CSHARP-2096: Make EnumRepresentationConvention also affect collections of Enums

src/MongoDB.Bson/Serialization/Attributes/BsonDateOnlyOptionsAttribute.cs

@@ -61,8 +61,10 @@ public BsonDateOnlyOptionsAttribute(BsonType representation, DateOnlyDocumentFor
         /// <returns>A reconfigured serializer.</returns>
         protected override IBsonSerializer Apply(IBsonSerializer serializer)
         {
-            var reconfiguredSerializer = SerializerConfigurator.ReconfigureSerializer(serializer, (DateOnlySerializer s) => s.WithRepresentation(_representation, _documentFormat));
-            return reconfiguredSerializer ?? base.Apply(serializer);
+            return SerializerConfigurator.ReconfigureSerializerRecursively(serializer, Reconfigure) ?? base.Apply(serializer);
+
+            IBsonSerializer Reconfigure(IBsonSerializer s)
+                => s is DateOnlySerializer dos ? dos.WithRepresentation(_representation, _documentFormat) : null;
         }
     }
 #endif

src/MongoDB.Bson/Serialization/Conventions/EnumRepresentationConvention.cs

@@ -14,7 +14,6 @@
 */
 
 using System;
-using System.Reflection;
 
 namespace MongoDB.Bson.Serialization.Conventions
 {
@@ -25,6 +24,7 @@ public class EnumRepresentationConvention : ConventionBase, IMemberMapConvention
     {
         // private fields
         private readonly BsonType _representation;
+        private readonly bool _topLevelOnly;
 
         // constructors
         /// <summary>
@@ -33,76 +33,62 @@ public class EnumRepresentationConvention : ConventionBase, IMemberMapConvention
         /// <param name="representation">The serialization representation. 0 is used to detect representation
         /// from the enum itself.</param>
         public EnumRepresentationConvention(BsonType representation)
+            :this(representation, true)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="EnumRepresentationConvention" /> class.
+        /// </summary>
+        /// <param name="representation">The serialization representation. 0 is used to detect representation
+        /// from the enum itself.</param>
+        /// <param name="topLevelOnly">If set to true, the convention will be applied only to top level enum properties, and not collections of enums, for example.</param>
+        public EnumRepresentationConvention(BsonType representation, bool topLevelOnly)
         {
             EnsureRepresentationIsValidForEnums(representation);
             _representation = representation;
+            _topLevelOnly = topLevelOnly;
         }
 
         /// <summary>
         /// Gets the representation.
         /// </summary>
         public BsonType Representation => _representation;
 
+        /// <summary>
+        /// Gets a boolean indicating if this convention should be also applied only to the top level enum properties and not to others,
+        /// collections of enums for example. True by default.
+        /// </summary>
+        public bool TopLevelOnly => _topLevelOnly;
+
         /// <summary>
         /// Applies a modification to the member map.
         /// </summary>
         /// <param name="memberMap">The member map.</param>
         public void Apply(BsonMemberMap memberMap)
         {
-            var memberType = memberMap.MemberType;
-            var memberTypeInfo = memberType.GetTypeInfo();
+            var serializer = memberMap.GetSerializer();
+            var reconfiguredSerializer = _topLevelOnly && !serializer.ValueType.IsNullableEnum() ?
+                Reconfigure(serializer) :
+                SerializerConfigurator.ReconfigureSerializerRecursively(serializer, Reconfigure);
 
-            if (memberTypeInfo.IsEnum)
+            if (reconfiguredSerializer is not null)
             {
-                var serializer = memberMap.GetSerializer();
-                var representationConfigurableSerializer = serializer as IRepresentationConfigurable;
-                if (representationConfigurableSerializer != null)
-                {
-                    var reconfiguredSerializer = representationConfigurableSerializer.WithRepresentation(_representation);
-                    memberMap.SetSerializer(reconfiguredSerializer);
-                }
-                return;
+                memberMap.SetSerializer(reconfiguredSerializer);
             }
 
