From 675e7e576f0aa8ed48a8645d6809fd5b700304f0 Mon Sep 17 00:00:00 2001
From: Takeshi KOMIYA <i.tkomiya@gmail.com>
Date: Mon, 24 Feb 2020 01:23:07 +0900
Subject: [PATCH] Add desc_sig_element and inherited nodes

---
 sphinx/addnodes.py                            | 30 +++++++++++++++-
 sphinx/transforms/post_transforms/__init__.py | 35 ++++++++++++++++++-
 2 files changed, 63 insertions(+), 2 deletions(-)

diff --git a/sphinx/addnodes.py b/sphinx/addnodes.py
index 15d5fc46be2..fa04e9344a3 100644
--- a/sphinx/addnodes.py
+++ b/sphinx/addnodes.py
@@ -12,7 +12,7 @@
 from typing import Any, Dict, List, Sequence
 
 from docutils import nodes
-from docutils.nodes import Node
+from docutils.nodes import Element, Node
 
 from sphinx.deprecation import RemovedInSphinx40Warning
 
@@ -174,6 +174,31 @@ class desc_content(nodes.General, nodes.Element):
     """
 
 
+class desc_sig_element(nodes.inline):
+    """Common parent class of nodes for inline text of a signature."""
+    classes = []  # type: List[str]
+
+    def __init__(self, rawsource: str = '', text: str = '',
+                 *children: Element, **attributes: Any) -> None:
+        super().__init__(rawsource, text, *children, **attributes)
+        self['classes'].extend(self.classes)
+
+
+class desc_sig_name(desc_sig_element):
+    """Node for a name in a signature."""
+    classes = ["n"]
+
+
+class desc_sig_operator(desc_sig_element):
+    """Node for an operator in a signature."""
+    classes = ["o"]
+
+
+class desc_sig_punctuation(desc_sig_element):
+    """Node for a punctuation in a signature."""
+    classes = ["p"]
+
+
 # new admonition-like constructs
 
 class versionmodified(nodes.Admonition, nodes.TextElement):
@@ -332,6 +357,9 @@ def setup(app: "Sphinx") -> Dict[str, Any]:
     app.add_node(desc_optional)
     app.add_node(desc_annotation)
     app.add_node(desc_content)
+    app.add_node(desc_sig_name)
+    app.add_node(desc_sig_operator)
+    app.add_node(desc_sig_punctuation)
     app.add_node(versionmodified)
     app.add_node(seealso)
     app.add_node(productionlist)
diff --git a/sphinx/transforms/post_transforms/__init__.py b/sphinx/transforms/post_transforms/__init__.py
index 6d7c3b0eb0f..48f5dc24821 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.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 @@ def run(self, **kwargs: Any) -> None:
         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',