Deprecate math_symbol_table function directive

Author: alexrudy

doc/sphinxext/math_symbol_table.py

@@ -1,4 +1,7 @@
+from docutils.parsers.rst import Directive
+
 from matplotlib import mathtext
+from matplotlib import cbook
 
 
 symbols = [
@@ -137,16 +140,26 @@ def get_n(n, l):
     return []
 
 
+@cbook.deprecated("3.2", alternative="MathSymbolTableDirective")
 def math_symbol_table_directive(
         name, arguments, options, content, lineno,
         content_offset, block_text, state, state_machine):
     return run(state_machine)
 
 
+class MathSymbolTableDirective(Directive):
+    has_content = False
+    required_arguments = 0
+    optional_arguments = 0
+    final_argument_whitespace = False
+    option_spec = {}
+
+    def run(self):
+        return run(self.state_machine)
+
+
 def setup(app):
-    app.add_directive(
-        'math_symbol_table', math_symbol_table_directive,
-        False, (0, 1, 0))
+    app.add_directive("math_symbol_table", MathSymbolTableDirective)
 
     metadata = {'parallel_read_safe': True, 'parallel_write_safe': True}
     return metadata