Handler (non-pointer) nested structs inside Circuits

[gbotrel]

// Circuit defines a simple circuit
// x**3 + x + 5 == y
type Circuit struct {
	// struct tags on a variable is optional
	// default uses variable name and secret visibility.
	D Data
}

type Data struct {
	X frontend.Variable `gnark:"x"`
	Y frontend.Variable `gnark:",public"`
}

// Define declares the circuit constraints
// x**3 + x + 5 == y
func (circuit Circuit) Define(curveID ecc.ID, api frontend.API) error {
	x3 := api.Mul(circuit.D.X, circuit.D.X, circuit.D.X)
	api.AssertIsEqual(circuit.D.Y, api.Add(x3, circuit.D.X, 5))
	return nil
}

Note the method definition on Circuit, not *Circuit.

The frontend.Compile doesn't allocate Variables correctly in this case.