-            if (IsNullableEnum(memberType))
-            {
-                var serializer = memberMap.GetSerializer();
-                var childSerializerConfigurableSerializer = serializer as IChildSerializerConfigurable;
-                if (childSerializerConfigurableSerializer != null)
-                {
-                    var childSerializer = childSerializerConfigurableSerializer.ChildSerializer;
-                    var representationConfigurableChildSerializer = childSerializer as IRepresentationConfigurable;
-                    if (representationConfigurableChildSerializer != null)
-                    {
-                        var reconfiguredChildSerializer = representationConfigurableChildSerializer.WithRepresentation(_representation);
-                        var reconfiguredSerializer = childSerializerConfigurableSerializer.WithChildSerializer(reconfiguredChildSerializer);
-                        memberMap.SetSerializer(reconfiguredSerializer);
-                    }
-                }
-                return;
-            }
+            IBsonSerializer Reconfigure(IBsonSerializer s)
+                => s.ValueType.IsEnum ? (s as IRepresentationConfigurable)?.WithRepresentation(_representation) : null;
         }
 
         // private methods
-        private bool IsNullableEnum(Type type)
-        {
-            return
-                type.GetTypeInfo().IsGenericType &&
-                type.GetGenericTypeDefinition() == typeof(Nullable<>) &&
-                Nullable.GetUnderlyingType(type).GetTypeInfo().IsEnum;
-        }
-
         private void EnsureRepresentationIsValidForEnums(BsonType representation)
         {
-            if (
-                representation == 0 ||
-                representation == BsonType.String ||
-                representation == BsonType.Int32 ||
-                representation == BsonType.Int64)
+            if (representation is 0 or BsonType.String or BsonType.Int32 or BsonType.Int64)
             {
                 return;
             }
-            throw new ArgumentException("Enums can only be represented as String, Int32, Int64 or the type of the enum", "representation");
+            throw new ArgumentException("Enums can only be represented as String, Int32, Int64 or the type of the enum", nameof(representation));
         }
     }
 }

src/MongoDB.Bson/Serialization/IMultipleChildSerializersConfigurable.cs

@@ -0,0 +1,38 @@
+/* Copyright 2010-present MongoDB Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace MongoDB.Bson.Serialization
+{
+    /// <summary>
+    /// Represents a serializer that has multiple child serializers that configuration attributes can be forwarded to.
+    /// </summary>
+    public interface IMultipleChildSerializersConfigurable
+    {
+        /// <summary>
+        /// Gets the child serializers.
+        /// </summary>
+        /// <value>
+        /// The child serializers.
+        /// </value>
+        IBsonSerializer[] ChildSerializers { get; }
+
+        /// <summary>
+        /// Returns a serializer that has been reconfigured with the specified child serializers.
+        /// </summary>
+        /// <param name="childSerializers">The child serializers.</param>
+        /// <returns>The reconfigured serializer.</returns>
+        IBsonSerializer WithChildSerializers(IBsonSerializer[] childSerializers);
+    }
+}

src/MongoDB.Bson/Serialization/SerializerConfigurator.cs

@@ -14,36 +14,45 @@
  */
 
 using System;
+using System.Collections.Generic;
 
 namespace MongoDB.Bson.Serialization
 {
     internal static class SerializerConfigurator
     {
-        /// <summary>
-        /// Reconfigures a serializer using the specified <paramref name="reconfigure"/> method.
-        /// If the serializer implements <see cref="IChildSerializerConfigurable"/>,
-        /// the method traverses and applies the reconfiguration to its child serializers recursively until an appropriate leaf serializer is found.
-        /// </summary>
-        /// <param name="serializer">The input serializer to be reconfigured.</param>
-        /// <param name="reconfigure">A function that defines how the serializer of type <typeparamref name="TSerializer"/> should be reconfigured.</param>
-        /// <typeparam name="TSerializer">The input type for the reconfigure method.</typeparam>
-        /// <returns>
-        /// The reconfigured serializer, or <c>null</c> if no leaf serializer could be reconfigured.
-        /// </returns>
-        internal static IBsonSerializer ReconfigureSerializer<TSerializer>(IBsonSerializer serializer, Func<TSerializer, IBsonSerializer> reconfigure)
+        // Reconfigures a serializer recursively.
+        // The reconfigure Func should return null if it does not apply to a given serializer.
+        internal static IBsonSerializer ReconfigureSerializerRecursively(
+            IBsonSerializer serializer,
+            Func<IBsonSerializer, IBsonSerializer> reconfigure)
         {
             switch (serializer)
             {
+                // check IMultipleChildSerializersConfigurableSerializer first because some serializers implement both interfaces
+                case IMultipleChildSerializersConfigurable multipleChildSerializerConfigurable:
+                {
+                    var anyChildSerializerWasReconfigured = false;
+                    var reconfiguredChildSerializers = new List<IBsonSerializer>();
+
+                    foreach (var childSerializer in multipleChildSerializerConfigurable.ChildSerializers)
+                    {
+                        var reconfiguredChildSerializer = ReconfigureSerializerRecursively(childSerializer, reconfigure);
+                        anyChildSerializerWasReconfigured |= reconfiguredChildSerializer != null;
+                        reconfiguredChildSerializers.Add(reconfiguredChildSerializer ?? childSerializer);
+                    }
+
+                    return anyChildSerializerWasReconfigured ? multipleChildSerializerConfigurable.WithChildSerializers(reconfiguredChildSerializers.ToArray()) : null;
+                }
+
                 case IChildSerializerConfigurable childSerializerConfigurable:
+                {
                     var childSerializer = childSerializerConfigurable.ChildSerializer;
-                    var reconfiguredChildSerializer = ReconfigureSerializer(childSerializer, reconfigure);
-                    return reconfiguredChildSerializer != null? childSerializerConfigurable.WithChildSerializer(reconfiguredChildSerializer) : null;
-
-                case TSerializer typedSerializer:
-                    return reconfigure(typedSerializer);
+                    var reconfiguredChildSerializer = ReconfigureSerializerRecursively(childSerializer, reconfigure);
+                    return reconfiguredChildSerializer != null ? childSerializerConfigurable.WithChildSerializer(reconfiguredChildSerializer) : null;
+                }
 
                 default:
-                    return null;
+                    return reconfigure(serializer);
             }
         }
     }

src/MongoDB.Bson/Serialization/Serializers/DictionaryInterfaceImplementerSerializer.cs

@@ -27,6 +27,7 @@ namespace MongoDB.Bson.Serialization.Serializers
     public sealed class DictionaryInterfaceImplementerSerializer<TDictionary> :
         DictionarySerializerBase<TDictionary>,
         IChildSerializerConfigurable,
+        IMultipleChildSerializersConfigurable,
         IDictionaryRepresentationConfigurable
             where TDictionary : class, IDictionary, new()
     {
@@ -153,6 +154,24 @@ IBsonSerializer IDictionaryRepresentationConfigurable.WithDictionaryRepresentati
         {
             return WithDictionaryRepresentation(dictionaryRepresentation);
         }
+
+        IBsonSerializer[] IMultipleChildSerializersConfigurable.ChildSerializers => [KeySerializer, ValueSerializer];
+
+        IBsonSerializer IMultipleChildSerializersConfigurable.WithChildSerializers(IBsonSerializer[] childSerializers)
+        {
+            if (childSerializers.Length != 2)
+            {
+                throw new Exception("Wrong number of child serializers passed.");
+            }
+
+            var newKeySerializer = childSerializers[0];
+            var newValueSerializer = childSerializers[1];
+
+            return newKeySerializer.Equals(KeySerializer) && newValueSerializer.Equals(ValueSerializer)
+                ? this
+                : new DictionaryInterfaceImplementerSerializer<TDictionary>(DictionaryRepresentation, newKeySerializer,
+                    newValueSerializer);
+        }
     }
 
