Backport PR matplotlib#22776: Fix colorbar stealing from a single axes and with panchor=False.

Author: oscargus

lib/matplotlib/colorbar.py

@@ -1599,7 +1599,7 @@ def make_axes_gridspec(parent, *, location=None, orientation=None,
             aspect = 1 / aspect
 
     parent.set_subplotspec(ss_main)
-    parent.set_anchor(panchor)
+    parent.set_anchor(loc_settings["panchor"])
 
     fig = parent.get_figure()
     cax = fig.add_subplot(ss_cb, label="<colorbar>")

lib/matplotlib/tests/test_colorbar.py

@@ -210,6 +210,14 @@ def test_colorbar_positioning(use_gridspec):
                  anchor=(0.8, 0.5), shrink=0.6, use_gridspec=use_gridspec)
 
 
+def test_colorbar_single_ax_panchor_false():
+    # Just smoketesting that this doesn't crash.  Note that this differs from
+    # the tests above with panchor=False because there use_gridspec is actually
+    # ineffective: passing *ax* as lists always disable use_gridspec.
+    plt.imshow([[0, 1]])
+    plt.colorbar(panchor=False)
+
+
 @image_comparison(['contour_colorbar.png'], remove_text=True)
 def test_contour_colorbar():
     fig, ax = plt.subplots(figsize=(4, 2))