Emit warning for nested numbered toctrees (refs: #3142)

CHANGES

@@ -6,6 +6,7 @@ Features added
 
 * #3241: emit latex warning if buggy titlesec (ref #3210)
 * #3194: Refer the $MAKE environment variable to determine ``make`` command
+* Emit warning for nested numbered toctrees (refs: #3142)
 
 Bugs fixed
 ----------

doc/config.rst

@@ -233,6 +233,7 @@ General configuration
    * ref.citation
    * ref.doc
    * misc.highlighting_failure
+   * toc.secnum
    * epub.unknown_project_files
 
    You can choose from these types.

sphinx/environment/managers/toctree.py

@@ -464,10 +464,14 @@ class Toctree(EnvironmentManager):
             if depth == 0:
                 return
             for (title, ref) in toctreenode['entries']:
-                if url_re.match(ref) or ref == 'self' or ref in assigned:
+                if url_re.match(ref) or ref == 'self':
                     # don't mess with those
                     continue
-                if ref in self.tocs:
+                elif ref in assigned:
+                    self.env.warn_node('%s is already assigned section numbers '
+                                       '(nested numbered toctree?)' % ref,
+                                       toctreenode, type='toc', subtype='secnum')
+                elif ref in self.tocs:
                     secnums = self.toc_secnumbers[ref] = {}
                     assigned.add(ref)
                     _walk_toc(self.tocs[ref], secnums, depth,