mercurial: implement import hook for handling C/Python modules

There are a handful of modules that have both pure Python and C
extension implementations. Currently, setup.py copies files from
mercurial/pure/*.py to mercurial/ during the install process if C
extensions are not available. This way, "import mercurial.X" will
work whether C extensions are available or not.

This approach has a few drawbacks. First, there aren't run-time checks
verifying the C extensions are loaded when they should be. This could
lead to accidental use of the slower pure Python modules. Second, the
C extensions aren't compatible with PyPy and running Mercurial with
PyPy requires installing Mercurial - you can't run ./hg from a source
checkout. This makes developing while running PyPy somewhat difficult.

This patch implements a PEP-302 import hook for finding and loading the
modules with both C and Python implementations. When a module with dual
implementations is requested for import, its import is handled by our
import hook.

The importer has a mechanism that controls what types of modules we
allow to load. We call this loading behavior the "module load policy."
There are 3 settings:

* Only load C extensions
* Only load pure Python
* Try to load C and fall back to Python

An environment variable allows overriding this policy at run time. This
is mainly useful for developers and for performing actions against the
source checkout (such as installing), which require overriding the
default (strict) policy about requiring C extensions.

The default mode for now is to allow both. This isn't proper and is
technically backwards incompatible. However, it is necessary to
implement a sane patch series that doesn't break the world during
future bisections. The behavior will be corrected in future patch.

We choose the main mercurial/__init__.py module for this code out of
necessity: in a future world, if the custom module importer isn't
registered, we'll fail to find/import certain modules when running
from a pure installation. Without the magical import-time side-effects,
*any* importer of mercurial.* modules would be required to call a
function to register our importer. I'm not a fan of import time side
effects and I initially attempted to do this. However, I was foiled by
our own test harness, which has numerous `python` invoked scripts that
"import mercurial" and fail because the importer isn't registered.
Realizing this problem is probably present in random Python scripts
that have been written over the years, I decided that sacrificing
purity for backwards compatibility is necessary. Plus, if you are
programming Python, "import" should probably "just work."

It's worth noting that now that we have a custom module loader, it
would be possible to hook up demand module proxies at this level
instead of replacing __import__. We leave this work for another time,
if it's even desired.

This patch breaks importing in environments where Mercurial modules
are loaded from a zip file (such as py2exe distributions). This will
be addressed in a subsequent patch.

mercurial/__init__.py

@@ -0,0 +1,109
+# __init__.py - Startup and module loading logic for Mercurial.
+#
+# Copyright 2015 Gregory Szorc <[e-mail]>
+#
+# 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
+
+__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
+modulepolicy = '@MODULELOADPOLICY@'
+
+# By default, require the C extensions for performance reasons.
+if modulepolicy == '@' 'MODULELOADPOLICY' '@':
+    # TODO change to 'c' once installer is changed.
+    modulepolicy = 'allow'
+
+# 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']
+
+        # 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.
+            # TODO uncomment once setup.py is updated to actually install
+            # into mercurial/pure.
+            #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())

setup.py

@@ -1,649 +1,647
 #
 # This is the mercurial setup script.
 #
 # 'python setup.py install', or
 # 'python setup.py --help' for more options
 
 import sys, platform
 if getattr(sys, 'version_info', (0, 0, 0)) < (2, 6, 0, 'final'):
     raise SystemExit("Mercurial requires Python 2.6 or later.")
 
 if sys.version_info[0] >= 3:
     def b(s):
         '''A helper function to emulate 2.6+ bytes literals using string
         literals.'''
         return s.encode('latin1')
     printf = eval('print')
     libdir_escape = 'unicode_escape'
 else:
     libdir_escape = 'string_escape'
     def b(s):
         '''A helper function to emulate 2.6+ bytes literals using string
         literals.'''
         return s
     def printf(*args, **kwargs):
         f = kwargs.get('file', sys.stdout)
         end = kwargs.get('end', '\n')
         f.write(b(' ').join(args) + end)
 
 # Solaris Python packaging brain damage
 try:
     import hashlib
     sha = hashlib.sha1()
 except ImportError:
     try:
         import sha
         sha.sha # silence unused import warning
     except ImportError:
         raise SystemExit(
             "Couldn't import standard hashlib (incomplete Python install).")
 
 try:
     import zlib
     zlib.compressobj # silence unused import warning
 except ImportError:
     raise SystemExit(
         "Couldn't import standard zlib (incomplete Python install).")
 
