Merge pull request #4144 from sphinx-doc/fix/referenced_todo

fix #4063: Sphinx crushes when there are referenced todolist

CHANGES

@@ -30,6 +30,7 @@ Bugs fixed
 * #4108: Search word highlighting breaks SVG images
 * #3692: Unable to build HTML if writing .buildinfo failed
 * #4152: HTML writer crashes if a field list is placed on top of the document
+* #4063: Sphinx crashes when labelling directive '.. todolist::'
 
 Testing
 --------

sphinx/ext/todo.py

@@ -137,11 +137,14 @@ def process_todo_nodes(app, doctree, fromdocname):
         env.todo_all_todos = []  # type: ignore
 
     for node in doctree.traverse(todolist):
-        if not app.config['todo_include_todos']:
-            node.replace_self([])
-            continue
+        if node.get('ids'):
+            content = [nodes.target()]
+        else:
+            content = []
 
-        content = []
+        if not app.config['todo_include_todos']:
+            node.replace_self(content)
+            continue
 
         for todo_info in env.todo_all_todos:  # type: ignore
             para = nodes.paragraph(classes=['todo-source'])