Remove op validation when inserting into Circuit (quantumlib#4669)

Proposal to remove validation on op insertion methods quantumlib#4667

cirq/circuits/circuit.py

@@ -848,28 +848,6 @@ def _has_op_at(self, moment_index: int, qubits: Iterable['cirq.Qid']) -> bool:
             qubits
         )
 
-    def _validate_op_tree_qids(self, op_tree: 'cirq.OP_TREE') -> None:
-        """Raises an exception if any operation in `op_tree` has qids that don't
-        match its qid shape.
-
-        Args:
-            op_tree: The operation to validate.
-
-        Raises:
-            ValueError: The operation had qids that don't match its qid shape.
-        """
-        # Cast from Iterable[Operation, Moment] because preserve_moments is
-        # False.
-        for op in cast(Iterable['cirq.Operation'], ops.flatten_op_tree(op_tree)):
-            if protocols.qid_shape(op) != protocols.qid_shape(op.qubits):
-                raise ValueError(
-                    'Invalid operation. '
-                    'An operation has qid shape <{!r}> but is on qids with '
-                    'shape <{!r}>. The operation is <{!r}>.'.format(
-                        protocols.qid_shape(op), protocols.qid_shape(op.qubits), op
-                    )
-                )
-
     def all_qubits(self) -> FrozenSet['cirq.Qid']:
         """Returns the qubits acted upon by Operations in this circuit."""
         return frozenset(q for m in self.moments for q in m.qubits)
@@ -1705,15 +1683,13 @@ def __setitem__(self, key, value):
             if not isinstance(value, ops.Moment):
                 raise TypeError('Can only assign Moments into Circuits.')
             self._device.validate_moment(value)
-            self._validate_op_tree_qids(value)
 
         if isinstance(key, slice):
             value = list(value)
             if any(not isinstance(v, ops.Moment) for v in value):
                 raise TypeError('Can only assign Moments into Circuits.')
             for moment in value:
                 self._device.validate_moment(moment)
-                self._validate_op_tree_qids(moment)
 
         self._moments[key] = value
 
@@ -1968,7 +1944,6 @@ def insert(
                 self._device.validate_moment(cast(ops.Moment, moment_or_op))
             else:
                 self._device.validate_operation(cast(ops.Operation, moment_or_op))
-            self._validate_op_tree_qids(moment_or_op)
 
         # limit index to 0..len(self._moments), also deal with indices smaller 0
         k = max(min(index if index >= 0 else len(self._moments) + index, len(self._moments)), 0)
@@ -2012,7 +1987,6 @@ def insert_into_range(self, operations: 'cirq.OP_TREE', start: int, end: int) ->
         flat_ops = list(ops.flatten_to_ops(operations))
         for op in flat_ops:
             self._device.validate_operation(op)
-        self._validate_op_tree_qids(flat_ops)
 
         i = start
         op_index = 0
@@ -2207,7 +2181,6 @@ def batch_insert_into(self, insert_intos: Iterable[Tuple[int, 'cirq.OP_TREE']])
         for i, insertions in insert_intos:
             copy._moments[i] = copy._moments[i].with_operations(insertions)
         self._device.validate_circuit(copy)
-        self._validate_op_tree_qids(copy)
         self._moments = copy._moments
 
     def batch_insert(self, insertions: Iterable[Tuple[int, 'cirq.OP_TREE']]) -> None:

cirq/circuits/circuit_test.py

@@ -4025,37 +4025,6 @@ def test_moments_property(circuit_cls):
     assert c.moments[1] == cirq.Moment([cirq.Y(q)])
 
 
-@pytest.mark.parametrize('circuit_cls', [cirq.Circuit, cirq.FrozenCircuit])
-def test_operation_shape_validation(circuit_cls):
-    class BadOperation1(cirq.Operation):
-        def _qid_shape_(self):
-            return (1,)
-
-        @property
-        def qubits(self):
-            return cirq.LineQid.for_qid_shape((1, 2, 3))
-
-        def with_qubits(self, *qubits):
-            raise NotImplementedError
-
-    class BadOperation2(cirq.Operation):
-        def _qid_shape_(self):
-            return (1, 2, 3, 9)
-
-        @property
-        def qubits(self):
-            return cirq.LineQid.for_qid_shape((1, 2, 3))
-
-        def with_qubits(self, *qubits):
-            raise NotImplementedError
-
-    _ = circuit_cls(cirq.X(cirq.LineQid(0, 2)))  # Valid
-    with pytest.raises(ValueError, match='Invalid operation'):
-        _ = circuit_cls(BadOperation1())
-    with pytest.raises(ValueError, match='Invalid operation'):
-        _ = circuit_cls(BadOperation2())
-
-
 @pytest.mark.parametrize('circuit_cls', [cirq.Circuit, cirq.FrozenCircuit])
 def test_json_dict(circuit_cls):
     q0, q1 = cirq.LineQubit.range(2)