fix regression of axline behavior with non-linear scales

fixes matplotlib#19445

Author: johan12345

lib/matplotlib/lines.py

@@ -1432,7 +1432,8 @@ def __init__(self, xy1, xy2, slope, **kwargs):
 
     def get_transform(self):
         ax = self.axes
-        points_transform = self._transform + ax.transData.inverted()
+        points_transform = self._transform + ax.transData.inverted()\
+                           + ax.transScale
 
         if self._xy2 is not None:
             # two points were given

lib/matplotlib/tests/test_axes.py

@@ -4103,6 +4103,19 @@ def test_eb_line_zorder():
     ax.set_title("errorbar zorder test")
 
 
+@check_figures_equal()
+def test_axline_loglog(fig_test, fig_ref):
+    ax = fig_test.subplots()
+    ax.set(xlim=(0.1, 10), ylim=(1e-3, 1))
+    ax.loglog([.3, .6], [.3, .6], ".-")
+    ax.axline((1, 1e-3), (10, 1e-2), c="k")
+
+    ax = fig_ref.subplots()
+    ax.set(xlim=(0.1, 10), ylim=(1e-3, 1))
+    ax.loglog([.3, .6], [.3, .6], ".-")
+    ax.loglog([1, 10], [1e-3, 1e-2], c="k")
+
+
 @check_figures_equal()
 def test_axline(fig_test, fig_ref):
     ax = fig_test.subplots()