     /// <summary>
@@ -164,6 +183,7 @@ IBsonSerializer IDictionaryRepresentationConfigurable.WithDictionaryRepresentati
     public class DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue> :
         DictionarySerializerBase<TDictionary, TKey, TValue>,
         IChildSerializerConfigurable,
+        IMultipleChildSerializersConfigurable,
         IDictionaryRepresentationConfigurable<DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>>
             where TDictionary : class, IDictionary<TKey, TValue>
     {
@@ -281,6 +301,24 @@ IBsonSerializer IDictionaryRepresentationConfigurable.WithDictionaryRepresentati
             return WithDictionaryRepresentation(dictionaryRepresentation);
         }
 
+        IBsonSerializer[] IMultipleChildSerializersConfigurable.ChildSerializers => [KeySerializer, ValueSerializer];
+
+        IBsonSerializer IMultipleChildSerializersConfigurable.WithChildSerializers(IBsonSerializer[] childSerializers)
+        {
+            if (childSerializers.Length != 2)
+            {
+                throw new Exception("Wrong number of child serializers passed.");
+            }
+
+            var newKeySerializer = (IBsonSerializer<TKey>)childSerializers[0];
+            var newValueSerializer = (IBsonSerializer<TValue>)childSerializers[1];
+
+            return newKeySerializer.Equals(KeySerializer) && newValueSerializer.Equals(ValueSerializer)
+                ? this
+                : new DictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>(DictionaryRepresentation, newKeySerializer,
+                    newValueSerializer);
+        }
+
         /// <inheritdoc/>
         protected override ICollection<KeyValuePair<TKey, TValue>> CreateAccumulator()
         {

src/MongoDB.Bson/Serialization/Serializers/ReadOnlyDictionaryInterfaceImplementerSerializer.cs

@@ -28,6 +28,7 @@ namespace MongoDB.Bson.Serialization.Serializers
     public sealed class ReadOnlyDictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue> :
         DictionarySerializerBase<TDictionary, TKey, TValue>,
         IChildSerializerConfigurable,
+        IMultipleChildSerializersConfigurable,
         IDictionaryRepresentationConfigurable<ReadOnlyDictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>>
             where TDictionary : class, IReadOnlyDictionary<TKey, TValue>
     {
@@ -122,6 +123,24 @@ IBsonSerializer IDictionaryRepresentationConfigurable.WithDictionaryRepresentati
             return WithDictionaryRepresentation(dictionaryRepresentation);
         }
 
+        IBsonSerializer[] IMultipleChildSerializersConfigurable.ChildSerializers => [KeySerializer, ValueSerializer];
+
+        IBsonSerializer IMultipleChildSerializersConfigurable.WithChildSerializers(IBsonSerializer[] childSerializers)
+        {
+            if (childSerializers.Length != 2)
+            {
+                throw new Exception("Wrong number of child serializers passed.");
+            }
+
+            var newKeySerializer =  (IBsonSerializer<TKey>)childSerializers[0];
+            var newValueSerializer =  (IBsonSerializer<TValue>)childSerializers[1];
+
+            return newKeySerializer.Equals(KeySerializer) && newValueSerializer.Equals(ValueSerializer)
+                ? this
+                : new ReadOnlyDictionaryInterfaceImplementerSerializer<TDictionary, TKey, TValue>(DictionaryRepresentation, newKeySerializer,
+                    newValueSerializer);
+        }
+
         /// <inheritdoc/>
         protected override ICollection<KeyValuePair<TKey, TValue>> CreateAccumulator()
         {

src/MongoDB.Bson/Serialization/TypeExtensions.cs

@@ -29,5 +29,17 @@ public static bool IsAnonymousType(this Type type)
                 type.IsGenericType &&
                 type.Name.Contains("Anon"); // don't check for more than "Anon" so it works in mono also
         }
+
+        public static bool IsNullable(this Type type)
+        {
+            return type.IsConstructedGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>);
+        }
+
+        public static bool IsNullableEnum(this Type type)
+        {
+            return
+                type.IsNullable() &&
+                Nullable.GetUnderlyingType(type).IsEnum;
+        }
     }
 }