revlog: store flag processors per revlog
Previously, revlog flag processing would consult a global dict
when processing flags. This was simple. But it had the undesired
side-effect that any extension could load flag processors once
and those flag processors would be available to any revlog that was
subsequent loaded in the process. e.g. in hgweb, if the narrow
extension were loaded for repo A but not repo B, repo B would be
able to decode ellipsis flags even though it shouldn't be able to.
Making the flag processors dict per-revlog allows us to have per-revlog
controls over what flag processors are available, thus preserving
desired granular access to flag processors depending on the revlog's
needs.
If a flag processor is globally registered, it is still globally
available. So this commit should not meaningfully change behavior.
Differential Revision: https://phab.mercurial-scm.org/D4646
# 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 importlib.abc
import importlib.machinery
import importlib.util
import sys
_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 ignores:
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://bugs.python.org/issue26186 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),
)
ignores = set()
def init(ignoreset):
global ignores
ignores = ignoreset
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():
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