revert: add some inline comments

I spend some time understanding how this part of the revert code is
working. I'm adding some comments to help the code readability. I
expect most of them to disappear in a coming refactoring. But the
refactoring should be easier to follow with the comment.

mercurial/cmdutil.py

@@ -1,2511 +1,2531 b''
 # cmdutil.py - help for command processing in mercurial
 #
 # Copyright 2005-2007 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 node import hex, nullid, nullrev, short
 from i18n import _
 import os, sys, errno, re, tempfile
 import util, scmutil, templater, patch, error, templatekw, revlog, copies
 import match as matchmod
 import context, repair, graphmod, revset, phases, obsolete, pathutil
 import changelog
 import bookmarks
 import lock as lockmod
 
 def parsealiases(cmd):
     return cmd.lstrip("^").split("|")
 
 def findpossible(cmd, table, strict=False):
     """
     Return cmd -> (aliases, command table entry)
     for each matching command.
     Return debug commands (or their aliases) only if no normal command matches.
     """
     choice = {}
     debugchoice = {}
 
     if cmd in table:
         # short-circuit exact matches, "log" alias beats "^log|history"
         keys = [cmd]
     else:
         keys = table.keys()
 
     for e in keys:
         aliases = parsealiases(e)
         found = None
         if cmd in aliases:
             found = cmd
         elif not strict:
             for a in aliases:
                 if a.startswith(cmd):
                     found = a
                     break
         if found is not None:
             if aliases[0].startswith("debug") or found.startswith("debug"):
                 debugchoice[found] = (aliases, table[e])
             else:
                 choice[found] = (aliases, table[e])
 
     if not choice and debugchoice:
         choice = debugchoice
 
     return choice
 
 def findcmd(cmd, table, strict=True):
     """Return (aliases, command table entry) for command string."""
     choice = findpossible(cmd, table, strict)
 
     if cmd in choice:
         return choice[cmd]
 
     if len(choice) > 1:
         clist = choice.keys()
         clist.sort()
         raise error.AmbiguousCommand(cmd, clist)
 
     if choice:
         return choice.values()[0]
 
     raise error.UnknownCommand(cmd)
 
 def findrepo(p):
     while not os.path.isdir(os.path.join(p, ".hg")):
         oldp, p = p, os.path.dirname(p)
         if p == oldp:
             return None
 
     return p
 
 def bailifchanged(repo):
     if repo.dirstate.p2() != nullid:
         raise util.Abort(_('outstanding uncommitted merge'))
     modified, added, removed, deleted = repo.status()[:4]
     if modified or added or removed or deleted:
         raise util.Abort(_('uncommitted changes'))
     ctx = repo[None]
     for s in sorted(ctx.substate):
         if ctx.sub(s).dirty():
             raise util.Abort(_("uncommitted changes in subrepo %s") % s)
 
 def logmessage(ui, opts):
     """ get the log message according to -m and -l option """
     message = opts.get('message')
     logfile = opts.get('logfile')
 
     if message and logfile:
         raise util.Abort(_('options --message and --logfile are mutually '
                            'exclusive'))
     if not message and logfile:
         try:
             if logfile == '-':
                 message = ui.fin.read()
             else:
                 message = '\n'.join(util.readfile(logfile).splitlines())
         except IOError, inst:
             raise util.Abort(_("can't read commit message '%s': %s") %
                              (logfile, inst.strerror))
     return message
 
 def getcommiteditor(edit=False, finishdesc=None, extramsg=None, **opts):
     """get appropriate commit message editor according to '--edit' option
 
     'finishdesc' is a function to be called with edited commit message
     (= 'description' of the new changeset) just after editing, but
     before checking empty-ness. It should return actual text to be
     stored into history. This allows to change description before
     storing.
 
     'extramsg' is a extra message to be shown in the editor instead of
     'Leave message empty to abort commit' line. 'HG: ' prefix and EOL
     is automatically added.
 
     'getcommiteditor' returns 'commitforceeditor' regardless of
     'edit', if one of 'finishdesc' or 'extramsg' is specified, because
     they are specific for usage in MQ.
     """
     if edit or finishdesc or extramsg:
         return lambda r, c, s: commitforceeditor(r, c, s,
                                                  finishdesc=finishdesc,
                                                  extramsg=extramsg)
     else:
         return commiteditor
 
 def loglimit(opts):
     """get the log limit according to option -l/--limit"""
     limit = opts.get('limit')
     if limit:
         try:
             limit = int(limit)
         except ValueError:
             raise util.Abort(_('limit must be a positive integer'))
         if limit <= 0:
             raise util.Abort(_('limit must be positive'))
     else:
         limit = None
     return limit
 
 def makefilename(repo, pat, node, desc=None,
                   total=None, seqno=None, revwidth=None, pathname=None):
     node_expander = {
         'H': lambda: hex(node),
         'R': lambda: str(repo.changelog.rev(node)),
         'h': lambda: short(node),
         'm': lambda: re.sub('[^\w]', '_', str(desc))
         }
     expander = {
         '%': lambda: '%',
         'b': lambda: os.path.basename(repo.root),
         }
 
     try:
         if node:
             expander.update(node_expander)
         if node:
             expander['r'] = (lambda:
                     str(repo.changelog.rev(node)).zfill(revwidth or 0))
         if total is not None:
             expander['N'] = lambda: str(total)
         if seqno is not None:
             expander['n'] = lambda: str(seqno)
         if total is not None and seqno is not None:
             expander['n'] = lambda: str(seqno).zfill(len(str(total)))
         if pathname is not None:
             expander['s'] = lambda: os.path.basename(pathname)
             expander['d'] = lambda: os.path.dirname(pathname) or '.'
             expander['p'] = lambda: pathname
 
         newname = []
         patlen = len(pat)
         i = 0
         while i < patlen:
             c = pat[i]
             if c == '%':
                 i += 1
                 c = pat[i]
                 c = expander[c]()
             newname.append(c)
             i += 1
         return ''.join(newname)
     except KeyError, inst:
         raise util.Abort(_("invalid format spec '%%%s' in output filename") %
                          inst.args[0])
 
 def makefileobj(repo, pat, node=None, desc=None, total=None,
                 seqno=None, revwidth=None, mode='wb', modemap=None,
                 pathname=None):
 
     writable = mode not in ('r', 'rb')
 
     if not pat or pat == '-':
         fp = writable and repo.ui.fout or repo.ui.fin
         if util.safehasattr(fp, 'fileno'):
             return os.fdopen(os.dup(fp.fileno()), mode)
         else:
             # if this fp can't be duped properly, return
             # a dummy object that can be closed
             class wrappedfileobj(object):
                 noop = lambda x: None
                 def __init__(self, f):
                     self.f = f
                 def __getattr__(self, attr):
                     if attr == 'close':
                         return self.noop
                     else:
                         return getattr(self.f, attr)
 
             return wrappedfileobj(fp)
     if util.safehasattr(pat, 'write') and writable:
         return pat
     if util.safehasattr(pat, 'read') and 'r' in mode:
         return pat
     fn = makefilename(repo, pat, node, desc, total, seqno, revwidth, pathname)
     if modemap is not None:
         mode = modemap.get(fn, mode)
         if mode == 'wb':
             modemap[fn] = 'ab'
     return open(fn, mode)
 
 def openrevlog(repo, cmd, file_, opts):
     """opens the changelog, manifest, a filelog or a given revlog"""
     cl = opts['changelog']
     mf = opts['manifest']
     msg = None
     if cl and mf:
         msg = _('cannot specify --changelog and --manifest at the same time')
     elif cl or mf:
         if file_:
             msg = _('cannot specify filename with --changelog or --manifest')
         elif not repo:
             msg = _('cannot specify --changelog or --manifest '
                     'without a repository')
     if msg:
         raise util.Abort(msg)
 
     r = None
     if repo:
         if cl:
             r = repo.unfiltered().changelog
         elif mf:
             r = repo.manifest
         elif file_:
             filelog = repo.file(file_)
             if len(filelog):
                 r = filelog
     if not r:
         if not file_:
             raise error.CommandError(cmd, _('invalid arguments'))
         if not os.path.isfile(file_):
             raise util.Abort(_("revlog '%s' not found") % file_)
         r = revlog.revlog(scmutil.opener(os.getcwd(), audit=False),
                           file_[:-2] + ".i")
     return r
 
 def copy(ui, repo, pats, opts, rename=False):
     # called with the repo lock held
     #
     # hgsep => pathname that uses "/" to separate directories
     # ossep => pathname that uses os.sep to separate directories
     cwd = repo.getcwd()
     targets = {}
     after = opts.get("after")
     dryrun = opts.get("dry_run")
     wctx = repo[None]
 
     def walkpat(pat):
         srcs = []
         badstates = after and '?' or '?r'
         m = scmutil.match(repo[None], [pat], opts, globbed=True)
         for abs in repo.walk(m):
             state = repo.dirstate[abs]
             rel = m.rel(abs)
             exact = m.exact(abs)
             if state in badstates:
                 if exact and state == '?':
                     ui.warn(_('%s: not copying - file is not managed\n') % rel)
                 if exact and state == 'r':
                     ui.warn(_('%s: not copying - file has been marked for'
                               ' remove\n') % rel)
                 continue
             # abs: hgsep
             # rel: ossep
             srcs.append((abs, rel, exact))
         return srcs
 
     # abssrc: hgsep
     # relsrc: ossep
     # otarget: ossep
     def copyfile(abssrc, relsrc, otarget, exact):
         abstarget = pathutil.canonpath(repo.root, cwd, otarget)
         if '/' in abstarget:
             # We cannot normalize abstarget itself, this would prevent
             # case only renames, like a => A.
             abspath, absname = abstarget.rsplit('/', 1)
             abstarget = repo.dirstate.normalize(abspath) + '/' + absname
         reltarget = repo.pathto(abstarget, cwd)
         target = repo.wjoin(abstarget)
         src = repo.wjoin(abssrc)
         state = repo.dirstate[abstarget]
 
         scmutil.checkportable(ui, abstarget)
 
         # check for collisions
         prevsrc = targets.get(abstarget)
         if prevsrc is not None:
             ui.warn(_('%s: not overwriting - %s collides with %s\n') %
                     (reltarget, repo.pathto(abssrc, cwd),
                      repo.pathto(prevsrc, cwd)))
             return
 
