CSHARP-2150 Add check that the serializer's ValueType matches the type when registering the serializer

src/MongoDB.Bson/Serialization/BsonSerializerRegistry.cs

@@ -94,6 +94,7 @@ public void RegisterSerializer(Type type, IBsonSerializer serializer)
                 throw new ArgumentNullException("serializer");
             }
             EnsureRegisteringASerializerForThisTypeIsAllowed(type);
+            EnsureSerializerIsCompatibleWithType(serializer, type);
 
             if (!_cache.TryAdd(type, serializer))
             {
@@ -134,6 +135,7 @@ public bool TryRegisterSerializer(Type type, IBsonSerializer serializer)
                 throw new ArgumentNullException(nameof(serializer));
             }
             EnsureRegisteringASerializerForThisTypeIsAllowed(type);
+            EnsureSerializerIsCompatibleWithType(serializer, type);
 
             if (_cache.TryAdd(type, serializer))
             {
@@ -192,5 +194,13 @@ private void EnsureRegisteringASerializerForThisTypeIsAllowed(Type type)
                 throw new ArgumentException(message, "type");
             }
         }
+
+        private void EnsureSerializerIsCompatibleWithType(IBsonSerializer serializer, Type type)
+        {
+            if (!serializer.ValueType.IsAssignableFrom(type))
+            {
+                throw new ArgumentException($"A serializer for {BsonUtils.GetFriendlyTypeName(serializer.ValueType)} cannot be registered for type {BsonUtils.GetFriendlyTypeName(type)}.");
+            }
+        }
     }
 }

tests/MongoDB.Bson.Tests/Serialization/BsonSerializerRegistryTests.cs

@@ -97,6 +97,54 @@ public void RegisterSerializer_should_throw_when_serializer_is_already_registere
             exception.Message.Should().Contain("There is already a serializer registered for type Object");
         }
 
+        [Fact]
+        public void RegisterSerializer_should_throw_when_type_and_serializer_do_not_match()
+        {
+            var subject = new BsonSerializerRegistry();
+            var intSerializer = new Int32Serializer();
+
+            var exception = Record.Exception(() => subject.RegisterSerializer(typeof(long), intSerializer));
+
+            exception.Should().BeOfType<ArgumentException>();
+            exception.Message.Should().Be("A serializer for Int32 cannot be registered for type Int64.");
+        }
+
+        [Fact]
+        public void TryRegisterSerializer_should_throw_when_type_and_serializer_do_not_match()
+        {
+            var subject = new BsonSerializerRegistry();
+            var intSerializer = new Int32Serializer();
+
+            var tryException = Record.Exception(() => subject.TryRegisterSerializer(typeof(long), intSerializer));
+
+            tryException.Should().BeOfType<ArgumentException>();
+            tryException.Message.Should().Be("A serializer for Int32 cannot be registered for type Int64.");
+        }
+
+        [Fact]
+        public void RegisterSerializer_should_allow_serializer_for_base_type()
+        {
+            var subject = new BsonSerializerRegistry();
+            var serializer = new PeopleSerializer();
+
+            var exception = Record.Exception(() => subject.RegisterSerializer(typeof(List<Person>), serializer));
+            exception.Should().BeNull();
+
+            subject.GetSerializer(typeof(List<Person>)).Should().BeSameAs(serializer);
+        }
+
+        [Fact]
+        public void TryRegisterSerializer_should_allow_serializer_for_base_type()
+        {
+            var subject = new BsonSerializerRegistry();
+            var serializer = new PeopleSerializer();
+
+            var result = subject.TryRegisterSerializer(typeof(List<Person>), serializer);
+            result.Should().BeTrue();
+
+            subject.GetSerializer(typeof(List<Person>)).Should().BeSameAs(serializer);
+        }
+
         [Fact]
         public void TryRegisterSerializer_should_return_true_when_serializer_is_not_already_registered()
         {
@@ -189,5 +237,19 @@ public void TryRegisterSerializer_should_throw_when_different_serializer_is_alre
             exception.Should().BeOfType<BsonSerializationException>();
             exception.Message.Should().Contain("There is already a different serializer registered for type Object");
         }
+
+        private class Person
+        {
+            public string Name { get; set; }
+        }
+
+        private class PeopleSerializer : SerializerBase<IEnumerable<Person>>
+        {
+            public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, IEnumerable<Person> value)
+                => throw new NotImplementedException();
+
+            public override IEnumerable<Person> Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
+                => throw new NotImplementedException();
+        }
     }
 }