Deprecate qubit_set in cirq-core/devices (#4965)

This deprecates qubit_set on `UnconstrainedDevice`, `Device` and `HyperGraphDevice` in contrib. Note that device already has metadata. UnconstrainedDevice probably shouldn't have a metadata and to add Metadata for HyperGraphDevice, might take a non-trivial amount of work. Maybe we open an issue for this ?

xref: #4744 .

cirq-core/cirq/contrib/graph_device/graph_device.py

@@ -155,6 +155,7 @@ def __init__(
     def qubits(self) -> Tuple['cirq.Qid', ...]:
         return cast(Tuple['cirq.Qid', ...], tuple(sorted(self.device_graph.vertices)))
 
+    @_compat.deprecated(fix='Please use UndirectedGraphDevice.qubits', deadline='v0.15')
     def qubit_set(self) -> FrozenSet['cirq.Qid']:
         return frozenset(self.qubits)
 

cirq-core/cirq/contrib/graph_device/graph_device_test.py

@@ -175,11 +175,12 @@ def test_graph_device_copy_and_add():
     assert device_copy == device_sum
 
 
-def test_qubit_set():
+def test_qubit_set_deprecated():
     a, b, c, d = cirq.LineQubit.range(4)
     device_graph = ccgd.UndirectedHypergraph(labelled_edges={(a, b): None, (c, d): None})
     device = ccgd.UndirectedGraphDevice(device_graph=device_graph)
-    assert device.qubit_set() == {a, b, c, d}
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert device.qubit_set() == {a, b, c, d}
 
 
 def test_qid_pairs_deprecated():

cirq-core/cirq/devices/device.py

@@ -34,6 +34,7 @@
 class Device(metaclass=abc.ABCMeta):
     """Hardware constraints for validating circuits."""
 
+    @_compat.deprecated(fix='Use metadata.qubit_set if applicable.', deadline='v0.15')
     def qubit_set(self) -> Optional[AbstractSet['cirq.Qid']]:
         """Returns a set or frozenset of qubits on the device, if possible.
 
@@ -77,7 +78,7 @@ def qid_pairs(self) -> Optional[FrozenSet['cirq.SymmetricalQidPair']]:
             `cirq.UnconstrainedDevice` has this property), then `None` is
             returned.
         """
-        with _compat.block_overlapping_deprecation('device\\.metadata'):
+        with _compat.block_overlapping_deprecation('(device\\.metadata|qubit_set)'):
             qs = self.qubit_set()
             if qs is None:
                 return None

cirq-core/cirq/devices/device_test.py

@@ -4,35 +4,40 @@
 import cirq
 
 
-def test_qubit_set():
+def test_qubit_set_deprecated():
     class RawDevice(cirq.Device):
         pass
 
-    assert RawDevice().qubit_set() is None
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert RawDevice().qubit_set() is None
 
     class QubitFieldDevice(cirq.Device):
         def __init__(self):
             self.qubits = cirq.LineQubit.range(3)
 
-    assert QubitFieldDevice().qubit_set() == frozenset(cirq.LineQubit.range(3))
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert QubitFieldDevice().qubit_set() == frozenset(cirq.LineQubit.range(3))
 
     class PrivateQubitFieldDevice(cirq.Device):
         def __init__(self):
             self._qubits = cirq.LineQubit.range(4)
 
-    assert PrivateQubitFieldDevice().qubit_set() == frozenset(cirq.LineQubit.range(4))
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert PrivateQubitFieldDevice().qubit_set() == frozenset(cirq.LineQubit.range(4))
 
     class QubitMethodDevice(cirq.Device):
         def qubits(self):
             return cirq.LineQubit.range(5)
 
-    assert QubitMethodDevice().qubit_set() == frozenset(cirq.LineQubit.range(5))
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert QubitMethodDevice().qubit_set() == frozenset(cirq.LineQubit.range(5))
 
     class PrivateQubitMethodDevice(cirq.Device):
         def _qubits(self):
             return cirq.LineQubit.range(6)
 
-    assert PrivateQubitMethodDevice().qubit_set() == frozenset(cirq.LineQubit.range(6))
+    with cirq.testing.assert_deprecated('qubit_set', deadline='v0.15'):
+        assert PrivateQubitMethodDevice().qubit_set() == frozenset(cirq.LineQubit.range(6))
 
 
 def test_qid_pairs():

cirq-core/cirq/devices/unconstrained_device.py

@@ -14,7 +14,7 @@
 
 from typing import Any, Dict, TYPE_CHECKING
 
-from cirq import value, protocols
+from cirq import _compat, value, protocols
 from cirq._doc import document
 from cirq.devices import device
 
@@ -26,6 +26,7 @@
 class _UnconstrainedDevice(device.Device):
     """A device that allows everything, infinitely fast."""
 
+    @_compat.deprecated(fix='qubit_set on UnconstrainedDevice is always None.', deadline='v0.15')
     def qubit_set(self) -> None:
         return None
 

cirq-core/cirq/devices/unconstrained_device_test.py

@@ -25,5 +25,6 @@ def test_infinitely_fast():
     )
 
 
-def test_qubit_set():
-    assert cirq.UNCONSTRAINED_DEVICE.qubit_set() is None
+def test_qubit_set_deprecated():
+    with cirq.testing.assert_deprecated('None', deadline='v0.15'):
+        assert cirq.UNCONSTRAINED_DEVICE.qubit_set() is None