Compose mappers (Azure#153)

* Use object spread to add parent properties to mapper

* Regenerate

src/DSL/TSObject.cs

@@ -1,6 +1,6 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License. See License.txt in the project root for license information.
-// 
+//
 
 using System;
 
@@ -105,6 +105,17 @@ public void Property(string propertyName, Action<TSValue> propertyValueAction)
             builder.Value(propertyValueAction);
         }
 
+        /// <summary>
+        /// Spreads the properties of the given object expression into this TSObject.
+        /// </summary>
+        /// <param name="objectExpression">The object expression to spread in this object.</param>
+        public void Spread(string objectExpression)
+        {
+            SetCurrentState(State.Property);
+            builder.Text("...");
+            builder.Text(objectExpression);
+        }
+
         /// <summary>
         /// Add a property to this TSObject with the provided name and null value.
         /// </summary>

src/vanilla/ClientModelExtensions.cs

@@ -871,7 +871,12 @@ public static void ConstructMapper(TSValue value, IModelType type, string serial
                         {
                             mapper.ObjectProperty("modelProperties", modelProperties =>
                             {
-                                foreach (Property prop in composite.ComposedProperties)
+
+                                if (composite.BaseModelType != null && composite.BaseModelType.ComposedProperties.Any())
+                                {
+                                    modelProperties.Spread(composite.BaseModelType.Name + ".type.modelProperties");
+                                }
+                                foreach (Property prop in composite.Properties)
                                 {
                                     var serializedPropertyName = prop.SerializedName;
                                     if (isPageable)