OpenQASM3 dumper does not work with repeated conditionals

[1ucian0]

Environment

• Qiskit version: 1.1.0.dev0+197e78c
• Python version: 3.11.7
• Operating system: MacOS

What is happening?

While I was trying to reproduce #11935 (and succeeding), I noticed that the OpenQASM3 dumper has the same problem. It seems that is not working with repeated conditionals

How can we reproduce the issue?

from qiskit import QuantumCircuit, ClassicalRegister, QuantumRegister
from qiskit.circuit.library.standard_gates import CXGate

qr = QuantumRegister(2, name='qr')
cr = ClassicalRegister(2, name='cr')
qc = QuantumCircuit(qr, cr, name='qc')
qc.append(CXGate().c_if(cr, 0).repeat(1), qargs=qr)

from qiskit.qasm3 import dumps

print(dumps(qc))

KeyError: "'ClassicalRegister(2, 'cr')' is not defined in the current context"

What should happen?

Notice that the example works with OpenQASM 2 dumper:

from qiskit.qasm2 import dumps

print(dumps(qc))

OPENQASM 2.0;
include "qelib1.inc";
gate cx_1 q0,q1 { if(cr==0) cx q0,q1; }
qreg qr[2];
creg cr[2];
cx_1 qr[0],qr[1];

Any suggestions?

No response

[jakelishman]

The problem here is happening some time before we get to the OQ2 and OQ3 dumpers (note that the OQ2 dumper's output is invalid OQ2). Looks like a Gate with a condition is being allowed to be used in some other Gate object, but classical conditions aren't unitary so that should have been forbidden. The error's more likely in Gate.repeat than the dumpers, here.