MNT: make orphaned colorbar depreacte versus raise

jklymak · jklymak · commit 06ecfd4aed5c · 2022-10-03T17:11:17.000-07:00
diff --git a/lib/matplotlib/figure.py b/lib/matplotlib/figure.py
@@ -1253,11 +1253,13 @@ def colorbar(
         # Store the value of gca so that we can set it back later on.
         if cax is None:
             if ax is None:
-                raise ValueError(
+                _api.warn_deprecated(3.6, message=(
                     'Unable to determine Axes to steal space for Colorbar. '
+                    'Using gca(), but will raise in the future. '
                     'Either provide the *cax* argument to use as the Axes for '
                     'the Colorbar, provide the *ax* argument to steal space '
-                    'from it, or add *mappable* to an Axes.')
+                    'from it, or add *mappable* to an Axes.'))
+                ax = self.gca()
             current_ax = self.gca()
             userax = False
             if (use_gridspec and isinstance(ax, SubplotBase)):
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -1,10 +1,12 @@
 import numpy as np
 import pytest
 
+from matplotlib import _api
 from matplotlib import cm
 import matplotlib.colors as mcolors
 import matplotlib as mpl
 
+
 from matplotlib import rc_context
 from matplotlib.testing.decorators import image_comparison
 import matplotlib.pyplot as plt
@@ -319,7 +321,8 @@ def test_parentless_mappable():
     pc = mpl.collections.PatchCollection([], cmap=plt.get_cmap('viridis'))
     pc.set_array([])
 
-    with pytest.raises(ValueError, match='Unable to determine Axes to steal'):
+    with pytest.warns(_api.MatplotlibDeprecationWarning,
+                      match='Unable to determine Axes to steal'):
         plt.colorbar(pc)
 
 
