view mercurial/scmutil.py @ 30000:9766d88c2465

vfs: use checkambigatclosing in checkambig=True but atomictemp=False case

In Mercurial source tree, opening a file in "a"/"a+" mode like below
doesn't specify atomictemp=True for vfs, and this avoids file stat
ambiguity check by atomictempfile.

  - writing changes out in revlog layer uses "a+" mode
  - truncation in repair.strip() uses "a" mode
  - truncation in transaction._playback() uses "a" mode

If steps below occurs at "the same time in sec", all of mtime, ctime
and size are same between (1) and (3).

  1. append data to revlog-style file (and close transaction)
  2. discard appended data by truncation (strip or rollback)
  3. append same size but different data to revlog-style file again

Therefore, cache validation doesn't work after (3) as expected.

This patch uses checkambigatclosing in checkambig=True but
atomictemp=False case, to check (and get rid of) file stat ambiguity
at closing.

This is a part of ExactCacheValidationPlan.

    https://www.mercurial-scm.org/wiki/ExactCacheValidationPlan

# scmutil.py - Mercurial core utility functions
#
#  Copyright Matt Mackall <[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 contextlib
import errno
import glob
import hashlib
import os
import re
import shutil
import stat
import tempfile
import threading

from .i18n import _
from .node import wdirrev
from . import (
    encoding,
    error,
    match as matchmod,
    osutil,
    pathutil,
    phases,
    revset,
    similar,
    util,
)

if os.name == 'nt':
    from . import scmwindows as scmplatform
else:
    from . import scmposix as scmplatform

systemrcpath = scmplatform.systemrcpath
userrcpath = scmplatform.userrcpath

class status(tuple):
    '''Named tuple with a list of files per status. The 'deleted', 'unknown'
       and 'ignored' properties are only relevant to the working copy.
    '''

    __slots__ = ()

    def __new__(cls, modified, added, removed, deleted, unknown, ignored,
                clean):
        return tuple.__new__(cls, (modified, added, removed, deleted, unknown,
                                   ignored, clean))

    @property
    def modified(self):
        '''files that have been modified'''
        return self[0]

    @property
    def added(self):
        '''files that have been added'''
        return self[1]

    @property
    def removed(self):
        '''files that have been removed'''
        return self[2]

    @property
    def deleted(self):
        '''files that are in the dirstate, but have been deleted from the
           working copy (aka "missing")
        '''
        return self[3]

    @property
    def unknown(self):
        '''files not in the dirstate that are not ignored'''
        return self[4]

    @property
    def ignored(self):
        '''files not in the dirstate that are ignored (by _dirignore())'''
        return self[5]

    @property
    def clean(self):
        '''files that have not been modified'''
        return self[6]

    def __repr__(self, *args, **kwargs):
        return (('<status modified=%r, added=%r, removed=%r, deleted=%r, '
                 'unknown=%r, ignored=%r, clean=%r>') % self)

def itersubrepos(ctx1, ctx2):
    """find subrepos in ctx1 or ctx2"""
    # Create a (subpath, ctx) mapping where we prefer subpaths from
    # ctx1. The subpaths from ctx2 are important when the .hgsub file
    # has been modified (in ctx2) but not yet committed (in ctx1).
    subpaths = dict.fromkeys(ctx2.substate, ctx2)
    subpaths.update(dict.fromkeys(ctx1.substate, ctx1))

    missing = set()

    for subpath in ctx2.substate:
        if subpath not in ctx1.substate:
            del subpaths[subpath]
            missing.add(subpath)

    for subpath, ctx in sorted(subpaths.iteritems()):
        yield subpath, ctx.sub(subpath)

    # Yield an empty subrepo based on ctx1 for anything only in ctx2.  That way,
    # status and diff will have an accurate result when it does
    # 'sub.{status|diff}(rev2)'.  Otherwise, the ctx2 subrepo is compared
    # against itself.
    for subpath in missing:
        yield subpath, ctx2.nullsub(subpath, ctx1)

def nochangesfound(ui, repo, excluded=None):
    '''Report no changes for push/pull, excluded is None or a list of
    nodes excluded from the push/pull.
    '''
    secretlist = []
    if excluded:
        for n in excluded:
            if n not in repo:
                # discovery should not have included the filtered revision,
                # we have to explicitly exclude it until discovery is cleanup.
                continue
            ctx = repo[n]
            if ctx.phase() >= phases.secret and not ctx.extinct():
                secretlist.append(n)

    if secretlist:
        ui.status(_("no changes found (ignored %d secret changesets)\n")
                  % len(secretlist))
    else:
        ui.status(_("no changes found\n"))

def checknewlabel(repo, lbl, kind):
    # Do not use the "kind" parameter in ui output.
    # It makes strings difficult to translate.
    if lbl in ['tip', '.', 'null']:
        raise error.Abort(_("the name '%s' is reserved") % lbl)
    for c in (':', '\0', '\n', '\r'):
        if c in lbl:
            raise error.Abort(_("%r cannot be used in a name") % c)
    try:
        int(lbl)
        raise error.Abort(_("cannot use an integer as a name"))
    except ValueError:
        pass

def checkfilename(f):
    '''Check that the filename f is an acceptable filename for a tracked file'''
    if '\r' in f or '\n' in f:
        raise error.Abort(_("'\\n' and '\\r' disallowed in filenames: %r") % f)

def checkportable(ui, f):
    '''Check if filename f is portable and warn or abort depending on config'''
    checkfilename(f)
    abort, warn = checkportabilityalert(ui)
    if abort or warn:
        msg = util.checkwinfilename(f)
        if msg:
            msg = "%s: %r" % (msg, f)
            if abort:
                raise error.Abort(msg)
            ui.warn(_("warning: %s\n") % msg)

