CSHARP-5952: SerializerFinder resolve wrong serializer for BsonDocument members

src/MongoDB.Driver/Linq/Linq3Implementation/SerializerFinders/SerializerFinderVisitMember.cs

@@ -46,6 +46,7 @@ protected override Expression VisitMember(MemberExpression node)
 
                 var resultSerializer = node.Member switch
                 {
+                    _ when typeof(BsonDocument).IsAssignableFrom(declaringType) => UnknowableSerializer.Create(node.Type), // we do not support translation of BsonDocument properties
                     _ when declaringType == typeof(BsonValue) => GetBsonValuePropertySerializer(),
                     _ when IsCollectionCountOrLengthProperty() => GetCollectionCountOrLengthPropertySerializer(),
                     _ when declaringType == typeof(DateTime) => GetDateTimePropertySerializer(),

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/SerializerFinders/BsonDocumentTests.cs

@@ -0,0 +1,74 @@
+/* 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.
+ */
+
+using System.Linq.Expressions;
+using FluentAssertions;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization;
+using MongoDB.Bson.Serialization.Serializers;
+using MongoDB.Driver.Linq;
+using MongoDB.Driver.Linq.Linq3Implementation.SerializerFinders;
+using MongoDB.Driver.Linq.Linq3Implementation.Serializers;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.SerializerFinders;
+
+public class BsonDocumentTests
+{
+    [Theory]
+    [MemberData(nameof(SupportedTestCases))]
+    public void SerializerFinder_should_resolve_serializer_for_BsonDocument_members(LambdaExpression expression, IBsonSerializer expected)
+    {
+        var serializerMap = TestHelpers.CreateSerializerMap(expression);
+
+        SerializerFinder.FindSerializers(expression.Body, null, serializerMap);
+
+        serializerMap.IsKnown(expression.Body, out _).Should().BeTrue();
+        serializerMap.GetSerializer(expression.Body).Should().Be(expected);
+    }
+
+    [Theory]
+    [MemberData(nameof(NotSupportedTestCases))]
+    public void SerializerFinder_resolve_unknowable_serializer_for_unsupported_BsonDocument_members(LambdaExpression expression)
+    {
+        var serializerMap = TestHelpers.CreateSerializerMap(expression);
+
+        SerializerFinder.FindSerializers(expression.Body, null, serializerMap);
+
+        serializerMap.IsKnown(expression.Body, out var serializer).Should().BeTrue();
+        serializer.Should().BeOfType(typeof(UnknowableSerializer<>).MakeGenericType(expression.Body.Type));
+        var exception = Record.Exception(() => serializerMap.GetSerializer(expression.Body));
+        exception.Should().BeOfType<ExpressionNotSupportedException>();
+    }
+
+    public static readonly object[][] SupportedTestCases =
+    [
+        [TestHelpers.MakeLambda((BsonDocument d) => d["name"]), BsonValueSerializer.Instance]
+    ];
+
+    public static readonly object[][] NotSupportedTestCases =
+    [
+        [TestHelpers.MakeLambda((BsonDocument d) => d.ElementCount)],
+        [TestHelpers.MakeLambda((BsonDocument d) => d.Elements)],
+        [TestHelpers.MakeLambda((BsonDocument d) => d.Values)],
+        [TestHelpers.MakeLambda((BsonDocument d) => d.Names)],
+
+        [TestHelpers.MakeLambda((RawBsonDocument d) => d.ElementCount)],
+        [TestHelpers.MakeLambda((RawBsonDocument d) => d.Elements)],
+        [TestHelpers.MakeLambda((RawBsonDocument d) => d.Values)],
+        [TestHelpers.MakeLambda((RawBsonDocument d) => d.Names)],
+    ];
+}
+