Legacy _t_complexity_ still supported via getattr

qualtran/cirq_interop/t_complexity_protocol.py

@@ -19,6 +19,7 @@
 
 from qualtran import Bloq
 from qualtran.symbolics import ceil, log2, SymbolicFloat, SymbolicInt
+
 from .decompose_protocol import _decompose_once_considering_known_decomposition
 
 _T_GATESET = cirq.Gateset(cirq.T, cirq.T**-1, unroll_circuit_op=False)

qualtran/cirq_interop/t_complexity_protocol_test.py

@@ -11,7 +11,6 @@
 #  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
-from typing import TYPE_CHECKING
 
 import cirq
 import pytest
@@ -30,9 +29,6 @@
 from qualtran.cirq_interop.testing import GateHelper
 from qualtran.testing import execute_notebook
 
-if TYPE_CHECKING:
-    pass
-
 
 class DoesNotSupportTComplexity: ...
 
@@ -66,6 +62,11 @@ def signature(self) -> 'Signature':
         return Signature.build(q=1)
 
 
+def test_legacy_t_complexity_annotation():
+    # Test the deprecated `getattr(.., '_t_complexity_')
+    assert SupportsTComplexityGateWithRegisters().t_complexity() == TComplexity(t=1, clifford=2)
+
+
 def test_t_complexity_for_bloq_does_not_support():
     with pytest.raises(DecomposeNotImplementedError):
         _ = t_complexity(DoesNotSupportTComplexityBloq())

qualtran/resource_counting/_bloq_counts.py

@@ -12,6 +12,7 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 import logging
+import warnings
 from collections import defaultdict
 from typing import Callable, cast, Dict, Sequence, Tuple, TYPE_CHECKING
 
@@ -295,6 +296,21 @@ def compute(self, bloq: 'Bloq', get_callee_cost: Callable[['Bloq'], GateCounts])
         from qualtran.bloqs.bookkeeping._bookkeeping_bloq import _BookkeepingBloq
         from qualtran.bloqs.mcmt import And, MultiTargetCNOT
 
+        if self.legacy_shims:
+            if hasattr(bloq, '_t_complexity_'):
+                legacy_val = bloq._t_complexity_()
+            else:
+                legacy_val = NotImplemented
+            if legacy_val is not NotImplemented:
+                warnings.warn(
+                    "Please migrate explicit cost annotations to the general "
+                    "`Bloq.my_static_costs` method override.",
+                    DeprecationWarning,
+                )
+                return GateCounts(
+                    t=legacy_val.t, clifford=legacy_val.clifford, rotation=legacy_val.rotations
+                )
+
         # T gates
         if bloq_is_t_like(bloq):
             return GateCounts(t=1)