Support interfaces implmenting interfaces when --includeDirectives is…

fixtures/directiveSchemas/baseTypes.graphql

@@ -1,4 +1,13 @@
-type Foo @noArg {
+interface BarInterface {
+  bar: String!
+}
+
+interface FooInterface implements BarInterface {
+  bar: String!
+  nestedFoo: NestedFoo! @nullArg(stringArg: null)
+}
+
+type Foo implements FooInterface @noArg {
   bar: String!
   qux: Int!
   nestedFoo: NestedFoo! @nullArg(stringArg: null)

fixtures/expectedOutput/directiveSchemas/printedDefault.graphql

@@ -9,7 +9,16 @@ directive @nullArg(stringArg: String) on ENUM_VALUE | FIELD_DEFINITION | INPUT_F
 """The directives decorates unions."""
 directive @nestedFooUnion on UNION
 
-type Foo {
+interface BarInterface {
+  bar: String!
+}
+
+interface FooInterface implements BarInterface {
+  bar: String!
+  nestedFoo: NestedFoo!
+}
+
+type Foo implements FooInterface {
   bar: String!
   qux: Int!
   nestedFoo: NestedFoo!

fixtures/expectedOutput/directiveSchemas/printedWithDirectives.graphql

@@ -15,12 +15,21 @@ enum Bar {
   EVERYONE
 }
 
-type Foo @noArg {
+interface BarInterface {
+  bar: String!
+}
+
+type Foo implements FooInterface @noArg {
   bar: String!
   qux: Int!
   nestedFoo: NestedFoo! @nullArg(stringArg: null)
 }
 
+interface FooInterface implements BarInterface {
+  bar: String!
+  nestedFoo: NestedFoo! @nullArg(stringArg: null)
+}
+
 input Input {
   field: String @nullArg(stringArg: "string")
   oldAttribute: String! @deprecated(reason: "reason")

src/printers.ts

@@ -107,22 +107,28 @@ function printScalar(type: GraphQLScalarType): string {
     return printDescription(type) + `scalar ${type.name}`;
 }
 
-function printObject(type: GraphQLObjectType): string {
+
+function getImplementedInterfaces(type: GraphQLObjectType | GraphQLInterfaceType): string {
     const interfaces = type.getInterfaces();
     const implementedInterfaces = interfaces.length
         ? ' implements ' + interfaces.map((i) => i.name).join(' & ')
         : '';
+    return implementedInterfaces;
+}
+
+function printInterface(type: GraphQLInterfaceType): string {
+    const implementedInterfaces = getImplementedInterfaces(type);
     return (
         printDescription(type) +
-        `type ${type.name}${implementedInterfaces}` +
+        `interface ${type.name}${implementedInterfaces}` +
         printFields(type)
     );
 }
-
-function printInterface(type: GraphQLInterfaceType): string {
+function printObject(type: GraphQLObjectType): string {
+    const implementedInterfaces = getImplementedInterfaces(type);
     return (
         printDescription(type) +
-        `interface ${type.name}` +
+        `type ${type.name}${implementedInterfaces}` +
         printFields(type)
     );
 }