Fix mpl circuit drawer with fold=-1 hanging with ControlFlow ops (#12016

) (#12037)

* Fix typing-extensions

* Fix control flow with fold minus one

(cherry picked from commit 43381ae)

Co-authored-by: Edwin Navarro <enavarro@comcast.net>

qiskit/visualization/circuit/matplotlib.py

@@ -1544,7 +1544,7 @@ def _flow_op_gate(self, node, node_data, glob_data):
         while end_x > 0.0:
             x_shift = fold_level * self._fold
             y_shift = fold_level * (glob_data["n_lines"] + 1)
-            end_x = xpos + box_width - x_shift
+            end_x = xpos + box_width - x_shift if self._fold > 0 else 0.0
 
             if isinstance(node.op, IfElseOp):
                 flow_text = "  If"

releasenotes/notes/fix-control-flow-fold-minus-one-f2af168a5313385f.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixed an issue with the :func:`circuit_drawer` or :meth:`QuantumCircuit.draw`
+    when using the ``mpl`` output option where the program would hang if the
+    circuit being drawn had a ControlFlow operation in it and the ``fold`` option
+    was set to -1 (meaning no fold).
+    Fixed `#12012 <https://github.com/Qiskit/qiskit/issues/12012>`__.

test/visual/mpl/circuit/test_circuit_matplotlib_drawer.py

@@ -2228,6 +2228,27 @@ def test_control_flow_nested_layout(self):
         )
         self.assertGreaterEqual(ratio, self.threshold)
 
+    def test_control_flow_with_fold_minus_one(self):
+        """Test control flow works with fold=-1. Qiskit issue #12012"""
+        qreg = QuantumRegister(2, "qr")
+        creg = ClassicalRegister(2, "cr")
+        circuit = QuantumCircuit(qreg, creg)
+        with circuit.if_test((creg[1], 1)):
+            circuit.h(0)
+            circuit.cx(0, 1)
+
+        fname = "control_flow_fold_minus_one.png"
+        self.circuit_drawer(circuit, output="mpl", filename=fname, fold=-1)
+
+        ratio = VisualTestUtilities._save_diff(
+            self._image_path(fname),
+            self._reference_path(fname),
+            fname,
+            FAILURE_DIFF_DIR,
+            FAILURE_PREFIX,
+        )
+        self.assertGreaterEqual(ratio, self.threshold)
+
     def test_annotated_operation(self):
         """Test AnnotatedOperations and other non-Instructions."""
         circuit = QuantumCircuit(3)