 # The base IronPython distribution (as of 2.7.1) doesn't support bz2
 isironpython = False
 try:
     isironpython = (platform.python_implementation()
                     .lower().find("ironpython") != -1)
 except AttributeError:
     pass
 
 if isironpython:
     sys.stderr.write("warning: IronPython detected (no bz2 support)\n")
 else:
     try:
         import bz2
         bz2.BZ2Compressor # silence unused import warning
     except ImportError:
         raise SystemExit(
             "Couldn't import standard bz2 (incomplete Python install).")
 
 ispypy = "PyPy" in sys.version
 
 import os, stat, subprocess, time
 import re
 import shutil
 import tempfile
 from distutils import log
 if 'FORCE_SETUPTOOLS' in os.environ:
     from setuptools import setup
 else:
     from distutils.core import setup
 from distutils.core import Command, Extension
 from distutils.dist import Distribution
 from distutils.command.build import build
 from distutils.command.build_ext import build_ext
 from distutils.command.build_py import build_py
 from distutils.command.install_lib import install_lib
 from distutils.command.install_scripts import install_scripts
 from distutils.spawn import spawn, find_executable
 from distutils import file_util
 from distutils.errors import CCompilerError, DistutilsExecError
 from distutils.sysconfig import get_python_inc, get_config_var
 from distutils.version import StrictVersion
 
 convert2to3 = '--c2to3' in sys.argv
 if convert2to3:
     try:
         from distutils.command.build_py import build_py_2to3 as build_py
         from lib2to3.refactor import get_fixers_from_package as getfixers
     except ImportError:
         if sys.version_info[0] < 3:
             raise SystemExit("--c2to3 is only compatible with python3.")
         raise
     sys.path.append('contrib')
 elif sys.version_info[0] >= 3:
     raise SystemExit("setup.py with python3 needs --c2to3 (experimental)")
 
 scripts = ['hg']
 if os.name == 'nt':
     scripts.append('contrib/win32/hg.bat')
 
 # simplified version of distutils.ccompiler.CCompiler.has_function
 # that actually removes its temporary files.
 def hasfunction(cc, funcname):
     tmpdir = tempfile.mkdtemp(prefix='hg-install-')
     devnull = oldstderr = None
     try:
         fname = os.path.join(tmpdir, 'funcname.c')
         f = open(fname, 'w')
         f.write('int main(void) {\n')
         f.write('    %s();\n' % funcname)
         f.write('}\n')
         f.close()
         # Redirect stderr to /dev/null to hide any error messages
         # from the compiler.
         # This will have to be changed if we ever have to check
         # for a function on Windows.
         devnull = open('/dev/null', 'w')
         oldstderr = os.dup(sys.stderr.fileno())
         os.dup2(devnull.fileno(), sys.stderr.fileno())
         objects = cc.compile([fname], output_dir=tmpdir)
         cc.link_executable(objects, os.path.join(tmpdir, "a.out"))
         return True
     except Exception:
         return False
     finally:
         if oldstderr is not None:
             os.dup2(oldstderr, sys.stderr.fileno())
         if devnull is not None:
             devnull.close()
         shutil.rmtree(tmpdir)
 
 # py2exe needs to be installed to work
 try:
     import py2exe
     py2exe.Distribution # silence unused import warning
     py2exeloaded = True
     # import py2exe's patched Distribution class
     from distutils.core import Distribution
 except ImportError:
     py2exeloaded = False
 
 def runcmd(cmd, env):
     if (sys.platform == 'plan9'
        and (sys.version_info[0] == 2 and sys.version_info[1] < 7)):
         # subprocess kludge to work around issues in half-baked Python
         # ports, notably bichued/python:
         _, out, err = os.popen3(cmd)
         return str(out), str(err)
     else:
         p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
                              stderr=subprocess.PIPE, env=env)
         out, err = p.communicate()
         return out, err
 
 def runhg(cmd, env):
     out, err = runcmd(cmd, env)
     # If root is executing setup.py, but the repository is owned by
     # another user (as in "sudo python setup.py install") we will get
     # trust warnings since the .hg/hgrc file is untrusted. That is
     # fine, we don't want to load it anyway.  Python may warn about
     # a missing __init__.py in mercurial/locale, we also ignore that.
     err = [e for e in err.splitlines()
            if not e.startswith(b('not trusting file')) \
               and not e.startswith(b('warning: Not importing')) \
               and not e.startswith(b('obsolete feature not enabled'))]
     if err:
         printf("stderr from '%s':" % (' '.join(cmd)), file=sys.stderr)
         printf(b('\n').join([b('  ') + e for e in err]), file=sys.stderr)
         return ''
     return out
 
 version = ''
 
