(In reply to comment #0)

This finds af125df5199b5c232bf335d735cecc6d8f8e9784 as the change which
caused this bug.

CC'ing author and reviewer.

For the record, here is the traceback:

0. wfRunHooks at GlobalFunctions.php:3885

1. Hooks::run at Hooks.php:136
2. wfProfileIn at Profiler.php:38
3. Profiler::profileIn at Profiler.php:207
4. Profiler::debug at Profiler.php:719
5. wfDebug at GlobalFunctions.php:934
6. wfRunHooks at GlobalFunctions.php:3885

This is all because of the undocumented Debug hook in wfDebug. The Debug hook is used if an extension wants to stop a debug message from being sent out (it cannot change the message because it's not sent by reference).

I really don't see the point of this hook, and ideally the wfDebug and related functions should be as low-level and avoid calling other code as much as possible to avoid situations like this. So I suggest just removing that hook, which would solve this loop.

Change 90453 had a related patch set uploaded by EBernhardson:
Remove 'Debug' hook from wfDebug and wfDebugLog

https://gerrit.wikimedia.org/r/90453

Change 90453 merged by jenkins-bot:
Remove 'Debug' hook from wfDebug and wfDebugLog

https://gerrit.wikimedia.org/r/90453

(In reply to comment #2)

This is all because of the undocumented Debug hook in wfDebug. The Debug hook
is used if an extension wants to stop a debug message from being sent out (it
cannot change the message because it's not sent by reference).

I really don't see the point of this hook, ...

It was added in r88843 (bug 29140) and in fact documented.

bug 29140 does seem like a reasonable use case, but i wonder if it could be implemented such that it doesn't hook into each call to wfDebug. I havn't fully investigated whats happening here in mw, but in libraries like Monolog they have the ability to build a list of messages and cache them in-process, to be flushed to an external source(like firebug) with a single call at the end of the request rather than every ->log() call. I wonder if something similar could be appropriate for re-enabling firebug.