fix: fix render_toc_url method for rendering empty iterable, via #407

Author: lepture

src/mistune/toc.py

@@ -86,7 +86,7 @@ def render_toc_ul(toc: Iterable[Tuple[int, str, str]]) -> str:
     if not toc:
         return ''
 
-    s = '<ul>\n'
+    s = ''
     levels: List[int] = []
     for level, k, text in toc:
         item = '<a href="#{}">{}</a>'.format(k, text)
@@ -121,4 +121,6 @@ def render_toc_ul(toc: Iterable[Tuple[int, str, str]]) -> str:
         s += '</li>\n</ul>\n'
         levels.pop()
 
-    return s + '</li>\n</ul>\n'
+    if not s:
+        return ''
+    return '<ul>\n' + s + '</li>\n</ul>\n'

tests/test_hooks.py

@@ -22,5 +22,8 @@ def heading_id(token, i):
         html = md('# h1')
         self.assertEqual(html, '<h1 id="t-1">h1</h1>\n')
 
+    def test_render_empty_toc(self):
+        self.assertEqual(render_toc_ul([]), '')
+        self.assertEqual(render_toc_ul(filter(lambda _: False, [])), '')
 
 TestTocHook.load_fixtures('hook_toc.txt')