Validation for non-breakable chains of circular references in Input Objects

modules/core/src/main/scala/sangria/schema/SchemaValidationRule.scala

@@ -1,6 +1,6 @@
 package sangria.schema
 
-import sangria.ast.{AstLocation, Document, ObjectTypeDefinition, ObjectTypeExtensionDefinition, UnionTypeDefinition, UnionTypeExtensionDefinition}
+import sangria.ast.{AstLocation, Document, NamedType, NotNullType, ObjectTypeDefinition, ObjectTypeExtensionDefinition, UnionTypeDefinition, UnionTypeExtensionDefinition}
 
 import language.higherKinds
 import sangria.execution._
@@ -24,7 +24,8 @@ object SchemaValidationRule {
     EnumValueReservedNameValidator,
     ContainerMembersValidator,
     ValidNamesValidator,
-    IntrospectionNamesValidator)
+    IntrospectionNamesValidator,
+    InputObjectTypeRecursionValidator)
 
   val default: List[SchemaValidationRule] = List(
     DefaultValuesValidationRule,
@@ -410,6 +411,29 @@ object EnumValueReservedNameValidator extends SchemaElementValidator {
     else Vector.empty
 }
 
+object InputObjectTypeRecursionValidator extends SchemaElementValidator {
+  override def validateInputObjectType(schema: Schema[_, _], tpe: InputObjectType[_]): Vector[Violation] = {
+    containsRecursiveInputObject(tpe.namedType.name, List(), schema, tpe)
+  }
+
+  private def containsRecursiveInputObject(rootTypeName: String, path: List[String], schema: Schema[_, _], tpe: InputObjectType[_]): Vector[Violation] = {
+    val recursiveFields = tpe.fields.filter(childField => childField.fieldType.namedType.name == rootTypeName && !childField.fieldType.isOptional && !childField.fieldType.isList)
+    if (recursiveFields.nonEmpty) {
+      recursiveFields.flatMap(field => Vector(InputObjectTypeRecursion(tpe.name, field.name, path, None, Nil))).toVector
+    } else {
+      val childTypesToCheck = tpe.fields.filter(field => !field.fieldType.isOptional && !field.fieldType.isList && field.fieldType.isInstanceOf[InputObjectType[_]])
+      childTypesToCheck.foldLeft(Vector.empty[Violation]) { case (acc, field) =>
+        schema.getInputType(NotNullType(NamedType(field.fieldType.namedType.name))) match {
+          case Some(objectType: InputObjectType[_]) if objectType != tpe =>
+            val updatedPath = path :+ field.name
+            acc ++ containsRecursiveInputObject(rootTypeName, updatedPath, schema, objectType)
+          case _ => acc
+        }
+      }
+    }
+  }
+}
+
 trait SchemaElementValidator {
   def validateUnionType(schema: Schema[_, _], tpe: UnionType[_]): Vector[Violation] = Vector.empty
 

modules/core/src/main/scala/sangria/validation/Violation.scala

@@ -608,3 +608,7 @@ case class ExistingTypeViolation(typeName: String, sourceMapper: Option[SourceMa
 case class InvalidTypeUsageViolation(expectedTypeKind: String, tpe: String, sourceMapper: Option[SourceMapper], locations: List[AstLocation]) extends AstNodeViolation {
   lazy val simpleErrorMessage = s"Type '$tpe' is not an $expectedTypeKind type."
 }
+
+case class InputObjectTypeRecursion(name: String, fieldName: String, path: List[String], sourceMapper: Option[SourceMapper], locations: List[AstLocation]) extends AstNodeViolation  {
+  lazy val simpleErrorMessage: String = s"Cannot reference InputObjectType '$name' within itself through a series of non-null fields: '$fieldName${if (path.isEmpty) "" else "."}${path.mkString(".")}'."
+}

modules/core/src/test/scala/sangria/schema/AstSchemaMaterializerSpec.scala

@@ -882,6 +882,116 @@ class AstSchemaMaterializerSpec extends WordSpec with Matchers with FutureResult
         error.getMessage should include ("Object type 'Query' can include field 'field1' only once.")
       }
 
+      "accepts an Input Object with breakable circular reference" in {
+        val ast =
+          graphql"""
+            schema {
+              query: Query
+            }
+
+            type Query {
+              field(arg: SomeInputObject): String
+            }
+
+            input SomeInputObject {
+              self: SomeInputObject
+              arrayOfSelf: [SomeInputObject]
+              nonNullArrayOfSelf: [SomeInputObject]!
+              nonNullArrayOfNonNullSelf: [SomeInputObject!]!
+              intermediateSelf: AnotherInputObject
+            }
+
+            input AnotherInputObject {
+              parent: SomeInputObject
+            }
+          """
+
+        noException should be thrownBy (Schema.buildFromAst(ast))
+      }
+
+      "rejects an Input Object with non-breakable circular reference" in {
+        val ast =
+          graphql"""
+            schema {
+              query: Query
+            }
+
+            type Query {
+              field(arg: SomeInputObject): String
+            }
+
+            input SomeInputObject {
+              nonNullSelf: SomeInputObject!
+            }
+          """
+
+        val error = intercept [SchemaValidationException] (Schema.buildFromAst(ast))
+
+        error.getMessage should include ("Cannot reference InputObjectType 'SomeInputObject' within itself through a series of non-null fields: 'nonNullSelf'.")
+      }
+
+      "rejects Input Objects with non-breakable circular reference spread across them" in {
+        val ast =
+          graphql"""
+            schema {
+              query: Query
+            }
+
+            type Query {
+              field(arg: SomeInputObject): String
+            }
+
+            input SomeInputObject {
+              startLoop: AnotherInputObject!
+            }
+
+            input AnotherInputObject {
+              nextInLoop: YetAnotherInputObject!
+            }
+
+            input YetAnotherInputObject {
+              closeLoop: SomeInputObject!
+            }
+          """
+
+        val error = intercept [SchemaValidationException] (Schema.buildFromAst(ast))
+
+        error.getMessage should include ("Cannot reference InputObjectType 'SomeInputObject' within itself through a series of non-null fields: 'startLoop.nextInLoop.closeLoop'.")
+      }
+
+      "rejects Input Objects with multiple non-breakable circular reference" in {
+        val ast =
+          graphql"""
+            schema {
+              query: Query
+            }
+
+            type Query {
+              field(arg: SomeInputObject): String
+            }
+
+            input SomeInputObject {
+              startLoop: AnotherInputObject!
+            }
+
+            input AnotherInputObject {
+              closeLoop: SomeInputObject!
+              startSecondLoop: YetAnotherInputObject!
+            }
+
+            input YetAnotherInputObject {
+              closeSecondLoop: AnotherInputObject!
+              nonNullSelf: YetAnotherInputObject!
+            }
+          """
+
+        val error = intercept [SchemaValidationException] (Schema.buildFromAst(ast))
+
+        error.getMessage should include ("Cannot reference InputObjectType 'SomeInputObject' within itself through a series of non-null fields: 'startLoop.closeLoop'.")
+        error.getMessage should include ("Cannot reference InputObjectType 'AnotherInputObject' within itself through a series of non-null fields: 'closeLoop.startLoop'.")
+        error.getMessage should include ("Cannot reference InputObjectType 'YetAnotherInputObject' within itself through a series of non-null fields: 'nonNullSelf'.")
+      }
+
       "don't allow to have extensions on non-existing types" in {
         val ast =
           graphql"""