How to propagate constraints through a layered @vsc.randobj hierarchy?

[RasmusGOlsen]

I am building a layered data structure where a high-level object needs to control the size of a list buried several layers deep.

The hierarchy is:

1. Packet (Top): Has a size attribute.
2. Container (Middle): Has its own size and holds two different types of Payloads.
3. Payload (Leaf): Contains the actual vsc.randsz_list_t.

The Goal
I want to constrain Packet.size in a randomize_with block and have that value "drill down" through the Container to set the actual length of the list inside the Payload.

The Problem
While randomizing the leaf-level Payload and the Container works fine, randomizing the Packet results in a SolveFailure. It seems like the solver sees the top-level constraint but cannot "connect the dots" to the size in the Container and the size at the bottom of the chain.

Problem Set: 2 constraints
  <unknown>: (size == payload.size);
  <unknown>: (size == 5);
vsc.model.solve_failure.SolveFailure: solve failure

from enum import Enum, auto
import vsc


class CType(Enum):
    A = auto()
    B = auto()


@vsc.randobj
class Packet:
    def __init__(self):
        self.size = vsc.rand_uint16_t()
        self.payload = vsc.attr(Container())

    @vsc.constraint
    def size_c(self):
        self.size == self.payload.size

    def __str__(self):
        return str(self.payload)


@vsc.randobj
class Container:
    def __init__(self):
        self.type = vsc.rand_enum_t(CType)
        self.size = vsc.rand_uint16_t()
        self.a = vsc.attr(PayloadA())
        self.b = vsc.attr(PayloadB())

    @vsc.constraint
    def size_c(self):
        with vsc.if_then(self.type == CType.A):
            self.size == self.a.payload.size
        with vsc.else_then:
            self.size == self.b.payload.size

    def __str__(self):
        if self.type == CType.A:
            return str(self.a)
        elif self.type == CType.B:
            return str(self.b)


@vsc.randobj
class PayloadA:
    def __init__(self):
        self.payload = vsc.randsz_list_t(vsc.uint8_t())

    @vsc.constraint
    def size_c(self):
        self.payload.size < 100

    def __str__(self):
        return str(self.payload)


@vsc.randobj
class PayloadB:
    def __init__(self):
        self.payload = vsc.randsz_list_t(vsc.uint8_t())

    @vsc.constraint
    def size_c(self):
        self.payload.size < 100

    def __str__(self):
        return str(self.payload)


if __name__ == "__main__":
    p = PayloadA()
    with p.randomize_with(solve_fail_debug=1) as it:
      it.payload.size == 3
    print(p)

    p = Container()
    with p.randomize_with(solve_fail_debug=1) as it:
      it.size == 4
    print(p)

    p = Packet()
    with p.randomize_with(solve_fail_debug=1) as it:
      it.size == 5
    print(p)