I've got hgweb (the Mercurial web app) crashing on guess_type() in
2.6.2, but not in 2.5.4. I'm passing in a filename like
'/home/djc/src/hg/crew/templates/static/hglogo.png'. Doesn't happen on
the REPL, but happens in side the hg serve web server.

Traceback (most recent call last):
  File "/home/djc/src/hg/crew/mercurial/hgweb/server.py", line 67, in
do_POST
    self.do_write()
  File "/home/djc/src/hg/crew/mercurial/hgweb/server.py", line 60, in
do_write
    self.do_hgweb()
  File "/home/djc/src/hg/crew/mercurial/hgweb/server.py", line 124, in
do_hgweb
    for chunk in self.server.application(env, self._start_response):
  File "/home/djc/src/hg/crew/mercurial/hgweb/hgwebdir_mod.py", line 91,
in __call__
    return self.run_wsgi(req)
  File "/home/djc/src/hg/crew/mercurial/hgweb/hgwebdir_mod.py", line
132, in run_wsgi
    return (staticfile(static, fname, req),)
  File "/home/djc/src/hg/crew/mercurial/hgweb/common.py", line 73, in
staticfile
    ct = mimetypes.guess_type(path)[0] or "text/plain"
  File "/usr/lib/python2.6/mimetypes.py", line 244, in guess_type
    return guess_type(url, strict)
(... snip ...)
  File "/usr/lib/python2.6/mimetypes.py", line 244, in guess_type
    return guess_type(url, strict)
RuntimeError: maximum recursion depth exceeded

georg.brandl remarked it might be due to demandimport. That doesn't seem
to be the case:

>>> from mercurial import demandimport
>>> demandimport.enable()
>>> import mimetypes
>>>
mimetypes.guess_type('/home/djc/src/hg/crew/templates/static/hglogo.png')
('image/png', None)

This could well be due to the SocketServer.ThreadingMixIn that's being
used by the hg serve built-in web server (since it doesn't show on REPL
or, as far as I can see, when used from within Apache + mod_wsgi).

The function monkeypatching hack should be replaced with something more
robust.
(what might happen here is that init() is first called from another
thread, sets inited to True and then crashes for whatever reason, so
guess_type() isn't actually monkeypatched)

The plan is to replace init() with something like:

_db = None

def init():
    global _db
    db = ...   
    # initialize database
    # set it to global only when it's fully ready
    _db = db

and guess_type() with:

def guess_type():
    if _db is None:
       init()
    return _db.guess_type()

(same for other functions)

In the meantime, hgweb could probably call mimetypes.init() at the
beginning (before spawning threads).

For the record, here is a test script showcasing the problem.

Committed a fix in r72045. Thanks for the report!