Fix deprecation of encoding in plot_directive.

Author: QuLogic

lib/matplotlib/sphinxext/plot_directive.py

@@ -197,7 +197,7 @@ def _option_format(arg):
 
 
 def _deprecated_option_encoding(arg):
-    _api.warn_deprecated("3.5", "encoding", obj_type="option")
+    _api.warn_deprecated("3.5", name="encoding", obj_type="option")
     return directives.encoding(arg)
 
 

lib/matplotlib/tests/tinypages/some_plots.rst

@@ -120,9 +120,11 @@ Plot 14 uses ``include-source``:
 
     # Only a comment
 
-Plot 15 uses an external file with the plot commands and a caption:
+Plot 15 uses an external file with the plot commands and a caption (the
+encoding is ignored and just verifies the deprecation is not broken):
 
 .. plot:: range4.py
+   :encoding: utf-8
 
    This is the caption for plot 15.