`qasm3.Exporter` raises an obscure error on invalid basis-gate name

[t-imamichi]

Environment

• Qiskit version: 1.2.0 rc1
• Python version: 3.12.4
• Operating system: macOS 14.6

What is happening?

qasm3.Exporter raises an error with a simple case with 1.2.0 rc1 while 1.1.1 works fine.

How can we reproduce the issue?

from qiskit import QuantumCircuit, qasm3
from qiskit.providers.fake_provider import GenericBackendV2

circuit = QuantumCircuit(2)
backend = GenericBackendV2(2)
exporter = qasm3.Exporter(basis_gates=backend.operation_names)
result = exporter.dumps(circuit)
print(result)

qiskit 1.2.0 rc1

Traceback (most recent call last):
  File "/Users/ima/tasks/4_2024/qiskit/qasm3-import/tmp/test_min.py", line 7, in <module>
    result = exporter.dumps(circuit)
             ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ima/envs/qiskit312/lib/python3.12/site-packages/qiskit/qasm3/exporter.py", line 182, in dumps
    self.dump(circuit, stream)
  File "/Users/ima/envs/qiskit312/lib/python3.12/site-packages/qiskit/qasm3/exporter.py", line 196, in dump
    builder.build_program()
  File "/Users/ima/envs/qiskit312/lib/python3.12/site-packages/qiskit/qasm3/exporter.py", line 629, in build_program
    self.symbols.register_gate_without_definition(builtin, None)
  File "/Users/ima/envs/qiskit312/lib/python3.12/site-packages/qiskit/qasm3/exporter.py", line 435, in register_gate_without_definition
    name = self.escaped_declarable_name(name, allow_rename=False, unique=False)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/ima/envs/qiskit312/lib/python3.12/site-packages/qiskit/qasm3/exporter.py", line 352, in escaped_declarable_name
    raise QASM3ExporterError(f"cannot use the keyword '{name}' as a variable name")
qiskit.qasm3.exceptions.QASM3ExporterError: "cannot use the keyword 'reset' as a variable name"

qiskit 1.1.1

OPENQASM 3.0;
include "stdgates.inc";
qubit[1] q;

What should happen?

It would be nice to run without error or show a warning instead of the error.

Any suggestions?

No response

[jakelishman]

Imo it's right to error here, but the message could be a lot better. Passing arbitrary values in basis_gates is not really a good idea - the whole option is kind of a hack, because it causes invalid OQ3 to be generated (in general) by declaring gates that are not defined.

This code example is telling the exporter to treat reset as if it's a "basis gate" that will accept any number of parameters and qubits, so the exporter attempts to put that into its symbol table. That cannot succeed, because reset is a keyword of the language. The older versions of the exporter did far less symbol tracking (and had a lot more bugs as a result).

The code example here probably shouldn't set basis_gates at all, tbh.

[jakelishman]

Though that said, if there are backends doing this, including passing reset here, I'm open to making it a warning now and a hard error in the future (and the warning will have to explain that the call is invalid).

[t-imamichi]

Thank you for your information. I will stop passing backend's basis gates to basis_gates.
It would be nice to make the message a bit better. But, I don't have a strong opinion. So, you can close it.

[jakelishman]

Let's leave it open - the error message isn't good, and I'll write a better one.

[1ucian0]

Editing the title to reflect the discussion conclusion