Serialize QubitPermutationGate. (quantumlib#5092)

Step towards fixing quantumlib#5090

Author: MichaelBroughton

cirq/json_resolver_cache.py

@@ -145,6 +145,7 @@ def _parallel_gate_op(gate, qubits):
         'QasmUGate': cirq.circuits.qasm_output.QasmUGate,
         '_QubitAsQid': raw_types._QubitAsQid,
         'QuantumFourierTransformGate': cirq.QuantumFourierTransformGate,
+        'QubitPermutationGate': cirq.QubitPermutationGate,
         'RandomGateChannel': cirq.RandomGateChannel,
         'TensoredConfusionMatrices': cirq.TensoredConfusionMatrices,
         'RepetitionsStoppingCriteria': cirq.work.RepetitionsStoppingCriteria,

cirq/ops/permutation_gate.py

@@ -96,3 +96,7 @@ def __repr__(self) -> str:
 
     def _json_dict_(self) -> Dict[str, Any]:
         return protocols.obj_to_dict_helper(self, attribute_names=['permutation'])
+
+    @classmethod
+    def _from_json_dict_(cls, permutation: Sequence[int], **kwargs):
+        return cls(permutation)

cirq/protocols/json_test_data/QubitPermutationGate.json

@@ -0,0 +1,12 @@
+{
+  "cirq_type": "QubitPermutationGate",
+  "permutation": [
+    0,
+    5,
+    2,
+    1,
+    6,
+    3,
+    4
+  ]
+}

cirq/protocols/json_test_data/QubitPermutationGate.repr

@@ -0,0 +1 @@
+cirq.QubitPermutationGate([0, 5, 2, 1, 6, 3, 4])

cirq/protocols/json_test_data/spec.py

@@ -59,7 +59,6 @@
         'QasmOutput',
         'QuantumState',
         'QubitOrder',
-        'QubitPermutationGate',
         'QuilFormatter',
         'QuilOutput',
         'SimulationTrialResult',