# revset.py - revision set queries for mercurial
#
# Copyright 2010 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import absolute_import

import heapq
import re

from .i18n import _
from . import (
    destutil,
    encoding,
    error,
    hbisect,
    match as matchmod,
    node,
    obsolete as obsmod,
    pathutil,
    phases,
    registrar,
    repoview,
    revsetlang,
    scmutil,
    smartset,
    util,
)

# helpers for processing parsed tree
getsymbol = revsetlang.getsymbol
getstring = revsetlang.getstring
getinteger = revsetlang.getinteger
getboolean = revsetlang.getboolean
getlist = revsetlang.getlist
getrange = revsetlang.getrange
getargs = revsetlang.getargs
getargsdict = revsetlang.getargsdict

# constants used as an argument of match() and matchany()
anyorder = revsetlang.anyorder
defineorder = revsetlang.defineorder
followorder = revsetlang.followorder

baseset = smartset.baseset
generatorset = smartset.generatorset
spanset = smartset.spanset
fullreposet = smartset.fullreposet

def _revancestors(repo, revs, followfirst):
    """Like revlog.ancestors(), but supports followfirst."""
    if followfirst:
        cut = 1
    else:
        cut = None
    cl = repo.changelog

    def iterate():
        revs.sort(reverse=True)
        irevs = iter(revs)
        h = []

        inputrev = next(irevs, None)
        if inputrev is not None:
            heapq.heappush(h, -inputrev)

        seen = set()
        while h:
            current = -heapq.heappop(h)
            if current == inputrev:
                inputrev = next(irevs, None)
                if inputrev is not None:
                    heapq.heappush(h, -inputrev)
            if current not in seen:
                seen.add(current)
                yield current
                try:
                    for parent in cl.parentrevs(current)[:cut]:
                        if parent != node.nullrev:
                            heapq.heappush(h, -parent)
                except error.WdirUnsupported:
                    for parent in repo[current].parents()[:cut]:
                        if parent.rev() != node.nullrev:
                            heapq.heappush(h, -parent.rev())

    return generatorset(iterate(), iterasc=False)

def _revdescendants(repo, revs, followfirst):
    """Like revlog.descendants() but supports followfirst."""
    if followfirst:
        cut = 1
    else:
        cut = None

    def iterate():
        cl = repo.changelog
        # XXX this should be 'parentset.min()' assuming 'parentset' is a
        # smartset (and if it is not, it should.)
        first = min(revs)
        nullrev = node.nullrev
        if first == nullrev:
            # Are there nodes with a null first parent and a non-null
            # second one? Maybe. Do we care? Probably not.
            for i in cl:
                yield i
        else:
            seen = set(revs)
            for i in cl.revs(first + 1):
                for x in cl.parentrevs(i)[:cut]:
                    if x != nullrev and x in seen:
                        seen.add(i)
                        yield i
                        break

    return generatorset(iterate(), iterasc=True)

def _reachablerootspure(repo, minroot, roots, heads, includepath):
    """return (heads(::<roots> and ::<heads>))

    If includepath is True, return (<roots>::<heads>)."""
    if not roots:
        return []
    parentrevs = repo.changelog.parentrevs
    roots = set(roots)
    visit = list(heads)
    reachable = set()
    seen = {}
    # prefetch all the things! (because python is slow)
    reached = reachable.add
    dovisit = visit.append
    nextvisit = visit.pop
    # open-code the post-order traversal due to the tiny size of
    # sys.getrecursionlimit()
    while visit:
        rev = nextvisit()
        if rev in roots:
            reached(rev)
            if not includepath:
                continue
        parents = parentrevs(rev)
        seen[rev] = parents
        for parent in parents:
            if parent >= minroot and parent not in seen:
                dovisit(parent)
    if not reachable:
        return baseset()
    if not includepath:
        return reachable
    for rev in sorted(seen):
        for parent in seen[rev]:
            if parent in reachable:
                reached(rev)
    return reachable

def reachableroots(repo, roots, heads, includepath=False):
    """return (heads(::<roots> and ::<heads>))

    If includepath is True, return (<roots>::<heads>)."""
    if not roots:
        return baseset()
    minroot = roots.min()
    roots = list(roots)
    heads = list(heads)
    try:
        revs = repo.changelog.reachableroots(minroot, heads, roots, includepath)
    except AttributeError:
        revs = _reachablerootspure(repo, minroot, roots, heads, includepath)
    revs = baseset(revs)
    revs.sort()
    return revs