def checkportabilityalert(ui):
    '''check if the user's config requests nothing, a warning, or abort for
    non-portable filenames'''
    val = ui.config('ui', 'portablefilenames', 'warn')
    lval = val.lower()
    bval = util.parsebool(val)
    abort = os.name == 'nt' or lval == 'abort'
    warn = bval or lval == 'warn'
    if bval is None and not (warn or abort or lval == 'ignore'):
        raise error.ConfigError(
            _("ui.portablefilenames value is invalid ('%s')") % val)
    return abort, warn

class casecollisionauditor(object):
    def __init__(self, ui, abort, dirstate):
        self._ui = ui
        self._abort = abort
        allfiles = '\0'.join(dirstate._map)
        self._loweredfiles = set(encoding.lower(allfiles).split('\0'))
        self._dirstate = dirstate
        # The purpose of _newfiles is so that we don't complain about
        # case collisions if someone were to call this object with the
        # same filename twice.
        self._newfiles = set()

    def __call__(self, f):
        if f in self._newfiles:
            return
        fl = encoding.lower(f)
        if fl in self._loweredfiles and f not in self._dirstate:
            msg = _('possible case-folding collision for %s') % f
            if self._abort:
                raise error.Abort(msg)
            self._ui.warn(_("warning: %s\n") % msg)
        self._loweredfiles.add(fl)
        self._newfiles.add(f)

def filteredhash(repo, maxrev):
    """build hash of filtered revisions in the current repoview.

    Multiple caches perform up-to-date validation by checking that the
    tiprev and tipnode stored in the cache file match the current repository.
    However, this is not sufficient for validating repoviews because the set
    of revisions in the view may change without the repository tiprev and
    tipnode changing.

    This function hashes all the revs filtered from the view and returns
    that SHA-1 digest.
    """
    cl = repo.changelog
    if not cl.filteredrevs:
        return None
    key = None
    revs = sorted(r for r in cl.filteredrevs if r <= maxrev)
    if revs:
        s = hashlib.sha1()
        for rev in revs:
            s.update('%s;' % rev)
        key = s.digest()
    return key

class abstractvfs(object):
    """Abstract base class; cannot be instantiated"""

    def __init__(self, *args, **kwargs):
        '''Prevent instantiation; don't call this from subclasses.'''
        raise NotImplementedError('attempted instantiating ' + str(type(self)))

    def tryread(self, path):
        '''gracefully return an empty string for missing files'''
        try:
            return self.read(path)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
        return ""

    def tryreadlines(self, path, mode='rb'):
        '''gracefully return an empty array for missing files'''
        try:
            return self.readlines(path, mode=mode)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
        return []

    @util.propertycache
    def open(self):
        '''Open ``path`` file, which is relative to vfs root.

        Newly created directories are marked as "not to be indexed by
        the content indexing service", if ``notindexed`` is specified
        for "write" mode access.
        '''
        return self.__call__

    def read(self, path):
        with self(path, 'rb') as fp:
            return fp.read()

    def readlines(self, path, mode='rb'):
        with self(path, mode=mode) as fp:
            return fp.readlines()

    def write(self, path, data, backgroundclose=False):
        with self(path, 'wb', backgroundclose=backgroundclose) as fp:
            return fp.write(data)

    def writelines(self, path, data, mode='wb', notindexed=False):
        with self(path, mode=mode, notindexed=notindexed) as fp:
            return fp.writelines(data)

    def append(self, path, data):
        with self(path, 'ab') as fp:
            return fp.write(data)

    def basename(self, path):
        """return base element of a path (as os.path.basename would do)

        This exists to allow handling of strange encoding if needed."""
        return os.path.basename(path)

    def chmod(self, path, mode):
        return os.chmod(self.join(path), mode)

    def dirname(self, path):
        """return dirname element of a path (as os.path.dirname would do)

        This exists to allow handling of strange encoding if needed."""
        return os.path.dirname(path)

    def exists(self, path=None):
        return os.path.exists(self.join(path))

    def fstat(self, fp):
        return util.fstat(fp)

    def isdir(self, path=None):
        return os.path.isdir(self.join(path))

    def isfile(self, path=None):
        return os.path.isfile(self.join(path))

    def islink(self, path=None):
        return os.path.islink(self.join(path))

    def isfileorlink(self, path=None):
        '''return whether path is a regular file or a symlink

        Unlike isfile, this doesn't follow symlinks.'''
        try:
            st = self.lstat(path)
        except OSError:
            return False
        mode = st.st_mode
        return stat.S_ISREG(mode) or stat.S_ISLNK(mode)

    def reljoin(self, *paths):
        """join various elements of a path together (as os.path.join would do)

        The vfs base is not injected so that path stay relative. This exists
        to allow handling of strange encoding if needed."""
        return os.path.join(*paths)

    def split(self, path):
        """split top-most element of a path (as os.path.split would do)

