Use Docutils 0.19 footnote styles (#10599)

CHANGES

@@ -26,6 +26,9 @@ Features added
   Pradyun Gedam.
 * #10619: LaTeX: new ``shadowShadowColor`` and ``shadowBorderColor`` configurations
   for :ref:`'sphinxsetup' <latexsphinxsetup>` key of :confval:`latex_elements`
+* #10599: HTML Theme: Wrap consecutive footnotes in an ``<aside>`` element when
+  using Docutils 0.18 or later, to allow for easier styling. This matches the
+  behaviour introduced in Docutils 0.19. Patch by Adam Turner.
 
 Bugs fixed
 ----------

sphinx/themes/basic/static/basic.css_t

@@ -629,7 +629,7 @@ ul.simple p {
     margin-bottom: 0;
 }
 
-/* Docutils 0.17 and older (footnotes & citations) */
+{%- if docutils_version_info[:2] < (0, 18) %}
 dl.footnote > dt,
 dl.citation > dt {
     float: left;
@@ -646,8 +646,7 @@ dl.citation > dd:after {
     content: "";
     clear: both;
 }
-
-/* Docutils 0.18+ (footnotes & citations) */
+{%- elif docutils_version_info[:2] >= (0, 18) %}
 aside.footnote > span,
 div.citation > span {
     float: left;
@@ -671,8 +670,7 @@ div.citation > p:last-of-type:after {
     content: "";
     clear: both;
 }
-
-/* Footnotes & citations ends */
+{%- endif %}
 
 dl.field-list {
     display: grid;

sphinx/util/docutils.py

@@ -18,6 +18,7 @@
 from docutils.parsers.rst.states import Inliner
 from docutils.statemachine import State, StateMachine, StringList
 from docutils.utils import Reporter, unescape
+from docutils.writers._html_base import HTMLTranslator  # NoQA
 
 from sphinx.deprecation import RemovedInSphinx70Warning, deprecated_alias
 from sphinx.errors import SphinxError
@@ -182,10 +183,46 @@ def using_user_docutils_conf(confdir: Optional[str]) -> Generator[None, None, No
             os.environ['DOCUTILSCONFIG'] = docutilsconfig
 
 
+@contextmanager
+def du19_footnotes() -> Generator[None, None, None]:
+    def visit_footnote(self, node):
+        label_style = self.settings.footnote_references
+        if not isinstance(node.previous_sibling(), type(node)):
+            self.body.append(f'<aside class="footnote-list {label_style}">\n')
+        self.body.append(self.starttag(node, 'aside',
+                                       classes=[node.tagname, label_style],
+                                       role="note"))
+
+    def depart_footnote(self, node):
+        self.body.append('</aside>\n')
+        if not isinstance(node.next_node(descend=False, siblings=True),
+                          type(node)):
+            self.body.append('</aside>\n')
+
+    old_visit_footnote = HTMLTranslator.visit_footnote
+    old_depart_footnote = HTMLTranslator.depart_footnote
+
+    # Only apply on Docutils 0.18 or 0.18.1, as 0.17 and earlier used a <dl> based
+    # approach, and 0.19 and later use the fixed approach by default.
+    if docutils.__version_info__[:2] == (0, 18):
+        HTMLTranslator.visit_footnote = visit_footnote  # type: ignore[assignment]
+        HTMLTranslator.depart_footnote = depart_footnote  # type: ignore[assignment]
+
+    try:
+        yield
+    finally:
+        if docutils.__version_info__[:2] == (0, 18):
+            HTMLTranslator.visit_footnote = old_visit_footnote  # type: ignore[assignment]
+            HTMLTranslator.depart_footnote = old_depart_footnote  # type: ignore[assignment]
+
+
 @contextmanager
 def patch_docutils(confdir: Optional[str] = None) -> Generator[None, None, None]:
     """Patch to docutils temporarily."""
-    with patched_get_language(), patched_rst_get_language(), using_user_docutils_conf(confdir):
+    with patched_get_language(), \
+         patched_rst_get_language(), \
+         using_user_docutils_conf(confdir), \
+         du19_footnotes():
         yield