-# Execute hg out of this directory with a custom environment which
-# includes the pure Python modules in mercurial/pure. We also take
-# care to not use any hgrc files and do no localization.
-pypath = ['mercurial', os.path.join('mercurial', 'pure')]
-env = {'PYTHONPATH': os.pathsep.join(pypath),
+# Execute hg out of this directory with a custom environment which takes care
+# to not use any hgrc files and do no localization.
+env = {'HGMODULEPOLICY': 'py',
        'HGRCPATH': '',
        'LANGUAGE': 'C'}
 if 'LD_LIBRARY_PATH' in os.environ:
     env['LD_LIBRARY_PATH'] = os.environ['LD_LIBRARY_PATH']
 if 'SystemRoot' in os.environ:
     # Copy SystemRoot into the custom environment for Python 2.6
     # under Windows. Otherwise, the subprocess will fail with
     # error 0xc0150004. See: http://bugs.python.org/issue3440
     env['SystemRoot'] = os.environ['SystemRoot']
 
 if os.path.isdir('.hg'):
     cmd = [sys.executable, 'hg', 'log', '-r', '.', '--template', '{tags}\n']
     numerictags = [t for t in runhg(cmd, env).split() if t[0].isdigit()]
     hgid = runhg([sys.executable, 'hg', 'id', '-i'], env).strip()
     if numerictags: # tag(s) found
         version = numerictags[-1]
         if hgid.endswith('+'): # propagate the dirty status to the tag
             version += '+'
     else: # no tag found
         ltagcmd = [sys.executable, 'hg', 'parents', '--template',
                    '{latesttag}']
         ltag = runhg(ltagcmd, env)
         changessincecmd = [sys.executable, 'hg', 'log', '-T', 'x\n', '-r',
                            "only(.,'%s')" % ltag]
         changessince = len(runhg(changessincecmd, env).splitlines())
         version = '%s+%s-%s' % (ltag, changessince, hgid)
     if version.endswith('+'):
         version += time.strftime('%Y%m%d')
 elif os.path.exists('.hg_archival.txt'):
     kw = dict([[t.strip() for t in l.split(':', 1)]
                for l in open('.hg_archival.txt')])
     if 'tag' in kw:
         version =  kw['tag']
     elif 'latesttag' in kw:
         if 'changessincelatesttag' in kw:
             version = '%(latesttag)s+%(changessincelatesttag)s-%(node).12s' % kw
         else:
             version = '%(latesttag)s+%(latesttagdistance)s-%(node).12s' % kw
     else:
         version = kw.get('node', '')[:12]
 
 if version:
     f = open("mercurial/__version__.py", "w")
     f.write('# this file is autogenerated by setup.py\n')
     f.write('version = "%s"\n' % version)
     f.close()
 
 
 try:
     from mercurial import __version__
     version = __version__.version
 except ImportError:
     version = 'unknown'
 
 class hgbuild(build):
     # Insert hgbuildmo first so that files in mercurial/locale/ are found
     # when build_py is run next.
     sub_commands = [('build_mo', None),
 
     # We also need build_ext before build_py. Otherwise, when 2to3 is
     # called (in build_py), it will not find osutil & friends,
     # thinking that those modules are global and, consequently, making
     # a mess, now that all module imports are global.
 
                     ('build_ext', build.has_ext_modules),
                    ] + build.sub_commands
 
 class hgbuildmo(build):
 
     description = "build translations (.mo files)"
 
     def run(self):
         if not find_executable('msgfmt'):
             self.warn("could not find msgfmt executable, no translations "
                      "will be built")
             return
 
         podir = 'i18n'
         if not os.path.isdir(podir):
             self.warn("could not find %s/ directory" % podir)
             return
 
         join = os.path.join
         for po in os.listdir(podir):
             if not po.endswith('.po'):
                 continue
             pofile = join(podir, po)
             modir = join('locale', po[:-3], 'LC_MESSAGES')
             mofile = join(modir, 'hg.mo')
             mobuildfile = join('mercurial', mofile)
             cmd = ['msgfmt', '-v', '-o', mobuildfile, pofile]
             if sys.platform != 'sunos5':
                 # msgfmt on Solaris does not know about -c
                 cmd.append('-c')
             self.mkpath(join('mercurial', modir))
             self.make_file([pofile], mobuildfile, spawn, (cmd,))
 