        This exists to allow handling of strange encoding if needed."""
        return os.path.split(path)

    def lexists(self, path=None):
        return os.path.lexists(self.join(path))

    def lstat(self, path=None):
        return os.lstat(self.join(path))

    def listdir(self, path=None):
        return os.listdir(self.join(path))

    def makedir(self, path=None, notindexed=True):
        return util.makedir(self.join(path), notindexed)

    def makedirs(self, path=None, mode=None):
        return util.makedirs(self.join(path), mode)

    def makelock(self, info, path):
        return util.makelock(info, self.join(path))

    def mkdir(self, path=None):
        return os.mkdir(self.join(path))

    def mkstemp(self, suffix='', prefix='tmp', dir=None, text=False):
        fd, name = tempfile.mkstemp(suffix=suffix, prefix=prefix,
                                    dir=self.join(dir), text=text)
        dname, fname = util.split(name)
        if dir:
            return fd, os.path.join(dir, fname)
        else:
            return fd, fname

    def readdir(self, path=None, stat=None, skip=None):
        return osutil.listdir(self.join(path), stat, skip)

    def readlock(self, path):
        return util.readlock(self.join(path))

    def rename(self, src, dst, checkambig=False):
        """Rename from src to dst

        checkambig argument is used with util.filestat, and is useful
        only if destination file is guarded by any lock
        (e.g. repo.lock or repo.wlock).
        """
        dstpath = self.join(dst)
        oldstat = checkambig and util.filestat(dstpath)
        if oldstat and oldstat.stat:
            ret = util.rename(self.join(src), dstpath)
            newstat = util.filestat(dstpath)
            if newstat.isambig(oldstat):
                # stat of renamed file is ambiguous to original one
                advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
                os.utime(dstpath, (advanced, advanced))
            return ret
        return util.rename(self.join(src), dstpath)

    def readlink(self, path):
        return os.readlink(self.join(path))

    def removedirs(self, path=None):
        """Remove a leaf directory and all empty intermediate ones
        """
        return util.removedirs(self.join(path))

    def rmtree(self, path=None, ignore_errors=False, forcibly=False):
        """Remove a directory tree recursively

        If ``forcibly``, this tries to remove READ-ONLY files, too.
        """
        if forcibly:
            def onerror(function, path, excinfo):
                if function is not os.remove:
                    raise
                # read-only files cannot be unlinked under Windows
                s = os.stat(path)
                if (s.st_mode & stat.S_IWRITE) != 0:
                    raise
                os.chmod(path, stat.S_IMODE(s.st_mode) | stat.S_IWRITE)
                os.remove(path)
        else:
            onerror = None
        return shutil.rmtree(self.join(path),
                             ignore_errors=ignore_errors, onerror=onerror)

    def setflags(self, path, l, x):
        return util.setflags(self.join(path), l, x)

    def stat(self, path=None):
        return os.stat(self.join(path))

    def unlink(self, path=None):
        return util.unlink(self.join(path))

    def unlinkpath(self, path=None, ignoremissing=False):
        return util.unlinkpath(self.join(path), ignoremissing)

    def utime(self, path=None, t=None):
        return os.utime(self.join(path), t)

    def walk(self, path=None, onerror=None):
        """Yield (dirpath, dirs, files) tuple for each directories under path

        ``dirpath`` is relative one from the root of this vfs. This
        uses ``os.sep`` as path separator, even you specify POSIX
        style ``path``.

        "The root of this vfs" is represented as empty ``dirpath``.
        """
        root = os.path.normpath(self.join(None))
        # when dirpath == root, dirpath[prefixlen:] becomes empty
        # because len(dirpath) < prefixlen.
        prefixlen = len(pathutil.normasprefix(root))
        for dirpath, dirs, files in os.walk(self.join(path), onerror=onerror):
            yield (dirpath[prefixlen:], dirs, files)

    @contextlib.contextmanager
    def backgroundclosing(self, ui, expectedcount=-1):
        """Allow files to be closed asynchronously.

        When this context manager is active, ``backgroundclose`` can be passed
        to ``__call__``/``open`` to result in the file possibly being closed
        asynchronously, on a background thread.
        """
        # This is an arbitrary restriction and could be changed if we ever
        # have a use case.
        vfs = getattr(self, 'vfs', self)
        if getattr(vfs, '_backgroundfilecloser', None):
            raise error.Abort(
                _('can only have 1 active background file closer'))

        with backgroundfilecloser(ui, expectedcount=expectedcount) as bfc:
            try:
                vfs._backgroundfilecloser = bfc
                yield bfc
            finally:
                vfs._backgroundfilecloser = None

class vfs(abstractvfs):
    '''Operate files relative to a base directory

    This class is used to hide the details of COW semantics and
    remote file access from higher level code.
    '''
    def __init__(self, base, audit=True, expandpath=False, realpath=False):
        if expandpath:
            base = util.expandpath(base)
        if realpath:
            base = os.path.realpath(base)
        self.base = base
        self.mustaudit = audit
        self.createmode = None
        self._trustnlink = None

    @property
    def mustaudit(self):
        return self._audit

    @mustaudit.setter
    def mustaudit(self, onoff):
        self._audit = onoff
        if onoff:
            self.audit = pathutil.pathauditor(self.base)
        else:
            self.audit = util.always

    @util.propertycache
    def _cansymlink(self):
        return util.checklink(self.base)

    @util.propertycache
    def _chmod(self):
        return util.checkexec(self.base)

    def _fixfilemode(self, name):
        if self.createmode is None or not self._chmod:
            return
        os.chmod(name, self.createmode & 0o666)

    def __call__(self, path, mode="r", text=False, atomictemp=False,
                 notindexed=False, backgroundclose=False, checkambig=False):
        '''Open ``path`` file, which is relative to vfs root.

        Newly created directories are marked as "not to be indexed by
        the content indexing service", if ``notindexed`` is specified
        for "write" mode access.

        If ``backgroundclose`` is passed, the file may be closed asynchronously.
        It can only be used if the ``self.backgroundclosing()`` context manager
        is active. This should only be specified if the following criteria hold:

        1. There is a potential for writing thousands of files. Unless you
           are writing thousands of files, the performance benefits of
           asynchronously closing files is not realized.
        2. Files are opened exactly once for the ``backgroundclosing``
           active duration and are therefore free of race conditions between
           closing a file on a background thread and reopening it. (If the
           file were opened multiple times, there could be unflushed data
           because the original file handle hasn't been flushed/closed yet.)

