CSHARP-1891: Code review changes.

Author: rstam

src/MongoDB.Driver/FieldDefinition.cs

@@ -73,6 +73,16 @@ public sealed class RenderedFieldDefinition<TField>
         private readonly IBsonSerializer _underlyingSerializer;
         private readonly IBsonSerializer<TField> _valueSerializer;
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RenderedFieldDefinition{TField}" /> class.
+        /// </summary>
+        /// <param name="fieldName">The field name.</param>
+        /// <param name="fieldSerializer">The field serializer.</param>
+        public RenderedFieldDefinition(string fieldName, IBsonSerializer<TField> fieldSerializer)
+            : this(fieldName, fieldSerializer, fieldSerializer, fieldSerializer)
+        {
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="RenderedFieldDefinition{TField}" /> class.
         /// </summary>

src/MongoDB.Driver/FieldValueSerializerHelper.cs

@@ -32,6 +32,11 @@ public static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSer
 
         private static IBsonSerializer GetSerializerForValueType(IBsonSerializer fieldSerializer, Type valueType, int recursionLevel)
         {
+            if (recursionLevel > 1)
+            {
+                throw new ArgumentException("Unexpectedly high recursion level.", nameof(recursionLevel));
+            }
+
             var fieldType = fieldSerializer.ValueType;
 
             // these will normally be equal unless we've removed some Convert(s) that the compiler put in

src/MongoDB.Driver/MongoCollectionImpl.cs

@@ -562,28 +562,7 @@ private CountOperation CreateCountOperation(FilterDefinition<TDocument> filter,
         private DistinctOperation<TField> CreateDistinctOperation<TField>(FieldDefinition<TDocument, TField> field, FilterDefinition<TDocument> filter, DistinctOptions options)
         {
             var renderedField = field.Render(_documentSerializer, _settings.SerializerRegistry);
-
-            IBsonSerializer<TField> valueSerializer = null;
-            if (renderedField.UnderlyingSerializer != null)
-            {
-                IBsonArraySerializer arraySerializer;
-                BsonSerializationInfo itemSerializationInfo;
-                if (renderedField.UnderlyingSerializer.ValueType == typeof(TField))
-                {
-                    valueSerializer = (IBsonSerializer<TField>)renderedField.UnderlyingSerializer;
-                }
-                else if (
-                    (arraySerializer = renderedField.UnderlyingSerializer as IBsonArraySerializer) != null &&
-                    arraySerializer.TryGetItemSerializationInfo(out itemSerializationInfo) &&
-                    itemSerializationInfo.Serializer.ValueType == typeof(TField))
-                {
-                    valueSerializer = (IBsonSerializer<TField>)itemSerializationInfo.Serializer;
-                }
-            }
-            if (valueSerializer == null)
-            {
-                valueSerializer = _settings.SerializerRegistry.GetSerializer<TField>();
-            }
+            var valueSerializer = GetValueSerializerForDistinct(renderedField, _settings.SerializerRegistry);
 
             return new DistinctOperation<TField>(
                 _collectionNamespace,
@@ -759,6 +738,32 @@ private FindOperation<TResult> CreateMapReduceOutputToCollectionFindOperation<TR
             };
         }
 
+        private IBsonSerializer<TField> GetValueSerializerForDistinct<TField>(RenderedFieldDefinition<TField> renderedField, IBsonSerializerRegistry serializerRegistry)
+        {
+            if (renderedField.UnderlyingSerializer != null)
+            {
+                if (renderedField.UnderlyingSerializer.ValueType == typeof(TField))
+                {
+                    return (IBsonSerializer<TField>)renderedField.UnderlyingSerializer;
+                }
+
+                var arraySerializer = renderedField.UnderlyingSerializer as IBsonArraySerializer;
+                if (arraySerializer != null)
+                {
+                    BsonSerializationInfo itemSerializationInfo;
+                    if (arraySerializer.TryGetItemSerializationInfo(out itemSerializationInfo))
+                    {
+                        if (itemSerializationInfo.Serializer.ValueType == typeof(TField))
+                        {
+                            return (IBsonSerializer<TField>)itemSerializationInfo.Serializer;
+                        }
+                    }
+                }
+            }
+
+            return serializerRegistry.GetSerializer<TField>();
+        }
+
         private TResult ExecuteReadOperation<TResult>(IReadOperation<TResult> operation, CancellationToken cancellationToken)
         {
             return ExecuteReadOperation(operation, _settings.ReadPreference, cancellationToken);