Fix transpile() with a Target containing an ideal Measure

qiskit/transpiler/target.py

@@ -1043,24 +1043,25 @@ def target_to_backend_properties(target: Target):
                     continue
                 qubit = qargs[0]
                 props_list = []
-                if props.error is not None:
-                    props_list.append(
-                        {
-                            "date": datetime.datetime.utcnow(),
-                            "name": "readout_error",
-                            "unit": "",
-                            "value": props.error,
-                        }
-                    )
-                if props.duration is not None:
-                    props_list.append(
-                        {
-                            "date": datetime.datetime.utcnow(),
-                            "name": "readout_length",
-                            "unit": "s",
-                            "value": props.duration,
-                        }
-                    )
+                if props is not None:
+                    if props.error is not None:
+                        props_list.append(
+                            {
+                                "date": datetime.datetime.utcnow(),
+                                "name": "readout_error",
+                                "unit": "",
+                                "value": props.error,
+                            }
+                        )
+                    if props.duration is not None:
+                        props_list.append(
+                            {
+                                "date": datetime.datetime.utcnow(),
+                                "name": "readout_length",
+                                "unit": "s",
+                                "value": props.duration,
+                            }
+                        )
                 if not props_list:
                     qubit_props = {}
                     break

releasenotes/notes/fix-transpile-ideal-measurement-c37e04533e196ded.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Fixed an issue with :func:`~.transpile` when targeting a :class:`~.Target`
+    (either directly via the ``target`` argument or via a
+    :class:`~.BackendV2` instance from the ``backend`` argument) that
+    contained an ideal :class:`~.Measure` instruction (one that does not have
+    any properties defined). Previously this would raise an exception
+    trying to parse the target.
+    Fixed `#8969 <https://github.com/Qiskit/qiskit-terra/issues/8969>`__

test/python/compiler/test_transpiler.py

@@ -1726,6 +1726,19 @@ def test_qasm3_output_control_flow(self, optimization_level):
         # itself doesn't throw an error, though.
         self.assertIsInstance(qasm3.dumps(transpiled).strip(), str)
 
+    @data(0, 1, 2, 3)
+    def test_transpile_target_no_measurement_error(self, opt_level):
+        """Test that transpile with a target which contains ideal measurement works
+
+        Reproduce from https://github.com/Qiskit/qiskit-terra/issues/8969
+        """
+        target = Target()
+        target.add_instruction(Measure(), {(0,): None})
+        qc = QuantumCircuit(1, 1)
+        qc.measure(0, 0)
+        res = transpile(qc, target=target, optimization_level=opt_level)
+        self.assertEqual(qc, res)
+
 
 class StreamHandlerRaiseException(StreamHandler):
     """Handler class that will raise an exception on formatting errors."""