        ``checkambig`` argument is passed to atomictemplfile (valid
        only for writing), and is useful only if target file is
        guarded by any lock (e.g. repo.lock or repo.wlock).
        '''
        if self._audit:
            r = util.checkosfilename(path)
            if r:
                raise error.Abort("%s: %r" % (r, path))
        self.audit(path)
        f = self.join(path)

        if not text and "b" not in mode:
            mode += "b" # for that other OS

        nlink = -1
        if mode not in ('r', 'rb'):
            dirname, basename = util.split(f)
            # If basename is empty, then the path is malformed because it points
            # to a directory. Let the posixfile() call below raise IOError.
            if basename:
                if atomictemp:
                    util.makedirs(dirname, self.createmode, notindexed)
                    return util.atomictempfile(f, mode, self.createmode,
                                               checkambig=checkambig)
                try:
                    if 'w' in mode:
                        util.unlink(f)
                        nlink = 0
                    else:
                        # nlinks() may behave differently for files on Windows
                        # shares if the file is open.
                        with util.posixfile(f):
                            nlink = util.nlinks(f)
                            if nlink < 1:
                                nlink = 2 # force mktempcopy (issue1922)
                except (OSError, IOError) as e:
                    if e.errno != errno.ENOENT:
                        raise
                    nlink = 0
                    util.makedirs(dirname, self.createmode, notindexed)
                if nlink > 0:
                    if self._trustnlink is None:
                        self._trustnlink = nlink > 1 or util.checknlink(f)
                    if nlink > 1 or not self._trustnlink:
                        util.rename(util.mktempcopy(f), f)
        fp = util.posixfile(f, mode)
        if nlink == 0:
            self._fixfilemode(f)

        if checkambig:
            if mode in ('r', 'rb'):
                raise error.Abort(_('implementation error: mode %s is not'
                                    ' valid for checkambig=True') % mode)
            fp = checkambigatclosing(fp)

        if backgroundclose:
            if not self._backgroundfilecloser:
                raise error.Abort(_('backgroundclose can only be used when a '
                                  'backgroundclosing context manager is active')
                                  )

            fp = delayclosedfile(fp, self._backgroundfilecloser)

        return fp

    def symlink(self, src, dst):
        self.audit(dst)
        linkname = self.join(dst)
        try:
            os.unlink(linkname)
        except OSError:
            pass

        util.makedirs(os.path.dirname(linkname), self.createmode)

        if self._cansymlink:
            try:
                os.symlink(src, linkname)
            except OSError as err:
                raise OSError(err.errno, _('could not symlink to %r: %s') %
                              (src, err.strerror), linkname)
        else:
            self.write(dst, src)

    def join(self, path, *insidef):
        if path:
            return os.path.join(self.base, path, *insidef)
        else:
            return self.base

opener = vfs

class auditvfs(object):
    def __init__(self, vfs):
        self.vfs = vfs

    @property
    def mustaudit(self):
        return self.vfs.mustaudit

    @mustaudit.setter
    def mustaudit(self, onoff):
        self.vfs.mustaudit = onoff

    @property
    def options(self):
        return self.vfs.options

    @options.setter
    def options(self, value):
        self.vfs.options = value

class filtervfs(abstractvfs, auditvfs):
    '''Wrapper vfs for filtering filenames with a function.'''

    def __init__(self, vfs, filter):
        auditvfs.__init__(self, vfs)
        self._filter = filter

    def __call__(self, path, *args, **kwargs):
        return self.vfs(self._filter(path), *args, **kwargs)

    def join(self, path, *insidef):
        if path:
            return self.vfs.join(self._filter(self.vfs.reljoin(path, *insidef)))
        else:
            return self.vfs.join(path)

filteropener = filtervfs

class readonlyvfs(abstractvfs, auditvfs):
    '''Wrapper vfs preventing any writing.'''

    def __init__(self, vfs):
        auditvfs.__init__(self, vfs)

    def __call__(self, path, mode='r', *args, **kw):
        if mode not in ('r', 'rb'):
            raise error.Abort(_('this vfs is read only'))
        return self.vfs(path, mode, *args, **kw)

    def join(self, path, *insidef):
        return self.vfs.join(path, *insidef)

def walkrepos(path, followsym=False, seen_dirs=None, recurse=False):
    '''yield every hg repository under path, always recursively.
    The recurse flag will only control recursion into repo working dirs'''
    def errhandler(err):
        if err.filename == path:
            raise err
    samestat = getattr(os.path, 'samestat', None)
    if followsym and samestat is not None:
        def adddir(dirlst, dirname):
            match = False
            dirstat = os.stat(dirname)
            for lstdirstat in dirlst:
                if samestat(dirstat, lstdirstat):
                    match = True
                    break
            if not match:
                dirlst.append(dirstat)
            return not match
    else:
        followsym = False

    if (seen_dirs is None) and followsym:
        seen_dirs = []
        adddir(seen_dirs, path)
    for root, dirs, files in os.walk(path, topdown=True, onerror=errhandler):
        dirs.sort()
        if '.hg' in dirs:
            yield root # found a repository
            qroot = os.path.join(root, '.hg', 'patches')
            if os.path.isdir(os.path.join(qroot, '.hg')):
                yield qroot # we have a patch queue repo here
            if recurse:
                # avoid recursing inside the .hg directory
                dirs.remove('.hg')
            else:
                dirs[:] = [] # don't descend further
        elif followsym:
            newdirs = []
            for d in dirs:
                fname = os.path.join(root, d)
                if adddir(seen_dirs, fname):
                    if os.path.islink(fname):
                        for hgname in walkrepos(fname, True, seen_dirs):
                            yield hgname
                    else:
                        newdirs.append(d)
            dirs[:] = newdirs

def osrcpath():
    '''return default os-specific hgrc search path'''
    path = []
    defaultpath = os.path.join(util.datapath, 'default.d')
    if os.path.isdir(defaultpath):
        for f, kind in osutil.listdir(defaultpath):
            if f.endswith('.rc'):
                path.append(os.path.join(defaultpath, f))
    path.extend(systemrcpath())
    path.extend(userrcpath())
    path = [os.path.normpath(f) for f in path]
    return path

