Create __InputValue type

graphql_schema/lib/src/argument.dart

@@ -4,10 +4,11 @@ class GraphQLFieldArgument<Value, Serialized> {
   final String name;
   final GraphQLType<Value, Serialized> type;
   final Value defaultValue;
+  final String description;
 
   /// If [defaultValue] is `null`, and `null` is a valid value for this argument, set this to `true`.
   final bool defaultsToNull;
 
   GraphQLFieldArgument(this.name, this.type,
-      {this.defaultValue, this.defaultsToNull: false});
+      {this.defaultValue, this.defaultsToNull: false, this.description});
 }

graphql_schema/lib/src/scalar.dart

@@ -30,7 +30,9 @@ final GraphQLScalarType<double, double> graphQLFloat =
 
 abstract class GraphQLScalarType<Value, Serialized>
     extends GraphQLType<Value, Serialized>
-    with _NonNullableMixin<Value, Serialized> {}
+    with _NonNullableMixin<Value, Serialized> {
+  Type get valueType => Value;
+}
 
 typedef bool _NumVerifier(x);
 

graphql_server/lib/graphql_server.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:graphql_parser/graphql_parser.dart';
 import 'package:graphql_schema/graphql_schema.dart';
+
 import 'introspection.dart';
 
 class GraphQL {
@@ -305,6 +306,7 @@ class GraphQL {
     }
 
     if (fieldType is GraphQLScalarType) {
+      try {
         var validation = fieldType.validate(fieldName, result);
 
         if (!validation.successful) {
@@ -312,6 +314,10 @@ class GraphQL {
         } else {
           return validation.value;
         }
+      } on TypeError {
+        throw new GraphQLException(
+            'Value of field "$fieldName" must be ${fieldType.valueType}, got $result instead.');
+      }
     }
 
     if (fieldType is GraphQLObjectType) {

graphql_server/lib/introspection.dart

@@ -36,6 +36,8 @@ GraphQLSchema reflectSchema(GraphQLSchema schema, List<GraphQLType> allTypes) {
     typeType,
     schemaType,
     _reflectFields(),
+    _reflectDirectiveType(),
+    _reflectInputValueType(),
   ]);
 
   var fields = <GraphQLField>[
@@ -86,6 +88,7 @@ GraphQLObjectType _reflectSchemaTypes() {
     );
 
     var fieldType = _reflectFields();
+    var inputValueType = _reflectInputValueType();
     var typeField = fieldType.fields
         .firstWhere((f) => f.name == 'type', orElse: () => null);
 
@@ -98,6 +101,19 @@ GraphQLObjectType _reflectSchemaTypes() {
         ),
       );
     }
+
+    typeField = fieldType.fields
+        .firstWhere((f) => f.name == 'type', orElse: () => null);
+
+    if (typeField == null) {
+      inputValueType.fields.add(
+        field(
+          'type',
+          type: _reflectSchemaTypes(),
+          resolve: (f, _) => (f as GraphQLFieldArgument).type,
+        ),
+      );
+    }
   }
 
   return _typeType;
@@ -155,6 +171,8 @@ GraphQLObjectType _reflectFields() {
 }
 
 GraphQLObjectType _createFieldType() {
+  var inputValueType = _reflectInputValueType();
+
   return objectType('__Field', fields: [
     field(
       'name',
@@ -163,7 +181,7 @@ GraphQLObjectType _createFieldType() {
     ),
     field(
       'isDeprecated',
-      type: graphQLString,
+      type: graphQLBoolean,
       resolve: (f, _) => (f as GraphQLField).isDeprecated,
     ),
     field(
@@ -173,13 +191,38 @@ GraphQLObjectType _createFieldType() {
     ),
     field(
       'args',
-      type: listType(graphQLString.nonNullable()).nonNullable(), // TODO: Input value type
+      type: listType(inputValueType.nonNullable()).nonNullable(),
       resolve: (f, _) => (f as GraphQLField).arguments,
     ),
   ]);
 }
 
+GraphQLObjectType _inputValueType;
+
+GraphQLObjectType _reflectInputValueType() {
+  return _inputValueType ??= objectType('__InputValue', fields: [
+    field(
+      'name',
+      type: graphQLString,
+      resolve: (obj, _) => (obj as GraphQLFieldArgument).name,
+    ),
+    field(
+      'description',
+      type: graphQLString,
+      resolve: (obj, _) => (obj as GraphQLFieldArgument).description,
+    ),
+    field(
+      'defaultValue',
+      type: graphQLString,
+      resolve: (obj, _) =>
+          (obj as GraphQLFieldArgument).defaultValue?.toString(),
+    ),
+  ]);
+}
+
 GraphQLObjectType _reflectDirectiveType() {
+  var inputValueType = _reflectInputValueType();
+
   // TODO: What actually is this???
   return objectType('__Directive', fields: [
     field(
@@ -194,12 +237,13 @@ GraphQLObjectType _reflectDirectiveType() {
     ),
     field(
       'locations',
-      type: listType(graphQLString.nonNullable()).nonNullable(), // TODO: Enum directiveLocation
+      type: listType(graphQLString.nonNullable()).nonNullable(),
+      // TODO: Enum directiveLocation
       resolve: (obj, _) => [],
     ),
     field(
       'args',
-      type: listType(graphQLString.nonNullable()).nonNullable(),
+      type: listType(inputValueType.nonNullable()).nonNullable(),
       resolve: (obj, _) => [],
     ),
   ]);