Relax wire_order restrictions in circuit visualization

qiskit/opflow/__init__.py

@@ -25,7 +25,7 @@
 
 Operators and State functions are the building blocks of Quantum Algorithms.
 
-A library for Quantum Algorithms & Applications is more than a collection of
+A library for Quantum Algorithms & Applications (QA&A) is more than a collection of
 algorithms wrapped in Python functions. It needs to provide tools to make writing
 algorithms simple and easy. This is the layer of modules between the circuits and algorithms,
 providing the language and computational primitives for QA&A research.

qiskit/visualization/circuit/circuit_visualization.py

@@ -101,7 +101,7 @@ def circuit_drawer(
             information on the contents.
         output (str): select the output method to use for drawing the circuit.
             Valid choices are ``text``, ``mpl``, ``latex``, ``latex_source``.
-            By default the `text` drawer is used unless the user config file
+            By default, the `text` drawer is used unless the user config file
             (usually ``~/.qiskit/settings.conf``) has an alternative backend set
             as the default. For example, ``circuit_drawer = latex``. If the output
             kwarg is set, that backend will always be used over the default in
@@ -205,27 +205,38 @@ def circuit_drawer(
         raise VisualizationError(
             "The wire_order option cannot be set when the reverse_bits option is True."
         )
-    if wire_order is not None and len(wire_order) != circuit.num_qubits + circuit.num_clbits:
-        raise VisualizationError(
-            "The wire_order list must be the same "
-            "length as the sum of the number of qubits and clbits in the circuit."
-        )
-    if wire_order is not None and set(wire_order) != set(
-        range(circuit.num_qubits + circuit.num_clbits)
-    ):
-        raise VisualizationError(
-            "There must be one and only one entry in the "
-            "wire_order list for the index of each qubit and each clbit in the circuit."
-        )
 
-    if circuit.clbits and (reverse_bits or wire_order is not None):
+    complete_wire_order = wire_order
+    if wire_order is not None:
+        wire_order_len = len(wire_order)
+        total_wire_len = circuit.num_qubits + circuit.num_clbits
+        if wire_order_len not in [circuit.num_qubits, total_wire_len]:
+            raise VisualizationError(
+                f"The wire_order list (length {wire_order_len}) should as long as "
+                f"the number of qubits ({circuit.num_qubits}) or the "
+                f"total numbers of qubits and classical bits {total_wire_len}."
+            )
+
+        if len(set(wire_order)) != len(wire_order):
+            raise VisualizationError("The wire_order list should not have repeated elements.")
+
+        if wire_order_len == circuit.num_qubits:
+            complete_wire_order = wire_order + list(range(circuit.num_qubits, total_wire_len))
+
+    if (
+        circuit.clbits
+        and (reverse_bits or wire_order is not None)
+        and not set(wire_order or []).issubset(set(range(circuit.num_qubits)))
+    ):
         if cregbundle:
             warn(
-                "cregbundle set to False since either reverse_bits or wire_order has been set.",
+                "cregbundle set to False since either reverse_bits or wire_order "
+                "(over classical bit) has been set.",
                 RuntimeWarning,
                 2,
             )
         cregbundle = False
+
     if output == "text":
         return _text_circuit_drawer(
             circuit,
@@ -239,7 +250,7 @@ def circuit_drawer(
             fold=fold,
             initial_state=initial_state,
             cregbundle=cregbundle,
-            wire_order=wire_order,
+            wire_order=complete_wire_order,
         )
     elif output == "latex":
         image = _latex_circuit_drawer(
@@ -254,7 +265,7 @@ def circuit_drawer(
             with_layout=with_layout,
             initial_state=initial_state,
             cregbundle=cregbundle,
-            wire_order=wire_order,
+            wire_order=complete_wire_order,
         )
     elif output == "latex_source":
         return _generate_latex_source(
@@ -269,7 +280,7 @@ def circuit_drawer(
             with_layout=with_layout,
             initial_state=initial_state,
             cregbundle=cregbundle,
-            wire_order=wire_order,
+            wire_order=complete_wire_order,
         )
     elif output == "mpl":
         image = _matplotlib_circuit_drawer(
@@ -286,7 +297,7 @@ def circuit_drawer(
             ax=ax,
             initial_state=initial_state,
             cregbundle=cregbundle,
-            wire_order=wire_order,
+            wire_order=complete_wire_order,
         )
     else:
         raise VisualizationError(
@@ -351,7 +362,7 @@ def _text_circuit_drawer(
         TextDrawing: An instance that, when printed, draws the circuit in ascii art.
 
