Filter pending_xref_condition node on failed resolution

sphinx/transforms/post_transforms/__init__.py

@@ -22,10 +22,14 @@
 from sphinx.transforms import SphinxTransform
 from sphinx.util import logging
 from sphinx.util.docutils import SphinxTranslator
-from sphinx.util.nodes import process_only_nodes
+from sphinx.util.nodes import find_pending_xref_condition, process_only_nodes
 
 logger = logging.getLogger(__name__)
 
+if False:
+    # For type annotation
+    from docutils.nodes import Node
+
 
 class SphinxPostTransform(SphinxTransform):
     """A base class of post-transforms.
@@ -97,8 +101,21 @@ def run(self, **kwargs: Any) -> None:
                     if newnode is None:
                         self.warn_missing_reference(refdoc, typ, target, node, domain)
             except NoUri:
-                newnode = contnode
-            node.replace_self(newnode or contnode)
+                newnode = None
+
+            if newnode:
+                newnodes = [newnode]  # type: List[Node]
+            else:
+                newnodes = [contnode]
+                if newnode is None and isinstance(node[0], addnodes.pending_xref_condition):
+                    matched = find_pending_xref_condition(node, "*")
+                    if matched:
+                        newnodes = matched.children
+                    else:
+                        logger.warning(__('Could not determine the fallback text for the '
+                                          'cross-reference. Might be a bug.'), location=node)
+
+            node.replace_self(newnodes)
 
     def resolve_anyref(self, refdoc: str, node: pending_xref, contnode: Element) -> Element:
         """Resolve reference generated by the "any" role."""

sphinx/util/nodes.py

@@ -531,6 +531,16 @@ def make_id(env: "BuildEnvironment", document: nodes.document,
     return node_id
 
 
+def find_pending_xref_condition(node: addnodes.pending_xref, condition: str) -> Element:
+    """Pick matched pending_xref_condition node up from the pending_xref."""
+    for subnode in node:
+        if (isinstance(subnode, addnodes.pending_xref_condition) and
+                subnode.get('condition') == condition):
+            return subnode
+    else:
+        return None
+
+
 def make_refnode(builder: "Builder", fromdocname: str, todocname: str, targetid: str,
                  child: Node, title: str = None) -> nodes.reference:
     """Shortcut to create a reference node."""