Cleaned up branch for PR graphql-java-kickstart#407

src/main/kotlin/graphql/kickstart/tools/resolver/FieldResolverScanner.kt

@@ -40,6 +40,7 @@ internal class FieldResolverScanner(val options: SchemaParserOptions) {
                 // discard any methods that are coming off the root of the class hierarchy
                 // to avoid issues with duplicate method declarations
                 .filter { it.declaringClass != Object::class.java }
+                .sortedBy { it.returnType.isInterface }
                 .toList()
     }
 

src/test/groovy/graphql/kickstart/tools/BaseDevice.kt

@@ -0,0 +1,5 @@
+package graphql.kickstart.tools
+
+interface BaseDevice {
+    val meta: BaseMeta?
+}

src/test/groovy/graphql/kickstart/tools/BaseMeta.kt

@@ -0,0 +1,3 @@
+package graphql.kickstart.tools;
+
+interface BaseMeta

src/test/groovy/graphql/kickstart/tools/FieldResolverScannerSpec.groovy

@@ -75,6 +75,18 @@ class FieldResolverScannerSpec extends Specification {
         users instanceof MethodFieldResolver
     }
 
+    def "scanner prefers concrete resolver"() {
+        setup:
+        def resolver = new DataClassResolverInfo(Device.class)
+
+        when:
+        def meta = scanner.findFieldResolver(new FieldDefinition("meta", new TypeName("Meta")), resolver)
+
+        then:
+        meta instanceof MethodFieldResolver
+        !((MethodFieldResolver) meta).getMethod().getReturnType().isInterface()
+    }
+
     class RootQuery1 implements GraphQLQueryResolver {
         def field1() {}
     }
@@ -102,4 +114,16 @@ class FieldResolverScannerSpec extends Specification {
     class GenericQuery implements GraphQLQueryResolver {
         Connection<User> getUsers() {}
     }
-}
+
+    abstract class ParentDevice implements BaseDevice {
+        ConcreteMeta getMeta() { return this.meta; }
+    }
+
+    class ConcreteMeta implements BaseMeta {}
+
+    class Device extends ParentDevice implements BaseDevice {}
+
+    class InterfaceQuery implements GraphQLQueryResolver {
+        Device getDevice() { return new Device() }
+    }
+}