         # check for overwrites
         exists = os.path.lexists(target)
         samefile = False
         if exists and abssrc != abstarget:
             if (repo.dirstate.normalize(abssrc) ==
                 repo.dirstate.normalize(abstarget)):
                 if not rename:
                     ui.warn(_("%s: can't copy - same file\n") % reltarget)
                     return
                 exists = False
                 samefile = True
 
         if not after and exists or after and state in 'mn':
             if not opts['force']:
                 ui.warn(_('%s: not overwriting - file exists\n') %
                         reltarget)
                 return
 
         if after:
             if not exists:
                 if rename:
                     ui.warn(_('%s: not recording move - %s does not exist\n') %
                             (relsrc, reltarget))
                 else:
                     ui.warn(_('%s: not recording copy - %s does not exist\n') %
                             (relsrc, reltarget))
                 return
         elif not dryrun:
             try:
                 if exists:
                     os.unlink(target)
                 targetdir = os.path.dirname(target) or '.'
                 if not os.path.isdir(targetdir):
                     os.makedirs(targetdir)
                 if samefile:
                     tmp = target + "~hgrename"
                     os.rename(src, tmp)
                     os.rename(tmp, target)
                 else:
                     util.copyfile(src, target)
                 srcexists = True
             except IOError, inst:
                 if inst.errno == errno.ENOENT:
                     ui.warn(_('%s: deleted in working copy\n') % relsrc)
                     srcexists = False
                 else:
                     ui.warn(_('%s: cannot copy - %s\n') %
                             (relsrc, inst.strerror))
                     return True # report a failure
 
         if ui.verbose or not exact:
             if rename:
                 ui.status(_('moving %s to %s\n') % (relsrc, reltarget))
             else:
                 ui.status(_('copying %s to %s\n') % (relsrc, reltarget))
 
         targets[abstarget] = abssrc
 
         # fix up dirstate
         scmutil.dirstatecopy(ui, repo, wctx, abssrc, abstarget,
                              dryrun=dryrun, cwd=cwd)
         if rename and not dryrun:
             if not after and srcexists and not samefile:
                 util.unlinkpath(repo.wjoin(abssrc))
             wctx.forget([abssrc])
 
     # pat: ossep
     # dest ossep
     # srcs: list of (hgsep, hgsep, ossep, bool)
     # return: function that takes hgsep and returns ossep
     def targetpathfn(pat, dest, srcs):
         if os.path.isdir(pat):
             abspfx = pathutil.canonpath(repo.root, cwd, pat)
             abspfx = util.localpath(abspfx)
             if destdirexists:
                 striplen = len(os.path.split(abspfx)[0])
             else:
                 striplen = len(abspfx)
             if striplen:
                 striplen += len(os.sep)
             res = lambda p: os.path.join(dest, util.localpath(p)[striplen:])
         elif destdirexists:
             res = lambda p: os.path.join(dest,
                                          os.path.basename(util.localpath(p)))
         else:
             res = lambda p: dest
         return res
 
     # pat: ossep
     # dest ossep
     # srcs: list of (hgsep, hgsep, ossep, bool)
     # return: function that takes hgsep and returns ossep
     def targetpathafterfn(pat, dest, srcs):
         if matchmod.patkind(pat):
             # a mercurial pattern
             res = lambda p: os.path.join(dest,
                                          os.path.basename(util.localpath(p)))
         else:
             abspfx = pathutil.canonpath(repo.root, cwd, pat)
             if len(abspfx) < len(srcs[0][0]):
                 # A directory. Either the target path contains the last
                 # component of the source path or it does not.
                 def evalpath(striplen):
                     score = 0
                     for s in srcs:
                         t = os.path.join(dest, util.localpath(s[0])[striplen:])
                         if os.path.lexists(t):
                             score += 1
                     return score
 
                 abspfx = util.localpath(abspfx)
                 striplen = len(abspfx)
                 if striplen:
                     striplen += len(os.sep)
                 if os.path.isdir(os.path.join(dest, os.path.split(abspfx)[1])):
                     score = evalpath(striplen)
                     striplen1 = len(os.path.split(abspfx)[0])
                     if striplen1:
                         striplen1 += len(os.sep)
                     if evalpath(striplen1) > score:
                         striplen = striplen1
                 res = lambda p: os.path.join(dest,
                                              util.localpath(p)[striplen:])
             else:
                 # a file
                 if destdirexists:
                     res = lambda p: os.path.join(dest,
                                         os.path.basename(util.localpath(p)))
                 else:
                     res = lambda p: dest
         return res
 
 
     pats = scmutil.expandpats(pats)
     if not pats:
         raise util.Abort(_('no source or destination specified'))
     if len(pats) == 1:
         raise util.Abort(_('no destination specified'))
     dest = pats.pop()
     destdirexists = os.path.isdir(dest) and not os.path.islink(dest)
     if not destdirexists:
         if len(pats) > 1 or matchmod.patkind(pats[0]):
             raise util.Abort(_('with multiple sources, destination must be an '
                                'existing directory'))
         if util.endswithsep(dest):
             raise util.Abort(_('destination %s is not a directory') % dest)
 
     tfn = targetpathfn
     if after:
         tfn = targetpathafterfn
     copylist = []
     for pat in pats:
         srcs = walkpat(pat)
         if not srcs:
             continue
         copylist.append((tfn(pat, dest, srcs), srcs))
     if not copylist:
         raise util.Abort(_('no files to copy'))
 
     errors = 0
     for targetpath, srcs in copylist:
         for abssrc, relsrc, exact in srcs:
             if copyfile(abssrc, relsrc, targetpath(abssrc), exact):
                 errors += 1
 
     if errors:
         ui.warn(_('(consider using --after)\n'))
 
     return errors != 0
 
 def service(opts, parentfn=None, initfn=None, runfn=None, logfile=None,
     runargs=None, appendpid=False):
     '''Run a command as a service.'''
 
     def writepid(pid):
         if opts['pid_file']:
             mode = appendpid and 'a' or 'w'
             fp = open(opts['pid_file'], mode)
             fp.write(str(pid) + '\n')
             fp.close()
 
     if opts['daemon'] and not opts['daemon_pipefds']:
         # Signal child process startup with file removal
         lockfd, lockpath = tempfile.mkstemp(prefix='hg-service-')
         os.close(lockfd)
         try:
             if not runargs:
                 runargs = util.hgcmd() + sys.argv[1:]
             runargs.append('--daemon-pipefds=%s' % lockpath)
             # Don't pass --cwd to the child process, because we've already
             # changed directory.
             for i in xrange(1, len(runargs)):
                 if runargs[i].startswith('--cwd='):
                     del runargs[i]
                     break
                 elif runargs[i].startswith('--cwd'):
                     del runargs[i:i + 2]
                     break
             def condfn():
                 return not os.path.exists(lockpath)
             pid = util.rundetached(runargs, condfn)
             if pid < 0:
                 raise util.Abort(_('child process failed to start'))
             writepid(pid)
         finally:
             try:
                 os.unlink(lockpath)
             except OSError, e:
                 if e.errno != errno.ENOENT:
                     raise
         if parentfn:
             return parentfn(pid)
         else:
             return
 
     if initfn:
         initfn()
 
     if not opts['daemon']:
         writepid(os.getpid())
 
     if opts['daemon_pipefds']:
         lockpath = opts['daemon_pipefds']
         try:
             os.setsid()
         except AttributeError:
             pass
         os.unlink(lockpath)
         util.hidewindow()
         sys.stdout.flush()
         sys.stderr.flush()
 
         nullfd = os.open(os.devnull, os.O_RDWR)
         logfilefd = nullfd
         if logfile:
             logfilefd = os.open(logfile, os.O_RDWR | os.O_CREAT | os.O_APPEND)
         os.dup2(nullfd, 0)
         os.dup2(logfilefd, 1)
         os.dup2(logfilefd, 2)
         if nullfd not in (0, 1, 2):
             os.close(nullfd)
         if logfile and logfilefd not in (0, 1, 2):
             os.close(logfilefd)
 
     if runfn:
         return runfn()
 
 def tryimportone(ui, repo, hunk, parents, opts, msgs, updatefunc):
     """Utility function used by commands.import to import a single patch
 
     This function is explicitly defined here to help the evolve extension to
     wrap this part of the import logic.
 
     The API is currently a bit ugly because it a simple code translation from
     the import command. Feel free to make it better.
 
     :hunk: a patch (as a binary string)
     :parents: nodes that will be parent of the created commit
     :opts: the full dict of option passed to the import command
     :msgs: list to save commit message to.
            (used in case we need to save it when failing)
     :updatefunc: a function that update a repo to a given node
                  updatefunc(<repo>, <node>)
     """
     tmpname, message, user, date, branch, nodeid, p1, p2 = \
         patch.extract(ui, hunk)
 
     editor = getcommiteditor(**opts)
     update = not opts.get('bypass')
     strip = opts["strip"]
     sim = float(opts.get('similarity') or 0)
     if not tmpname:
         return (None, None, False)
     msg = _('applied to working directory')
 
     rejects = False
 
     try:
         cmdline_message = logmessage(ui, opts)
         if cmdline_message:
             # pickup the cmdline msg
             message = cmdline_message
         elif message:
             # pickup the patch msg
             message = message.strip()
         else:
             # launch the editor
             message = None
         ui.debug('message:\n%s\n' % message)
 
         if len(parents) == 1:
             parents.append(repo[nullid])
         if opts.get('exact'):
             if not nodeid or not p1:
                 raise util.Abort(_('not a Mercurial patch'))
             p1 = repo[p1]
             p2 = repo[p2 or nullid]
         elif p2:
             try:
                 p1 = repo[p1]
                 p2 = repo[p2]
                 # Without any options, consider p2 only if the
                 # patch is being applied on top of the recorded
                 # first parent.
                 if p1 != parents[0]:
                     p1 = parents[0]
                     p2 = repo[nullid]
             except error.RepoError:
                 p1, p2 = parents
         else:
             p1, p2 = parents
 
         n = None
         if update:
             if p1 != parents[0]:
                 updatefunc(repo, p1.node())
             if p2 != parents[1]:
                 repo.setparents(p1.node(), p2.node())
 
             if opts.get('exact') or opts.get('import_branch'):
                 repo.dirstate.setbranch(branch or 'default')
 
             partial = opts.get('partial', False)
             files = set()
             try:
                 patch.patch(ui, repo, tmpname, strip=strip, files=files,
                             eolmode=None, similarity=sim / 100.0)
             except patch.PatchError, e:
                 if not partial:
                     raise util.Abort(str(e))
                 if partial:
                     rejects = True
 
