Show deprecation warning in directive_helper()

CHANGES

@@ -25,6 +25,7 @@ Deprecated
   ``sphinx.util.import_object()`` instead.
 * Drop function based directive support.  For now, Sphinx only supports class
   based directives.
+* ``sphinx.util.docutils.directive_helper()`` is deprecated.
 
 Features added
 --------------

sphinx/application.py

@@ -703,13 +703,12 @@ class Sphinx(object):
                               'already registered, it will be overridden'),
                            self._setting_up_extension[-1], name,
                            type='app', subtype='add_directive')
-        directive = directive_helper(obj, content, arguments, **options)
-        directives.register_directive(name, directive)
 
         if not isclass(obj) or not issubclass(obj, Directive):
-            warnings.warn('function based directive support is now deprecated. '
-                          'Use class based directive instead.',
-                          RemovedInSphinx30Warning)
+            directive = directive_helper(obj, content, arguments, **options)
+            directives.register_directive(name, directive)
+        else:
+            directives.register_directive(name, obj)
 
     def add_role(self, name, role):
         # type: (unicode, Any) -> None

sphinx/registry.py

@@ -12,9 +12,11 @@ from __future__ import print_function
 
 import traceback
 import warnings
+from inspect import isclass
 from types import MethodType
 from typing import TYPE_CHECKING
 
+from docutils.parsers.rst import Directive
 from pkg_resources import iter_entry_points
 from six import iteritems, itervalues
 
@@ -186,8 +188,12 @@ class SphinxComponentRegistry(object):
                      (domain, name, obj, has_content, argument_spec, option_spec))
         if domain not in self.domains:
             raise ExtensionError(__('domain %s not yet registered') % domain)
+
         directives = self.domain_directives.setdefault(domain, {})
-        directives[name] = directive_helper(obj, has_content, argument_spec, **option_spec)
+        if not isclass(obj) or not issubclass(obj, Directive):
+            directives[name] = directive_helper(obj, has_content, argument_spec, **option_spec)
+        else:
+            directives[name] = obj
 
     def add_role_to_domain(self, domain, name, role):
         # type: (unicode, unicode, Union[RoleFunction, XRefRole]) -> None

sphinx/util/docutils.py

@@ -12,6 +12,7 @@ from __future__ import absolute_import
 
 import re
 import types
+import warnings
 from contextlib import contextmanager
 from copy import copy
 from distutils.version import LooseVersion
@@ -24,6 +25,7 @@ from docutils.parsers.rst import directives, roles, convert_directive_function
 from docutils.statemachine import StateMachine
 from docutils.utils import Reporter
 
+from sphinx.deprecation import RemovedInSphinx30Warning
 from sphinx.errors import ExtensionError
 from sphinx.locale import __
 from sphinx.util import logging
@@ -192,6 +194,10 @@ def is_html5_writer_available():
 
 def directive_helper(obj, has_content=None, argument_spec=None, **option_spec):
     # type: (Any, bool, Tuple[int, int, bool], Any) -> Any
+    warnings.warn('function based directive support is now deprecated. '
+                  'Use class based directive instead.',
+                  RemovedInSphinx30Warning)
+
     if isinstance(obj, (types.FunctionType, types.MethodType)):
         obj.content = has_content                       # type: ignore
         obj.arguments = argument_spec or (0, 0, False)  # type: ignore