Unitary synthesis bug fix (Qiskit#15286)

Author: alexanderivrii

qiskit/transpiler/passes/synthesis/unitary_synthesis.py

@@ -143,6 +143,7 @@ def __init__(
         self._target = target if target is not None and len(target.operation_names) > 0 else None
         if target is not None:
             self._coupling_map = target.build_coupling_map()
+            self._basis_gates = set(target.operation_names)
         if synth_gates:
             self._synth_gates = synth_gates
         else:

releasenotes/notes/fix-target-overrides-basis-7802f9918933e12d.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fixed a bug in :class:`.UnitarySynthesis` transpiler pass, when it is called
+    with a non-default synthesis plugin (specified via ``method``) that supports
+    ``basis_gates`` but not ``target``. The pass now correctly passes the basis
+    gates from the ``target`` to the plugin.

test/python/transpiler/test_unitary_synthesis_plugin.py

@@ -23,7 +23,7 @@
 
 from qiskit.circuit import QuantumCircuit
 from qiskit.converters import circuit_to_dag
-from qiskit.transpiler import PassManager
+from qiskit.transpiler import PassManager, Target, CouplingMap
 from qiskit.transpiler.passes import UnitarySynthesis
 from qiskit.transpiler.passes.synthesis.plugin import (
     UnitarySynthesisPlugin,
@@ -304,6 +304,40 @@ def test_config_not_passed_to_default_on_fallback(self):
         self.MOCK_PLUGINS["_controllable"].run.assert_not_called()
         self.assertNotIn("config", call_kwargs)
 
+    def test_target_overrides_basis_gates(self):
+        """Test that when both target and basis gates are specified, but the plugin only supports
+        basis gates, the basis gates that it gets come from the target."""
+
+        self.MOCK_PLUGINS["_controllable"].support(["basis_gates"])
+
+        qc = QuantumCircuit(2)
+        qc.unitary(np.eye(4, dtype=np.complex128), [0, 1])
+
+        target_basis_gates = ["rx", "rz"]
+        standalone_basis_gates = ["cx", "u"]
+        target = Target.from_configuration(
+            num_qubits=2, basis_gates=target_basis_gates, coupling_map=CouplingMap.from_line(2)
+        )
+        pm = PassManager(
+            [
+                UnitarySynthesis(
+                    target=target, basis_gates=standalone_basis_gates, method="_controllable"
+                )
+            ]
+        )
+
+        with self.mock_default_run_method():
+            pm.run(qc)
+            self.DEFAULT_PLUGIN.run.assert_not_called()  # pylint: disable=no-member
+            self.MOCK_PLUGINS["_controllable"].run.assert_called()  # pylint: disable=no-member
+            call_kwargs = self.MOCK_PLUGINS["_controllable"].run.call_args[
+                1
+            ]  # pylint: disable=no-member
+
+        self.assertIn("basis_gates", call_kwargs)
+        self.assertEqual(call_kwargs["basis_gates"], set(target_basis_gates))
+        self.assertNotEqual(call_kwargs["basis_gates"], set(standalone_basis_gates))
+
 
 if __name__ == "__main__":
     unittest.main()