_rcpath = None

def rcpath():
    '''return hgrc search path. if env var HGRCPATH is set, use it.
    for each item in path, if directory, use files ending in .rc,
    else use item.
    make HGRCPATH empty to only look in .hg/hgrc of current repo.
    if no HGRCPATH, use default os-specific path.'''
    global _rcpath
    if _rcpath is None:
        if 'HGRCPATH' in os.environ:
            _rcpath = []
            for p in os.environ['HGRCPATH'].split(os.pathsep):
                if not p:
                    continue
                p = util.expandpath(p)
                if os.path.isdir(p):
                    for f, kind in osutil.listdir(p):
                        if f.endswith('.rc'):
                            _rcpath.append(os.path.join(p, f))
                else:
                    _rcpath.append(p)
        else:
            _rcpath = osrcpath()
    return _rcpath

def intrev(rev):
    """Return integer for a given revision that can be used in comparison or
    arithmetic operation"""
    if rev is None:
        return wdirrev
    return rev

def revsingle(repo, revspec, default='.'):
    if not revspec and revspec != 0:
        return repo[default]

    l = revrange(repo, [revspec])
    if not l:
        raise error.Abort(_('empty revision set'))
    return repo[l.last()]

def _pairspec(revspec):
    tree = revset.parse(revspec)
    return tree and tree[0] in ('range', 'rangepre', 'rangepost', 'rangeall')

def revpair(repo, revs):
    if not revs:
        return repo.dirstate.p1(), None

    l = revrange(repo, revs)

    if not l:
        first = second = None
    elif l.isascending():
        first = l.min()
        second = l.max()
    elif l.isdescending():
        first = l.max()
        second = l.min()
    else:
        first = l.first()
        second = l.last()

    if first is None:
        raise error.Abort(_('empty revision range'))
    if (first == second and len(revs) >= 2
        and not all(revrange(repo, [r]) for r in revs)):
        raise error.Abort(_('empty revision on one side of range'))

    # if top-level is range expression, the result must always be a pair
    if first == second and len(revs) == 1 and not _pairspec(revs[0]):
        return repo.lookup(first), None

    return repo.lookup(first), repo.lookup(second)

def revrange(repo, specs):
    """Execute 1 to many revsets and return the union.

    This is the preferred mechanism for executing revsets using user-specified
    config options, such as revset aliases.

    The revsets specified by ``specs`` will be executed via a chained ``OR``
    expression. If ``specs`` is empty, an empty result is returned.

    ``specs`` can contain integers, in which case they are assumed to be
    revision numbers.

    It is assumed the revsets are already formatted. If you have arguments
    that need to be expanded in the revset, call ``revset.formatspec()``
    and pass the result as an element of ``specs``.

    Specifying a single revset is allowed.

    Returns a ``revset.abstractsmartset`` which is a list-like interface over
    integer revisions.
    """
    allspecs = []
    for spec in specs:
        if isinstance(spec, int):
            spec = revset.formatspec('rev(%d)', spec)
        allspecs.append(spec)
    m = revset.matchany(repo.ui, allspecs, repo)
    return m(repo)

def meaningfulparents(repo, ctx):
    """Return list of meaningful (or all if debug) parentrevs for rev.

    For merges (two non-nullrev revisions) both parents are meaningful.
    Otherwise the first parent revision is considered meaningful if it
    is not the preceding revision.
    """
    parents = ctx.parents()
    if len(parents) > 1:
        return parents
    if repo.ui.debugflag:
        return [parents[0], repo['null']]
    if parents[0].rev() >= intrev(ctx.rev()) - 1:
        return []
    return parents

def expandpats(pats):
    '''Expand bare globs when running on windows.
    On posix we assume it already has already been done by sh.'''
    if not util.expandglobs:
        return list(pats)
    ret = []
    for kindpat in pats:
        kind, pat = matchmod._patsplit(kindpat, None)
        if kind is None:
            try:
                globbed = glob.glob(pat)
            except re.error:
                globbed = [pat]
            if globbed:
                ret.extend(globbed)
                continue
        ret.append(kindpat)
    return ret

def matchandpats(ctx, pats=(), opts=None, globbed=False, default='relpath',
                 badfn=None):
    '''Return a matcher and the patterns that were used.
    The matcher will warn about bad matches, unless an alternate badfn callback
    is provided.'''
    if pats == ("",):
        pats = []
    if opts is None:
        opts = {}
    if not globbed and default == 'relpath':
        pats = expandpats(pats or [])

    def bad(f, msg):
        ctx.repo().ui.warn("%s: %s\n" % (m.rel(f), msg))

    if badfn is None:
        badfn = bad

    m = ctx.match(pats, opts.get('include'), opts.get('exclude'),
                  default, listsubrepos=opts.get('subrepos'), badfn=badfn)

    if m.always():
        pats = []
    return m, pats

def match(ctx, pats=(), opts=None, globbed=False, default='relpath',
          badfn=None):
    '''Return a matcher that will warn about bad matches.'''
    return matchandpats(ctx, pats, opts, globbed, default, badfn=badfn)[0]

