FIX: fully invalidate TransformWrapper parents before swapping

The issue is that TransformedPath only regenerates its cache for changes to the
non-affine part of the transform.  When TransformWrapper for tranScale changes
from log -> linear the non-affine part of the log transform is still cached,
but when the transforms are invalidated after switching to linear the
invalidation only reports changing the affine part so the cache in
TransformedPath escapes being updated (nulled out in this case) and when we
re-draw with linear is drawing the line off screen (or at least clipped).

This change invalidates all of the parents before changing the internals of
TransformWrapper before we switch it which will cause the non-affine part to be
correctly recomputed the next time we need it.

closes matplotlib#25124

Author: tacaswell

lib/matplotlib/tests/test_transforms.py

@@ -10,7 +10,7 @@
 import matplotlib.patches as mpatches
 import matplotlib.transforms as mtransforms
 from matplotlib.path import Path
-from matplotlib.testing.decorators import image_comparison
+from matplotlib.testing.decorators import image_comparison, check_figures_equal
 
 
 def test_non_affine_caching():
@@ -730,3 +730,17 @@ def test_transformwrapper():
             r"The input and output dims of the new child \(1, 1\) "
             r"do not match those of current child \(2, 2\)")):
         t.set(scale.LogTransform(10))
+
+
+@check_figures_equal(extensions=["png"])
+def test_scale_swapping(fig_test, fig_ref):
+    np.random.seed(19680801)
+    samples = np.random.normal(size=10)
+    x = np.linspace(-5, 5, 10)
+
+    for fig, log_state in zip([fig_test, fig_ref], [True, False]):
+        ax = fig.subplots()
+        ax.hist(samples, log=log_state, density=True)
+        ax.plot(x, np.exp(-(x**2) / 2) / np.sqrt(2 * np.pi))
+        fig.canvas.draw()
+        ax.set_yscale('linear')

lib/matplotlib/transforms.py

@@ -1732,6 +1732,7 @@ def set(self, child):
         dimensions as the current child.
         """
         if hasattr(self, "_child"):  # Absent during init.
+            self.invalidate()
             new_dims = (child.input_dims, child.output_dims)
             old_dims = (self._child.input_dims, self._child.output_dims)
             if new_dims != old_dims: