Allow deprecating fields

graphql_schema/lib/src/field.dart

@@ -8,14 +8,18 @@ class GraphQLField<Value, Serialized> {
   final String name;
   final GraphQLFieldResolver<Value, Serialized> resolve;
   final GraphQLType<Value, Serialized> type;
+  final String deprecationReason;
 
   GraphQLField(this.name,
       {Iterable<GraphQLFieldArgument> arguments: const <GraphQLFieldArgument>[],
       @required this.resolve,
-      this.type}) {
+      this.type,
+      this.deprecationReason}) {
     this.arguments.addAll(arguments ?? <GraphQLFieldArgument>[]);
   }
 
+  bool get isDeprecated => deprecationReason?.isNotEmpty == true;
+
   FutureOr<Serialized> serialize(Value value) {
     return type.serialize(value);
   }

graphql_server/lib/introspection.dart

@@ -161,16 +161,47 @@ GraphQLObjectType _createFieldType() {
       type: graphQLString,
       resolve: (f, _) => (f as GraphQLField).name,
     ),
+    field(
+      'isDeprecated',
+      type: graphQLString,
+      resolve: (f, _) => (f as GraphQLField).isDeprecated,
+    ),
+    field(
+      'deprecationReason',
+      type: graphQLString,
+      resolve: (f, _) => (f as GraphQLField).deprecationReason,
+    ),
+    field(
+      'args',
+      type: listType(graphQLString.nonNullable()).nonNullable(), // TODO: Input value type
+      resolve: (f, _) => (f as GraphQLField).arguments,
+    ),
   ]);
 }
 
 GraphQLObjectType _reflectDirectiveType() {
+  // TODO: What actually is this???
   return objectType('__Directive', fields: [
     field(
       'name',
-      type: graphQLString,
+      type: graphQLString.nonNullable(),
       resolve: (obj, _) => (obj as DirectiveContext).NAME.span.text,
     ),
+    field(
+      'description',
+      type: graphQLString,
+      resolve: (obj, _) => null,
+    ),
+    field(
+      'locations',
+      type: listType(graphQLString.nonNullable()).nonNullable(), // TODO: Enum directiveLocation
+      resolve: (obj, _) => [],
+    ),
+    field(
+      'args',
+      type: listType(graphQLString.nonNullable()).nonNullable(),
+      resolve: (obj, _) => [],
+    ),
   ]);
 }