             files = list(files)
             if opts.get('no_commit'):
                 if message:
                     msgs.append(message)
             else:
                 if opts.get('exact') or p2:
                     # If you got here, you either use --force and know what
                     # you are doing or used --exact or a merge patch while
                     # being updated to its first parent.
                     m = None
                 else:
                     m = scmutil.matchfiles(repo, files or [])
                 n = repo.commit(message, opts.get('user') or user,
                                 opts.get('date') or date, match=m,
                                 editor=editor, force=partial)
         else:
             if opts.get('exact') or opts.get('import_branch'):
                 branch = branch or 'default'
             else:
                 branch = p1.branch()
             store = patch.filestore()
             try:
                 files = set()
                 try:
                     patch.patchrepo(ui, repo, p1, store, tmpname, strip,
                                     files, eolmode=None)
                 except patch.PatchError, e:
                     raise util.Abort(str(e))
                 memctx = context.makememctx(repo, (p1.node(), p2.node()),
                                             message,
                                             opts.get('user') or user,
                                             opts.get('date') or date,
                                             branch, files, store,
                                             editor=getcommiteditor())
                 n = memctx.commit()
             finally:
                 store.close()
         if opts.get('exact') and hex(n) != nodeid:
             raise util.Abort(_('patch is damaged or loses information'))
         if n:
             # i18n: refers to a short changeset id
             msg = _('created %s') % short(n)
         return (msg, n, rejects)
     finally:
         os.unlink(tmpname)
 
 def export(repo, revs, template='hg-%h.patch', fp=None, switch_parent=False,
            opts=None):
     '''export changesets as hg patches.'''
 
     total = len(revs)
     revwidth = max([len(str(rev)) for rev in revs])
     filemode = {}
 
     def single(rev, seqno, fp):
         ctx = repo[rev]
         node = ctx.node()
         parents = [p.node() for p in ctx.parents() if p]
         branch = ctx.branch()
         if switch_parent:
             parents.reverse()
         prev = (parents and parents[0]) or nullid
 
         shouldclose = False
         if not fp and len(template) > 0:
             desc_lines = ctx.description().rstrip().split('\n')
             desc = desc_lines[0]    #Commit always has a first line.
             fp = makefileobj(repo, template, node, desc=desc, total=total,
                              seqno=seqno, revwidth=revwidth, mode='wb',
                              modemap=filemode)
             if fp != template:
                 shouldclose = True
         if fp and fp != sys.stdout and util.safehasattr(fp, 'name'):
             repo.ui.note("%s\n" % fp.name)
 
         if not fp:
             write = repo.ui.write
         else:
             def write(s, **kw):
                 fp.write(s)
 
 
         write("# HG changeset patch\n")
         write("# User %s\n" % ctx.user())
         write("# Date %d %d\n" % ctx.date())
         write("#      %s\n" % util.datestr(ctx.date()))
         if branch and branch != 'default':
             write("# Branch %s\n" % branch)
         write("# Node ID %s\n" % hex(node))
         write("# Parent  %s\n" % hex(prev))
         if len(parents) > 1:
             write("# Parent  %s\n" % hex(parents[1]))
         write(ctx.description().rstrip())
         write("\n\n")
 
         for chunk, label in patch.diffui(repo, prev, node, opts=opts):
             write(chunk, label=label)
 
         if shouldclose:
             fp.close()
 
     for seqno, rev in enumerate(revs):
         single(rev, seqno + 1, fp)
 
 def diffordiffstat(ui, repo, diffopts, node1, node2, match,
                    changes=None, stat=False, fp=None, prefix='',
                    listsubrepos=False):
     '''show diff or diffstat.'''
     if fp is None:
         write = ui.write
     else:
         def write(s, **kw):
             fp.write(s)
 
     if stat:
         diffopts = diffopts.copy(context=0)
         width = 80
         if not ui.plain():
             width = ui.termwidth()
         chunks = patch.diff(repo, node1, node2, match, changes, diffopts,
                             prefix=prefix)
         for chunk, label in patch.diffstatui(util.iterlines(chunks),
                                              width=width,
                                              git=diffopts.git):
             write(chunk, label=label)
     else:
         for chunk, label in patch.diffui(repo, node1, node2, match,
                                          changes, diffopts, prefix=prefix):
             write(chunk, label=label)
 
     if listsubrepos:
         ctx1 = repo[node1]
         ctx2 = repo[node2]
         for subpath, sub in scmutil.itersubrepos(ctx1, ctx2):
             tempnode2 = node2
             try:
                 if node2 is not None:
                     tempnode2 = ctx2.substate[subpath][1]
             except KeyError:
                 # A subrepo that existed in node1 was deleted between node1 and
                 # node2 (inclusive). Thus, ctx2's substate won't contain that
                 # subpath. The best we can do is to ignore it.
                 tempnode2 = None
             submatch = matchmod.narrowmatcher(subpath, match)
             sub.diff(ui, diffopts, tempnode2, submatch, changes=changes,
                      stat=stat, fp=fp, prefix=prefix)
 
 class changeset_printer(object):
     '''show changeset information when templating not requested.'''
 
     def __init__(self, ui, repo, patch, diffopts, buffered):
         self.ui = ui
         self.repo = repo
         self.buffered = buffered
         self.patch = patch
         self.diffopts = diffopts
         self.header = {}
         self.hunk = {}
         self.lastheader = None
         self.footer = None
 
     def flush(self, rev):
         if rev in self.header:
             h = self.header[rev]
             if h != self.lastheader:
                 self.lastheader = h
                 self.ui.write(h)
             del self.header[rev]
         if rev in self.hunk:
             self.ui.write(self.hunk[rev])
             del self.hunk[rev]
             return 1
         return 0
 
     def close(self):
         if self.footer:
             self.ui.write(self.footer)
 
     def show(self, ctx, copies=None, matchfn=None, **props):
         if self.buffered:
             self.ui.pushbuffer()
             self._show(ctx, copies, matchfn, props)
             self.hunk[ctx.rev()] = self.ui.popbuffer(labeled=True)
         else:
             self._show(ctx, copies, matchfn, props)
 
     def _show(self, ctx, copies, matchfn, props):
         '''show a single changeset or file revision'''
         changenode = ctx.node()
         rev = ctx.rev()
 
         if self.ui.quiet:
             self.ui.write("%d:%s\n" % (rev, short(changenode)),
                           label='log.node')
             return
 
         log = self.repo.changelog
         date = util.datestr(ctx.date())
 
         hexfunc = self.ui.debugflag and hex or short
 
         parents = [(p, hexfunc(log.node(p)))
                    for p in self._meaningful_parentrevs(log, rev)]
 
         # i18n: column positioning for "hg log"
         self.ui.write(_("changeset:   %d:%s\n") % (rev, hexfunc(changenode)),
                       label='log.changeset changeset.%s' % ctx.phasestr())
 
         branch = ctx.branch()
         # don't show the default branch name
         if branch != 'default':
             # i18n: column positioning for "hg log"
             self.ui.write(_("branch:      %s\n") % branch,
                           label='log.branch')
         for bookmark in self.repo.nodebookmarks(changenode):
             # i18n: column positioning for "hg log"
             self.ui.write(_("bookmark:    %s\n") % bookmark,
                     label='log.bookmark')
         for tag in self.repo.nodetags(changenode):
             # i18n: column positioning for "hg log"
             self.ui.write(_("tag:         %s\n") % tag,
                           label='log.tag')
         if self.ui.debugflag and ctx.phase():
             # i18n: column positioning for "hg log"
             self.ui.write(_("phase:       %s\n") % _(ctx.phasestr()),
                           label='log.phase')
         for parent in parents:
             # i18n: column positioning for "hg log"
             self.ui.write(_("parent:      %d:%s\n") % parent,
                           label='log.parent changeset.%s' % ctx.phasestr())
 
         if self.ui.debugflag:
             mnode = ctx.manifestnode()
             # i18n: column positioning for "hg log"
             self.ui.write(_("manifest:    %d:%s\n") %
                           (self.repo.manifest.rev(mnode), hex(mnode)),
                           label='ui.debug log.manifest')
         # i18n: column positioning for "hg log"
         self.ui.write(_("user:        %s\n") % ctx.user(),
                       label='log.user')
         # i18n: column positioning for "hg log"
         self.ui.write(_("date:        %s\n") % date,
                       label='log.date')
 
         if self.ui.debugflag:
             files = self.repo.status(log.parents(changenode)[0], changenode)[:3]
             for key, value in zip([# i18n: column positioning for "hg log"
                                    _("files:"),
                                    # i18n: column positioning for "hg log"
                                    _("files+:"),
                                    # i18n: column positioning for "hg log"
                                    _("files-:")], files):
                 if value:
                     self.ui.write("%-12s %s\n" % (key, " ".join(value)),
                                   label='ui.debug log.files')
         elif ctx.files() and self.ui.verbose:
             # i18n: column positioning for "hg log"
             self.ui.write(_("files:       %s\n") % " ".join(ctx.files()),
                           label='ui.note log.files')
         if copies and self.ui.verbose:
             copies = ['%s (%s)' % c for c in copies]
             # i18n: column positioning for "hg log"
             self.ui.write(_("copies:      %s\n") % ' '.join(copies),
                           label='ui.note log.copies')
 
         extra = ctx.extra()
         if extra and self.ui.debugflag:
             for key, value in sorted(extra.items()):
                 # i18n: column positioning for "hg log"
                 self.ui.write(_("extra:       %s=%s\n")
                               % (key, value.encode('string_escape')),
                               label='ui.debug log.extra')
 
         description = ctx.description().strip()
         if description:
             if self.ui.verbose:
                 self.ui.write(_("description:\n"),
                               label='ui.note log.description')
                 self.ui.write(description,
                               label='ui.note log.description')
                 self.ui.write("\n\n")
             else:
                 # i18n: column positioning for "hg log"
                 self.ui.write(_("summary:     %s\n") %
                               description.splitlines()[0],
                               label='log.summary')
         self.ui.write("\n")
 
         self.showpatch(changenode, matchfn)
 
     def showpatch(self, node, matchfn):
         if not matchfn:
             matchfn = self.patch
         if matchfn:
             stat = self.diffopts.get('stat')
             diff = self.diffopts.get('patch')
             diffopts = patch.diffopts(self.ui, self.diffopts)
             prev = self.repo.changelog.parents(node)[0]
             if stat:
                 diffordiffstat(self.ui, self.repo, diffopts, prev, node,
                                match=matchfn, stat=True)
             if diff:
                 if stat:
                     self.ui.write("\n")
                 diffordiffstat(self.ui, self.repo, diffopts, prev, node,
                                match=matchfn, stat=False)
             self.ui.write("\n")
 
     def _meaningful_parentrevs(self, log, rev):
         """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 = log.parentrevs(rev)
         if not self.ui.debugflag and parents[1] == nullrev:
             if parents[0] >= rev - 1:
                 parents = []
             else:
                 parents = [parents[0]]
         return parents
 
 
 class changeset_templater(changeset_printer):
     '''format changeset information.'''
 