     Raises:
-        VisualizationError: When the filename extenstion is not .txt.
+        VisualizationError: When the filename extension is not .txt.
     """
     qubits, clbits, nodes = _utils._get_layered_instructions(
         circuit,

releasenotes/notes/relax_wire_order_restrictions-ffc0cfeacd7b8d4b.yaml

@@ -0,0 +1,34 @@
+---
+features:
+  - |
+    Some restrictions when using ``wire_order`` in the circuit drawers had been relaxed.
+    Now, ``wire_order`` can list just qubits and, in that case, it can be used
+    with ``cregbundle=True``, since it will not affect the classical bits.
+
+    .. code-block::
+
+      from qiskit import QuantumCircuit, QuantumRegister, ClassicalRegister
+
+      qr = QuantumRegister(4, "q")
+      cr = ClassicalRegister(4, "c")
+      cr2 = ClassicalRegister(2, "ca")
+      circuit = QuantumCircuit(qr, cr, cr2)
+      circuit.h(0)
+      circuit.h(3)
+      circuit.x(1)
+      circuit.x(3).c_if(cr, 10)
+      circuit.draw('text', wire_order=[2, 3], cregbundle=True)
+
+    .. parsed-literal::
+
+       q_2: ────────────
+            ┌───┐ ┌───┐
+       q_3: ┤ H ├─┤ X ├─
+            ├───┤ └─╥─┘
+       q_0: ┤ H ├───╫───
+            ├───┤   ║
+       q_1: ┤ X ├───╫───
+            └───┘┌──╨──┐
+       c: 4/═════╡ 0xa ╞
+                 └─────┘
+      ca: 2/════════════

test/python/visualization/references/test_wire_order_only_qubits.tex

@@ -0,0 +1,20 @@
+\documentclass[border=2px]{standalone}
+
+\usepackage[braket, qm]{qcircuit}
+\usepackage{graphicx}
+
+\begin{document}
+\scalebox{1.0}{
+\Qcircuit @C=1.0em @R=0.2em @!R { \\
+	 	\nghost{{q}_{2} :  } & \lstick{{q}_{2} :  } & \qw & \qw & \qw & \qw\\
+	 	\nghost{{q}_{1} :  } & \lstick{{q}_{1} :  } & \gate{\mathrm{X}} & \qw & \qw & \qw\\
+	 	\nghost{{q}_{3} :  } & \lstick{{q}_{3} :  } & \gate{\mathrm{H}} & \gate{\mathrm{X}} & \qw & \qw\\
+	 	\nghost{{q}_{0} :  } & \lstick{{q}_{0} :  } & \gate{\mathrm{H}} & \qw & \qw & \qw\\
+	 	\nghost{{c}_{0} :  } & \lstick{{c}_{0} :  } & \cw & \controlo \cw \cwx[-2] & \cw & \cw\\
+	 	\nghost{{c}_{1} :  } & \lstick{{c}_{1} :  } & \cw & \controlo \cw \cwx[-1] & \cw & \cw\\
+	 	\nghost{{c}_{2} :  } & \lstick{{c}_{2} :  } & \cw & \control \cw \cwx[-1] & \cw & \cw\\
+	 	\nghost{{c}_{3} :  } & \lstick{{c}_{3} :  } & \cw & \control \cw^(0.0){^{\mathtt{0xc}}} \cwx[-1] & \cw & \cw\\
+	 	\nghost{{ca}_{0} :  } & \lstick{{ca}_{0} :  } & \cw & \cw & \cw & \cw\\
+	 	\nghost{{ca}_{1} :  } & \lstick{{ca}_{1} :  } & \cw & \cw & \cw & \cw\\
+\\ }}
+\end{document}

test/python/visualization/test_circuit_drawer.py

@@ -108,10 +108,8 @@ def test_wire_order_raises(self):
 
         circuit = QuantumCircuit(3, 3)
         circuit.x(1)
-        with self.assertRaisesRegex(VisualizationError, "the same length as"):
-            visualization.circuit_drawer(circuit, wire_order=[0, 1, 2])
 
