Partial support of reset gate in cirq_google protos (#7095)

* Remove arg_function_language

- We have no need for this parameter and it is pretty much
always set to the most permissive parameter.
- Removes this parameter to simplify serialization.

* Fix some typecheck stuff.

* Fix test

* Address comments.

* Partial support of reset gate in cirq_google protos

- This change adds reset gate to the list of gates and adds
a default deserialization to cirq.ResetChannel.
- Other internal hardware reset mechanisms are not yet supported,
and will be added later using custom deserializers.

* Address comments.

Author: dstrain115

cirq-google/cirq_google/api/v2/program.proto

@@ -246,6 +246,7 @@ message Operation {
     IdentityGate identitygate = 19;
     HPowGate hpowgate = 20;
     SingleQubitCliffordGate singlequbitcliffordgate = 21;
+    ResetGate resetgate = 24;
   }
 
   // Map from the argument name to the Argument needed to fully specify
@@ -617,3 +618,14 @@ message IdentityGate {
 message HPowGate {
   FloatArg exponent = 1;
 }
+
+message ResetGate {
+    // Type of reset to be executed (hardware dependent)
+    // Internal users should use the name of the class.
+    // (Note that this is not used for public-facing circuits,
+    //  which will default to cirq.ResetChannel)
+    string reset_type = 1;
+
+    // Additional arguments that can be sent to the reset implementation.
+    map<string, Arg> arguments = 2;
+}

cirq-google/cirq_google/api/v2/program_pb2.py

@@ -237,6 +237,8 @@ def _serialize_gate_op(
             arg_func_langs.float_arg_to_proto(
                 gate.duration.total_nanos(), out=msg.waitgate.duration_nanos
             )
+        elif isinstance(gate, cirq.ResetChannel):
+            arg_func_langs.arg_to_proto(gate.dimension, out=msg.resetgate.arguments['dimension'])
         elif isinstance(gate, CouplerPulse):
             arg_func_langs.float_arg_to_proto(
                 gate.hold_time.total_picos(), out=msg.couplerpulsegate.hold_time_ps
@@ -648,6 +650,14 @@ def _deserialize_gate_op(
                 operation_proto.waitgate.duration_nanos, required_arg_name=None
             )
             op = cirq.WaitGate(duration=cirq.Duration(nanos=total_nanos or 0.0))(*qubits)
+        elif which_gate_type == 'resetgate':
+            dimensions = arg_func_langs.arg_from_proto(
+                operation_proto.resetgate.arguments.get('dimension', 2)
+            )
+            if not isinstance(dimensions, int):
+                # This should always be int, if serialized from cirq.
+                raise ValueError(f"dimensions {dimensions} for ResetChannel must be an integer!")
+            op = cirq.ResetChannel(dimension=dimensions)(*qubits)
         elif which_gate_type == 'internalgate':
             op = arg_func_langs.internal_gate_from_proto(operation_proto.internalgate)(*qubits)
         elif which_gate_type == 'couplerpulsegate':

cirq-google/cirq_google/api/v2/program_pb2.pyi

@@ -263,6 +263,15 @@ def circuit_proto(json: Dict, qubits: List[str]):
             {'waitgate': {'duration_nanos': {'float_value': 15}}, 'qubit_constant_index': [0]}
         ),
     ),
+    (
+        cirq.R(Q0),
+        op_proto(
+            {
+                'resetgate': {'arguments': {'dimension': {'arg_value': {'float_value': 2}}}},
+                'qubit_constant_index': [0],
+            }
+        ),
+    ),
     (
         cirq.MeasurementGate(num_qubits=2, key='iron', invert_mask=(True, False))(Q0, Q1),
         op_proto(
@@ -1006,3 +1015,22 @@ def test_custom_serializer(use_constants_table: bool):
     assert isinstance(op.gate, BingBongGate)
     assert op.gate.param == 2.5
     assert op.qubits == (cirq.q(0, 0),)
+
+
+def test_reset_gate_with_improper_argument():
+    serializer = cg.CircuitSerializer()
+
+    op = v2.program_pb2.Operation()
+    op.resetgate.arguments['dimension'].arg_value.float_value = 2.5
+    op.qubit_constant_index.append(0)
+    circuit_proto = v2.program_pb2.Program(
+        language=v2.program_pb2.Language(arg_function_language='exp', gate_set=_SERIALIZER_NAME),
+        circuit=v2.program_pb2.Circuit(
+            scheduling_strategy=v2.program_pb2.Circuit.MOMENT_BY_MOMENT,
+            moments=[v2.program_pb2.Moment(operations=[op])],
+        ),
+        constants=[v2.program_pb2.Constant(qubit=v2.program_pb2.Qubit(id='1_2'))],
+    )
+
+    with pytest.raises(ValueError, match="must be an integer"):
+        serializer.deserialize(circuit_proto)