     def __init__(self, ui, repo, patch, diffopts, tmpl, mapfile, buffered):
         changeset_printer.__init__(self, ui, repo, patch, diffopts, buffered)
         formatnode = ui.debugflag and (lambda x: x) or (lambda x: x[:12])
         defaulttempl = {
             'parent': '{rev}:{node|formatnode} ',
             'manifest': '{rev}:{node|formatnode}',
             'file_copy': '{name} ({source})',
             'extra': '{key}={value|stringescape}'
             }
         # filecopy is preserved for compatibility reasons
         defaulttempl['filecopy'] = defaulttempl['file_copy']
         self.t = templater.templater(mapfile, {'formatnode': formatnode},
                                      cache=defaulttempl)
         if tmpl:
             self.t.cache['changeset'] = tmpl
 
         self.cache = {}
 
     def _meaningful_parentrevs(self, ctx):
         """Return list of meaningful (or all if debug) parentrevs for rev.
         """
         parents = ctx.parents()
         if len(parents) > 1:
             return parents
         if self.ui.debugflag:
             return [parents[0], self.repo['null']]
         if parents[0].rev() >= ctx.rev() - 1:
             return []
         return parents
 
     def _show(self, ctx, copies, matchfn, props):
         '''show a single changeset or file revision'''
 
         showlist = templatekw.showlist
 
         # showparents() behaviour depends on ui trace level which
         # causes unexpected behaviours at templating level and makes
         # it harder to extract it in a standalone function. Its
         # behaviour cannot be changed so leave it here for now.
         def showparents(**args):
             ctx = args['ctx']
             parents = [[('rev', p.rev()), ('node', p.hex())]
                        for p in self._meaningful_parentrevs(ctx)]
             return showlist('parent', parents, **args)
 
         props = props.copy()
         props.update(templatekw.keywords)
         props['parents'] = showparents
         props['templ'] = self.t
         props['ctx'] = ctx
         props['repo'] = self.repo
         props['revcache'] = {'copies': copies}
         props['cache'] = self.cache
 
         # find correct templates for current mode
 
         tmplmodes = [
             (True, None),
             (self.ui.verbose, 'verbose'),
             (self.ui.quiet, 'quiet'),
             (self.ui.debugflag, 'debug'),
         ]
 
         types = {'header': '', 'footer':'', 'changeset': 'changeset'}
         for mode, postfix  in tmplmodes:
             for type in types:
                 cur = postfix and ('%s_%s' % (type, postfix)) or type
                 if mode and cur in self.t:
                     types[type] = cur
 
         try:
 
             # write header
             if types['header']:
                 h = templater.stringify(self.t(types['header'], **props))
                 if self.buffered:
                     self.header[ctx.rev()] = h
                 else:
                     if self.lastheader != h:
                         self.lastheader = h
                         self.ui.write(h)
 
             # write changeset metadata, then patch if requested
             key = types['changeset']
             self.ui.write(templater.stringify(self.t(key, **props)))
             self.showpatch(ctx.node(), matchfn)
 
             if types['footer']:
                 if not self.footer:
                     self.footer = templater.stringify(self.t(types['footer'],
                                                       **props))
 
         except KeyError, inst:
             msg = _("%s: no key named '%s'")
             raise util.Abort(msg % (self.t.mapfile, inst.args[0]))
         except SyntaxError, inst:
             raise util.Abort('%s: %s' % (self.t.mapfile, inst.args[0]))
 
 def gettemplate(ui, tmpl, style):
     """
     Find the template matching the given template spec or style.
     """
 
     # ui settings
     if not tmpl and not style:
         tmpl = ui.config('ui', 'logtemplate')
         if tmpl:
             try:
                 tmpl = templater.parsestring(tmpl)
             except SyntaxError:
                 tmpl = templater.parsestring(tmpl, quoted=False)
             return tmpl, None
         else:
             style = util.expandpath(ui.config('ui', 'style', ''))
 
     if style:
         mapfile = style
         if not os.path.split(mapfile)[0]:
             mapname = (templater.templatepath('map-cmdline.' + mapfile)
                        or templater.templatepath(mapfile))
             if mapname:
                 mapfile = mapname
         return None, mapfile
 
     if not tmpl:
         return None, None
 
     # looks like a literal template?
     if '{' in tmpl:
         return tmpl, None
 
     # perhaps a stock style?
     if not os.path.split(tmpl)[0]:
         mapname = (templater.templatepath('map-cmdline.' + tmpl)
                    or templater.templatepath(tmpl))
         if mapname and os.path.isfile(mapname):
             return None, mapname
 
     # perhaps it's a reference to [templates]
     t = ui.config('templates', tmpl)
     if t:
         try:
             tmpl = templater.parsestring(t)
         except SyntaxError:
             tmpl = templater.parsestring(t, quoted=False)
         return tmpl, None
 
     # perhaps it's a path to a map or a template
     if ('/' in tmpl or '\\' in tmpl) and os.path.isfile(tmpl):
         # is it a mapfile for a style?
         if os.path.basename(tmpl).startswith("map-"):
             return None, os.path.realpath(tmpl)
         tmpl = open(tmpl).read()
         return tmpl, None
 
     # constant string?
     return tmpl, None
 
 def show_changeset(ui, repo, opts, buffered=False):
     """show one changeset using template or regular display.
 
     Display format will be the first non-empty hit of:
     1. option 'template'
     2. option 'style'
     3. [ui] setting 'logtemplate'
     4. [ui] setting 'style'
     If all of these values are either the unset or the empty string,
     regular display via changeset_printer() is done.
     """
     # options
     patch = None
     if opts.get('patch') or opts.get('stat'):
         patch = scmutil.matchall(repo)
 
     tmpl, mapfile = gettemplate(ui, opts.get('template'), opts.get('style'))
 
     if not tmpl and not mapfile:
         return changeset_printer(ui, repo, patch, opts, buffered)
 
     try:
         t = changeset_templater(ui, repo, patch, opts, tmpl, mapfile, buffered)
     except SyntaxError, inst:
         raise util.Abort(inst.args[0])
     return t
 
 def showmarker(ui, marker):
     """utility function to display obsolescence marker in a readable way
 
     To be used by debug function."""
     ui.write(hex(marker.precnode()))
     for repl in marker.succnodes():
         ui.write(' ')
         ui.write(hex(repl))
     ui.write(' %X ' % marker._data[2])
     ui.write('{%s}' % (', '.join('%r: %r' % t for t in
                                  sorted(marker.metadata().items()))))
     ui.write('\n')
 
 def finddate(ui, repo, date):
     """Find the tipmost changeset that matches the given date spec"""
 
     df = util.matchdate(date)
     m = scmutil.matchall(repo)
     results = {}
 
     def prep(ctx, fns):
         d = ctx.date()
         if df(d[0]):
             results[ctx.rev()] = d
 
     for ctx in walkchangerevs(repo, m, {'rev': None}, prep):
         rev = ctx.rev()
         if rev in results:
             ui.status(_("found revision %s from %s\n") %
                       (rev, util.datestr(results[rev])))
             return str(rev)
 
     raise util.Abort(_("revision matching date not found"))
 
 def increasingwindows(windowsize=8, sizelimit=512):
     while True:
         yield windowsize
         if windowsize < sizelimit:
             windowsize *= 2
 
 class FileWalkError(Exception):
     pass
 
 def walkfilerevs(repo, match, follow, revs, fncache):
     '''Walks the file history for the matched files.
 
     Returns the changeset revs that are involved in the file history.
 
     Throws FileWalkError if the file history can't be walked using
     filelogs alone.
     '''
     wanted = set()
     copies = []
     minrev, maxrev = min(revs), max(revs)
     def filerevgen(filelog, last):
         """
         Only files, no patterns.  Check the history of each file.
 
         Examines filelog entries within minrev, maxrev linkrev range
         Returns an iterator yielding (linkrev, parentlinkrevs, copied)
         tuples in backwards order
         """
         cl_count = len(repo)
         revs = []
         for j in xrange(0, last + 1):
             linkrev = filelog.linkrev(j)
             if linkrev < minrev:
                 continue
             # only yield rev for which we have the changelog, it can
             # happen while doing "hg log" during a pull or commit
             if linkrev >= cl_count:
                 break
 
             parentlinkrevs = []
             for p in filelog.parentrevs(j):
                 if p != nullrev:
                     parentlinkrevs.append(filelog.linkrev(p))
             n = filelog.node(j)
             revs.append((linkrev, parentlinkrevs,
                          follow and filelog.renamed(n)))
 
         return reversed(revs)
     def iterfiles():
         pctx = repo['.']
         for filename in match.files():
             if follow:
                 if filename not in pctx:
                     raise util.Abort(_('cannot follow file not in parent '
                                        'revision: "%s"') % filename)
                 yield filename, pctx[filename].filenode()
             else:
                 yield filename, None
         for filename_node in copies:
             yield filename_node
 
     for file_, node in iterfiles():
         filelog = repo.file(file_)
         if not len(filelog):
             if node is None:
                 # A zero count may be a directory or deleted file, so
                 # try to find matching entries on the slow path.
                 if follow:
                     raise util.Abort(
                         _('cannot follow nonexistent file: "%s"') % file_)
                 raise FileWalkError("Cannot walk via filelog")
             else:
                 continue
 
         if node is None:
             last = len(filelog) - 1
         else:
             last = filelog.rev(node)
 
 
         # keep track of all ancestors of the file
         ancestors = set([filelog.linkrev(last)])
 
         # iterate from latest to oldest revision
         for rev, flparentlinkrevs, copied in filerevgen(filelog, last):
             if not follow:
                 if rev > maxrev:
                     continue
             else:
                 # Note that last might not be the first interesting
                 # rev to us:
                 # if the file has been changed after maxrev, we'll
                 # have linkrev(last) > maxrev, and we still need
                 # to explore the file graph
                 if rev not in ancestors:
                     continue
                 # XXX insert 1327 fix here
                 if flparentlinkrevs:
                     ancestors.update(flparentlinkrevs)
 
             fncache.setdefault(rev, []).append(file_)
             wanted.add(rev)
             if copied:
                 copies.append(copied)
 
     return wanted
 
 def walkchangerevs(repo, match, opts, prepare):
     '''Iterate over files and the revs in which they changed.
 
