Types used in lists must be declared beforehand

[zhaakhi]

If you have a field with a type like list<T>, T must already have been declared, or the field will be serialized wrong.

How to reproduce:
In tests/container.thrift, move ListStruct to the top of the file, before ListItem,
Run the tests and test_container.py will fail:

    def test_list_struct():
        l_item = container.ListItem()
        l_item.list_string = ['foo', 'bar'] * 100
        l_item.list_list_string = [['foo', 'bar']] * 100
    
        l_struct = container.ListStruct()
        l_struct.list_items = [l_item] * 100
    
        b = serialize(l_struct)
        l_struct2 = deserialize(container.ListStruct(), b)
>       assert l_struct == l_struct2
E       AssertionError: assert ListStruct(list_items=[ListItem(list_string=['foo', 'bar', 'foo', 'bar', 'foo', 'bar', 'foo', 'bar', 'foo', 'bar', 'fo...r'], ['foo', 'bar'], ['foo', 'bar'], ['foo', 'bar'], ['foo', 'bar'], ['foo', 'bar'], ['foo', 'bar'], ['foo', 'bar']])])
== ListStruct(list_items=[None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None,...one, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None, None])

test_container.py:55: AssertionError

It looks like fill_incomplete_ttype should deal with declaration order, but misses the list field. I would also expect serializing or deserializing incomplete types to fail instead of silently substituting 'None', since this makes bugs hard to debug.

[ethe]

Thanks for reporting, I am turning to fix it.