Support Full AOT (Ahead of Time compilation).

[veblush]

In full AOT environment like iOS, runtime jitting is not allowed, which means no runtime code generation at all.
For example, it's impossible to emit code and use a generic type which parameter types are not determined at compile time.

To support this, we need to put workaround code for every dynamic code. For example, CodeGenerator.GenerateWriteAllFieldsDelegate can be changed like:

private static ValueWriter GenerateWriteAllFieldsDelegate(
    List<ValueWriter> fieldWriters)
{
    if (fieldWriters == null)
        throw new ArgumentNullException(nameof(fieldWriters));

    if (use_dynamic_code) // CHECK SERIALIZER OPTION TO USE DYNAMIC CODE
    {
        // fast but not working code on AOT.
        var streamParam = Parameter(typeof (Stream));
        var objectParam = Parameter(typeof (object));
        var sessionParam = Parameter(typeof (SerializerSession));
        var xs = fieldWriters
            .Select(Constant)
            .Select(
                fieldWriterExpression =>
                    Invoke(fieldWriterExpression, streamParam, objectParam, sessionParam))
            .ToList();
        var body = Block(xs);
        var writeallFields =
            Lambda<ValueWriter>(body, streamParam, objectParam,
                sessionParam)
                .Compile();
        return writeallFields;
    }
    else
    {
        // slow but working code on AOT.
        return (stream, obj, session) => fieldWriters.ForEach(w => w(stream, obj, session));
    }
}

How about this?

[rogeralsing]

Asked on Gitter but Ill add it here too.
How does the AOT path work? it will end up using reflection with FieldInfo.Get/SetValue or how does that work?

[veblush]

Yes. It usually ends up with a bunch of Get/SetValue that is safe on AOT environment. And it's also possible to use generic types or methods which can be instantiated in compile-time.

[rogeralsing]

I will close this one as it is out of scope