     Callers most commonly need to iterate backwards over the history
     in which they are interested. Doing so has awful (quadratic-looking)
     performance, so we use iterators in a "windowed" way.
 
     We walk a window of revisions in the desired order.  Within the
     window, we first walk forwards to gather data, then in the desired
     order (usually backwards) to display it.
 
     This function returns an iterator yielding contexts. Before
     yielding each context, the iterator will first call the prepare
     function on each context in the window in forward order.'''
 
     follow = opts.get('follow') or opts.get('follow_first')
 
     if opts.get('rev'):
         revs = scmutil.revrange(repo, opts.get('rev'))
     elif follow:
         revs = repo.revs('reverse(:.)')
     else:
         revs = revset.spanset(repo)
         revs.reverse()
     if not revs:
         return []
     wanted = set()
     slowpath = match.anypats() or (match.files() and opts.get('removed'))
     fncache = {}
     change = repo.changectx
 
     # First step is to fill wanted, the set of revisions that we want to yield.
     # When it does not induce extra cost, we also fill fncache for revisions in
     # wanted: a cache of filenames that were changed (ctx.files()) and that
     # match the file filtering conditions.
 
     if not slowpath and not match.files():
         # No files, no patterns.  Display all revs.
         wanted = revs
 
     if not slowpath and match.files():
         # We only have to read through the filelog to find wanted revisions
 
         try:
             wanted = walkfilerevs(repo, match, follow, revs, fncache)
         except FileWalkError:
             slowpath = True
 
             # We decided to fall back to the slowpath because at least one
             # of the paths was not a file. Check to see if at least one of them
             # existed in history, otherwise simply return
             for path in match.files():
                 if path == '.' or path in repo.store:
                     break
             else:
                 return []
 
     if slowpath:
         # We have to read the changelog to match filenames against
         # changed files
 
         if follow:
             raise util.Abort(_('can only follow copies/renames for explicit '
                                'filenames'))
 
         # The slow path checks files modified in every changeset.
         # This is really slow on large repos, so compute the set lazily.
         class lazywantedset(object):
             def __init__(self):
                 self.set = set()
                 self.revs = set(revs)
 
             # No need to worry about locality here because it will be accessed
             # in the same order as the increasing window below.
             def __contains__(self, value):
                 if value in self.set:
                     return True
                 elif not value in self.revs:
                     return False
                 else:
                     self.revs.discard(value)
                     ctx = change(value)
                     matches = filter(match, ctx.files())
                     if matches:
                         fncache[value] = matches
                         self.set.add(value)
                         return True
                     return False
 
             def discard(self, value):
                 self.revs.discard(value)
                 self.set.discard(value)
 
         wanted = lazywantedset()
 
     class followfilter(object):
         def __init__(self, onlyfirst=False):
             self.startrev = nullrev
             self.roots = set()
             self.onlyfirst = onlyfirst
 
         def match(self, rev):
             def realparents(rev):
                 if self.onlyfirst:
                     return repo.changelog.parentrevs(rev)[0:1]
                 else:
                     return filter(lambda x: x != nullrev,
                                   repo.changelog.parentrevs(rev))
 
             if self.startrev == nullrev:
                 self.startrev = rev
                 return True
 
             if rev > self.startrev:
                 # forward: all descendants
                 if not self.roots:
                     self.roots.add(self.startrev)
                 for parent in realparents(rev):
                     if parent in self.roots:
                         self.roots.add(rev)
                         return True
             else:
                 # backwards: all parents
                 if not self.roots:
                     self.roots.update(realparents(self.startrev))
                 if rev in self.roots:
                     self.roots.remove(rev)
                     self.roots.update(realparents(rev))
                     return True
 
             return False
 
     # it might be worthwhile to do this in the iterator if the rev range
     # is descending and the prune args are all within that range
     for rev in opts.get('prune', ()):
         rev = repo[rev].rev()
         ff = followfilter()
         stop = min(revs[0], revs[-1])
         for x in xrange(rev, stop - 1, -1):
             if ff.match(x):
                 wanted = wanted - [x]
 
     # Now that wanted is correctly initialized, we can iterate over the
     # revision range, yielding only revisions in wanted.
     def iterate():
         if follow and not match.files():
             ff = followfilter(onlyfirst=opts.get('follow_first'))
             def want(rev):
                 return ff.match(rev) and rev in wanted
         else:
             def want(rev):
                 return rev in wanted
 
         it = iter(revs)
         stopiteration = False
         for windowsize in increasingwindows():
             nrevs = []
             for i in xrange(windowsize):
                 try:
                     rev = it.next()
                     if want(rev):
                         nrevs.append(rev)
                 except (StopIteration):
                     stopiteration = True
                     break
             for rev in sorted(nrevs):
                 fns = fncache.get(rev)
                 ctx = change(rev)
                 if not fns:
                     def fns_generator():
                         for f in ctx.files():
                             if match(f):
                                 yield f
                     fns = fns_generator()
                 prepare(ctx, fns)
             for rev in nrevs:
                 yield change(rev)
 
             if stopiteration:
                 break
 
     return iterate()
 
 def _makelogfilematcher(repo, pats, followfirst):
     # When displaying a revision with --patch --follow FILE, we have
     # to know which file of the revision must be diffed. With
     # --follow, we want the names of the ancestors of FILE in the
     # revision, stored in "fcache". "fcache" is populated by
     # reproducing the graph traversal already done by --follow revset
     # and relating linkrevs to file names (which is not "correct" but
     # good enough).
     fcache = {}
     fcacheready = [False]
     pctx = repo['.']
     wctx = repo[None]
 
     def populate():
         for fn in pats:
             for i in ((pctx[fn],), pctx[fn].ancestors(followfirst=followfirst)):
                 for c in i:
                     fcache.setdefault(c.linkrev(), set()).add(c.path())
 
     def filematcher(rev):
         if not fcacheready[0]:
             # Lazy initialization
             fcacheready[0] = True
             populate()
         return scmutil.match(wctx, fcache.get(rev, []), default='path')
 
     return filematcher
 
 def _makelogrevset(repo, pats, opts, revs):
     """Return (expr, filematcher) where expr is a revset string built
     from log options and file patterns or None. If --stat or --patch
     are not passed filematcher is None. Otherwise it is a callable
     taking a revision number and returning a match objects filtering
     the files to be detailed when displaying the revision.
     """
     opt2revset = {
         'no_merges':        ('not merge()', None),
         'only_merges':      ('merge()', None),
         '_ancestors':       ('ancestors(%(val)s)', None),
         '_fancestors':      ('_firstancestors(%(val)s)', None),
         '_descendants':     ('descendants(%(val)s)', None),
         '_fdescendants':    ('_firstdescendants(%(val)s)', None),
         '_matchfiles':      ('_matchfiles(%(val)s)', None),
         'date':             ('date(%(val)r)', None),
         'branch':           ('branch(%(val)r)', ' or '),
         '_patslog':         ('filelog(%(val)r)', ' or '),
         '_patsfollow':      ('follow(%(val)r)', ' or '),
         '_patsfollowfirst': ('_followfirst(%(val)r)', ' or '),
         'keyword':          ('keyword(%(val)r)', ' or '),
         'prune':            ('not (%(val)r or ancestors(%(val)r))', ' and '),
         'user':             ('user(%(val)r)', ' or '),
         }
 
     opts = dict(opts)
     # follow or not follow?
     follow = opts.get('follow') or opts.get('follow_first')
     followfirst = opts.get('follow_first') and 1 or 0
     # --follow with FILE behaviour depends on revs...
     it = iter(revs)
     startrev = it.next()
     try:
         followdescendants = startrev < it.next()
     except (StopIteration):
         followdescendants = False
 
     # branch and only_branch are really aliases and must be handled at
     # the same time
     opts['branch'] = opts.get('branch', []) + opts.get('only_branch', [])
     opts['branch'] = [repo.lookupbranch(b) for b in opts['branch']]
     # pats/include/exclude are passed to match.match() directly in
     # _matchfiles() revset but walkchangerevs() builds its matcher with
     # scmutil.match(). The difference is input pats are globbed on
     # platforms without shell expansion (windows).
     pctx = repo[None]
     match, pats = scmutil.matchandpats(pctx, pats, opts)
     slowpath = match.anypats() or (match.files() and opts.get('removed'))
     if not slowpath:
         for f in match.files():
             if follow and f not in pctx:
                 raise util.Abort(_('cannot follow file not in parent '
                                    'revision: "%s"') % f)
             filelog = repo.file(f)
             if not filelog:
                 # A zero count may be a directory or deleted file, so
                 # try to find matching entries on the slow path.
                 if follow:
                     raise util.Abort(
                         _('cannot follow nonexistent file: "%s"') % f)
                 slowpath = True
 
