remove internal add_control (#13177)

* rename module

* simplify tests

* reno

* Reword release note

---------

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>
Co-authored-by: Jake Lishman <jake@binhbar.com>

Author: 3 people

qiskit/circuit/add_control.py qiskit/circuit/_add_control.pyqiskit/circuit/add_control.py renamed to qiskit/circuit/_add_control.py

@@ -135,7 +135,7 @@ def control(
         """
         if not annotated:  # captures both None and False
             # pylint: disable=cyclic-import
-            from .add_control import add_control
+            from ._add_control import add_control
 
             return add_control(self, num_ctrl_qubits, label, ctrl_state)
 

qiskit/circuit/gate.py

@@ -0,0 +1,6 @@
+---
+upgrade_circuits:
+  - |
+    The internal function ``qiskit.circuit.add_control.add_control`` was removed, as it is not part of the
+    public API. It had fragile preconditions to uphold and was a common source of bugs. Uses of ``add_control(SomeGate(...), ...)``
+    should change to ``SomeGate(...).control(...)`` using :meth:`.Gate.control` instead, which is far safer.

releasenotes/notes/private-add_control-2367872c0f7136c4.yaml

@@ -27,7 +27,6 @@
 from qiskit.quantum_info.operators.predicates import matrix_equal, is_unitary_matrix
 from qiskit.quantum_info.random import random_unitary
 from qiskit.quantum_info.states import Statevector
-import qiskit.circuit.add_control as ac
 from qiskit.transpiler.passes import UnrollCustomDefinitions, BasisTranslator
 from qiskit.transpiler.preset_passmanagers import generate_preset_pass_manager
 from qiskit.converters.circuit_to_dag import circuit_to_dag
@@ -1584,10 +1583,10 @@ class TestSingleControlledRotationGates(QiskitTestCase):
     gry = ry.RYGate(theta)
     grz = rz.RZGate(theta)
 
-    ugu1 = ac._unroll_gate(gu1, ["p", "u", "cx"])
-    ugrx = ac._unroll_gate(grx, ["p", "u", "cx"])
-    ugry = ac._unroll_gate(gry, ["p", "u", "cx"])
-    ugrz = ac._unroll_gate(grz, ["p", "u", "cx"])
+    ugu1 = u1.U1Gate(theta).definition
+    ugrx = rx.RXGate(theta).definition
+    ugry = ry.RYGate(theta).definition
+    ugrz = rz.RZGate(theta).definition
     ugrz.params = grz.params
 
     cgu1 = ugu1.control(num_ctrl)