From 49f39e3a6c35922fc7cedf944936df902a1425dc Mon Sep 17 00:00:00 2001
From: Matthew Treinish <mtreinish@kortar.org>
Date: Mon, 2 May 2022 11:12:32 -0400
Subject: [PATCH] Fix instruction durations in transpile() with BackendV2
 (#8001)

* Fix instruction durations in transpile() with BackendV2

When running transpile() with BackendV2 based backends the instruction
durations property from the backend would not be processed correctly
resulting in the absence of the default durations for instructions
supported on the target backend. This commit fixes this by correctly
handling BackendV2 based backends and using those instruction durations
by default for transpile().

* Update test/python/compiler/test_transpiler.py

Co-authored-by: Kevin Hartman <kevin@hart.mn>

Co-authored-by: Kevin Hartman <kevin@hart.mn>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
---
 qiskit/compiler/transpiler.py                      | 14 +++++++++-----
 ...spile-backendv2-durations-dbc85688564cc271.yaml |  8 ++++++++
 test/python/compiler/test_transpiler.py            | 14 +++++++++++++-
 3 files changed, 30 insertions(+), 6 deletions(-)
 create mode 100644 releasenotes/notes/fix-transpile-backendv2-durations-dbc85688564cc271.yaml

diff --git a/qiskit/compiler/transpiler.py b/qiskit/compiler/transpiler.py
index 4b7b0bbf0869..6eb851910ddd 100644
--- a/qiskit/compiler/transpiler.py
+++ b/qiskit/compiler/transpiler.py
@@ -921,11 +921,15 @@ def _parse_instruction_durations(backend, inst_durations, dt, circuits):
     take precedence over backend durations, but be superceded by ``inst_duration``s.
     """
     if not inst_durations:
-        backend_durations = InstructionDurations()
-        try:
-            backend_durations = InstructionDurations.from_backend(backend)
-        except AttributeError:
-            pass
+        backend_version = getattr(backend, "version", 0)
+        if backend_version <= 1:
+            backend_durations = InstructionDurations()
+            try:
+                backend_durations = InstructionDurations.from_backend(backend)
+            except AttributeError:
+                pass
+        else:
+            backend_durations = backend.instruction_durations
 
     durations = []
     for circ in circuits:
diff --git a/releasenotes/notes/fix-transpile-backendv2-durations-dbc85688564cc271.yaml b/releasenotes/notes/fix-transpile-backendv2-durations-dbc85688564cc271.yaml
new file mode 100644
index 000000000000..00e7886468ba
--- /dev/null
+++ b/releasenotes/notes/fix-transpile-backendv2-durations-dbc85688564cc271.yaml
@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixed an issue with the :func:`~.transpile` function when run with a
+    :class:`~.BackendV2` based backend and setting the ``scheduling_method``
+    keyword argument. Previously, the function would not correctly process
+    the default durations of the instructions supported by the backend which
+    would lead to an error.
diff --git a/test/python/compiler/test_transpiler.py b/test/python/compiler/test_transpiler.py
index 3a6de35f49a7..83fa89503027 100644
--- a/test/python/compiler/test_transpiler.py
+++ b/test/python/compiler/test_transpiler.py
@@ -35,7 +35,7 @@
 from qiskit.circuit.library import CXGate, U3Gate, U2Gate, U1Gate, RXGate, RYGate, RZGate, UGate
 from qiskit.circuit.measure import Measure
 from qiskit.test import QiskitTestCase
-from qiskit.test.mock import FakeMelbourne, FakeRueschlikon, FakeAlmaden
+from qiskit.test.mock import FakeMelbourne, FakeRueschlikon, FakeAlmaden, FakeMumbaiV2
 from qiskit.transpiler import Layout, CouplingMap
 from qiskit.transpiler import PassManager
 from qiskit.transpiler.target import Target
@@ -1242,6 +1242,18 @@ def test_delay_converts_to_dt(self):
         out = transpile(qc, dt=1e-9)
         self.assertEqual(out.data[0][0].unit, "dt")
 
+    def test_scheduling_backend_v2(self):
+        """Test that scheduling method works with Backendv2."""
+        qc = QuantumCircuit(2)
+        qc.h(0)
+        qc.cx(0, 1)
+        qc.measure_all()
+
+        backend = FakeMumbaiV2()
+        out = transpile([qc, qc], backend, scheduling_method="alap")
+        self.assertIn("delay", out[0].count_ops())
+        self.assertIn("delay", out[1].count_ops())
+
     @data(1, 2, 3)
     def test_no_infinite_loop(self, optimization_level):
         """Verify circuit cost always descends and optimization does not flip flop indefinitely."""