Fix duplicate entries in TOC when using mixed headers

lib/markdown2.py

@@ -1811,7 +1811,7 @@ def _header_id_exists(self, text):
         prefix = self.extras['header-ids'].get('prefix')
         if prefix and isinstance(prefix, str):
             header_id = prefix + '-' + header_id
-        return header_id in self._count_from_header_id
+        return header_id in self._count_from_header_id or header_id in map(lambda x: x[1], self._toc)
 
     def _toc_add_entry(self, level, id, name):
         if level > self._toc_depth:

test/tm-cases/toc_duplicate_entries.html

@@ -0,0 +1,5 @@
+<h1 id="abc">abc</h1>
+
+<h1 id="abc-2">abc</h1>
+
+<h1 id="abc-3">abc</h1>

test/tm-cases/toc_duplicate_entries.opts

@@ -0,0 +1,6 @@
+{
+  "extras": {
+    "toc": {"depth": 3},
+    "header-ids": {"mixed": True}
+  }
+}

test/tm-cases/toc_duplicate_entries.text

@@ -0,0 +1,3 @@
+# abc
+# abc
+# abc

test/tm-cases/toc_duplicate_entries.toc_html

@@ -0,0 +1,5 @@
+<ul>
+  <li><a href="#abc">abc</a></li>
+  <li><a href="#abc-2">abc</a></li>
+  <li><a href="#abc-3">abc</a></li>
+</ul>