 
 class hgdist(Distribution):
     pure = ispypy
 
     global_options = Distribution.global_options + \
                      [('pure', None, "use pure (slow) Python "
                         "code instead of C extensions"),
                       ('c2to3', None, "(experimental!) convert "
                         "code with 2to3"),
                      ]
 
     def has_ext_modules(self):
         # self.ext_modules is emptied in hgbuildpy.finalize_options which is
         # too late for some cases
         return not self.pure and Distribution.has_ext_modules(self)
 
 class hgbuildext(build_ext):
 
     def build_extension(self, ext):
         try:
             build_ext.build_extension(self, ext)
         except CCompilerError:
             if not getattr(ext, 'optional', False):
                 raise
             log.warn("Failed to build optional extension '%s' (skipping)",
                      ext.name)
 
 class hgbuildpy(build_py):
     if convert2to3:
         fixer_names = sorted(set(getfixers("lib2to3.fixes") +
                                  getfixers("hgfixes")))
 
     def finalize_options(self):
         build_py.finalize_options(self)
 
         if self.distribution.pure:
             if self.py_modules is None:
                 self.py_modules = []
             for ext in self.distribution.ext_modules:
                 if ext.name.startswith("mercurial."):
                     self.py_modules.append("mercurial.pure.%s" % ext.name[10:])
             self.distribution.ext_modules = []
         else:
             h = os.path.join(get_python_inc(), 'Python.h')
             if not os.path.exists(h):
                 raise SystemExit('Python headers are required to build '
                                  'Mercurial but weren\'t found in %s' % h)
 
     def find_modules(self):
         modules = build_py.find_modules(self)
         for module in modules:
             if module[0] == "mercurial.pure":
                 if module[1] != "__init__":
                     yield ("mercurial", module[1], module[2])
             else:
                 yield module
 
 class buildhgextindex(Command):
     description = 'generate prebuilt index of hgext (for frozen package)'
     user_options = []
     _indexfilename = 'hgext/__index__.py'
 
     def initialize_options(self):
         pass
 
     def finalize_options(self):
         pass
 
     def run(self):
         if os.path.exists(self._indexfilename):
             f = open(self._indexfilename, 'w')
             f.write('# empty\n')
             f.close()
 
         # here no extension enabled, disabled() lists up everything
         code = ('import pprint; from mercurial import extensions; '
                 'pprint.pprint(extensions.disabled())')
         out, err = runcmd([sys.executable, '-c', code], env)
         if err:
             raise DistutilsExecError(err)
 
         f = open(self._indexfilename, 'w')
         f.write('# this file is autogenerated by setup.py\n')
         f.write('docs = ')
         f.write(out)
         f.close()
 
 class buildhgexe(build_ext):
     description = 'compile hg.exe from mercurial/exewrapper.c'
 
     def build_extensions(self):
         if os.name != 'nt':
             return
         if isinstance(self.compiler, HackedMingw32CCompiler):
             self.compiler.compiler_so = self.compiler.compiler # no -mdll
             self.compiler.dll_libraries = [] # no -lmsrvc90
         hv = sys.hexversion
         pythonlib = 'python%d%d' % (hv >> 24, (hv >> 16) & 0xff)
         f = open('mercurial/hgpythonlib.h', 'wb')
         f.write('/* this file is autogenerated by setup.py */\n')
         f.write('#define HGPYTHONLIB "%s"\n' % pythonlib)
         f.close()
         objects = self.compiler.compile(['mercurial/exewrapper.c'],
                                          output_dir=self.build_temp)
         dir = os.path.dirname(self.get_ext_fullpath('dummy'))
         target = os.path.join(dir, 'hg')
         self.compiler.link_executable(objects, target,
                                       libraries=[],
                                       output_dir=self.build_temp)
 
 class hginstalllib(install_lib):
     '''
     This is a specialization of install_lib that replaces the copy_file used
     there so that it supports setting the mode of files after copying them,
     instead of just preserving the mode that the files originally had.  If your
     system has a umask of something like 027, preserving the permissions when
     copying will lead to a broken install.
 
