Slightly simplify toctree code

While working on sphinx-doc#12720, I noticed that `parse_content` creates and
returns an empty node list. It does not do anything with it.

This PR moves the node out of `parse_content`, so that `parse_content`
only populates the toctree entries. The complete node creation logic
is now united in `TocTree.run`.

sphinx/directives/other.py

@@ -78,17 +78,19 @@ def run(self) -> list[Node]:
         subnode['numbered'] = self.options.get('numbered', 0)
         subnode['titlesonly'] = 'titlesonly' in self.options
         self.set_source_info(subnode)
+        self.parse_content(subnode)
+
         wrappernode = nodes.compound(
             classes=['toctree-wrapper', *self.options.get('class', ())],
         )
         wrappernode.append(subnode)
         self.add_name(wrappernode)
+        return [wrappernode]
 
-        ret = self.parse_content(subnode)
-        ret.append(wrappernode)
-        return ret
-
-    def parse_content(self, toctree: addnodes.toctree) -> list[Node]:
+    def parse_content(self, toctree: addnodes.toctree) -> None:
+        """
+        Populate ``toctree['entries']`` and ``toctree['includefiles']`` from content.
+        """
         generated_docnames = frozenset(StandardDomain._virtual_doc_names)
         suffixes = self.config.source_suffix
         current_docname = self.env.docname
@@ -99,7 +101,6 @@ def parse_content(self, toctree: addnodes.toctree) -> list[Node]:
         all_docnames.remove(current_docname)  # remove current document
         frozen_all_docnames = frozenset(all_docnames)
 
-        ret: list[Node] = []
         excluded = Matcher(self.config.exclude_patterns)
         for entry in self.content:
             if not entry:
@@ -170,8 +171,6 @@ def parse_content(self, toctree: addnodes.toctree) -> list[Node]:
             toctree['entries'] = list(reversed(toctree['entries']))
             toctree['includefiles'] = list(reversed(toctree['includefiles']))
 
-        return ret
-
 
 class Author(SphinxDirective):
     """