Circuits with control flow now raise a proper error when circuit_to_instruction is called (Qiskit#13921)

* Circuits with control flow now raise a proper error when circuit_to_instruction is called

* test

* cyclic import

* Update qiskit/converters/circuit_to_instruction.py

Co-authored-by: Elena Peña Tapia <[email protected]>

---------

Co-authored-by: Elena Peña Tapia <[email protected]>

Author: 1ucian0

qiskit/converters/circuit_to_instruction.py

@@ -11,6 +11,7 @@
 # that they have been altered from the originals.
 
 """Helper function for converting a circuit to an instruction."""
+from qiskit.circuit.controlflow.control_flow import ControlFlowOp
 from qiskit.exceptions import QiskitError
 from qiskit.circuit.instruction import Instruction
 from qiskit.circuit.quantumregister import QuantumRegister
@@ -84,6 +85,13 @@ def circuit_to_instruction(circuit, parameter_map=None, equivalence_library=None
             " You may be able to use `QuantumCircuit.compose` to inline this circuit into another."
         )
 
+    for inst in circuit.data:
+        if isinstance(inst.operation, ControlFlowOp):
+            raise QiskitError(
+                f"Circuits with control flow operations ({type(inst.operation)}) "
+                "cannot be converted to an instruction."
+            )
+
     if parameter_map is None:
         parameter_dict = {p: p for p in circuit.parameters}
     else:

releasenotes/notes/fixes_11379-4c4d6d71213a1c8c.yaml

@@ -0,0 +1,5 @@
+---
+upgrade_circuits:
+  - |
+    Converting a quantum circuit to a gate with :func:`.converters.circuit_to_instruction` fails properly when given
+    circuit contains control flow instructions.

test/python/converters/test_circuit_to_instruction.py

@@ -143,6 +143,17 @@ def test_underspecified_parameter_map_raises(self):
             QiskitError, circuit_to_instruction, qc, {theta: gamma, phi: phi, delta: delta}
         )
 
+    def test_control_flow_raises(self):
+        """Raising if a circuit to convert has control flow.
+        See https://github.com/Qiskit/qiskit/issues/11379"""
+        qc = QuantumCircuit(2)
+        qc.h(0)
+        qc.cx(0, 1)
+        qc.measure_all()
+        with qc.if_test((qc.clbits[0], 0)):
+            qc.x(0)
+        self.assertRaises(QiskitError, circuit_to_instruction, qc)
+
     def test_parameter_map(self):
         """Verify alternate parameter specification"""
         qr = QuantumRegister(3, "qr")