From c15366469390048c1fe0e56d026f8309ce656165 Mon Sep 17 00:00:00 2001
From: MichaelBroughton <MichaelBroughton@users.noreply.github.com>
Date: Wed, 16 Mar 2022 20:50:07 -0700
Subject: [PATCH] Serialize QubitPermutationGate. (#5092)

Step towards fixing #5090
---
 cirq-core/cirq/json_resolver_cache.py                |  1 +
 cirq-core/cirq/ops/permutation_gate.py               |  4 ++++
 .../json_test_data/QubitPermutationGate.json         | 12 ++++++++++++
 .../json_test_data/QubitPermutationGate.repr         |  1 +
 cirq-core/cirq/protocols/json_test_data/spec.py      |  1 -
 5 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.json
 create mode 100644 cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.repr

diff --git a/cirq-core/cirq/json_resolver_cache.py b/cirq-core/cirq/json_resolver_cache.py
index f15252c3256..ca7d2065e26 100644
--- a/cirq-core/cirq/json_resolver_cache.py
+++ b/cirq-core/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,
diff --git a/cirq-core/cirq/ops/permutation_gate.py b/cirq-core/cirq/ops/permutation_gate.py
index e3fb9bfff02..188e82f4da2 100644
--- a/cirq-core/cirq/ops/permutation_gate.py
+++ b/cirq-core/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)
diff --git a/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.json b/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.json
new file mode 100644
index 00000000000..1b84ad232c1
--- /dev/null
+++ b/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.json
@@ -0,0 +1,12 @@
+{
+  "cirq_type": "QubitPermutationGate",
+  "permutation": [
+    0,
+    5,
+    2,
+    1,
+    6,
+    3,
+    4
+  ]
+}
diff --git a/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.repr b/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.repr
new file mode 100644
index 00000000000..f31702b5713
--- /dev/null
+++ b/cirq-core/cirq/protocols/json_test_data/QubitPermutationGate.repr
@@ -0,0 +1 @@
+cirq.QubitPermutationGate([0, 5, 2, 1, 6, 3, 4])
diff --git a/cirq-core/cirq/protocols/json_test_data/spec.py b/cirq-core/cirq/protocols/json_test_data/spec.py
index f23a193d5ac..57374985c77 100644
--- a/cirq-core/cirq/protocols/json_test_data/spec.py
+++ b/cirq-core/cirq/protocols/json_test_data/spec.py
@@ -59,7 +59,6 @@
         'QasmOutput',
         'QuantumState',
         'QubitOrder',
-        'QubitPermutationGate',
         'QuilFormatter',
         'QuilOutput',
         'SimulationTrialResult',