Sphinx prior to v4.0 uses different classes for rendering elements of
documentation objects; add some compatibility classes to use the right
node classes conditionally.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 docs/sphinx/compat.py | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/docs/sphinx/compat.py b/docs/sphinx/compat.py
index 39b859a25e3..6bc698c5ada 100644
--- a/docs/sphinx/compat.py
+++ b/docs/sphinx/compat.py
@@ -2,12 +2,27 @@
 Sphinx cross-version compatibility goop
 """
 
-from docutils.nodes import Element
+from typing import Callable
 
+from docutils.nodes import Element, Node, Text
+
+import sphinx
+from sphinx import addnodes
 from sphinx.util import nodes
 from sphinx.util.docutils import SphinxDirective, switch_source_input
 
 
+SpaceNode: Callable[[str], Node]
+KeywordNode: Callable[[str, str], Node]
+
+if sphinx.version_info[:3] >= (4, 0, 0):
+    SpaceNode = addnodes.desc_sig_space
+    KeywordNode = addnodes.desc_sig_keyword
+else:
+    SpaceNode = Text
+    KeywordNode = addnodes.desc_annotation
+
+
 def nested_parse_with_titles(
     directive: SphinxDirective, content_node: Element
 ) -> None:
-- 
2.48.1