Make subtyping reflexive

Author: lukel97

Sources/GraphQL/Type/Definition.swift

@@ -84,7 +84,7 @@ extension GraphQLInputObjectType : GraphQLTypeReferenceContainer {}
 /**
  * These types may describe the parent context of a selection set.
  */
-public protocol GraphQLAbstractType : GraphQLNamedType {
+public protocol GraphQLAbstractType : GraphQLCompositeType {
     var resolveType: GraphQLTypeResolve? { get }
 }
 

Sources/GraphQL/Type/Schema.swift

@@ -120,13 +120,17 @@ public final class GraphQLSchema {
     }
 
     public func isSubType(
-      abstractType: GraphQLAbstractType,
+      abstractType: GraphQLCompositeType,
       maybeSubType: GraphQLNamedType
     ) -> Bool {
         var map = subTypeMap[abstractType.name]
 
         if map == nil {
             map = [:]
+            
+            if let objectType = abstractType as? GraphQLObjectType {
+                map?[objectType.name] = true
+            }
 
             if let unionType = abstractType as? GraphQLUnionType {
                 for type in unionType.types {

Tests/GraphQLTests/TypeTests/GraphQLSchemaTests.swift

@@ -151,4 +151,14 @@ class GraphQLSchemaTests: XCTestCase {
             XCTAssertEqual(graphQLError.message, "Object.fieldWithoutArg includes required argument (addedRequiredArg:) that is missing from the Interface field Interface.fieldWithoutArg.")
         }
     }
+    
+    func testSubtypingIsReflexive() throws {
+        let object = try GraphQLObjectType(
+            name: "Object",
+            fields: ["foo": GraphQLField(type: GraphQLInt)],
+            interfaces: []
+        )
+        let schema = try GraphQLSchema(query: object, types: [object])
+        XCTAssert(schema.isSubType(abstractType: object, maybeSubType: object))
+    }
 }