         # We decided to fall back to the slowpath because at least one
         # of the paths was not a file. Check to see if at least one of them
         # existed in history - in that case, we'll continue down the
         # slowpath; otherwise, we can turn off the slowpath
         if slowpath:
             for path in match.files():
                 if path == '.' or path in repo.store:
                     break
             else:
                 slowpath = False
 
     if slowpath:
         # See walkchangerevs() slow path.
         #
         if follow:
             raise util.Abort(_('can only follow copies/renames for explicit '
                                'filenames'))
         # pats/include/exclude cannot be represented as separate
         # revset expressions as their filtering logic applies at file
         # level. For instance "-I a -X a" matches a revision touching
         # "a" and "b" while "file(a) and not file(b)" does
         # not. Besides, filesets are evaluated against the working
         # directory.
         matchargs = ['r:', 'd:relpath']
         for p in pats:
             matchargs.append('p:' + p)
         for p in opts.get('include', []):
             matchargs.append('i:' + p)
         for p in opts.get('exclude', []):
             matchargs.append('x:' + p)
         matchargs = ','.join(('%r' % p) for p in matchargs)
         opts['_matchfiles'] = matchargs
     else:
         if follow:
             fpats = ('_patsfollow', '_patsfollowfirst')
             fnopats = (('_ancestors', '_fancestors'),
                        ('_descendants', '_fdescendants'))
             if pats:
                 # follow() revset interprets its file argument as a
                 # manifest entry, so use match.files(), not pats.
                 opts[fpats[followfirst]] = list(match.files())
             else:
                 opts[fnopats[followdescendants][followfirst]] = str(startrev)
         else:
             opts['_patslog'] = list(pats)
 
     filematcher = None
     if opts.get('patch') or opts.get('stat'):
         if follow:
             filematcher = _makelogfilematcher(repo, pats, followfirst)
         else:
             filematcher = lambda rev: match
 
     expr = []
     for op, val in opts.iteritems():
         if not val:
             continue
         if op not in opt2revset:
             continue
         revop, andor = opt2revset[op]
         if '%(val)' not in revop:
             expr.append(revop)
         else:
             if not isinstance(val, list):
                 e = revop % {'val': val}
             else:
                 e = '(' + andor.join((revop % {'val': v}) for v in val) + ')'
             expr.append(e)
 
     if expr:
         expr = '(' + ' and '.join(expr) + ')'
     else:
         expr = None
     return expr, filematcher
 
 def getgraphlogrevs(repo, pats, opts):
     """Return (revs, expr, filematcher) where revs is an iterable of
     revision numbers, expr is a revset string built from log options
     and file patterns or None, and used to filter 'revs'. If --stat or
     --patch are not passed filematcher is None. Otherwise it is a
     callable taking a revision number and returning a match objects
     filtering the files to be detailed when displaying the revision.
     """
     if not len(repo):
         return [], None, None
     limit = loglimit(opts)
     # Default --rev value depends on --follow but --follow behaviour
     # depends on revisions resolved from --rev...
     follow = opts.get('follow') or opts.get('follow_first')
     possiblyunsorted = False # whether revs might need sorting
     if opts.get('rev'):
         revs = scmutil.revrange(repo, opts['rev'])
         # Don't sort here because _makelogrevset might depend on the
         # order of revs
         possiblyunsorted = True
     else:
         if follow and len(repo) > 0:
             revs = repo.revs('reverse(:.)')
         else:
             revs = revset.spanset(repo)
             revs.reverse()
     if not revs:
         return revset.baseset(), None, None
     expr, filematcher = _makelogrevset(repo, pats, opts, revs)
     if possiblyunsorted:
         revs.sort(reverse=True)
     if expr:
         # Revset matchers often operate faster on revisions in changelog
         # order, because most filters deal with the changelog.
         revs.reverse()
         matcher = revset.match(repo.ui, expr)
         # Revset matches can reorder revisions. "A or B" typically returns
         # returns the revision matching A then the revision matching B. Sort
         # again to fix that.
         revs = matcher(repo, revs)
         revs.sort(reverse=True)
     if limit is not None:
         limitedrevs = revset.baseset()
         for idx, rev in enumerate(revs):
             if idx >= limit:
                 break
             limitedrevs.append(rev)
         revs = limitedrevs
 
     return revs, expr, filematcher
 
 def getlogrevs(repo, pats, opts):
     """Return (revs, expr, filematcher) where revs is an iterable of
     revision numbers, expr is a revset string built from log options
     and file patterns or None, and used to filter 'revs'. If --stat or
     --patch are not passed filematcher is None. Otherwise it is a
     callable taking a revision number and returning a match objects
     filtering the files to be detailed when displaying the revision.
     """
     limit = loglimit(opts)
     # Default --rev value depends on --follow but --follow behaviour
     # depends on revisions resolved from --rev...
     follow = opts.get('follow') or opts.get('follow_first')
     if opts.get('rev'):
         revs = scmutil.revrange(repo, opts['rev'])
     elif follow:
         revs = revset.baseset(repo.revs('reverse(:.)'))
     else:
         revs = revset.spanset(repo)
         revs.reverse()
     if not revs:
         return revset.baseset([]), None, None
     expr, filematcher = _makelogrevset(repo, pats, opts, revs)
     if expr:
         # Revset matchers often operate faster on revisions in changelog
         # order, because most filters deal with the changelog.
         if not opts.get('rev'):
             revs.reverse()
         matcher = revset.match(repo.ui, expr)
         # Revset matches can reorder revisions. "A or B" typically returns
         # returns the revision matching A then the revision matching B. Sort
         # again to fix that.
         revs = matcher(repo, revs)
         if not opts.get('rev'):
             revs.sort(reverse=True)
     if limit is not None:
         count = 0
         limitedrevs = revset.baseset([])
         it = iter(revs)
         while count < limit:
             try:
                 limitedrevs.append(it.next())
             except (StopIteration):
                 break
             count += 1
         revs = limitedrevs
 
     return revs, expr, filematcher
 
 def displaygraph(ui, dag, displayer, showparents, edgefn, getrenamed=None,
                  filematcher=None):
     seen, state = [], graphmod.asciistate()
     for rev, type, ctx, parents in dag:
         char = 'o'
         if ctx.node() in showparents:
             char = '@'
         elif ctx.obsolete():
             char = 'x'
         copies = None
         if getrenamed and ctx.rev():
             copies = []
             for fn in ctx.files():
                 rename = getrenamed(fn, ctx.rev())
                 if rename:
                     copies.append((fn, rename[0]))
         revmatchfn = None
         if filematcher is not None:
             revmatchfn = filematcher(ctx.rev())
         displayer.show(ctx, copies=copies, matchfn=revmatchfn)
         lines = displayer.hunk.pop(rev).split('\n')
         if not lines[-1]:
             del lines[-1]
         displayer.flush(rev)
         edges = edgefn(type, char, lines, seen, rev, parents)
         for type, char, lines, coldata in edges:
             graphmod.ascii(ui, state, type, char, lines, coldata)
     displayer.close()
 
 def graphlog(ui, repo, *pats, **opts):
     # Parameters are identical to log command ones
     revs, expr, filematcher = getgraphlogrevs(repo, pats, opts)
     revdag = graphmod.dagwalker(repo, revs)
 
     getrenamed = None
     if opts.get('copies'):
         endrev = None
         if opts.get('rev'):
             endrev = scmutil.revrange(repo, opts.get('rev')).max() + 1
         getrenamed = templatekw.getrenamedfn(repo, endrev=endrev)
     displayer = show_changeset(ui, repo, opts, buffered=True)
     showparents = [ctx.node() for ctx in repo[None].parents()]
     displaygraph(ui, revdag, displayer, showparents,
                  graphmod.asciiedges, getrenamed, filematcher)
 
 def checkunsupportedgraphflags(pats, opts):
     for op in ["newest_first"]:
         if op in opts and opts[op]:
             raise util.Abort(_("-G/--graph option is incompatible with --%s")
                              % op.replace("_", "-"))
 
 def graphrevs(repo, nodes, opts):
     limit = loglimit(opts)
     nodes.reverse()
     if limit is not None:
         nodes = nodes[:limit]
     return graphmod.nodes(repo, nodes)
 
 def add(ui, repo, match, dryrun, listsubrepos, prefix, explicitonly):
     join = lambda f: os.path.join(prefix, f)
     bad = []
     oldbad = match.bad
     match.bad = lambda x, y: bad.append(x) or oldbad(x, y)
     names = []
     wctx = repo[None]
     cca = None
     abort, warn = scmutil.checkportabilityalert(ui)
     if abort or warn:
         cca = scmutil.casecollisionauditor(ui, abort, repo.dirstate)
     for f in repo.walk(match):
         exact = match.exact(f)
         if exact or not explicitonly and f not in repo.dirstate:
             if cca:
                 cca(f)
             names.append(f)
             if ui.verbose or not exact:
                 ui.status(_('adding %s\n') % match.rel(join(f)))
 
     for subpath in sorted(wctx.substate):
         sub = wctx.sub(subpath)
         try:
             submatch = matchmod.narrowmatcher(subpath, match)
             if listsubrepos:
                 bad.extend(sub.add(ui, submatch, dryrun, listsubrepos, prefix,
                                    False))
             else:
                 bad.extend(sub.add(ui, submatch, dryrun, listsubrepos, prefix,
                                    True))
         except error.LookupError:
             ui.status(_("skipping missing subrepository: %s\n")
                            % join(subpath))
 
     if not dryrun:
         rejected = wctx.add(names, prefix)
         bad.extend(f for f in rejected if f in match.files())
     return bad
 
 def forget(ui, repo, match, prefix, explicitonly):
     join = lambda f: os.path.join(prefix, f)
     bad = []
     oldbad = match.bad
     match.bad = lambda x, y: bad.append(x) or oldbad(x, y)
     wctx = repo[None]
     forgot = []
     s = repo.status(match=match, clean=True)
     forget = sorted(s[0] + s[1] + s[3] + s[6])
     if explicitonly:
         forget = [f for f in forget if match.exact(f)]
 
     for subpath in sorted(wctx.substate):
         sub = wctx.sub(subpath)
         try:
             submatch = matchmod.narrowmatcher(subpath, match)
             subbad, subforgot = sub.forget(ui, submatch, prefix)
             bad.extend([subpath + '/' + f for f in subbad])
             forgot.extend([subpath + '/' + f for f in subforgot])
         except error.LookupError:
             ui.status(_("skipping missing subrepository: %s\n")
                            % join(subpath))
 
     if not explicitonly:
         for f in match.files():
             if f not in repo.dirstate and not os.path.isdir(match.rel(join(f))):
                 if f not in forgot:
                     if os.path.exists(match.rel(join(f))):
                         ui.warn(_('not removing %s: '
                                   'file is already untracked\n')
                                 % match.rel(join(f)))
                     bad.append(f)
 
     for f in forget:
         if ui.verbose or not match.exact(f):
             ui.status(_('removing %s\n') % match.rel(join(f)))
 
     rejected = wctx.forget(forget, prefix)
     bad.extend(f for f in rejected if f in match.files())
     forgot.extend(forget)
     return bad, forgot
 
 def cat(ui, repo, ctx, matcher, prefix, **opts):
     err = 1
 
     def write(path):
         fp = makefileobj(repo, opts.get('output'), ctx.node(),
                          pathname=os.path.join(prefix, path))
         data = ctx[path].data()
         if opts.get('decode'):
             data = repo.wwritedata(path, data)
         fp.write(data)
         fp.close()
 
