'type error' when using QASM3 converter

[ArfatSalman]

Environment

• Qiskit Terra version: {'qiskit-terra': '0.23.1', 'qiskit-aer': '0.11.2', 'qiskit-ignis': None, 'qiskit-ibmq-provider': '0.20.0', 'qiskit': '0.41.0', 'qiskit-nature': None, 'qiskit-finance': None, 'qiskit-optimization': None, 'qiskit-machine-learning': None}
• Python version: Python 3.9.12
• Operating system: MacOS Ventura 13.1

What is happening?

Exporting and importing the same circuit in QASM3 throws '6,7: type error'.

How can we reproduce the issue?

from qiskit import transpile
from qiskit import QuantumCircuit, ClassicalRegister, QuantumRegister
from qiskit.circuit.library.standard_gates import *

qr = QuantumRegister(3, name="qr")
cr = ClassicalRegister(3, name="cr")

qc = QuantumCircuit(qr, cr, name="qc")
qc.append(XGate(), qargs=[qr[2]], cargs=[])
qc.append(SGate(), qargs=[qr[2]], cargs=[])

qc.measure(qr, cr)

qc = transpile(qc) # if this line is commented out, there's no error then

from qiskit.qasm3 import loads, dumps

qc = loads(dumps(qc))
# qiskit_qasm3_import.exceptions.ConversionError: 6,7: type error
# qiskit.qasm3.exceptions.QASM3ImporterError: '6,7: type error'

What should happen?

Using QASM2 round-trip (qc.from_qasm_str(qc.qasm())) works for the above circuit. I was expecting the QASM3 roundtrip to work as well.

Any suggestions?

No response

[jakelishman]

Thanks - this is a bug in the implicit-cast typing resolution of the importer; it's missing a rule to unify int * float, which is what's needed here.