Deprecate device.decompose_operation in cirq-core. (quantumlib#4922)

Yet another deprecation for quantumlib#4744 . Vendor deprecations of this fxn to follow.

cirq-core/cirq/circuits/circuit.py

@@ -1717,7 +1717,8 @@ def __init__(
         """
         self._moments: List['cirq.Moment'] = []
         self._device = device
-        self.append(contents, strategy=strategy)
+        with _compat.block_overlapping_deprecation('.*'):
+            self.append(contents, strategy=strategy)
 
     @property  # type: ignore
     @_compat.deprecated(
@@ -2045,15 +2046,32 @@ def insert(
         Raises:
             ValueError: Bad insertion strategy.
         """
-        moments_and_operations = list(
-            ops.flatten_to_ops_or_moments(
-                ops.transform_op_tree(
-                    moment_or_operation_tree,
-                    self._device.decompose_operation,
-                    preserve_moments=True,
-                ),
+        if self._device == devices.UNCONSTRAINED_DEVICE:
+            moments_and_operations = list(
+                ops.flatten_to_ops_or_moments(
+                    ops.transform_op_tree(
+                        moment_or_operation_tree,
+                        preserve_moments=True,
+                    ),
+                )
             )
-        )
+        else:
+            _compat._warn_or_error(
+                'circuit.insert behavior relies on circuit.device.\n'
+                'The ability to construct a circuit with a device\n'
+                'will be removed in cirq v0.15. please update this use of\n'
+                'insert.'
+            )
+            with _compat.block_overlapping_deprecation('decompose'):
+                moments_and_operations = list(
+                    ops.flatten_to_ops_or_moments(
+                        ops.transform_op_tree(
+                            moment_or_operation_tree,
+                            self._device.decompose_operation,
+                            preserve_moments=True,
+                        ),
+                    )
+                )
 
         for moment_or_op in moments_and_operations:
             if isinstance(moment_or_op, ops.Moment):
@@ -2114,13 +2132,14 @@ def insert_into_range(self, operations: 'cirq.OP_TREE', start: int, end: int) ->
             )
             cannot_add_lambda = lambda a, b: not self._device.can_add_operation_into_moment(a, b)
 
-        with _compat.block_overlapping_deprecation('can_add_operation_into_moment'):
+        with _compat.block_overlapping_deprecation('(can_add_operation_into_moment|insert)'):
             while op_index < len(flat_ops):
                 op = flat_ops[op_index]
                 while i < end and cannot_add_lambda(op, self._moments[i]):
                     i += 1
                 if i >= end:
                     break
+
                 self._moments[i] = self._moments[i].with_operation(op)
                 op_index += 1
 

cirq-core/cirq/circuits/circuit_test.py

@@ -107,10 +107,12 @@ def test_insert_moment_types_deprecated():
         circuit = cirq.Circuit(device=moment_and_op_type_validating_device)
 
     moment_or_operation_tree = [cirq.X(x), cirq.Moment([cirq.Y(x)])]
-    circuit.insert(0, moment_or_operation_tree)
+    with cirq.testing.assert_deprecated('insert', deadline='v0.15'):
+        circuit.insert(0, moment_or_operation_tree)
 
     moment_or_operation_tree = [[cirq.Moment([cirq.X(x)])]]
-    circuit.insert(0, moment_or_operation_tree)
+    with cirq.testing.assert_deprecated('insert', deadline='v0.15'):
+        circuit.insert(0, moment_or_operation_tree)
 
 
 def test_setitem():

cirq-core/cirq/devices/device.py

@@ -100,6 +100,10 @@ def qid_pairs(self) -> Optional[FrozenSet['cirq.SymmetricalQidPair']]:
                 )
             return frozenset([SymmetricalQidPair(q, q2) for q in qs for q2 in qs if q < q2])
 
+    @_compat.deprecated(
+        deadline='v0.15',
+        fix='Devices will no longer decompose operations.',
+    )
     def decompose_operation(self, operation: 'cirq.Operation') -> 'cirq.OP_TREE':
         """Returns a device-valid decomposition for the given operation.
 

cirq-core/cirq/devices/device_test.py

@@ -53,6 +53,16 @@ def __init__(self, qubits):
         assert len(QubitFieldDevice([cirq.NamedQubit(str(s)) for s in range(10)]).qid_pairs()) == 45
 
 
+def test_decompose_operation_deprecated():
+    q0 = cirq.GridQubit(0, 0)
+
+    class RawDevice(cirq.Device):
+        pass
+
+    with cirq.testing.assert_deprecated('decompose', deadline='v0.15'):
+        RawDevice().decompose_operation(cirq.H(q0))
+
+
 def test_qid_pair_deprecated():
     q0, q1, q2, q3 = cirq.LineQubit.range(4)
     with cirq.testing.assert_deprecated('device.metadata', deadline='v0.15', count=3):

cirq-pasqal/cirq_pasqal/pasqal_device_test.py

@@ -191,7 +191,7 @@ def test_validate_operation_errors_deprecated():
     with pytest.raises(
         NotImplementedError, match="Measurements on Pasqal devices don't support invert_mask."
     ):
-        with cirq.testing.assert_deprecated('decompose', deadline='v0.15'):
+        with cirq.testing.assert_deprecated('insert', deadline='v0.15'):
             circuit.append(cirq.measure(*d.qubits, invert_mask=(True, False, False)))