Add DAGDependencyV2 and Converters (#11705)

* Fix typing-extensions

* Add dagdependency_v2 and converters

* Add V2 tests

* Cleanup testing

* Move import

* Add copy_empty_like and topological_op_nodes

* Lint and providers update

* Change to apply_operation_back

* Fix converter init

* Cleanup and remove indices methods

* Change to _get_node and cleanup

* Add reno

* Fix node_id bug in dag_drawer

* Lint

* Convert to using leading _ for class and functions

* Cleanup test file import

* Fix converters

* Restart CI

* Remove reno and remove_ops functions and fix typo

* Remove init entries for v2

* Remove meaningless methods

These `quantum_successors` etc have no meaning in `DAGDependency` (and
V2) since the edges don't carry the data that the `DAGCircuit` functions
check for; `DAGDependency` is in part a deliberate erasure of this data.

---------

Co-authored-by: Jake Lishman <jake.lishman@ibm.com>

qiskit/converters/circuit_to_dagdependency_v2.py

@@ -0,0 +1,47 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2020.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Helper function for converting a circuit to a dag dependency"""
+
+from qiskit.dagcircuit.dagdependency_v2 import _DAGDependencyV2
+
+
+def _circuit_to_dagdependency_v2(circuit):
+    """Build a ``_DAGDependencyV2`` object from a :class:`~.QuantumCircuit`.
+
+    Args:
+        circuit (QuantumCircuit): the input circuit.
+
+    Return:
+        _DAGDependencyV2: the DAG representing the input circuit as a dag dependency.
+    """
+    dagdependency = _DAGDependencyV2()
+    dagdependency.name = circuit.name
+    dagdependency.metadata = circuit.metadata
+    dagdependency.calibrations = circuit.calibrations
+    dagdependency.global_phase = circuit.global_phase
+
+    dagdependency.add_qubits(circuit.qubits)
+    dagdependency.add_clbits(circuit.clbits)
+
+    for register in circuit.qregs:
+        dagdependency.add_qreg(register)
+
+    for register in circuit.cregs:
+        dagdependency.add_creg(register)
+
+    for instruction in circuit.data:
+        dagdependency.apply_operation_back(
+            instruction.operation, instruction.qubits, instruction.clbits
+        )
+
+    return dagdependency

qiskit/converters/dag_to_dagdependency_v2.py

@@ -0,0 +1,44 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2020.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+"""Helper function for converting a dag circuit to a dag dependency"""
+from qiskit.dagcircuit.dagdependency_v2 import _DAGDependencyV2
+
+
+def _dag_to_dagdependency_v2(dag):
+    """Build a ``_DAGDependencyV2`` object from a ``DAGCircuit``.
+
+    Args:
+        dag (DAGCircuit): the input dag.
+
+    Return:
+        _DAGDependencyV2: the DAG representing the input circuit as a dag dependency.
+    """
+    dagdependency = _DAGDependencyV2()
+    dagdependency.name = dag.name
+    dagdependency.metadata = dag.metadata
+    dagdependency.global_phase = dag.global_phase
+    dagdependency.calibrations = dag.calibrations
+
+    dagdependency.add_qubits(dag.qubits)
+    dagdependency.add_clbits(dag.clbits)
+
+    for register in dag.qregs.values():
+        dagdependency.add_qreg(register)
+
+    for register in dag.cregs.values():
+        dagdependency.add_creg(register)
+
+    for node in dag.topological_op_nodes():
+        dagdependency.apply_operation_back(node.op.copy(), node.qargs, node.cargs)
+
+    return dagdependency