     # Automation often uses hg cat on single files, so special case it
     # for performance to avoid the cost of parsing the manifest.
     if len(matcher.files()) == 1 and not matcher.anypats():
         file = matcher.files()[0]
         mf = repo.manifest
         mfnode = ctx._changeset[0]
         if mf.find(mfnode, file)[0]:
             write(file)
             return 0
 
     # Don't warn about "missing" files that are really in subrepos
     bad = matcher.bad
 
     def badfn(path, msg):
         for subpath in ctx.substate:
             if path.startswith(subpath):
                 return
         bad(path, msg)
 
     matcher.bad = badfn
 
     for abs in ctx.walk(matcher):
         write(abs)
         err = 0
 
     matcher.bad = bad
 
     for subpath in sorted(ctx.substate):
         sub = ctx.sub(subpath)
         try:
             submatch = matchmod.narrowmatcher(subpath, matcher)
 
             if not sub.cat(ui, submatch, os.path.join(prefix, sub._path),
                            **opts):
                 err = 0
         except error.RepoLookupError:
             ui.status(_("skipping missing subrepository: %s\n")
                            % os.path.join(prefix, subpath))
 
     return err
 
 def duplicatecopies(repo, rev, fromrev):
     '''reproduce copies from fromrev to rev in the dirstate'''
     for dst, src in copies.pathcopies(repo[fromrev], repo[rev]).iteritems():
         # copies.pathcopies returns backward renames, so dst might not
         # actually be in the dirstate
         if repo.dirstate[dst] in "nma":
             repo.dirstate.copy(src, dst)
 
 def commit(ui, repo, commitfunc, pats, opts):
     '''commit the specified files or all outstanding changes'''
     date = opts.get('date')
     if date:
         opts['date'] = util.parsedate(date)
     message = logmessage(ui, opts)
 
     # extract addremove carefully -- this function can be called from a command
     # that doesn't support addremove
     if opts.get('addremove'):
         scmutil.addremove(repo, pats, opts)
 
     return commitfunc(ui, repo, message,
                       scmutil.match(repo[None], pats, opts), opts)
 
 def amend(ui, repo, commitfunc, old, extra, pats, opts):
     ui.note(_('amending changeset %s\n') % old)
     base = old.p1()
 
     wlock = lock = newid = None
     try:
         wlock = repo.wlock()
         lock = repo.lock()
         tr = repo.transaction('amend')
         try:
             # See if we got a message from -m or -l, if not, open the editor
             # with the message of the changeset to amend
             message = logmessage(ui, opts)
             # ensure logfile does not conflict with later enforcement of the
             # message. potential logfile content has been processed by
             # `logmessage` anyway.
             opts.pop('logfile')
             # First, do a regular commit to record all changes in the working
             # directory (if there are any)
             ui.callhooks = False
             currentbookmark = repo._bookmarkcurrent
             try:
                 repo._bookmarkcurrent = None
                 opts['message'] = 'temporary amend commit for %s' % old
                 node = commit(ui, repo, commitfunc, pats, opts)
             finally:
                 repo._bookmarkcurrent = currentbookmark
                 ui.callhooks = True
             ctx = repo[node]
 
             # Participating changesets:
             #
             # node/ctx o - new (intermediate) commit that contains changes
             #          |   from working dir to go into amending commit
             #          |   (or a workingctx if there were no changes)
             #          |
             # old      o - changeset to amend
             #          |
             # base     o - parent of amending changeset
 
             # Update extra dict from amended commit (e.g. to preserve graft
             # source)
             extra.update(old.extra())
 
             # Also update it from the intermediate commit or from the wctx
             extra.update(ctx.extra())
 
             if len(old.parents()) > 1:
                 # ctx.files() isn't reliable for merges, so fall back to the
                 # slower repo.status() method
                 files = set([fn for st in repo.status(base, old)[:3]
                              for fn in st])
             else:
                 files = set(old.files())
 
             # Second, we use either the commit we just did, or if there were no
             # changes the parent of the working directory as the version of the
             # files in the final amend commit
             if node:
                 ui.note(_('copying changeset %s to %s\n') % (ctx, base))
 
                 user = ctx.user()
                 date = ctx.date()
                 # Recompute copies (avoid recording a -> b -> a)
                 copied = copies.pathcopies(base, ctx)
 
                 # Prune files which were reverted by the updates: if old
                 # introduced file X and our intermediate commit, node,
                 # renamed that file, then those two files are the same and
                 # we can discard X from our list of files. Likewise if X
                 # was deleted, it's no longer relevant
                 files.update(ctx.files())
 
                 def samefile(f):
                     if f in ctx.manifest():
                         a = ctx.filectx(f)
                         if f in base.manifest():
                             b = base.filectx(f)
                             return (not a.cmp(b)
                                     and a.flags() == b.flags())
                         else:
                             return False
                     else:
                         return f not in base.manifest()
                 files = [f for f in files if not samefile(f)]
 
                 def filectxfn(repo, ctx_, path):
                     try:
                         fctx = ctx[path]
                         flags = fctx.flags()
                         mctx = context.memfilectx(fctx.path(), fctx.data(),
                                                   islink='l' in flags,
                                                   isexec='x' in flags,
                                                   copied=copied.get(path))
                         return mctx
                     except KeyError:
                         raise IOError
             else:
                 ui.note(_('copying changeset %s to %s\n') % (old, base))
 
                 # Use version of files as in the old cset
                 def filectxfn(repo, ctx_, path):
                     try:
                         return old.filectx(path)
                     except KeyError:
                         raise IOError
 
                 user = opts.get('user') or old.user()
                 date = opts.get('date') or old.date()
             editor = getcommiteditor(**opts)
             if not message:
                 editor = getcommiteditor(edit=True)
                 message = old.description()
 
             pureextra = extra.copy()
             extra['amend_source'] = old.hex()
 
             new = context.memctx(repo,
                                  parents=[base.node(), old.p2().node()],
                                  text=message,
                                  files=files,
                                  filectxfn=filectxfn,
                                  user=user,
                                  date=date,
                                  extra=extra,
                                  editor=editor)
 
             newdesc =  changelog.stripdesc(new.description())
             if ((not node)
                 and newdesc == old.description()
                 and user == old.user()
                 and date == old.date()
                 and pureextra == old.extra()):
                 # nothing changed. continuing here would create a new node
                 # anyway because of the amend_source noise.
                 #
                 # This not what we expect from amend.
                 return old.node()
 
             ph = repo.ui.config('phases', 'new-commit', phases.draft)
             try:
                 if opts.get('secret'):
                     commitphase = 'secret'
                 else:
                     commitphase = old.phase()
                 repo.ui.setconfig('phases', 'new-commit', commitphase, 'amend')
                 newid = repo.commitctx(new)
             finally:
                 repo.ui.setconfig('phases', 'new-commit', ph, 'amend')
             if newid != old.node():
                 # Reroute the working copy parent to the new changeset
                 repo.setparents(newid, nullid)
 
                 # Move bookmarks from old parent to amend commit
                 bms = repo.nodebookmarks(old.node())
                 if bms:
                     marks = repo._bookmarks
                     for bm in bms:
                         marks[bm] = newid
                     marks.write()
             #commit the whole amend process
             if obsolete._enabled and newid != old.node():
                 # mark the new changeset as successor of the rewritten one
                 new = repo[newid]
                 obs = [(old, (new,))]
                 if node:
                     obs.append((ctx, ()))
 
                 obsolete.createmarkers(repo, obs)
             tr.close()
         finally:
             tr.release()
         if (not obsolete._enabled) and newid != old.node():
             # Strip the intermediate commit (if there was one) and the amended
             # commit
             if node:
                 ui.note(_('stripping intermediate changeset %s\n') % ctx)
             ui.note(_('stripping amended changeset %s\n') % old)
             repair.strip(ui, repo, old.node(), topic='amend-backup')
     finally:
         if newid is None:
             repo.dirstate.invalidate()
         lockmod.release(lock, wlock)
     return newid
 
 def commiteditor(repo, ctx, subs):
     if ctx.description():
         return ctx.description()
     return commitforceeditor(repo, ctx, subs)
 
 def commitforceeditor(repo, ctx, subs, finishdesc=None, extramsg=None):
     edittext = []
     modified, added, removed = ctx.modified(), ctx.added(), ctx.removed()
     if ctx.description():
         edittext.append(ctx.description())
     edittext.append("")
     edittext.append("") # Empty line between message and comments.
     edittext.append(_("HG: Enter commit message."
                       "  Lines beginning with 'HG:' are removed."))
     if extramsg:
         edittext.append("HG: %s" % extramsg)
     else:
         edittext.append(_("HG: Leave message empty to abort commit."))
     edittext.append("HG: --")
     edittext.append(_("HG: user: %s") % ctx.user())
     if ctx.p2():
         edittext.append(_("HG: branch merge"))
     if ctx.branch():
         edittext.append(_("HG: branch '%s'") % ctx.branch())
     if bookmarks.iscurrent(repo):
         edittext.append(_("HG: bookmark '%s'") % repo._bookmarkcurrent)
     edittext.extend([_("HG: subrepo %s") % s for s in subs])
     edittext.extend([_("HG: added %s") % f for f in added])
     edittext.extend([_("HG: changed %s") % f for f in modified])
     edittext.extend([_("HG: removed %s") % f for f in removed])
     if not added and not modified and not removed:
         edittext.append(_("HG: no files changed"))
     edittext.append("")
     # run editor in the repository root
     olddir = os.getcwd()
     os.chdir(repo.root)
     text = repo.ui.edit("\n".join(edittext), ctx.user(), ctx.extra())
     text = re.sub("(?m)^HG:.*(\n|$)", "", text)
     os.chdir(olddir)
 
     if finishdesc:
         text = finishdesc(text)
     if not text.strip():
         raise util.Abort(_("empty commit message"))
 
     return text
 
 def commitstatus(repo, node, branch, bheads=None, opts={}):
     ctx = repo[node]
     parents = ctx.parents()
 
     if (not opts.get('amend') and bheads and node not in bheads and not
         [x for x in parents if x.node() in bheads and x.branch() == branch]):
         repo.ui.status(_('created new head\n'))
         # The message is not printed for initial roots. For the other
         # changesets, it is printed in the following situations:
         #
         # Par column: for the 2 parents with ...
         #   N: null or no parent
         #   B: parent is on another named branch
         #   C: parent is a regular non head changeset
         #   H: parent was a branch head of the current branch
         # Msg column: whether we print "created new head" message
         # In the following, it is assumed that there already exists some
         # initial branch heads of the current branch, otherwise nothing is
         # printed anyway.
         #
         # Par Msg Comment
         # N N  y  additional topo root
         #
         # B N  y  additional branch root
         # C N  y  additional topo head
         # H N  n  usual case
         #
         # B B  y  weird additional branch root
         # C B  y  branch merge
         # H B  n  merge with named branch
         #
         # C C  y  additional head from merge
         # C H  n  merge with a head
         #
         # H H  n  head merge: head count decreases
 
     if not opts.get('close_branch'):
         for r in parents:
             if r.closesbranch() and r.branch() == branch:
                 repo.ui.status(_('reopening closed branch head %d\n') % r)
 
     if repo.ui.debugflag:
         repo.ui.write(_('committed changeset %d:%s\n') % (int(ctx), ctx.hex()))
     elif repo.ui.verbose:
         repo.ui.write(_('committed changeset %d:%s\n') % (int(ctx), ctx))
 
 def revert(ui, repo, ctx, parents, *pats, **opts):
     parent, p2 = parents
     node = ctx.node()
 
     mf = ctx.manifest()
     if node == parent:
         pmf = mf
     else:
         pmf = None
 
     # need all matching names in dirstate and manifest of target rev,
     # so have to walk both. do not print errors if files exist in one
     # but not other.
 
