view tests/test-devel-warnings.t @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

  $ cat << EOF > buggylocking.py
  > """A small extension that tests our developer warnings
  > """
  > 
  > from mercurial import error, registrar, repair, util
  > 
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > 
  > @command(b'buggylocking', [], '')
  > def buggylocking(ui, repo):
  >     lo = repo.lock()
  >     wl = repo.wlock()
  >     wl.release()
  >     lo.release()
  > 
  > @command(b'buggytransaction', [], '')
  > def buggylocking(ui, repo):
  >     tr = repo.transaction(b'buggy')
  >     # make sure we rollback the transaction as we don't want to rely on the__del__
  >     tr.release()
  > 
  > @command(b'properlocking', [], '')
  > def properlocking(ui, repo):
  >     """check that reentrance is fine"""
  >     wl = repo.wlock()
  >     lo = repo.lock()
  >     tr = repo.transaction(b'proper')
  >     tr2 = repo.transaction(b'proper')
  >     lo2 = repo.lock()
  >     wl2 = repo.wlock()
  >     wl2.release()
  >     lo2.release()
  >     tr2.close()
  >     tr.close()
  >     lo.release()
  >     wl.release()
  > 
  > @command(b'nowaitlocking', [], '')
  > def nowaitlocking(ui, repo):
  >     lo = repo.lock()
  >     wl = repo.wlock(wait=False)
  >     wl.release()
  >     lo.release()
  > 
  > @command(b'no-wlock-write', [], '')
  > def nowlockwrite(ui, repo):
  >     with repo.vfs(b'branch', b'a'):
  >         pass
  > 
  > @command(b'no-lock-write', [], '')
  > def nolockwrite(ui, repo):
  >     with repo.svfs(b'fncache', b'a'):
  >         pass
  > 
  > @command(b'stripintr', [], '')
  > def stripintr(ui, repo):
  >     lo = repo.lock()
  >     tr = repo.transaction(b'foobar')
  >     try:
  >         repair.strip(repo.ui, repo, [repo[b'.'].node()])
  >     finally:
  >         lo.release()
  > @command(b'oldanddeprecated', [], '')
  > def oldanddeprecated(ui, repo):
  >     """test deprecation warning API"""
  >     def foobar(ui):
  >         ui.deprecwarn(b'foorbar is deprecated, go shopping', b'42.1337')
  >     foobar(ui)
  > @command(b'nouiwarning', [], '')
  > def nouiwarning(ui, repo):
  >     util.nouideprecwarn(b'this is a test', b'13.37')
  > @command(b'programmingerror', [], '')
  > def programmingerror(ui, repo):
  >     raise error.ProgrammingError(b'something went wrong', hint=b'try again')
  > EOF

  $ cat << EOF >> $HGRCPATH
  > [extensions]
  > buggylocking=$TESTTMP/buggylocking.py
  > mock=$TESTDIR/mockblackbox.py
  > blackbox=
  > [devel]
  > all-warnings=1
  > [blackbox]
  > track = command, commandexception, commandfinish, develwarn
  > EOF

