Unroller raises unclear error when reaching a node without a definition #5840
Description
Information
- Qiskit Terra version: master @ 06dd155
- Python version: 3.7.9
- Operating system: macOS Big Sur
What is the current behavior?
Using the Unroller to unroll a circuit can fail, while using transpile with optimization_level=0 works fine.
Steps to reproduce the problem
from qiskit import transpile
from qiskit.circuit.library import ZGate
from qiskit.transpiler.passes import Unroller
basis = ['u1', 'u2', 'u3', 'cx']
unroller = Unroller(basis)
circuit = ZGate().control().definition # circuit with CZ gate
unroller(circuit) # works
circuit = ZGate().control(2).definition # circuit with CCZ gate
unroller(circuit) # error, see traceback below
transpile(circuit, basis_gates=basis, optimization_level=0) # worksThe error in the unroller is:
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
~/Qiskit/qiskit-terra/qiskit/transpiler/passes/basis/unroller.py in run(self, dag)
82 try:
---> 83 rule = rule[0][0].definition.data
84 except (TypeError, AttributeError) as err:
AttributeError: 'NoneType' object has no attribute 'data'
During handling of the above exception, another exception occurred:
QiskitError Traceback (most recent call last)
<ipython-input-17-c2529f65b3ed> in <module>
----> 1 Unroller(ubasis)(ZGate().control(2).definition)
~/Qiskit/qiskit-terra/qiskit/transpiler/basepasses.py in __call__(self, circuit, property_set)
118 self.property_set = property_set_
119
--> 120 result = self.run(circuit_to_dag(circuit))
121
122 result_circuit = circuit
~/Qiskit/qiskit-terra/qiskit/transpiler/passes/basis/unroller.py in run(self, dag)
83 rule = rule[0][0].definition.data
84 except (TypeError, AttributeError) as err:
---> 85 raise QiskitError('Error decomposing node {}: {}'.format(node.name, err))
86
87 else:
QiskitError: "Error decomposing node p: 'NoneType' object has no attribute 'data'"
What is the expected behavior?
The unroller should be able to unroll any circuit if the basis is sufficient.
Suggested solutions
Not sure!