Add desc_sig_element and inherited nodes

1 files changed, 34 insertions, 1 deletions

diff --git a/sphinx/transforms/post_transforms/__init__.py b/sphinx/transforms/post_transforms/__init__.py
index 6d7c3b0eb..48f5dc248 100644
--- a/sphinx/transforms/post_transforms/__init__.py
+++ b/sphinx/transforms/post_transforms/__init__.py
@@ -8,7 +8,7 @@
     :license: BSD, see LICENSE for details.
 """
 
-from typing import Any, Dict, List, Tuple
+from typing import Any, Dict, List, Tuple, Type
 from typing import cast
 
 from docutils import nodes
@@ -22,6 +22,7 @@ from sphinx.errors import NoUri
 from sphinx.locale import __
 from sphinx.transforms import SphinxTransform
 from sphinx.util import logging
+from sphinx.util.docutils import SphinxTranslator
 from sphinx.util.nodes import process_only_nodes
 
 
@@ -186,9 +187,41 @@ class OnlyNodeTransform(SphinxPostTransform):
         process_only_nodes(self.document, self.app.builder.tags)
 
 
+class SigElementFallbackTransform(SphinxPostTransform):
+    """Fallback desc_sig_element nodes to inline if translator does not supported them."""
+    default_priority = 200
+
+    SIG_ELEMENTS = [addnodes.desc_sig_name,
+                    addnodes.desc_sig_operator,
+                    addnodes.desc_sig_punctuation]
+
+    def run(self, **kwargs: Any) -> None:
+        def has_visitor(translator: Type[nodes.NodeVisitor], node: Type[Element]) -> bool:
+            return hasattr(translator, "visit_%s" % node.__name__)
+
+        translator = self.app.builder.get_translator_class()
+        if isinstance(translator, SphinxTranslator):
+            # subclass of SphinxTranslator supports desc_sig_element nodes automatically.
+            return
+
+        if all(has_visitor(translator, node) for node in self.SIG_ELEMENTS):
+            # the translator supports all desc_sig_element nodes
+            return
+        else:
+            self.fallback()
+
+    def fallback(self):
+        for node in self.document.traverse(addnodes.desc_sig_element):
+            newnode = nodes.inline()
+            newnode.update_all_atts(node)
+            newnode.extend(node)
+            node.replace_self(newnode)
+
+
 def setup(app: Sphinx) -> Dict[str, Any]:
     app.add_post_transform(ReferencesResolver)
     app.add_post_transform(OnlyNodeTransform)
+    app.add_post_transform(SigElementFallbackTransform)
 
     return {
         'version': 'builtin',