CSHARP-4731: Support assigning List<T> value to IList<T> property in …

…Select.

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MemberInitExpressionToAggregationExpressionTranslator.cs

@@ -21,6 +21,7 @@
 using MongoDB.Bson.Serialization;
 using MongoDB.Driver.Linq.Linq3Implementation.Ast;
 using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
+using MongoDB.Driver.Linq.Linq3Implementation.Misc;
 
 namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators
 {
@@ -57,7 +58,8 @@ public static AggregationExpression Translate(TranslationContext context, Member
                     var constructorArgumentSerializer = constructorArgumentTranslation.Serializer ?? BsonSerializer.LookupSerializer(constructorArgumentType);
                     var memberMap = EnsureMemberMap(expression, classMap, creatorMapParameter);
                     EnsureDefaultValue(memberMap);
-                    memberMap.SetSerializer(constructorArgumentSerializer);
+                    var memberSerializer = CoerceSourceSerializerToMemberSerializer(memberMap, constructorArgumentSerializer);
+                    memberMap.SetSerializer(memberSerializer);
                     computedFields.Add(AstExpression.ComputedField(memberMap.ElementName, constructorArgumentTranslation.Ast));
                 }
             }
@@ -69,7 +71,8 @@ public static AggregationExpression Translate(TranslationContext context, Member
                 var memberMap = FindMemberMap(expression, classMap, member.Name);
                 var valueExpression = memberAssignment.Expression;
                 var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, valueExpression);
-                memberMap.SetSerializer(valueTranslation.Serializer);
+                var memberSerializer = CoerceSourceSerializerToMemberSerializer(memberMap, valueTranslation.Serializer);
+                memberMap.SetSerializer(memberSerializer);
                 computedFields.Add(AstExpression.ComputedField(memberMap.ElementName, valueTranslation.Ast));
             }
 
@@ -107,6 +110,27 @@ private static BsonClassMap CreateClassMap(Type classType, ConstructorInfo const
             return classMap;
         }
 
+        private static IBsonSerializer CoerceSourceSerializerToMemberSerializer(BsonMemberMap memberMap, IBsonSerializer sourceSerializer)
+        {
+            var memberType = memberMap.MemberType;
+            var memberSerializer = memberMap.GetSerializer();
+            var sourceType = sourceSerializer.ValueType;
+
+            if (memberType != sourceType &&
+                memberType.ImplementsIEnumerable(out var memberItemType) &&
+                sourceType.ImplementsIEnumerable(out var sourceItemType) &&
+                sourceItemType == memberItemType &&
+                sourceSerializer is IBsonArraySerializer sourceArraySerializer &&
+                sourceArraySerializer.TryGetItemSerializationInfo(out var sourceItemSerializationInfo) &&
+                memberSerializer is IChildSerializerConfigurable memberChildSerializerConfigurable)
+            {
+                var sourceItemSerializer = sourceItemSerializationInfo.Serializer;
+                return memberChildSerializerConfigurable.WithChildSerializer(sourceItemSerializer);
+            }
+
+            return sourceSerializer;
+        }
+
         private static BsonMemberMap EnsureMemberMap(Expression expression, BsonClassMap classMap, MemberInfo creatorMapParameter)
         {
             var declaringClassMap = classMap;

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp4731Tests.cs

@@ -0,0 +1,119 @@
+/* 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;
+using System.Collections.Generic;
+using System.Linq;
+using FluentAssertions;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+using MongoDB.Driver.Linq;
+using MongoDB.TestHelpers.XunitExtensions;
+using Xunit;
+
+namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Jira
+{
+    public class CSharp4731Tests : Linq3IntegrationTest
+    {
+        [Theory]
+        [ParameterAttributeData]
+        public void Select_setting_IList_from_List_should_work(
+            [Values(LinqProvider.V2, LinqProvider.V3)] LinqProvider linqProvider)
+        {
+            var collection = GetCollection(linqProvider);
+
+            var queryable = collection
+                .AsQueryable()
+                .Select(x => new P { IList = x.List })
+                .Where(x => x.IList.Contains(E.A));
+
+            if (linqProvider == LinqProvider.V2)
+            {
+                var exception = Record.Exception(() => Translate(collection, queryable));
+                exception.Should().BeOfType<ArgumentException>();
+            }
+            else
+            {
+                var stages = Translate(collection, queryable);
+                AssertStages(
+                    stages,
+                    "{ $project : { IList : '$List', _id : 0 } }",
+                    "{ $match : { IList : 'A' } }");
+
+                var result = queryable.Single();
+                result.IList.Should().Equal(E.A, E.B);
+            }
+        }
+
+        [Theory]
+        [ParameterAttributeData]
+        public void Select_setting_IReadOnlyList_from_List_should_work(
+            [Values(LinqProvider.V2, LinqProvider.V3)] LinqProvider linqProvider)
+        {
+            var collection = GetCollection(linqProvider);
+
+            var queryable = collection
+                .AsQueryable()
+                .Select(x => new Q { IReadOnlyList = x.List })
+                .Where(x => x.IReadOnlyList.Contains(E.A));
+
+            if (linqProvider == LinqProvider.V2)
+            {
+                var exception = Record.Exception(() => Translate(collection, queryable));
+                exception.Should().BeOfType<ArgumentException>();
+            }
+            else
+            {
+                var stages = Translate(collection, queryable);
+                AssertStages(
+                    stages,
+                    "{ $project : { IReadOnlyList : '$List', _id : 0 } }",
+                    "{ $match : { IReadOnlyList : 'A' } }");
+
+                var result = queryable.Single();
+                result.IReadOnlyList.Should().Equal(E.A, E.B);
+            }
+        }
+
+        private IMongoCollection<Test> GetCollection(LinqProvider linqProvider)
+        {
+            var collection = GetCollection<Test>("test", linqProvider);
+            CreateCollection(
+                collection,
+                new Test { Id = 1, List = new List<E> { E.A, E.B } },
+                new Test { Id = 2, List = new List<E> { E.C, E.D } });
+            return collection;
+        }
+
+        private class Test
+        {
+            public int Id { get; set; }
+            [BsonRepresentation(BsonType.String)]
+            public List<E> List { get; set; }
+        }
+
+        private class P
+        {
+            public IList<E> IList { get; set; }
+        }
+
+        private class Q
+        {
+            public IReadOnlyList<E> IReadOnlyList { get; set; }
+        }
+
+        private enum E { A, B, C, D };
+    }
+}