# helpers

def getset(repo, subset, x):
    if not x:
        raise error.ParseError(_("missing argument"))
    return methods[x[0]](repo, subset, *x[1:])

def _getrevsource(repo, r):
    extra = repo[r].extra()
    for label in ('source', 'transplant_source', 'rebase_source'):
        if label in extra:
            try:
                return repo[extra[label]].rev()
            except error.RepoLookupError:
                pass
    return None

# operator methods

def stringset(repo, subset, x):
    x = scmutil.intrev(repo[x])
    if (x in subset
        or x == node.nullrev and isinstance(subset, fullreposet)):
        return baseset([x])
    return baseset()

def rangeset(repo, subset, x, y, order):
    m = getset(repo, fullreposet(repo), x)
    n = getset(repo, fullreposet(repo), y)

    if not m or not n:
        return baseset()
    return _makerangeset(repo, subset, m.first(), n.last(), order)

def rangeall(repo, subset, x, order):
    assert x is None
    return _makerangeset(repo, subset, 0, len(repo) - 1, order)

def rangepre(repo, subset, y, order):
    # ':y' can't be rewritten to '0:y' since '0' may be hidden
    n = getset(repo, fullreposet(repo), y)
    if not n:
        return baseset()
    return _makerangeset(repo, subset, 0, n.last(), order)

def rangepost(repo, subset, x, order):
    m = getset(repo, fullreposet(repo), x)
    if not m:
        return baseset()
    return _makerangeset(repo, subset, m.first(), len(repo) - 1, order)

def _makerangeset(repo, subset, m, n, order):
    if m == n:
        r = baseset([m])
    elif n == node.wdirrev:
        r = spanset(repo, m, len(repo)) + baseset([n])
    elif m == node.wdirrev:
        r = baseset([m]) + spanset(repo, len(repo) - 1, n - 1)
    elif m < n:
        r = spanset(repo, m, n + 1)
    else:
        r = spanset(repo, m, n - 1)

    if order == defineorder:
        return r & subset
    else:
        # carrying the sorting over when possible would be more efficient
        return subset & r

def dagrange(repo, subset, x, y, order):
    r = fullreposet(repo)
    xs = reachableroots(repo, getset(repo, r, x), getset(repo, r, y),
                         includepath=True)
    return subset & xs

def andset(repo, subset, x, y, order):
    return getset(repo, getset(repo, subset, x), y)

def differenceset(repo, subset, x, y, order):
    return getset(repo, subset, x) - getset(repo, subset, y)

def _orsetlist(repo, subset, xs):
    assert xs
    if len(xs) == 1:
        return getset(repo, subset, xs[0])
    p = len(xs) // 2
    a = _orsetlist(repo, subset, xs[:p])
    b = _orsetlist(repo, subset, xs[p:])
    return a + b

def orset(repo, subset, x, order):
    xs = getlist(x)
    if order == followorder:
        # slow path to take the subset order
        return subset & _orsetlist(repo, fullreposet(repo), xs)
    else:
        return _orsetlist(repo, subset, xs)

def notset(repo, subset, x, order):
    return subset - getset(repo, subset, x)

def listset(repo, subset, *xs):
    raise error.ParseError(_("can't use a list in this context"),
                           hint=_('see hg help "revsets.x or y"'))

def keyvaluepair(repo, subset, k, v):
    raise error.ParseError(_("can't use a key-value pair in this context"))

def func(repo, subset, a, b, order):
    f = getsymbol(a)
    if f in symbols:
        func = symbols[f]
        if getattr(func, '_takeorder', False):
            return func(repo, subset, b, order)
        return func(repo, subset, b)

    keep = lambda fn: getattr(fn, '__doc__', None) is not None

    syms = [s for (s, fn) in symbols.items() if keep(fn)]
    raise error.UnknownIdentifier(f, syms)

# functions

# symbols are callables like:
#   fn(repo, subset, x)
# with:
#   repo - current repository instance
#   subset - of revisions to be examined
#   x - argument in tree form
symbols = {}

# symbols which can't be used for a DoS attack for any given input
# (e.g. those which accept regexes as plain strings shouldn't be included)
# functions that just return a lot of changesets (like all) don't count here
safesymbols = set()

predicate = registrar.revsetpredicate()

@predicate('_destupdate')
def _destupdate(repo, subset, x):
    # experimental revset for update destination
    args = getargsdict(x, 'limit', 'clean')
    return subset & baseset([destutil.destupdate(repo, **args)[0]])

@predicate('_destmerge')
def _destmerge(repo, subset, x):
    # experimental revset for merge destination
    sourceset = None
    if x is not None:
        sourceset = getset(repo, fullreposet(repo), x)
    return subset & baseset([destutil.destmerge(repo, sourceset=sourceset)])

@predicate('adds(pattern)', safe=True)
def adds(repo, subset, x):
    """Changesets that add a file matching pattern.

