OpenQASM3 exporter emits variables with reserved keywords

[taalexander]

Environment

• Qiskit Terra version: 0.19.2
• Python version: 3.8
• Operating system: OSX

What is happening?

When dumping QASM3 from a Qiskit circuit the emitted QASM3 has variables with names that are reserved keywords.

How can we reproduce the issue?

from qiskit import IBMQ, transpile, qasm3
from qiskit_experiments.library import QuantumVolume

from qiskit.test.mock import FakeMontreal

qv_exp = QuantumVolume([0, 1], seed=42)
circuits = qv_exp.circuits()

backend = FakeMontreal()

def dump_qasm3(circuit, backend=backend):
    return qasm3.Exporter(includes=[], basis_gates=backend.configuration().basis_gates).dumps(circuit)

transpiled_circuits = transpile(circuits, backend, optimization_level=0)
print(dump_qasm3(transpiled_circuits[0]))

Emits:

OPENQASM 3;
bit[2] measure;
rz(-0.527043787493904) $0;
sx $0;
rz(5.16854203223675) $0;
sx $0;
rz(7.52041849263069) $0;
rz(2.52883547684609) $1;
sx $1;
rz(4.18263287241389) $1;
sx $1;
rz(11.4206034322753) $1;
cx $0, $1;
rz(pi/2) $0;
sx $0;
rz(3.83403185518176) $0;
sx $0;
rz(5*pi/2) $0;
rz(-3.13722964498385) $1;
sx $1;
rz(3.43607384014569) $1;
sx $1;
rz(7.84942236436758) $1;
cx $0, $1;
rz(pi/2) $0;
sx $0;
rz(3.15129722109744) $0;
sx $0;
rz(2*pi) $0;
rz(-pi) $1;
sx $1;
rz(4.71106568778747) $1;
sx $1;
rz(10.9942509926498) $1;
cx $0, $1;
rz(0.0407864518524126) $0;
sx $0;
rz(3.68646663680408) $0;
sx $0;
rz(8.261303299549) $0;
rz(0.384886550311654) $0;
sx $0;
rz(4.72101136719892) $0;
sx $0;
rz(7.05118934560937) $0;
rz(0.360649613151623) $1;
sx $1;
rz(4.92286155451527) $1;
sx $1;
rz(11.7465986327618) $1;
rz(-0.879779034806911) $1;
sx $1;
rz(5.92954645622555) $1;
sx $1;
rz(7.17120533229796) $1;
cx $0, $1;
rz(pi/2) $0;
sx $0;
rz(4.06066473777189) $0;
sx $0;
rz(5*pi/2) $0;
rz(-3.1391797270208) $1;
sx $1;
rz(3.64322156481995) $1;
sx $1;
rz(7.85122966784221) $1;
cx $0, $1;
rz(-pi/2) $0;
sx $0;
rz(3.7166355179822) $0;
sx $0;
rz(3*pi) $0;
rz(-pi) $1;
sx $1;
rz(4.71106568778747) $1;
sx $1;
rz(10.9942509926498) $1;
cx $0, $1;
rz(-1.47560665166994) $0;
sx $0;
rz(4.18505473328482) $0;
sx $0;
rz(9.47043569736961) $0;
rz(0.398413507779781) $1;
sx $1;
rz(4.1804199287629) $1;
sx $1;
rz(12.3633552711276) $1;
barrier $0, $1;
measure[0] = measure $0;
measure[1] = measure $1;

Note the bit[2] measure; declaration which is invalid.

What should happen?

The QASM3 exporter should mangle the names of reserved keywords for classical/qubit registers with names that collied.

Any suggestions?

No response

[jakelishman]

Good point, thanks for the report. I've pushed up a simple symbol table add-on to the exporter in #7744 that also handles generating new names when there are clashes. There's still a lot of work to be done in the QASM 3 exporter before 0.20 (see also #7136 and #7335 for example), and when I'm back from writing up my thesis we'll get a bit more on top of getting these things done.