  $ hg init lock-checker
  $ cd lock-checker
  $ hg buggylocking
  devel-warn: "wlock" acquired after "lock" at: $TESTTMP/buggylocking.py:* (buggylocking) (glob)
  $ cat << EOF >> $HGRCPATH
  > [devel]
  > all=0
  > check-locks=1
  > EOF
  $ hg buggylocking
  devel-warn: "wlock" acquired after "lock" at: $TESTTMP/buggylocking.py:* (buggylocking) (glob)
#if no-chg no-pyoxidizer
  $ hg buggylocking --traceback
  devel-warn: "wlock" acquired after "lock" at:
   */hg:* in <module> (glob) (?)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in buggylocking (glob)
#endif
#if chg no-pyoxidizer
  $ hg buggylocking --traceback
  devel-warn: "wlock" acquired after "lock" at:
   */hg:* in <module> (glob) (?)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   */mercurial/commands.py:* in serve (glob)
   */mercurial/server.py:* in runservice (glob)
   */mercurial/commandserver.py:* in run (glob)
   */mercurial/commandserver.py:* in _mainloop (glob)
   */mercurial/commandserver.py:* in _acceptnewconnection (glob)
   */mercurial/commandserver.py:* in _runworker (glob)
   */mercurial/commandserver.py:* in _serverequest (glob)
   */mercurial/commandserver.py:* in serve (glob)
   */mercurial/commandserver.py:* in serveone (glob)
   */mercurial/chgserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in _dispatchcommand (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in buggylocking (glob)
#endif
#if pyoxidizer
  $ hg buggylocking --traceback
  devel-warn: "wlock" acquired after "lock" at:
   <string>:* (glob)
   mercurial.dispatch:* in run (glob)
   mercurial.dispatch:* in dispatch (glob)
   mercurial.dispatch:* in _rundispatch (glob)
   mercurial.dispatch:* in _runcatch (glob)
   mercurial.dispatch:* in _callcatch (glob)
   mercurial.scmutil:* in callcatch (glob)
   mercurial.dispatch:* in _runcatchfunc (glob)
   mercurial.dispatch:* in _dispatch (glob)
   mercurial.dispatch:* in runcommand (glob)
   mercurial.dispatch:* in _runcommand (glob)
   mercurial.dispatch:* in <lambda> (glob)
   mercurial.util:* in check (glob)
   $TESTTMP/buggylocking.py:* in buggylocking (glob)
#endif
  $ hg properlocking
  $ hg nowaitlocking

Writing without lock

  $ hg no-wlock-write
  devel-warn: write with no wlock: "branch" at: $TESTTMP/buggylocking.py:* (nowlockwrite) (glob)

  $ hg no-lock-write
  devel-warn: write with no lock: "fncache" at: $TESTTMP/buggylocking.py:* (nolockwrite) (glob)

Stripping from a transaction

  $ echo a > a
  $ hg add a
  $ hg commit -m a
  $ hg stripintr 2>&1 | egrep -v '^(\*\*|  )'
  Traceback (most recent call last):
  *ProgrammingError: cannot strip from inside a transaction (glob)

  $ hg oldanddeprecated
  devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at: $TESTTMP/buggylocking.py:* (oldanddeprecated) (glob)

#if no-chg no-pyoxidizer
  $ hg oldanddeprecated --traceback
  devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   */hg:* in <module> (glob) (?)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
#endif
#if chg no-pyoxidizer
  $ hg oldanddeprecated --traceback
  devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   */hg:* in <module> (glob)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   */mercurial/commands.py:* in serve (glob)
   */mercurial/server.py:* in runservice (glob)
   */mercurial/commandserver.py:* in run (glob)
   */mercurial/commandserver.py:* in _mainloop (glob)
   */mercurial/commandserver.py:* in _acceptnewconnection (glob)
   */mercurial/commandserver.py:* in _runworker (glob)
   */mercurial/commandserver.py:* in _serverequest (glob)
   */mercurial/commandserver.py:* in serve (glob)
   */mercurial/commandserver.py:* in serveone (glob)
   */mercurial/chgserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in _dispatchcommand (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
#endif
#if pyoxidizer
  $ hg oldanddeprecated --traceback
  devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   <string>:* (glob)
   mercurial.dispatch:* in run (glob)
   mercurial.dispatch:* in dispatch (glob)
   mercurial.dispatch:* in _rundispatch (glob)
   mercurial.dispatch:* in _runcatch (glob)
   mercurial.dispatch:* in _callcatch (glob)
   mercurial.scmutil:* in callcatch (glob)
   mercurial.dispatch:* in _runcatchfunc (glob)
   mercurial.dispatch:* in _dispatch (glob)
   mercurial.dispatch:* in runcommand (glob)
   mercurial.dispatch:* in _runcommand (glob)
   mercurial.dispatch:* in <lambda> (glob)
   mercurial.util:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
#endif