def matchall(repo):
    '''Return a matcher that will efficiently match everything.'''
    return matchmod.always(repo.root, repo.getcwd())

def matchfiles(repo, files, badfn=None):
    '''Return a matcher that will efficiently match exactly these files.'''
    return matchmod.exact(repo.root, repo.getcwd(), files, badfn=badfn)

def origpath(ui, repo, filepath):
    '''customize where .orig files are created

    Fetch user defined path from config file: [ui] origbackuppath = <path>
    Fall back to default (filepath) if not specified
    '''
    origbackuppath = ui.config('ui', 'origbackuppath', None)
    if origbackuppath is None:
        return filepath + ".orig"

    filepathfromroot = os.path.relpath(filepath, start=repo.root)
    fullorigpath = repo.wjoin(origbackuppath, filepathfromroot)

    origbackupdir = repo.vfs.dirname(fullorigpath)
    if not repo.vfs.exists(origbackupdir):
        ui.note(_('creating directory: %s\n') % origbackupdir)
        util.makedirs(origbackupdir)

    return fullorigpath + ".orig"

def addremove(repo, matcher, prefix, opts=None, dry_run=None, similarity=None):
    if opts is None:
        opts = {}
    m = matcher
    if dry_run is None:
        dry_run = opts.get('dry_run')
    if similarity is None:
        similarity = float(opts.get('similarity') or 0)

    ret = 0
    join = lambda f: os.path.join(prefix, f)

    wctx = repo[None]
    for subpath in sorted(wctx.substate):
        submatch = matchmod.subdirmatcher(subpath, m)
        if opts.get('subrepos') or m.exact(subpath) or any(submatch.files()):
            sub = wctx.sub(subpath)
            try:
                if sub.addremove(submatch, prefix, opts, dry_run, similarity):
                    ret = 1
            except error.LookupError:
                repo.ui.status(_("skipping missing subrepository: %s\n")
                                 % join(subpath))

    rejected = []
    def badfn(f, msg):
        if f in m.files():
            m.bad(f, msg)
        rejected.append(f)

    badmatch = matchmod.badmatch(m, badfn)
    added, unknown, deleted, removed, forgotten = _interestingfiles(repo,
                                                                    badmatch)

    unknownset = set(unknown + forgotten)
    toprint = unknownset.copy()
    toprint.update(deleted)
    for abs in sorted(toprint):
        if repo.ui.verbose or not m.exact(abs):
            if abs in unknownset:
                status = _('adding %s\n') % m.uipath(abs)
            else:
                status = _('removing %s\n') % m.uipath(abs)
            repo.ui.status(status)

    renames = _findrenames(repo, m, added + unknown, removed + deleted,
                           similarity)

    if not dry_run:
        _markchanges(repo, unknown + forgotten, deleted, renames)

    for f in rejected:
        if f in m.files():
            return 1
    return ret

def marktouched(repo, files, similarity=0.0):
    '''Assert that files have somehow been operated upon. files are relative to
    the repo root.'''
    m = matchfiles(repo, files, badfn=lambda x, y: rejected.append(x))
    rejected = []

    added, unknown, deleted, removed, forgotten = _interestingfiles(repo, m)

    if repo.ui.verbose:
        unknownset = set(unknown + forgotten)
        toprint = unknownset.copy()
        toprint.update(deleted)
        for abs in sorted(toprint):
            if abs in unknownset:
                status = _('adding %s\n') % abs
            else:
                status = _('removing %s\n') % abs
            repo.ui.status(status)

    renames = _findrenames(repo, m, added + unknown, removed + deleted,
                           similarity)

    _markchanges(repo, unknown + forgotten, deleted, renames)

    for f in rejected:
        if f in m.files():
            return 1
    return 0

def _interestingfiles(repo, matcher):
    '''Walk dirstate with matcher, looking for files that addremove would care
    about.

    This is different from dirstate.status because it doesn't care about
    whether files are modified or clean.'''
    added, unknown, deleted, removed, forgotten = [], [], [], [], []
    audit_path = pathutil.pathauditor(repo.root)

    ctx = repo[None]
    dirstate = repo.dirstate
    walkresults = dirstate.walk(matcher, sorted(ctx.substate), True, False,
                                full=False)
    for abs, st in walkresults.iteritems():
        dstate = dirstate[abs]
        if dstate == '?' and audit_path.check(abs):
            unknown.append(abs)
        elif dstate != 'r' and not st:
            deleted.append(abs)
        elif dstate == 'r' and st:
            forgotten.append(abs)
        # for finding renames
        elif dstate == 'r' and not st:
            removed.append(abs)
        elif dstate == 'a':
            added.append(abs)

    return added, unknown, deleted, removed, forgotten

def _findrenames(repo, matcher, added, removed, similarity):
    '''Find renames from removed files to added ones.'''
    renames = {}
    if similarity > 0:
        for old, new, score in similar.findrenames(repo, added, removed,
                                                   similarity):
            if (repo.ui.verbose or not matcher.exact(old)
                or not matcher.exact(new)):
                repo.ui.status(_('recording removal of %s as rename to %s '
                                 '(%d%% similar)\n') %
                               (matcher.rel(old), matcher.rel(new),
                                score * 100))
            renames[new] = old
    return renames

def _markchanges(repo, unknown, deleted, renames):
    '''Marks the files in unknown as added, the files in deleted as removed,
    and the files in renames as copied.'''
    wctx = repo[None]
    with repo.wlock():
        wctx.forget(deleted)
        wctx.add(unknown)
        for new, old in renames.iteritems():
            wctx.copy(old, new)

