Warn when wrapping a bloq

Author: mpharrigan

qualtran/cirq_interop/_cirq_to_bloq.py

@@ -16,6 +16,7 @@
 import abc
 import itertools
 import numbers
+import warnings
 from functools import cached_property
 from typing import Any, Dict, List, Optional, Sequence, Tuple, TYPE_CHECKING, TypeVar, Union
 
@@ -32,6 +33,7 @@
     CtrlSpec,
     DecomposeNotImplementedError,
     DecomposeTypeError,
+    GateWithRegisters,
     QAny,
     QBit,
     QDType,
@@ -151,6 +153,14 @@ class CirqGateAsBloq(CirqGateAsBloqBase):
 
     gate: cirq.Gate
 
+    def __attrs_post_init__(self):
+        if isinstance(self.gate, GateWithRegisters):
+            warnings.warn(
+                f"Tried to use `CirqGateAsBloq` to adapt a `qualtran.GateWithRegisters`, "
+                f"which already satisfies the Bloq API. Consider using {self.gate} "
+                f"directly (without the adapter)."
+            )
+
     @property
     def cirq_gate(self) -> cirq.Gate:
         return self.gate

qualtran/cirq_interop/_cirq_to_bloq_test.py

@@ -88,7 +88,9 @@ def test_cirq_gate_as_bloq_tensor_contract_for_and_gate():
     ctrl = [bb.add(OneState()) for _ in range(2)]
     target = bb.add(ZeroState())
     q = [*ctrl, target]
-    c0, c1, target = bb.add(CirqGateAsBloq(and_gate), q=q)
+    with pytest.warns(UserWarning):
+        # It's odd to use CirqGateAsBloq to wrap a GateWithRegisters, which is already a bloq.
+        c0, c1, target = bb.add(CirqGateAsBloq(and_gate), q=q)
     cbloq = bb.finalize(ctrl=np.array([c0, c1]), target=target)
     state_vector = cbloq.tensor_contract()
     assert np.isclose(state_vector[7], 1)