fix #1058 Footnote backlinks do not work

tests/root/contents.txt

@@ -28,6 +28,7 @@ Contents:
    extensions
    versioning/index
    only
+   footnote
    i18n/index
 
    Python <http://python.org/>

tests/root/footnote.txt

@@ -0,0 +1,40 @@
+:tocdepth: 2
+
+Testing footnote and citation
+================================
+.. #1058 footnote-backlinks-do-not-work
+
+numbered footnote
+--------------------
+
+[1]_
+
+auto-numbered footnote
+------------------------------
+
+[#]_
+
+named footnote
+--------------------
+
+[#foo]_
+
+citation
+--------------------
+
+[bar]_
+
+footenotes
+--------------------
+
+.. rubric:: Footnotes
+
+.. [1] numbered
+
+.. [#] auto numbered
+
+.. [#foo] named
+
+.. rubric:: Citations
+
+.. [bar] cite

tests/test_footnote.py

@@ -0,0 +1,37 @@
+# -*- coding: utf-8 -*-
+"""
+    test_footnote
+    ~~~~~~~~~~~~~
+
+    Test for footnote and citation.
+
+    :copyright: Copyright 2010 by the Sphinx team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import re
+
+from util import *
+
+
+def teardown_module():
+    (test_root / '_build').rmtree(True)
+
+
+@with_app(buildername='html')
+def test_html(app):
+    app.builder.build(['footnote'])
+    result = (app.outdir / 'footnote.html').text(encoding='utf-8')
+    expects = [
+        '<a class="footnote-reference" href="#id5" id="id1">[1]</a>',
+        '<a class="footnote-reference" href="#id6" id="id2">[2]</a>',
+        '<a class="footnote-reference" href="#foo" id="id3">[3]</a>',
+        '<a class="reference internal" href="#bar" id="id4">[bar]</a>',
+        '<a class="fn-backref" href="#id1">[1]</a>',
+        '<a class="fn-backref" href="#id2">[2]</a>',
+        '<a class="fn-backref" href="#id3">[3]</a>',
+        '<a class="fn-backref" href="#id4">[bar]</a>',
+        ]
+    for expect in expects:
+        matches = re.findall(re.escape(expect), result)
+        assert len(matches) == 1