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−# demandimportpy3 - global demand-loading of modules for Mercurial
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−#
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−# Copyright 2017 Facebook Inc.
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−#
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−# This software may be used and distributed according to the terms of the
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−# GNU General Public License version 2 or any later version.
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−
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−"""Lazy loading for Python 3.6 and above.
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−
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−This uses the new importlib finder/loader functionality available in Python 3.5
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−and up. The code reuses most of the mechanics implemented inside importlib.util,
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−but with a few additions:
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−
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−* Allow excluding certain modules from lazy imports.
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−* Expose an interface that's substantially the same as demandimport for
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−  Python 2.
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−
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−This also has some limitations compared to the Python 2 implementation:
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−
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−* Much of the logic is per-package, not per-module, so any packages loaded
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−  before demandimport is enabled will not be lazily imported in the future. In
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−  practice, we only expect builtins to be loaded before demandimport is
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−  enabled.
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−"""
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−
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−# This line is unnecessary, but it satisfies test-check-py3-compat.t.
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−from __future__ import absolute_import
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−
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−import contextlib
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−import os
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−import sys
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−
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−import importlib.abc
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−import importlib.machinery
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−import importlib.util
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−
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−_deactivated = False
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−
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−class _lazyloaderex(importlib.util.LazyLoader):
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−    """This is a LazyLoader except it also follows the _deactivated global and
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−    the ignore list.
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−    """
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−    def exec_module(self, module):
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−        """Make the module load lazily."""
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−        if _deactivated or module.__name__ in ignore:
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−            self.loader.exec_module(module)
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−        else:
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−            super().exec_module(module)
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−
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−# This is 3.6+ because with Python 3.5 it isn't possible to lazily load
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−# extensions. See the discussion in https://python.org/sf/26186 for more.
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−_extensions_loader = _lazyloaderex.factory(
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−    importlib.machinery.ExtensionFileLoader)
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−_bytecode_loader = _lazyloaderex.factory(
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−    importlib.machinery.SourcelessFileLoader)
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−_source_loader = _lazyloaderex.factory(importlib.machinery.SourceFileLoader)
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−
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−def _makefinder(path):
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−    return importlib.machinery.FileFinder(
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−        path,
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−        # This is the order in which loaders are passed in in core Python.
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−        (_extensions_loader, importlib.machinery.EXTENSION_SUFFIXES),
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−        (_source_loader, importlib.machinery.SOURCE_SUFFIXES),
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−        (_bytecode_loader, importlib.machinery.BYTECODE_SUFFIXES),
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−    )
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−
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−ignore = []
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−
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−def init(ignorelist):
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−    global ignore
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−    ignore = ignorelist
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−
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−def isenabled():
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−    return _makefinder in sys.path_hooks and not _deactivated
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−
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−def disable():
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−    try:
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−        while True:
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−            sys.path_hooks.remove(_makefinder)
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−    except ValueError:
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−        pass
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−
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−def enable():
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−    if os.environ.get('HGDEMANDIMPORT') != 'disable':
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−        sys.path_hooks.insert(0, _makefinder)
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−
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−@contextlib.contextmanager
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−def deactivated():
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−    # This implementation is a bit different from Python 2's. Python 3
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−    # maintains a per-package finder cache in sys.path_importer_cache (see
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−    # PEP 302). This means that we can't just call disable + enable.
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−    # If we do that, in situations like:
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−    #
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−    #   demandimport.enable()
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−    #   ...
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−    #   from foo.bar import mod1
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−    #   with demandimport.deactivated():
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−    #       from foo.bar import mod2
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−    #
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−    # mod2 will be imported lazily. (The converse also holds -- whatever finder
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−    # first gets cached will be used.)
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−    #
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−    # Instead, have a global flag the LazyLoader can use.
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−    global _deactivated
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−    demandenabled = isenabled()
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−    if demandenabled:
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−        _deactivated = True
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−    try:
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−        yield
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−    finally:
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−        if demandenabled:
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−            _deactivated = False