Fix Barrier broadcast arguments

qiskit/circuit/barrier.py

@@ -47,8 +47,5 @@ def inverse(self):
         """Special case. Return self."""
         return Barrier(self.num_qubits)
 
-    def broadcast_arguments(self, qargs, cargs):
-        yield [qarg for sublist in qargs for qarg in sublist], []
-
     def c_if(self, classical, val):
         raise QiskitError("Barriers are compiler directives and cannot be conditional.")

releasenotes/notes/fix-barrier-arg-list-check-ff69f37ede6bdf6c.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed an issue with the :class:`.Barrier` class. When adding a
+    :class:`.Barrier` instance to a :class:`.QuantumCircuit` with the
+    :meth:`.QuantumCircuit.append` method previously there was no validation
+    that the size of the barrier matched the qargs specified.

test/python/circuit/test_circuit_operations.py

@@ -17,7 +17,7 @@
 from ddt import data, ddt
 
 from qiskit import BasicAer, ClassicalRegister, QuantumCircuit, QuantumRegister, execute
-from qiskit.circuit import Gate, Instruction, Measure, Parameter
+from qiskit.circuit import Gate, Instruction, Measure, Parameter, Barrier
 from qiskit.circuit.bit import Bit
 from qiskit.circuit.classicalregister import Clbit
 from qiskit.circuit.exceptions import CircuitError
@@ -156,6 +156,8 @@ def test_append_rejects_bad_arguments_opaque(self, bad_arg):
             qc.append(inst, bad_arg, [0, 1])
         with self.assertRaisesRegex(CircuitError, "The amount of clbit arguments"):
             qc.append(inst, [0, 1], bad_arg)
+        with self.assertRaisesRegex(CircuitError, "The amount of qubit arguments"):
+            qc.append(Barrier(4), bad_arg)
 
     def test_anding_self(self):
         """Test that qc &= qc finishes, which can be prone to infinite while-loops.