hgdemandimport/demandimportpy3.py

rebase: use scmutil.cleanupnodes (issue5606) (BC)

This patch migrates rebase to use scmutil.cleanupnodes API. It simplifies
the code and makes rebase code reusable inside a transaction.

This is a BC because the backup file is no longer strip-backup/*-backup.hg,
but strip-backup/*-rebase.hg. The latter looks more reasonable since the
directory name is "strip-backup" so there is no need to repeat "backup".

I think the backup file name change is probably fine as a BC, since we have
changed it before (aa4a1672583e) and didn't get complains. The end result
of this series will be a much more consistent and unified backup names:

  command  | old backup file suffix       | new backup file suffix
  -------------------------------------------------------------------
  amend    | amend-backup.hg              | amend.hg
  histedit | backup.hg (could be 2 files) | histedit.hg (single file)
  rebase   | backup.hg                    | rebase.hg
  strip    | backup.hg                    | backup.hg

(note: backup files are under .hg/strip-backup)

It also fixes issue5606 as a side effect because the new "delayedstrip" code
path will carefully examine nodes (safestriproots) to make sure orphaned
changesets won't get stripped by accident.

Some warning messages are changed to the new "warning: orphaned descendants
detected, not stripping HASHES", which provides more information about
exactly what changesets are left behind.

Another minor behavior change is when there is an obsoleted changeset with a
successor in the destination branch, bookmarks pointing to that obsoleted
changeset will not be moved. I have commented in test-rebase-obsolete.t
explaining why that is more desirable.

# 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.
from __future__ import absolute_import

import contextlib
import os
import sys

import importlib.abc
import importlib.machinery
import importlib.util

_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."""
        if _deactivated or module.__name__ in ignore:
            self.loader.exec_module(module)
        else:
            super().exec_module(module)

# This is 3.6+ because with Python 3.5 it isn't possible to lazily load
# extensions. See the discussion in https://python.org/sf/26186 for more.
_extensions_loader = _lazyloaderex.factory(
    importlib.machinery.ExtensionFileLoader)
_bytecode_loader = _lazyloaderex.factory(
    importlib.machinery.SourcelessFileLoader)
_source_loader = _lazyloaderex.factory(importlib.machinery.SourceFileLoader)

def _makefinder(path):
    return importlib.machinery.FileFinder(
        path,
        # This is the order in which loaders are passed in in core Python.
        (_extensions_loader, importlib.machinery.EXTENSION_SUFFIXES),
        (_source_loader, importlib.machinery.SOURCE_SUFFIXES),
        (_bytecode_loader, importlib.machinery.BYTECODE_SUFFIXES),
    )

ignore = []

def init(ignorelist):
    global ignore
    ignore = ignorelist

def isenabled():
    return _makefinder in sys.path_hooks and not _deactivated

def disable():
    try:
        while True:
            sys.path_hooks.remove(_makefinder)
    except ValueError:
        pass

def enable():
    if os.environ.get('HGDEMANDIMPORT') != 'disable':
        sys.path_hooks.insert(0, _makefinder)

@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