graphql.generator.extensions.getGraphQLDescription
 import com.expedia.graphql.generator.extensions.getSimpleName
+import com.expedia.graphql.generator.extensions.getValidFunctions
+import com.expedia.graphql.generator.extensions.getValidProperties
 import graphql.TypeResolutionEnvironment
 import graphql.schema.GraphQLInterfaceType
 import graphql.schema.GraphQLType
@@ -33,10 +33,11 @@ internal class InterfaceTypeBuilder(generator: SchemaGenerator) : TypeBuilder(ge
             implementations.forEach {
                 val objectType = generator.objectType(it.kotlin, interfaceType)
 
+                // Only update the state if the object is fully constructed and not a reference
                 if (objectType !is GraphQLTypeReference) {
                     state.additionalTypes.add(objectType)
+                    state.cache.removeTypeUnderConstruction(it.kotlin)
                 }
-                state.cache.removeTypeUnderConstruction(it.kotlin)
             }
 
             interfaceType

src/main/kotlin/com/expedia/graphql/generator/types/ObjectTypeBuilder.kt

@@ -30,7 +30,7 @@ internal class ObjectTypeBuilder(generator: SchemaGenerator) : TypeBuilder(gener
                 builder.withInterface(interfaceType)
             } else {
                 kClass.getValidSuperclasses(config.hooks)
-                    .map { objectFromReflection(it.createType(), false) as? GraphQLInterfaceType }
+                    .mapNotNull { objectFromReflection(it.createType(), false) as? GraphQLInterfaceType }
                     .forEach { builder.withInterface(it) }
             }
 

src/test/kotlin/com/expedia/graphql/integration/NodeGraphTest.kt

@@ -0,0 +1,54 @@
+package com.expedia.graphql.integration
+
+import com.expedia.graphql.TopLevelObject
+import com.expedia.graphql.testSchemaConfig
+import com.expedia.graphql.toSchema
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class NodeGraphTest {
+
+    @Test
+    fun nodeGraph() {
+        val root = Node(id = 0, value = "root", parent = null, children = emptyList())
+        val nodeA = Node(id = 1, value = "A", parent = root, children = emptyList())
+        val nodeB = Node(id = 2, value = "B", parent = root, children = emptyList())
+        val nodeC = Node(id = 3, value = "C", parent = nodeB, children = emptyList())
+
+        root.children = listOf(nodeA, nodeB)
+        nodeB.children = listOf(nodeC)
+
+        val queries = listOf(TopLevelObject(NodeQuery()))
+
+        val schema = toSchema(queries = queries, config = testSchemaConfig)
+
+        assertEquals(expected = 1, actual = schema.queryType.fieldDefinitions.size)
+        assertEquals(expected = "nodeGraph", actual = schema.queryType.fieldDefinitions.first().name)
+    }
+}
+
+/**
+ * Represents a recursive type that references itself,
+ * similar to a tree node structure.
+ */
+data class Node(
+    val id: Int,
+    val value: String,
+    val parent: Node?,
+    var children: List<Node>
+)
+
+class NodeQuery {
+
+    private val root = Node(id = 0, value = "root", parent = null, children = emptyList())
+    private val nodeA = Node(id = 1, value = "A", parent = root, children = emptyList())
+    private val nodeB = Node(id = 2, value = "B", parent = root, children = emptyList())
+    private val nodeC = Node(id = 3, value = "C", parent = nodeB, children = emptyList())
+
+    init {
+        root.children = listOf(nodeA, nodeB)
+        nodeB.children = listOf(nodeC)
+    }
+
+    fun nodeGraph() = root
+}

src/test/kotlin/com/expedia/graphql/integration/RecursiveInterfaceTest.kt

@@ -0,0 +1,37 @@
+package com.expedia.graphql.integration
+
+import com.expedia.graphql.TopLevelObject
+import com.expedia.graphql.testSchemaConfig
+import com.expedia.graphql.toSchema
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class RecursiveInterfaceTest {
+
+    @Test
+    fun recursiveInterface() {
+        val queries = listOf(TopLevelObject(RecursiveInterfaceQuery()))
+        val schema = toSchema(queries = queries, config = testSchemaConfig)
+        assertEquals(1, schema.queryType.fieldDefinitions.size)
+        val field = schema.queryType.fieldDefinitions.first()
+        assertEquals("getRoot", field.name)
+    }
+}
+
+class RecursiveInterfaceQuery {
+    fun getRoot() = RecursiveInterfaceA()
+}
+
+interface SomeInterface {
+    val id: String
+}
+
+class RecursiveInterfaceA : SomeInterface {
+    override val id = "A"
+    fun getB() = RecursiveInterfaceB()
+}
+
+class RecursiveInterfaceB : SomeInterface {
+    override val id = "B"
+    fun getA() = RecursiveInterfaceA()
+}

src/test/kotlin/com/expedia/graphql/integration/RecursiveUnionTest.kt

@@ -0,0 +1,33 @@
+package com.expedia.graphql.integration
+
+import com.expedia.graphql.TopLevelObject
+import com.expedia.graphql.testSchemaConfig
+import com.expedia.graphql.toSchema
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class RecursiveUnionTest {
+
+    @Test
+    fun recursiveUnion() {
+        val queries = listOf(TopLevelObject(RecursiveUnionQuery()))
+        val schema = toSchema(queries = queries, config = testSchemaConfig)
+        assertEquals(1, schema.queryType.fieldDefinitions.size)
+        val field = schema.queryType.fieldDefinitions.first()
+        assertEquals("getRoot", field.name)
+    }
+}
+
+class RecursiveUnionQuery {
+    fun getRoot() = RecursiveUnionA()
+}
+
+interface SomeUnion
+
+class RecursiveUnionA : SomeUnion {
+    fun getB() = RecursiveUnionB()
+}
+
+class RecursiveUnionB : SomeUnion {
+    fun getA() = RecursiveUnionA()
+}