extensions: also search for extension in the 'hgext3rd' package
Mercurial extensions are not meant to be normal python package/module. Yet the
lack of an official location to install them means that a lot of them actually
install as root level python package, polluting the global Python package
namespace and risking collision with more legit packages. As we recently
discovered, core python actually support namespace package. A way for multiples
distinct "distribution" to share a common top level package without fear of
installation headache. (Namespace package allow submodule installed in different
location (of the 'sys.path') to be imported properly. So we are fine as long as
extension includes a proper 'hgext3rd.__init__.py' to declare the namespace
package.)
Therefore we introduce a 'hgext3rd' namespace packages and search for extension
in it. We'll then recommend third extensions to install themselves in it.
Strictly speaking we could just get third party extensions to install in 'hgext'
as it is also a namespace package. However, this would make the integration of
formerly third party extensions in the main distribution more complicated as the third
party install would overwrite the file from the main install. Moreover, having an
explicit split between third party and core extensions seems like a good idea.
The name 'hgext3rd' have been picked because it is short and seems explicit enough.
Other alternative I could think of where:
- hgextcontrib
- hgextother
- hgextunofficial
# __init__.py - Startup and module loading logic for Mercurial.
#
# Copyright 2015 Gregory Szorc <gregory.szorc@gmail.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import
import imp
import os
import sys
import zipimport
__all__ = []
# Rules for how modules can be loaded. Values are:
#
# c - require C extensions
# allow - allow pure Python implementation when C loading fails
# py - only load pure Python modules
#
# By default, require the C extensions for performance reasons.
modulepolicy = 'c'
try:
from . import __modulepolicy__
modulepolicy = __modulepolicy__.modulepolicy
except ImportError:
pass
# PyPy doesn't load C extensions.
#
# The canonical way to do this is to test platform.python_implementation().
# But we don't import platform and don't bloat for it here.
if '__pypy__' in sys.builtin_module_names:
modulepolicy = 'py'
# Our C extensions aren't yet compatible with Python 3. So use pure Python
# on Python 3 for now.
if sys.version_info[0] >= 3:
modulepolicy = 'py'
# Environment variable can always force settings.
modulepolicy = os.environ.get('HGMODULEPOLICY', modulepolicy)
# Modules that have both Python and C implementations. See also the
# set of .py files under mercurial/pure/.
_dualmodules = set([
'mercurial.base85',
'mercurial.bdiff',
'mercurial.diffhelpers',
'mercurial.mpatch',
'mercurial.osutil',
'mercurial.parsers',
])
class hgimporter(object):
"""Object that conforms to import hook interface defined in PEP-302."""
def find_module(self, name, path=None):
# We only care about modules that have both C and pure implementations.
if name in _dualmodules:
return self
return None
def load_module(self, name):
mod = sys.modules.get(name, None)
if mod:
return mod
mercurial = sys.modules['mercurial']
# The zip importer behaves sufficiently differently from the default
# importer to warrant its own code path.
loader = getattr(mercurial, '__loader__', None)
if isinstance(loader, zipimport.zipimporter):
def ziploader(*paths):
"""Obtain a zipimporter for a directory under the main zip."""
path = os.path.join(loader.archive, *paths)
zl = sys.path_importer_cache.get(path)
if not zl:
zl = zipimport.zipimporter(path)
return zl
try:
if modulepolicy == 'py':
raise ImportError()
zl = ziploader('mercurial')
mod = zl.load_module(name)
# Unlike imp, ziploader doesn't expose module metadata that
# indicates the type of module. So just assume what we found
# is OK (even though it could be a pure Python module).
except ImportError:
if modulepolicy == 'c':
raise
zl = ziploader('mercurial', 'pure')
mod = zl.load_module(name)
sys.modules[name] = mod
return mod
# Unlike the default importer which searches special locations and
# sys.path, we only look in the directory where "mercurial" was
# imported from.
# imp.find_module doesn't support submodules (modules with ".").
# Instead you have to pass the parent package's __path__ attribute
# as the path argument.
stem = name.split('.')[-1]
try:
if modulepolicy == 'py':
raise ImportError()
modinfo = imp.find_module(stem, mercurial.__path__)
# The Mercurial installer used to copy files from
# mercurial/pure/*.py to mercurial/*.py. Therefore, it's possible
# for some installations to have .py files under mercurial/*.
# Loading Python modules when we expected C versions could result
# in a) poor performance b) loading a version from a previous
# Mercurial version, potentially leading to incompatibility. Either
# scenario is bad. So we verify that modules loaded from
# mercurial/* are C extensions. If the current policy allows the
# loading of .py modules, the module will be re-imported from
# mercurial/pure/* below.
if modinfo[2][2] != imp.C_EXTENSION:
raise ImportError('.py version of %s found where C '
'version should exist' % name)
except ImportError:
if modulepolicy == 'c':
raise
# Could not load the C extension and pure Python is allowed. So
# try to load them.
from . import pure
modinfo = imp.find_module(stem, pure.__path__)
if not modinfo:
raise ImportError('could not find mercurial module %s' %
name)
mod = imp.load_module(name, *modinfo)
sys.modules[name] = mod
return mod
# We automagically register our custom importer as a side-effect of loading.
# This is necessary to ensure that any entry points are able to import
# mercurial.* modules without having to perform this registration themselves.
if not any(isinstance(x, hgimporter) for x in sys.meta_path):
# meta_path is used before any implicit finders and before sys.path.
sys.meta_path.insert(0, hgimporter())