def dirstatecopy(ui, repo, wctx, src, dst, dryrun=False, cwd=None):
    """Update the dirstate to reflect the intent of copying src to dst. For
    different reasons it might not end with dst being marked as copied from src.
    """
    origsrc = repo.dirstate.copied(src) or src
    if dst == origsrc: # copying back a copy?
        if repo.dirstate[dst] not in 'mn' and not dryrun:
            repo.dirstate.normallookup(dst)
    else:
        if repo.dirstate[origsrc] == 'a' and origsrc == src:
            if not ui.quiet:
                ui.warn(_("%s has not been committed yet, so no copy "
                          "data will be stored for %s.\n")
                        % (repo.pathto(origsrc, cwd), repo.pathto(dst, cwd)))
            if repo.dirstate[dst] in '?r' and not dryrun:
                wctx.add([dst])
        elif not dryrun:
            wctx.copy(origsrc, dst)

def readrequires(opener, supported):
    '''Reads and parses .hg/requires and checks if all entries found
    are in the list of supported features.'''
    requirements = set(opener.read("requires").splitlines())
    missings = []
    for r in requirements:
        if r not in supported:
            if not r or not r[0].isalnum():
                raise error.RequirementError(_(".hg/requires file is corrupt"))
            missings.append(r)
    missings.sort()
    if missings:
        raise error.RequirementError(
            _("repository requires features unknown to this Mercurial: %s")
            % " ".join(missings),
            hint=_("see https://mercurial-scm.org/wiki/MissingRequirement"
                   " for more information"))
    return requirements

def writerequires(opener, requirements):
    with opener('requires', 'w') as fp:
        for r in sorted(requirements):
            fp.write("%s\n" % r)

class filecachesubentry(object):
    def __init__(self, path, stat):
        self.path = path
        self.cachestat = None
        self._cacheable = None

        if stat:
            self.cachestat = filecachesubentry.stat(self.path)

            if self.cachestat:
                self._cacheable = self.cachestat.cacheable()
            else:
                # None means we don't know yet
                self._cacheable = None

    def refresh(self):
        if self.cacheable():
            self.cachestat = filecachesubentry.stat(self.path)

    def cacheable(self):
        if self._cacheable is not None:
            return self._cacheable

        # we don't know yet, assume it is for now
        return True

    def changed(self):
        # no point in going further if we can't cache it
        if not self.cacheable():
            return True

        newstat = filecachesubentry.stat(self.path)

        # we may not know if it's cacheable yet, check again now
        if newstat and self._cacheable is None:
            self._cacheable = newstat.cacheable()

            # check again
            if not self._cacheable:
                return True

        if self.cachestat != newstat:
            self.cachestat = newstat
            return True
        else:
            return False

    @staticmethod
    def stat(path):
        try:
            return util.cachestat(path)
        except OSError as e:
            if e.errno != errno.ENOENT:
                raise

class filecacheentry(object):
    def __init__(self, paths, stat=True):
        self._entries = []
        for path in paths:
            self._entries.append(filecachesubentry(path, stat))

    def changed(self):
        '''true if any entry has changed'''
        for entry in self._entries:
            if entry.changed():
                return True
        return False

    def refresh(self):
        for entry in self._entries:
            entry.refresh()

class filecache(object):
    '''A property like decorator that tracks files under .hg/ for updates.

    Records stat info when called in _filecache.

    On subsequent calls, compares old stat info with new info, and recreates the
    object when any of the files changes, updating the new stat info in
    _filecache.

    Mercurial either atomic renames or appends for files under .hg,
    so to ensure the cache is reliable we need the filesystem to be able
    to tell us if a file has been replaced. If it can't, we fallback to
    recreating the object on every call (essentially the same behavior as
    propertycache).

    '''
    def __init__(self, *paths):
        self.paths = paths

    def join(self, obj, fname):
        """Used to compute the runtime path of a cached file.

        Users should subclass filecache and provide their own version of this
        function to call the appropriate join function on 'obj' (an instance
        of the class that its member function was decorated).
        """
        return obj.join(fname)

    def __call__(self, func):
        self.func = func
        self.name = func.__name__
        return self

    def __get__(self, obj, type=None):
        # if accessed on the class, return the descriptor itself.
        if obj is None:
            return self
        # do we need to check if the file changed?
        if self.name in obj.__dict__:
            assert self.name in obj._filecache, self.name
            return obj.__dict__[self.name]

        entry = obj._filecache.get(self.name)

        if entry:
            if entry.changed():
                entry.obj = self.func(obj)
        else:
            paths = [self.join(obj, path) for path in self.paths]

            # We stat -before- creating the object so our cache doesn't lie if
            # a writer modified between the time we read and stat
            entry = filecacheentry(paths, True)
            entry.obj = self.func(obj)

            obj._filecache[self.name] = entry

        obj.__dict__[self.name] = entry.obj
        return entry.obj

    def __set__(self, obj, value):
        if self.name not in obj._filecache:
            # we add an entry for the missing value because X in __dict__
            # implies X in _filecache
            paths = [self.join(obj, path) for path in self.paths]
            ce = filecacheentry(paths, False)
            obj._filecache[self.name] = ce
        else:
            ce = obj._filecache[self.name]

        ce.obj = value # update cached copy
        obj.__dict__[self.name] = value # update copy returned by obj.x

    def __delete__(self, obj):
        try:
            del obj.__dict__[self.name]
        except KeyError:
            raise AttributeError(self.name)

def _locksub(repo, lock, envvar, cmd, environ=None, *args, **kwargs):
    if lock is None:
        raise error.LockInheritanceContractViolation(
            'lock can only be inherited while held')
    if environ is None:
        environ = {}
    with lock.inherit() as locker:
        environ[envvar] = locker
        return repo.ui.system(cmd, environ=environ, *args, **kwargs)

def wlocksub(repo, cmd, *args, **kwargs):
    """run cmd as a subprocess that allows inheriting repo's wlock

