Bugfixes in handling nested tags_to_ignore + deep=True in cirq.map_moments and cirq.map_operations transformer primitives (#5109)

- Fixes a few more bugs in the handling of deep=True flag and nested operations to ignore using `tags_to_ignore` in `cirq.map_operations` and `cirq.map_moments` transformer primitives. Also added more tests. 
- Step towards fixing #5039

Author: tanujkhattar

cirq-core/cirq/transformers/transformer_primitives.py

@@ -87,7 +87,9 @@ def map_moments(
                 continue
             op_untagged = cast(circuits.CircuitOperation, op.untagged)
             mapped_op = op_untagged.replace(
-                circuit=map_moments(op_untagged.circuit, map_func, deep=deep)
+                circuit=map_moments(
+                    op_untagged.circuit, map_func, tags_to_ignore=tags_to_ignore, deep=deep
+                )
             ).with_tags(*op.tags)
             batch_replace.append((i, op, mapped_op))
         mutable_circuit = circuit.unfreeze(copy=True)
@@ -149,7 +151,10 @@ def apply_map(op: ops.Operation, idx: int) -> ops.OP_TREE:
         return circuit_op
 
     return map_moments(
-        circuit, lambda m, i: [circuits.Moment(apply_map(op, i) for op in m.operations)], deep=deep
+        circuit,
+        lambda m, i: [circuits.Moment(apply_map(op, i) for op in m.operations)],
+        deep=deep,
+        tags_to_ignore=tags_to_ignore,
     )
 
 

cirq-core/cirq/transformers/transformer_primitives_test.py

@@ -213,6 +213,47 @@ def map_func(op: cirq.Operation, _: int) -> cirq.OP_TREE:
 # pylint: enable=line-too-long
 
 
+def test_map_operations_deep_respects_tags_to_ignore():
+    q = cirq.LineQubit.range(2)
+    c_nested = cirq.FrozenCircuit(cirq.CX(*q), cirq.CX(*q).with_tags("ignore"), cirq.CX(*q))
+    c_nested_mapped = cirq.FrozenCircuit(cirq.CZ(*q), cirq.CX(*q).with_tags("ignore"), cirq.CZ(*q))
+    c_orig = cirq.Circuit(
+        c_nested,
+        cirq.CircuitOperation(c_nested).repeat(4).with_tags("ignore"),
+        c_nested,
+        cirq.CircuitOperation(
+            cirq.FrozenCircuit(
+                cirq.CircuitOperation(c_nested).repeat(5).with_tags("preserve_tag"),
+                cirq.CircuitOperation(c_nested).repeat(6).with_tags("ignore"),
+                cirq.CircuitOperation(c_nested).repeat(7),
+            )
+        ),
+        c_nested,
+    )
+    c_expected = cirq.Circuit(
+        c_nested_mapped,
+        cirq.CircuitOperation(c_nested).repeat(4).with_tags("ignore"),
+        c_nested_mapped,
+        cirq.CircuitOperation(
+            cirq.FrozenCircuit(
+                cirq.CircuitOperation(c_nested_mapped).repeat(5).with_tags("preserve_tag"),
+                cirq.CircuitOperation(c_nested).repeat(6).with_tags("ignore"),
+                cirq.CircuitOperation(c_nested_mapped).repeat(7),
+            )
+        ),
+        c_nested_mapped,
+    )
+    cirq.testing.assert_same_circuits(
+        cirq.map_operations(
+            c_orig,
+            lambda op, _: cirq.CZ(*op.qubits) if op.gate == cirq.CX else op,
+            tags_to_ignore=["ignore"],
+            deep=True,
+        ),
+        c_expected,
+    )
+
+
 def test_map_operations_respects_tags_to_ignore():
     q = cirq.LineQubit.range(2)
     c = cirq.Circuit(cirq.CNOT(*q), cirq.CNOT(*q).with_tags("ignore"), cirq.CNOT(*q))
@@ -402,17 +443,29 @@ def test_map_moments_drop_empty_moments():
 def test_map_moments_drop_empty_moments_deep():
     op = cirq.X(cirq.NamedQubit("q"))
     c_nested = cirq.FrozenCircuit(cirq.Moment(op), cirq.Moment(), cirq.Moment(op))
+    circuit_op = cirq.CircuitOperation(c_nested).repeat(2)
+    circuit_op_dropped = cirq.CircuitOperation(cirq.FrozenCircuit([op, op])).repeat(2)
     c_orig = cirq.Circuit(
         c_nested,
         cirq.CircuitOperation(c_nested).repeat(6).with_tags("ignore"),
         c_nested,
-        cirq.CircuitOperation(c_nested).repeat(5).with_tags("preserve_tag"),
+        cirq.CircuitOperation(
+            cirq.FrozenCircuit(circuit_op, circuit_op.with_tags("ignore"), circuit_op)
+        )
+        .repeat(5)
+        .with_tags("preserve_tag"),
     )
     c_expected = cirq.Circuit(
         [op, op],
         cirq.CircuitOperation(c_nested).repeat(6).with_tags("ignore"),
         [op, op],
-        cirq.CircuitOperation(cirq.FrozenCircuit([op, op])).repeat(5).with_tags("preserve_tag"),
+        cirq.CircuitOperation(
+            cirq.FrozenCircuit(
+                circuit_op_dropped, circuit_op.with_tags("ignore"), circuit_op_dropped
+            )
+        )
+        .repeat(5)
+        .with_tags("preserve_tag"),
     )
     c_mapped = cirq.map_moments(
         c_orig, lambda m, i: [] if len(m) == 0 else [m], deep=True, tags_to_ignore=("ignore",)