Wikimedia Bugzilla is closed!

Created attachment 6172 [details]
Minimal patch against r51213 to fix the bug

The code that lays out the TOC corrects non-continuous sequences, for example a level-2 heading followed by a level-4. In looking over that code to answer a question as to how exactly that works, I found a bug in an odd case.

This wikitext:
 === A ===
 ==== B ====
 ===== C =====
 == D ==

Generates this TOC layout:
 1 A
   1.1 B
       1.1.1 C
       1.1.2 D

By any logic, it should do this instead:
 1 A
   1.1 B
       1.1.1 C
 2 D

The attached patch fixes this. This probably makes the special case for $toclevel == 2 && $level <= $levelCount[1] obsolete too, I'll attach that patch momentarily.