     Note that just passing keep_permissions=False to copy_file would be
     insufficient, as it might still be applying a umask.
     '''
 
     def run(self):
         realcopyfile = file_util.copy_file
         def copyfileandsetmode(*args, **kwargs):
             src, dst = args[0], args[1]
             dst, copied = realcopyfile(*args, **kwargs)
             if copied:
                 st = os.stat(src)
                 # Persist executable bit (apply it to group and other if user
                 # has it)
                 if st[stat.ST_MODE] & stat.S_IXUSR:
                     setmode = int('0755', 8)
                 else:
                     setmode = int('0644', 8)
                 m = stat.S_IMODE(st[stat.ST_MODE])
                 m = (m & ~int('0777', 8)) | setmode
                 os.chmod(dst, m)
         file_util.copy_file = copyfileandsetmode
         try:
             install_lib.run(self)
         finally:
             file_util.copy_file = realcopyfile
 
 class hginstallscripts(install_scripts):
     '''
     This is a specialization of install_scripts that replaces the @LIBDIR@ with
     the configured directory for modules. If possible, the path is made relative
     to the directory for scripts.
     '''
 
     def initialize_options(self):
         install_scripts.initialize_options(self)
 
         self.install_lib = None
 
     def finalize_options(self):
         install_scripts.finalize_options(self)
         self.set_undefined_options('install',
                                    ('install_lib', 'install_lib'))
 
     def run(self):
         install_scripts.run(self)
 
         if (os.path.splitdrive(self.install_dir)[0] !=
             os.path.splitdrive(self.install_lib)[0]):
             # can't make relative paths from one drive to another, so use an
             # absolute path instead
             libdir = self.install_lib
         else:
             common = os.path.commonprefix((self.install_dir, self.install_lib))
             rest = self.install_dir[len(common):]
             uplevel = len([n for n in os.path.split(rest) if n])
 
             libdir =  uplevel * ('..' + os.sep) + self.install_lib[len(common):]
 
         for outfile in self.outfiles:
             fp = open(outfile, 'rb')
             data = fp.read()
             fp.close()
 
             # skip binary files
             if b('\0') in data:
                 continue
 
             data = data.replace(b('@LIBDIR@'), libdir.encode(libdir_escape))
             fp = open(outfile, 'wb')
             fp.write(data)
             fp.close()
 
 cmdclass = {'build': hgbuild,
             'build_mo': hgbuildmo,
             'build_ext': hgbuildext,
             'build_py': hgbuildpy,
             'build_hgextindex': buildhgextindex,
             'install_lib': hginstalllib,
             'install_scripts': hginstallscripts,
             'build_hgexe': buildhgexe,
             }
 
 packages = ['mercurial', 'mercurial.hgweb', 'mercurial.httpclient',
             'hgext', 'hgext.convert', 'hgext.highlight', 'hgext.zeroconf',
             'hgext.largefiles']
 
 common_depends = ['mercurial/util.h']
 
 osutil_ldflags = []
 
 if sys.platform == 'darwin':
     osutil_ldflags += ['-framework', 'ApplicationServices']
 
 extmodules = [
     Extension('mercurial.base85', ['mercurial/base85.c'],
               depends=common_depends),
     Extension('mercurial.bdiff', ['mercurial/bdiff.c'],
               depends=common_depends),
     Extension('mercurial.diffhelpers', ['mercurial/diffhelpers.c'],
               depends=common_depends),
     Extension('mercurial.mpatch', ['mercurial/mpatch.c'],
               depends=common_depends),
     Extension('mercurial.parsers', ['mercurial/dirs.c',
                                     'mercurial/manifest.c',
                                     'mercurial/parsers.c',
                                     'mercurial/pathencode.c'],
               depends=common_depends),
     Extension('mercurial.osutil', ['mercurial/osutil.c'],
               extra_link_args=osutil_ldflags,
               depends=common_depends),
     ]
 
 try:
     from distutils import cygwinccompiler
 
     # the -mno-cygwin option has been deprecated for years
     compiler = cygwinccompiler.Mingw32CCompiler
 
     class HackedMingw32CCompiler(cygwinccompiler.Mingw32CCompiler):
         def __init__(self, *args, **kwargs):
             compiler.__init__(self, *args, **kwargs)
             for i in 'compiler compiler_so linker_exe linker_so'.split():
                 try:
                     getattr(self, i).remove('-mno-cygwin')
                 except ValueError:
                     pass
 
     cygwinccompiler.Mingw32CCompiler = HackedMingw32CCompiler
 except ImportError:
     # the cygwinccompiler package is not available on some Python
     # distributions like the ones from the optware project for Synology
     # DiskStation boxes
     class HackedMingw32CCompiler(object):
         pass
 
 packagedata = {'mercurial': ['locale/*/LC_MESSAGES/hg.mo',
                              'help/*.txt',
                              'default.d/*.rc',
                              'dummycert.pem']}
 
