Disallow passing types as tags

cirq-core/cirq/ops/raw_types.py

@@ -787,6 +787,8 @@ class TaggedOperation(Operation):
     def __init__(self, sub_operation: 'cirq.Operation', *tags: Hashable):
         self._sub_operation = sub_operation
         self._tags = tuple(tags)
+        if any(isinstance(tag, type) for tag in tags):
+            raise ValueError('Tags cannot be types.  Did you forget to instantiate the tag type?')
 
     @property
     def sub_operation(self) -> 'cirq.Operation':

cirq-core/cirq/ops/raw_types_test.py

@@ -458,6 +458,12 @@ def test_tagged_operation():
     assert op.with_qubits(q2).qubits == (q2,)
     assert not cirq.is_measurement(op)
 
+    # Tags can't be types
+    # This is to prevent typos of cirq.X(q1).with_tags(TagType)
+    # when you meant cirq.X(q1).with_tags(TagType())
+    with pytest.raises(ValueError, match="cannot be types"):
+        _ = cirq.X(q1).with_tags(cirq.Circuit)
+
 
 def test_with_tags_returns_same_instance_if_possible():
     untagged = cirq.X(cirq.GridQubit(1, 1))

cirq-google/cirq_google/devices/google_noise_properties.py

@@ -310,6 +310,6 @@ class NoiseModelFromGoogleNoiseProperties(devices.NoiseModelFromNoiseProperties)
     """A noise model defined from noise properties of a Google device."""
 
     def is_virtual(self, op: cirq.Operation) -> bool:
-        return isinstance(op.gate, cirq.ZPowGate) and cirq_google.PhysicalZTag not in op.tags
+        return isinstance(op.gate, cirq.ZPowGate) and cirq_google.PhysicalZTag() not in op.tags
 
     # noisy_moments is implemented by the superclass.

cirq-google/cirq_google/devices/google_noise_properties_test.py

@@ -204,7 +204,7 @@ def test_with_params_opid_with_gate():
 @pytest.mark.parametrize(
     'op',
     [
-        (cirq.Z(cirq.LineQubit(0)) ** 0.3).with_tags(cirq_google.PhysicalZTag),
+        (cirq.Z(cirq.LineQubit(0)) ** 0.3).with_tags(cirq_google.PhysicalZTag()),
         cirq.PhasedXZGate(x_exponent=0.8, z_exponent=0.2, axis_phase_exponent=0.1).on(
             cirq.LineQubit(0)
         ),