# 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"))

    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