demandimport: fix a crash in LazyFinder.__delattr__ I was tinkering with `with hgdemandimport.deactivated()` wrapped around loading the keyring module, and got spew that seemed to be confirmed by PyCharm. But I can't believe we haven't seen this before (and phabricator uses the same pattern): ** Unknown exception encountered with possibly-broken third-party extension "mercurial_keyring" 1.4.3 (keyring 23.11.0, backend unknown) ** which supports versions unknown of Mercurial. ** Please disable "mercurial_keyring" and try your action again. ** If that fixes the bug please report it to https://foss.heptapod.net/mercurial/mercurial_keyring/issues ** Python 3.9.15 (main, Oct 13 2022, 04:28:25) [GCC 7.5.0] ** Mercurial Distributed SCM (version 6.3.1) ** Extensions loaded: absorb, attorc 20220315, blackbox, eol, extdiff, fastannotate, lfs, mercurial_keyring 1.4.3 (keyring 23.11.0, backend unknown), phabblocker 20220315, phabricator 20220315, purge, rebase, schemes, share, show, strip, uncommit Traceback (most recent call last): File "/usr/local/bin/hg", line 59, in <module> dispatch.run() File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 143, in run status = dispatch(req) File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 232, in dispatch status = _rundispatch(req) File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 276, in _rundispatch ret = _runcatch(req) or 0 File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 451, in _runcatch return _callcatch(ui, _runcatchfunc) File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 461, in _callcatch return scmutil.callcatch(ui, func) File "/usr/local/lib/python3.9/site-packages/mercurial/scmutil.py", line 153, in callcatch return func() File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 441, in _runcatchfunc return _dispatch(req) File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 1265, in _dispatch return runcommand( File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 899, in runcommand ret = _runcommand(ui, options, cmd, d) File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 1277, in _runcommand return cmdfunc() File "/usr/local/lib/python3.9/site-packages/mercurial/dispatch.py", line 1263, in <lambda> d = lambda: util.checksignature(func)(ui, *args, **strcmdopt) File "/usr/local/lib/python3.9/site-packages/mercurial/util.py", line 1880, in check return func(*args, **kwargs) File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 962, in cmd_keyring_check user, pwd, source, final_url = handler.get_credentials( File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 497, in get_credentials keyring_pwd = password_store.get_http_password(keyring_url, actual_user) File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 287, in get_http_password return self._read_password_from_keyring( File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 335, in _read_password_from_keyring keyring = import_keyring() >> `with hgdemandimport.deactivated()` inserted here File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 120, in import_keyring return _import_keyring() File "/root/mercurial_keyring/mercurial_keyring/mercurial_keyring.py", line 133, in _import_keyring mod, was_imported_now = meu.direct_import_ext( File "/usr/lib/python3.9/site-packages/mercurial_extension_utils.py", line 1381, in direct_import_ext __import__(module_name) File "<frozen importlib._bootstrap>", line 1007, in _find_and_load File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 680, in _load_unlocked File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 46, in exec_module self.loader.exec_module(module) File "/usr/lib/python3.9/site-packages/keyring/__init__.py", line 1, in <module> from .core import ( File "<frozen importlib._bootstrap>", line 1007, in _find_and_load File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 680, in _load_unlocked File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 46, in exec_module self.loader.exec_module(module) File "/usr/lib/python3.9/site-packages/keyring/core.py", line 11, in <module> from . import backend, credentials File "<frozen importlib._bootstrap>", line 1007, in _find_and_load File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 680, in _load_unlocked File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 46, in exec_module self.loader.exec_module(module) File "/usr/lib/python3.9/site-packages/keyring/backend.py", line 13, in <module> from .py312compat import metadata File "<frozen importlib._bootstrap>", line 1007, in _find_and_load File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 680, in _load_unlocked File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 46, in exec_module self.loader.exec_module(module) File "/usr/lib/python3.9/site-packages/keyring/py312compat.py", line 10, in <module> import importlib_metadata as metadata # type: ignore File "<frozen importlib._bootstrap>", line 1007, in _find_and_load File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 680, in _load_unlocked File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 46, in exec_module self.loader.exec_module(module) File "/usr/lib/python3.9/site-packages/importlib_metadata/__init__.py", line 715, in <module> class MetadataPathFinder(NullFinder, DistributionFinder): File "/usr/lib/python3.9/site-packages/importlib_metadata/_compat.py", line 24, in install disable_stdlib_finder() File "/usr/lib/python3.9/site-packages/importlib_metadata/_compat.py", line 43, in disable_stdlib_finder del finder.find_distributions File "/usr/local/lib/python3.9/site-packages/hgdemandimport/demandimportpy3.py", line 88, in __delattr__ return delattr(object.__getattribute__(self, "_finder")) TypeError: delattr expected 2 arguments, got 1

# demandimportpy3 - global demand-loading of modules for Mercurial
#
# Copyright 2017 Facebook Inc.
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

"""Lazy loading for Python 3.6 and above.