 def ordinarypath(p):
     return p and p[0] != '.' and p[-1] != '~'
 
 for root in ('templates',):
     for curdir, dirs, files in os.walk(os.path.join('mercurial', root)):
         curdir = curdir.split(os.sep, 1)[1]
         dirs[:] = filter(ordinarypath, dirs)
         for f in filter(ordinarypath, files):
             f = os.path.join(curdir, f)
             packagedata['mercurial'].append(f)
 
 datafiles = []
 setupversion = version
 extra = {}
 
 if py2exeloaded:
     extra['console'] = [
         {'script':'hg',
          'copyright':'Copyright (C) 2005-2015 Matt Mackall and others',
          'product_version':version}]
     # sub command of 'build' because 'py2exe' does not handle sub_commands
     build.sub_commands.insert(0, ('build_hgextindex', None))
     # put dlls in sub directory so that they won't pollute PATH
     extra['zipfile'] = 'lib/library.zip'
 
 if os.name == 'nt':
     # Windows binary file versions for exe/dll files must have the
     # form W.X.Y.Z, where W,X,Y,Z are numbers in the range 0..65535
     setupversion = version.split('+', 1)[0]
 
 if sys.platform == 'darwin' and os.path.exists('/usr/bin/xcodebuild'):
     version = runcmd(['/usr/bin/xcodebuild', '-version'], {})[0].splitlines()
     if version:
         version = version[0]
         if sys.version_info[0] == 3:
             version = version.decode('utf-8')
         xcode4 = (version.startswith('Xcode') and
                   StrictVersion(version.split()[1]) >= StrictVersion('4.0'))
         xcode51 = re.match(r'^Xcode\s+5\.1', version) is not None
     else:
         # xcodebuild returns empty on OS X Lion with XCode 4.3 not
         # installed, but instead with only command-line tools. Assume
         # that only happens on >= Lion, thus no PPC support.
         xcode4 = True
         xcode51 = False
 
     # XCode 4.0 dropped support for ppc architecture, which is hardcoded in
     # distutils.sysconfig
     if xcode4:
         os.environ['ARCHFLAGS'] = ''
 
     # XCode 5.1 changes clang such that it now fails to compile if the
     # -mno-fused-madd flag is passed, but the version of Python shipped with
     # OS X 10.9 Mavericks includes this flag. This causes problems in all
     # C extension modules, and a bug has been filed upstream at
     # http://bugs.python.org/issue21244. We also need to patch this here
     # so Mercurial can continue to compile in the meantime.
     if xcode51:
         cflags = get_config_var('CFLAGS')
         if cflags and re.search(r'-mno-fused-madd\b', cflags) is not None:
             os.environ['CFLAGS'] = (
                 os.environ.get('CFLAGS', '') + ' -Qunused-arguments')
 
 setup(name='mercurial',
       version=setupversion,
       author='Matt Mackall and many others',
       author_email='[e-mail]',
       url='https://mercurial-scm.org/',
       download_url='https://mercurial-scm.org/release/',
       description=('Fast scalable distributed SCM (revision control, version '
                    'control) system'),
       long_description=('Mercurial is a distributed SCM tool written in Python.'
                         ' It is used by a number of large projects that require'
                         ' fast, reliable distributed revision control, such as '
                         'Mozilla.'),
       license='GNU GPLv2 or any later version',
       classifiers=[
           'Development Status :: 6 - Mature',
           'Environment :: Console',
           'Intended Audience :: Developers',
           'Intended Audience :: System Administrators',
           'License :: OSI Approved :: GNU General Public License (GPL)',
           'Natural Language :: Danish',
           'Natural Language :: English',
           'Natural Language :: German',
           'Natural Language :: Italian',
           'Natural Language :: Japanese',
           'Natural Language :: Portuguese (Brazilian)',
           'Operating System :: Microsoft :: Windows',
           'Operating System :: OS Independent',
           'Operating System :: POSIX',
           'Programming Language :: C',
           'Programming Language :: Python',
           'Topic :: Software Development :: Version Control',
       ],
       scripts=scripts,
       packages=packages,
       ext_modules=extmodules,
       data_files=datafiles,
       package_data=packagedata,
       cmdclass=cmdclass,
       distclass=hgdist,
       options={'py2exe': {'packages': ['hgext', 'email']},
                'bdist_mpkg': {'zipdist': False,
                               'license': 'COPYING',
                               'readme': 'contrib/macosx/Readme.html',
                               'welcome': 'contrib/macosx/Welcome.html',
                               },
                },
       **extra)