CSHARP-1719: supporting projections into identity type.

Author: craiggwilson

src/MongoDB.Driver/Linq/Processors/Pipeline/PipelineBindingContext.cs

@@ -100,7 +100,8 @@ public SerializationExpression BindProjector(ref Expression selector)
             var projector = selector as SerializationExpression;
             if (selector.NodeType == ExpressionType.MemberInit || selector.NodeType == ExpressionType.New)
             {
-                var serializer = GetSerializer(selector.Type, selector);
+                var serializer = SerializerBuilder.Build(selector, _serializerRegistry);
+
                 projector = new DocumentExpression(serializer);
             }
             else if (projector == null || projector is PipelineExpression || projector is IFieldExpression || projector is ArrayIndexExpression)

tests/MongoDB.Driver.Tests/Linq/MongoQueryableTests.cs

@@ -884,6 +884,16 @@ public void Select_identity()
             Assert(query, 2);
         }
 
+        [Fact]
+        public void Select_new_of_same()
+        {
+            var query = CreateQuery().Select(x => new Root { Id = x.Id, A = x.A });
+
+            Assert(query,
+                2,
+                "{ $project: { Id: '$_id', A: '$A', _id: 0} }");
+        }
+
         [Fact]
         public void Select_method_computed_scalar_followed_by_distinct_followed_by_where()
         {