#if no-chg no-pyoxidizer
  $ hg blackbox -l 7
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at: $TESTTMP/buggylocking.py:* (oldanddeprecated) (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   */hg:* in <module> (glob) (?)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> blackbox -l 7
#endif
#if chg no-pyoxidizer
  $ hg blackbox -l 7
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at: $TESTTMP/buggylocking.py:* (oldanddeprecated) (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   */hg:* in <module> (glob)
   */mercurial/dispatch.py:* in run (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   */mercurial/commands.py:* in serve (glob)
   */mercurial/server.py:* in runservice (glob)
   */mercurial/commandserver.py:* in run (glob)
   */mercurial/commandserver.py:* in _mainloop (glob)
   */mercurial/commandserver.py:* in _acceptnewconnection (glob)
   */mercurial/commandserver.py:* in _runworker (glob)
   */mercurial/commandserver.py:* in _serverequest (glob)
   */mercurial/commandserver.py:* in serve (glob)
   */mercurial/commandserver.py:* in serveone (glob)
   */mercurial/chgserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in runcommand (glob)
   */mercurial/commandserver.py:* in _dispatchcommand (glob)
   */mercurial/dispatch.py:* in dispatch (glob)
   */mercurial/dispatch.py:* in _rundispatch (glob)
   */mercurial/dispatch.py:* in _runcatch (glob)
   */mercurial/dispatch.py:* in _callcatch (glob)
   */mercurial/scmutil.py:* in callcatch (glob)
   */mercurial/dispatch.py:* in _runcatchfunc (glob)
   */mercurial/dispatch.py:* in _dispatch (glob)
   */mercurial/dispatch.py:* in runcommand (glob)
   */mercurial/dispatch.py:* in _runcommand (glob)
   */mercurial/dispatch.py:* in <lambda> (glob)
   */mercurial/util.py:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> blackbox -l 7
#endif
#if pyoxidizer
  $ hg blackbox -l 7
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at: $TESTTMP/buggylocking.py:* (oldanddeprecated) (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> devel-warn: foorbar is deprecated, go shopping
  (compatibility will be dropped after Mercurial-42.1337, update your code.) at:
   <string>:* in <module> (glob)
   mercurial.dispatch:* in run (glob)
   mercurial.dispatch:* in dispatch (glob)
   mercurial.dispatch:* in _rundispatch (glob)
   mercurial.dispatch:* in _runcatch (glob)
   mercurial.dispatch:* in _callcatch (glob)
   mercurial.scmutil* in callcatch (glob)
   mercurial.dispatch:* in _runcatchfunc (glob)
   mercurial.dispatch:* in _dispatch (glob)
   mercurial.dispatch:* in runcommand (glob)
   mercurial.dispatch:* in _runcommand (glob)
   mercurial.dispatch:* in <lambda> (glob)
   mercurial.util:* in check (glob)
   $TESTTMP/buggylocking.py:* in oldanddeprecated (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> oldanddeprecated --traceback exited 0 after * seconds (glob)
  1970-01-01 00:00:00.000 bob @cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b (5000)> blackbox -l 7
#endif

Test programming error failure:

  $ hg buggytransaction 2>&1 | egrep -v '^  '
  ** Unknown exception encountered with possibly-broken third-party extension "buggylocking" (version N/A)
  ** which supports versions unknown of Mercurial.
  ** Please disable "buggylocking" and try your action again.
  ** If that fixes the bug please report it to the extension author.
  ** Python * (glob)
  ** Mercurial Distributed SCM (*) (glob)
  ** Extensions loaded: * (glob)
  ** ProgrammingError: transaction requires locking
  Traceback (most recent call last):
  *ProgrammingError: transaction requires locking (glob)