    This can only be called while the wlock is held. This takes all the
    arguments that ui.system does, and returns the exit code of the
    subprocess."""
    return _locksub(repo, repo.currentwlock(), 'HG_WLOCK_LOCKER', cmd, *args,
                    **kwargs)

def gdinitconfig(ui):
    """helper function to know if a repo should be created as general delta
    """
    # experimental config: format.generaldelta
    return (ui.configbool('format', 'generaldelta', False)
            or ui.configbool('format', 'usegeneraldelta', True))

def gddeltaconfig(ui):
    """helper function to know if incoming delta should be optimised
    """
    # experimental config: format.generaldelta
    return ui.configbool('format', 'generaldelta', False)

class closewrapbase(object):
    """Base class of wrapper, which hooks closing

    Do not instantiate outside of the vfs layer.
    """
    def __init__(self, fh):
        object.__setattr__(self, '_origfh', fh)

    def __getattr__(self, attr):
        return getattr(self._origfh, attr)

    def __setattr__(self, attr, value):
        return setattr(self._origfh, attr, value)

    def __delattr__(self, attr):
        return delattr(self._origfh, attr)

    def __enter__(self):
        return self._origfh.__enter__()

    def __exit__(self, exc_type, exc_value, exc_tb):
        raise NotImplementedError('attempted instantiating ' + str(type(self)))

    def close(self):
        raise NotImplementedError('attempted instantiating ' + str(type(self)))

class delayclosedfile(closewrapbase):
    """Proxy for a file object whose close is delayed.

    Do not instantiate outside of the vfs layer.
    """
    def __init__(self, fh, closer):
        super(delayclosedfile, self).__init__(fh)
        object.__setattr__(self, '_closer', closer)

    def __exit__(self, exc_type, exc_value, exc_tb):
        self._closer.close(self._origfh)

    def close(self):
        self._closer.close(self._origfh)

class backgroundfilecloser(object):
    """Coordinates background closing of file handles on multiple threads."""
    def __init__(self, ui, expectedcount=-1):
        self._running = False
        self._entered = False
        self._threads = []
        self._threadexception = None

        # Only Windows/NTFS has slow file closing. So only enable by default
        # on that platform. But allow to be enabled elsewhere for testing.
        defaultenabled = os.name == 'nt'
        enabled = ui.configbool('worker', 'backgroundclose', defaultenabled)

        if not enabled:
            return

        # There is overhead to starting and stopping the background threads.
        # Don't do background processing unless the file count is large enough
        # to justify it.
        minfilecount = ui.configint('worker', 'backgroundcloseminfilecount',
                                    2048)
        # FUTURE dynamically start background threads after minfilecount closes.
        # (We don't currently have any callers that don't know their file count)
        if expectedcount > 0 and expectedcount < minfilecount:
            return

        # Windows defaults to a limit of 512 open files. A buffer of 128
        # should give us enough headway.
        maxqueue = ui.configint('worker', 'backgroundclosemaxqueue', 384)
        threadcount = ui.configint('worker', 'backgroundclosethreadcount', 4)

        ui.debug('starting %d threads for background file closing\n' %
                 threadcount)

        self._queue = util.queue(maxsize=maxqueue)
        self._running = True

        for i in range(threadcount):
            t = threading.Thread(target=self._worker, name='backgroundcloser')
            self._threads.append(t)
            t.start()

    def __enter__(self):
        self._entered = True
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self._running = False

        # Wait for threads to finish closing so open files don't linger for
        # longer than lifetime of context manager.
        for t in self._threads:
            t.join()

    def _worker(self):
        """Main routine for worker thread."""
        while True:
            try:
                fh = self._queue.get(block=True, timeout=0.100)
                # Need to catch or the thread will terminate and
                # we could orphan file descriptors.
                try:
                    fh.close()
                except Exception as e:
                    # Stash so can re-raise from main thread later.
                    self._threadexception = e
            except util.empty:
                if not self._running:
                    break

    def close(self, fh):
        """Schedule a file for closing."""
        if not self._entered:
            raise error.Abort(_('can only call close() when context manager '
                              'active'))

        # If a background thread encountered an exception, raise now so we fail
        # fast. Otherwise we may potentially go on for minutes until the error
        # is acted on.
        if self._threadexception:
            e = self._threadexception
            self._threadexception = None
            raise e

        # If we're not actively running, close synchronously.
        if not self._running:
            fh.close()
            return

        self._queue.put(fh, block=True, timeout=None)

class checkambigatclosing(closewrapbase):
    """Proxy for a file object, to avoid ambiguity of file stat

    See also util.filestat for detail about "ambiguity of file stat".

    This proxy is useful only if the target file is guarded by any
    lock (e.g. repo.lock or repo.wlock)

    Do not instantiate outside of the vfs layer.
    """
    def __init__(self, fh):
        super(checkambigatclosing, self).__init__(fh)
        object.__setattr__(self, '_oldstat', util.filestat(fh.name))

    def _checkambig(self):
        oldstat = self._oldstat
        if oldstat.stat:
            newstat = util.filestat(self._origfh.name)
            if newstat.isambig(oldstat):
                # stat of changed file is ambiguous to original one
                advanced = (oldstat.stat.st_mtime + 1) & 0x7fffffff
                os.utime(self._origfh.name, (advanced, advanced))

    def __exit__(self, exc_type, exc_value, exc_tb):
        self._origfh.__exit__(exc_type, exc_value, exc_tb)
        self._checkambig()

    def close(self):
        self._origfh.close()
        self._checkambig()