The unused parameter dag in DAGNode constructor is deprecated

crates/circuit/src/dag_node.rs

@@ -123,7 +123,7 @@ impl DAGOpNode {
         op: Bound<PyAny>,
         qargs: Option<TupleLikeArg>,
         cargs: Option<TupleLikeArg>,
-        #[allow(unused_variables)] dag: Option<Bound<PyAny>>,
+        dag: Option<Bound<PyAny>>,
     ) -> PyResult<Py<Self>> {
         let py_op = op.extract::<OperationFromPython>()?;
         let qargs = qargs.map_or_else(|| PyTuple::empty_bound(py), |q| q.value);
@@ -138,7 +138,19 @@ impl DAGOpNode {
             #[cfg(feature = "cache_pygates")]
             py_op: op.unbind().into(),
         };
-
+        if dag.is_some() {
+            WARNINGS_WARN.get_bound(py).call1((
+                intern!(
+                    py,
+                    concat!(
+                        "The ``dag`` parameter in DAGNode subclass constructors ",
+                        "is unused and it will be removed in Qiskit 2.0.",
+                    )
+                ),
+                py.get_type_bound::<PyDeprecationWarning>(),
+                2,
+            ))?;
+        }
         Py::new(
             py,
             (

qiskit/dagcircuit/dagdependency_v2.py

@@ -345,7 +345,6 @@ def apply_operation_back(self, operation, qargs=(), cargs=()):
             op=operation,
             qargs=qargs,
             cargs=cargs,
-            dag=self,
         )
         new_node._node_id = self._multi_graph.add_node(new_node)
         self._update_edges()

releasenotes/notes/deprecation_13022-9cf84f6c5ff13b29.yaml

@@ -0,0 +1,4 @@
+---
+deprecations_circuits:
+  - |
+    The ``DAGNode`` subclasses take a ``dag`` optional parameter when constructed that is currently unused and ignored. Now it is deprecated and will be removed in Qiskit 2.0