NBMsgPack030: Converters should not call top-level MessagePackSerializer methods

Custom converters (classes that derive from MessagePackConverter<T>) should not make calls to MessagePackSerializer. Such calls risk resetting the stack guard, unnecessary cache misses, etc.

A custom converter will often find itself in a situation where the type it is serializing is made up of sub-values that themselves can be serialized automatically, without a custom converter. In such cases, SerializationContext.GetConverter is the appropriate tool to delegate conversion of these sub-values.

Learn more about custom converters.

Example violations

public class MyTypeConverter : MessagePackConverter<MyType>
{
    public override MyType? Read(ref MessagePackReader reader, SerializationContext context) => throw new System.NotImplementedException();

    public override void Write(ref MessagePackWriter writer, in MyType? value, SerializationContext context)
    {
        var serializer = new MessagePackSerializer(); // NBMsgPack030
        serializer.Serialize(value.SomeProperty);     // NBMsgPack030
    }
}

public class MyType
{
    public SomeOtherType? SomeProperty { get; set; }
}

[GenerateShape]
public partial class SomeOtherType {}

Resolution

Replace top-level calls to the serializer to direct calls to a converter, which may come from SerializationContext.GetConverter.

public override void Write(ref MessagePackWriter writer, in MyType? value, SerializationContext context)
{
    SomeOtherType? someProperty = value.SomeProperty;
    context.GetConverter<SomeOtherType>().Write(ref writer, ref someProperty, context);
}