  $ hg programmingerror 2>&1 | egrep -v '^  '
  ** Unknown exception encountered with possibly-broken third-party extension "buggylocking" (version N/A)
  ** which supports versions unknown of Mercurial.
  ** Please disable "buggylocking" and try your action again.
  ** If that fixes the bug please report it to the extension author.
  ** Python * (glob)
  ** Mercurial Distributed SCM (*) (glob)
  ** Extensions loaded: * (glob)
  ** ProgrammingError: something went wrong
  ** (try again)
  Traceback (most recent call last):
  *ProgrammingError: something went wrong (glob)

Old style deprecation warning

  $ hg nouiwarning
  $TESTTMP/buggylocking.py:*: DeprecationWarning: this is a test (glob)
  (compatibility will be dropped after Mercurial-13.37, update your code.)
    util.nouideprecwarn(b'this is a test', b'13.37')

(disabled outside of test run)

  $ HGEMITWARNINGS= hg nouiwarning

Test warning on config option access and registration

  $ cat << EOF > ${TESTTMP}/buggyconfig.py
  > """A small extension that tests our developer warnings for config"""
  > 
  > from mercurial import configitems, registrar
  > 
  > cmdtable = {}
  > command = registrar.command(cmdtable)
  > 
  > configtable = {}
  > configitem = registrar.configitem(configtable)
  > 
  > configitem(b'test', b'some', default=b'foo')
  > configitem(b'test', b'dynamic', default=configitems.dynamicdefault)
  > configitem(b'test', b'callable', default=list)
  > # overwrite a core config
  > configitem(b'ui', b'quiet', default=False)
  > configitem(b'ui', b'interactive', default=None)
  > 
  > @command(b'buggyconfig')
  > def cmdbuggyconfig(ui, repo):
  >     repo.ui.config(b'ui', b'quiet', True)
  >     repo.ui.config(b'ui', b'interactive', False)
  >     repo.ui.config(b'test', b'some', b'bar')
  >     repo.ui.config(b'test', b'some', b'foo')
  >     repo.ui.config(b'test', b'dynamic', b'some-required-default')
  >     repo.ui.config(b'test', b'dynamic')
  >     repo.ui.config(b'test', b'callable', [])
  >     repo.ui.config(b'test', b'callable', b'foo')
  >     repo.ui.config(b'test', b'unregistered')
  >     repo.ui.config(b'unregistered', b'unregistered')
  > EOF

  $ hg --config "extensions.buggyconfig=${TESTTMP}/buggyconfig.py" buggyconfig
  devel-warn: extension 'buggyconfig' overwrite config item 'ui.interactive' at: */mercurial/extensions.py:* (_loadextra) (glob) (no-pyoxidizer !)
  devel-warn: extension 'buggyconfig' overwrite config item 'ui.quiet' at: */mercurial/extensions.py:* (_loadextra) (glob) (no-pyoxidizer !)
  devel-warn: extension 'buggyconfig' overwrite config item 'ui.interactive' at: mercurial.extensions:* (_loadextra) (glob) (pyoxidizer !)
  devel-warn: extension 'buggyconfig' overwrite config item 'ui.quiet' at: mercurial.extensions:* (_loadextra) (glob) (pyoxidizer !)
  devel-warn: specifying a mismatched default value for a registered config item: 'ui.quiet' 'True' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: specifying a mismatched default value for a registered config item: 'ui.interactive' 'False' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: specifying a mismatched default value for a registered config item: 'test.some' 'bar' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: config item requires an explicit default value: 'test.dynamic' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: specifying a mismatched default value for a registered config item: 'test.callable' 'foo' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: accessing unregistered config item: 'test.unregistered' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)
  devel-warn: accessing unregistered config item: 'unregistered.unregistered' at: $TESTTMP/buggyconfig.py:* (cmdbuggyconfig) (glob)

  $ cd ..