+    # `names` is a mapping for all elements in working copy and target revision
+    # The mapping is in the form:
+    #   <asb path in repo> -> (<path from CWD>, <exactly specified by matcher?>)
     names = {}
 
     wlock = repo.wlock()
     try:
-        # walk dirstate.
+        ## filling of the `names` mapping
+        # walk dirstate to fill `names`
 
         m = scmutil.match(repo[None], pats, opts)
         m.bad = lambda x, y: False
         for abs in repo.walk(m):
             names[abs] = m.rel(abs), m.exact(abs)
 
-        # walk target manifest.
+        # walk target manifest to fill `names`
 
         def badfn(path, msg):
             if path in names:
                 return
             if path in ctx.substate:
                 return
             path_ = path + '/'
             for f in names:
                 if f.startswith(path_):
                     return
             ui.warn("%s: %s\n" % (m.rel(path), msg))
 
         m = scmutil.match(ctx, pats, opts)
         m.bad = badfn
         for abs in ctx.walk(m):
             if abs not in names:
                 names[abs] = m.rel(abs), m.exact(abs)
 
         # get the list of subrepos that must be reverted
         targetsubs = sorted(s for s in ctx.substate if m(s))
+
+        # Find status of all file in `names`. (Against working directory parent)
         m = scmutil.matchfiles(repo, names)
         changes = repo.status(match=m)[:4]
         modified, added, removed, deleted = map(set, changes)
 
-        # if f is a rename, also revert the source
+        # if f is a rename, update `names` to also revert the source
         cwd = repo.getcwd()
         for f in added:
             src = repo.dirstate.copied(f)
             if src and src not in names and repo.dirstate[src] == 'r':
                 removed.add(src)
                 names[src] = (repo.pathto(src, cwd), True)
 
+        ## computation of the action to performs on `names` content.
+
         def removeforget(abs):
             if repo.dirstate[abs] == 'a':
                 return _('forgetting %s\n')
             return _('removing %s\n')
 
+        # action to be actually performed by revert
+        # (<list of file>, message>) tuple
         revert = ([], _('reverting %s\n'))
         add = ([], _('adding %s\n'))
         remove = ([], removeforget)
         undelete = ([], _('undeleting %s\n'))
 
         disptable = (
             # dispatch table:
             #   file state
             #   action if in target manifest
             #   action if not in target manifest
             #   make backup if in target manifest
             #   make backup if not in target manifest
             (modified, revert,   remove, True,  True),
             (added,    revert,   remove, True,  False),
             (removed,  undelete, None,   True,  False),
             (deleted,  revert,   remove, False, False),
             )
 
         for abs, (rel, exact) in sorted(names.items()):
+            # hash on file in target manifest (or None if missing from target)
             mfentry = mf.get(abs)
+            # target file to be touch on disk (relative to cwd)
             target = repo.wjoin(abs)
             def handle(xlist, dobackup):
                 xlist[0].append(abs)
                 if (dobackup and not opts.get('no_backup') and
                     os.path.lexists(target) and
                     abs in ctx and repo[None][abs].cmp(ctx[abs])):
                     bakname = "%s.orig" % rel
                     ui.note(_('saving current version of %s as %s\n') %
                             (rel, bakname))
                     if not opts.get('dry_run'):
                         util.rename(target, bakname)
                 if ui.verbose or not exact:
                     msg = xlist[1]
                     if not isinstance(msg, basestring):
                         msg = msg(abs)
                     ui.status(msg % rel)
+            # search the entry in the dispatch table.
+            # if the file is in any of this sets, it was touched in the working
+            # directory parent and we are sure it needs to be reverted.
             for table, hitlist, misslist, backuphit, backupmiss in disptable:
                 if abs not in table:
                     continue
                 # file has changed in dirstate
                 if mfentry:
                     handle(hitlist, backuphit)
                 elif misslist is not None:
                     handle(misslist, backupmiss)
                 break
             else:
+                # Not touched in current dirstate.
+
+                # file is unknown in parent, restore older version or ignore.
                 if abs not in repo.dirstate:
                     if mfentry:
                         handle(add, True)
                     elif exact:
                         ui.warn(_('file not managed: %s\n') % rel)
                     continue
-                # file has not changed in dirstate
+
+                # parent is target, no changes mean no changes
                 if node == parent:
                     if exact:
                         ui.warn(_('no changes needed to %s\n') % rel)
                     continue
+                # no change in dirstate but parent and target may differ
                 if pmf is None:
                     # only need parent manifest in this unlikely case,
                     # so do not read by default
                     pmf = repo[parent].manifest()
                 if abs in pmf and mfentry:
                     # if version of file is same in parent and target
                     # manifests, do nothing
                     if (pmf[abs] != mfentry or
                         pmf.flags(abs) != mf.flags(abs)):
                         handle(revert, False)
                 else:
                     handle(remove, False)
         if not opts.get('dry_run'):
             _performrevert(repo, parents, ctx, revert, add, remove, undelete)
 
             if targetsubs:
                 # Revert the subrepos on the revert list
                 for sub in targetsubs:
                     ctx.sub(sub).revert(ui, ctx.substate[sub], *pats, **opts)
     finally:
         wlock.release()
 
 def _performrevert(repo, parents, ctx, revert, add, remove, undelete):
     """function that actually perform all the action computed for revert
 
     This is an independent function to let extension to plug in and react to
     the imminent revert.
 
     Make sure you have the working directory locked when calling this function.
     """
     parent, p2 = parents
     node = ctx.node()
     def checkout(f):
         fc = ctx[f]
         repo.wwrite(f, fc.data(), fc.flags())
 
     audit_path = pathutil.pathauditor(repo.root)
     for f in remove[0]:
         if repo.dirstate[f] == 'a':
             repo.dirstate.drop(f)
             continue
         audit_path(f)
         try:
             util.unlinkpath(repo.wjoin(f))
         except OSError:
             pass
         repo.dirstate.remove(f)
 
     normal = None
     if node == parent:
         # We're reverting to our parent. If possible, we'd like status
         # to report the file as clean. We have to use normallookup for
         # merges to avoid losing information about merged/dirty files.
         if p2 != nullid:
             normal = repo.dirstate.normallookup
         else:
             normal = repo.dirstate.normal
     for f in revert[0]:
         checkout(f)
         if normal:
             normal(f)
 
     for f in add[0]:
         checkout(f)
         repo.dirstate.add(f)
 
     normal = repo.dirstate.normallookup
     if node == parent and p2 == nullid:
         normal = repo.dirstate.normal
     for f in undelete[0]:
         checkout(f)
         normal(f)
 
     copied = copies.pathcopies(repo[parent], ctx)
 
     for f in add[0] + undelete[0] + revert[0]:
         if f in copied:
             repo.dirstate.copy(copied[f], f)
 
 def command(table):
     '''returns a function object bound to table which can be used as
     a decorator for populating table as a command table'''
 
     def cmd(name, options=(), synopsis=None):
         def decorator(func):
             if synopsis:
                 table[name] = func, list(options), synopsis
             else:
                 table[name] = func, list(options)
             return func
         return decorator
 
     return cmd
 
 # a list of (ui, repo, otherpeer, opts, missing) functions called by
 # commands.outgoing.  "missing" is "missing" of the result of
 # "findcommonoutgoing()"
 outgoinghooks = util.hooks()
 
 # a list of (ui, repo) functions called by commands.summary
 summaryhooks = util.hooks()
 
 # a list of (ui, repo, opts, changes) functions called by commands.summary.
 #
 # functions should return tuple of booleans below, if 'changes' is None:
 #  (whether-incomings-are-needed, whether-outgoings-are-needed)
 #
 # otherwise, 'changes' is a tuple of tuples below:
 #  - (sourceurl, sourcebranch, sourcepeer, incoming)
 #  - (desturl,   destbranch,   destpeer,   outgoing)
 summaryremotehooks = util.hooks()
 
 # A list of state files kept by multistep operations like graft.
 # Since graft cannot be aborted, it is considered 'clearable' by update.
 # note: bisect is intentionally excluded
 # (state file, clearable, allowcommit, error, hint)
 unfinishedstates = [
     ('graftstate', True, False, _('graft in progress'),
      _("use 'hg graft --continue' or 'hg update' to abort")),
     ('updatestate', True, False, _('last update was interrupted'),
      _("use 'hg update' to get a consistent checkout"))
     ]
 
 def checkunfinished(repo, commit=False):
     '''Look for an unfinished multistep operation, like graft, and abort
     if found. It's probably good to check this right before
     bailifchanged().
     '''
     for f, clearable, allowcommit, msg, hint in unfinishedstates:
         if commit and allowcommit:
             continue
         if repo.vfs.exists(f):
             raise util.Abort(msg, hint=hint)
 
 def clearunfinished(repo):
     '''Check for unfinished operations (as above), and clear the ones
     that are clearable.
     '''
     for f, clearable, allowcommit, msg, hint in unfinishedstates:
         if not clearable and repo.vfs.exists(f):
             raise util.Abort(msg, hint=hint)
     for f, clearable, allowcommit, msg, hint in unfinishedstates:
         if clearable and repo.vfs.exists(f):
             util.unlink(repo.join(f))