-        with self.assertRaisesRegex(VisualizationError, "one and only one entry"):
+        with self.assertRaisesRegex(VisualizationError, "should not have repeated elements"):
             visualization.circuit_drawer(circuit, wire_order=[2, 1, 0, 3, 1, 5])
 
         with self.assertRaisesRegex(VisualizationError, "cannot be set when the reverse_bits"):

test/python/visualization/test_circuit_latex.py

@@ -681,7 +681,7 @@ def test_idle_wires_barrier(self):
 
     def test_wire_order(self):
         """Test the wire_order option to latex drawer"""
-        filename = self._get_resource_path("test_latex_wire_order.tex")
+        filename = self._get_resource_path("test_latex_wire_order_only.tex")
         qr = QuantumRegister(4, "q")
         cr = ClassicalRegister(4, "c")
         cr2 = ClassicalRegister(2, "ca")
@@ -699,6 +699,26 @@ def test_wire_order(self):
         )
         self.assertEqualToReference(filename)
 
+    def test_wire_order_only_qubits(self):
+        """Test the wire_order list with qubits only to latex drawer"""
+        filename = self._get_resource_path("test_wire_order_only_qubits.tex")
+        qr = QuantumRegister(4, "q")
+        cr = ClassicalRegister(4, "c")
+        cr2 = ClassicalRegister(2, "ca")
+        circuit = QuantumCircuit(qr, cr, cr2)
+        circuit.h(0)
+        circuit.h(3)
+        circuit.x(1)
+        circuit.x(3).c_if(cr, 12)
+        circuit_drawer(
+            circuit,
+            cregbundle=False,
+            wire_order=[2, 1, 3, 0, 4, 5, 6, 7, 8, 9],
+            filename=filename,
+            output="latex_source",
+        )
+        self.assertEqualToReference(filename)
+
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)

test/python/visualization/test_circuit_text_drawer.py

@@ -341,6 +341,37 @@ def test_wire_order(self):
             str(_text_circuit_drawer(circuit, wire_order=[2, 1, 3, 0, 6, 8, 9, 5, 4, 7])), expected
         )
 
+    def test_wire_order_only_qubits(self):
+        """Test the wire_order option with only qubits"""
+        expected = "\n".join(
+            [
+                "                    ",
+                "q_2: |0>────────────",
+                "        ┌───┐       ",
+                "q_1: |0>┤ X ├───────",
+                "        ├───┤ ┌───┐ ",
+                "q_3: |0>┤ H ├─┤ X ├─",
+                "        ├───┤ └─╥─┘ ",
+                "q_0: |0>┤ H ├───╫───",
+                "        └───┘┌──╨──┐",
+                " c: 0 4/═════╡ 0xa ╞",
+                "             └─────┘",
+                "ca: 0 2/════════════",
+                "                    ",
+            ]
+        )
+        qr = QuantumRegister(4, "q")
+        cr = ClassicalRegister(4, "c")
+        cr2 = ClassicalRegister(2, "ca")
+        circuit = QuantumCircuit(qr, cr, cr2)
+        circuit.h(0)
+        circuit.h(3)
+        circuit.x(1)
+        circuit.x(3).c_if(cr, 10)
+        self.assertEqual(
+            str(_text_circuit_drawer(circuit, wire_order=[2, 1, 3, 0, 4, 5, 6, 7, 8, 9])), expected
+        )
+
     def test_text_swap(self):
         """Swap drawing."""
         expected = "\n".join(