This uses the new importlib finder/loader functionality available in Python 3.5
and up. The code reuses most of the mechanics implemented inside importlib.util,
but with a few additions:

* Allow excluding certain modules from lazy imports.
* Expose an interface that's substantially the same as demandimport for
  Python 2.

This also has some limitations compared to the Python 2 implementation:

* Much of the logic is per-package, not per-module, so any packages loaded
  before demandimport is enabled will not be lazily imported in the future. In
  practice, we only expect builtins to be loaded before demandimport is
  enabled.
"""

# This line is unnecessary, but it satisfies test-check-py3-compat.t.

import contextlib
import importlib.util
import sys

from . import tracing

_deactivated = False


class _lazyloaderex(importlib.util.LazyLoader):
    """This is a LazyLoader except it also follows the _deactivated global and
    the ignore list.
    """

    def exec_module(self, module):
        """Make the module load lazily."""
        with tracing.log('demandimport %s', module):
            if _deactivated or module.__name__ in ignores:
                self.loader.exec_module(module)
            else:
                super().exec_module(module)


class LazyFinder:
    """A wrapper around a ``MetaPathFinder`` that makes loaders lazy.

    ``sys.meta_path`` finders have their ``find_spec()`` called to locate a
    module. This returns a ``ModuleSpec`` if found or ``None``. The
    ``ModuleSpec`` has a ``loader`` attribute, which is called to actually
    load a module.

    Our class wraps an existing finder and overloads its ``find_spec()`` to
    replace the ``loader`` with our lazy loader proxy.

    We have to use __getattribute__ to proxy the instance because some meta
    path finders don't support monkeypatching.
    """

    __slots__ = ("_finder",)

    def __init__(self, finder):
        object.__setattr__(self, "_finder", finder)

    def __repr__(self):
        return "<LazyFinder for %r>" % object.__getattribute__(self, "_finder")

    # __bool__ is canonical Python 3. But check-code insists on __nonzero__ being
    # defined via `def`.
    def __nonzero__(self):
        return bool(object.__getattribute__(self, "_finder"))

    __bool__ = __nonzero__

    def __getattribute__(self, name):
        if name in ("_finder", "find_spec"):
            return object.__getattribute__(self, name)

        return getattr(object.__getattribute__(self, "_finder"), name)

    def __delattr__(self, name):
        return delattr(object.__getattribute__(self, "_finder"), name)

    def __setattr__(self, name, value):
        return setattr(object.__getattribute__(self, "_finder"), name, value)

    def find_spec(self, fullname, path, target=None):
        finder = object.__getattribute__(self, "_finder")
        try:
            find_spec = finder.find_spec
        except AttributeError:
            loader = finder.find_module(fullname, path)
            if loader is None:
                spec = None
            else:
                spec = importlib.util.spec_from_loader(fullname, loader)
        else:
            spec = find_spec(fullname, path, target)

        # Lazy loader requires exec_module().
        if (
            spec is not None
            and spec.loader is not None
            and getattr(spec.loader, "exec_module", None)
        ):
            spec.loader = _lazyloaderex(spec.loader)

        return spec


ignores = set()


def init(ignoreset):
    global ignores
    ignores = ignoreset


def isenabled():
    return not _deactivated and any(
        isinstance(finder, LazyFinder) for finder in sys.meta_path
    )


def disable():
    new_finders = []
    for finder in sys.meta_path:
        new_finders.append(
            finder._finder if isinstance(finder, LazyFinder) else finder
        )
    sys.meta_path[:] = new_finders


def enable():
    new_finders = []
    for finder in sys.meta_path:
        new_finders.append(
            LazyFinder(finder) if not isinstance(finder, LazyFinder) else finder
        )
    sys.meta_path[:] = new_finders


@contextlib.contextmanager
def deactivated():
    # This implementation is a bit different from Python 2's. Python 3
    # maintains a per-package finder cache in sys.path_importer_cache (see
    # PEP 302). This means that we can't just call disable + enable.
    # If we do that, in situations like:
    #
    #   demandimport.enable()
    #   ...
    #   from foo.bar import mod1
    #   with demandimport.deactivated():
    #       from foo.bar import mod2
    #
    # mod2 will be imported lazily. (The converse also holds -- whatever finder
    # first gets cached will be used.)
    #
    # Instead, have a global flag the LazyLoader can use.
    global _deactivated
    demandenabled = isenabled()
    if demandenabled:
        _deactivated = True
    try:
        yield
    finally:
        if demandenabled:
            _deactivated = False