    The pattern without explicit kind like ``glob:`` is expected to be
    relative to the current directory and match against a file or a
    directory.
    """
    # i18n: "adds" is a keyword
    pat = getstring(x, _("adds requires a pattern"))
    return checkstatus(repo, subset, pat, 1)

@predicate('ancestor(*changeset)', safe=True)
def ancestor(repo, subset, x):
    """A greatest common ancestor of the changesets.

    Accepts 0 or more changesets.
    Will return empty list when passed no args.
    Greatest common ancestor of a single changeset is that changeset.
    """
    # i18n: "ancestor" is a keyword
    l = getlist(x)
    rl = fullreposet(repo)
    anc = None

    # (getset(repo, rl, i) for i in l) generates a list of lists
    for revs in (getset(repo, rl, i) for i in l):
        for r in revs:
            if anc is None:
                anc = repo[r]
            else:
                anc = anc.ancestor(repo[r])

    if anc is not None and anc.rev() in subset:
        return baseset([anc.rev()])
    return baseset()

def _ancestors(repo, subset, x, followfirst=False):
    heads = getset(repo, fullreposet(repo), x)
    if not heads:
        return baseset()
    s = _revancestors(repo, heads, followfirst)
    return subset & s

@predicate('ancestors(set)', safe=True)
def ancestors(repo, subset, x):
    """Changesets that are ancestors of a changeset in set.
    """
    return _ancestors(repo, subset, x)

@predicate('_firstancestors', safe=True)
def _firstancestors(repo, subset, x):
    # ``_firstancestors(set)``
    # Like ``ancestors(set)`` but follows only the first parents.
    return _ancestors(repo, subset, x, followfirst=True)

def ancestorspec(repo, subset, x, n, order):
    """``set~n``
    Changesets that are the Nth ancestor (first parents only) of a changeset
    in set.
    """
    n = getinteger(n, _("~ expects a number"))
    ps = set()
    cl = repo.changelog
    for r in getset(repo, fullreposet(repo), x):
        for i in range(n):
            try:
                r = cl.parentrevs(r)[0]
            except error.WdirUnsupported:
                r = repo[r].parents()[0].rev()
        ps.add(r)
    return subset & ps

@predicate('author(string)', safe=True)
def author(repo, subset, x):
    """Alias for ``user(string)``.
    """
    # i18n: "author" is a keyword
    n = getstring(x, _("author requires a string"))
    kind, pattern, matcher = _substringmatcher(n, casesensitive=False)
    return subset.filter(lambda x: matcher(repo[x].user()),
                         condrepr=('<user %r>', n))

@predicate('bisect(string)', safe=True)
def bisect(repo, subset, x):
    """Changesets marked in the specified bisect status:

    - ``good``, ``bad``, ``skip``: csets explicitly marked as good/bad/skip
    - ``goods``, ``bads``      : csets topologically good/bad
    - ``range``              : csets taking part in the bisection
    - ``pruned``             : csets that are goods, bads or skipped
    - ``untested``           : csets whose fate is yet unknown
    - ``ignored``            : csets ignored due to DAG topology
    - ``current``            : the cset currently being bisected
    """
    # i18n: "bisect" is a keyword
    status = getstring(x, _("bisect requires a string")).lower()
    state = set(hbisect.get(repo, status))
    return subset & state

# Backward-compatibility
# - no help entry so that we do not advertise it any more
@predicate('bisected', safe=True)
def bisected(repo, subset, x):
    return bisect(repo, subset, x)

@predicate('bookmark([name])', safe=True)
def bookmark(repo, subset, x):
    """The named bookmark or all bookmarks.

    Pattern matching is supported for `name`. See :hg:`help revisions.patterns`.
    """
    # i18n: "bookmark" is a keyword
    args = getargs(x, 0, 1, _('bookmark takes one or no arguments'))
    if args:
        bm = getstring(args[0],
                       # i18n: "bookmark" is a keyword
                       _('the argument to bookmark must be a string'))
        kind, pattern, matcher = util.stringmatcher(bm)
        bms = set()
        if kind == 'literal':
            bmrev = repo._bookmarks.get(pattern, None)
            if not bmrev:
                raise error.RepoLookupError(_("bookmark '%s' does not exist")
                                            % pattern)
            bms.add(repo[bmrev].rev())
        else:
            matchrevs = set()
            for name, bmrev in repo._bookmarks.iteritems():
                if matcher(name):
                    matchrevs.add(bmrev)
            if not matchrevs:
                raise error.RepoLookupError(_("no bookmarks exist"
                                              " that match '%s'") % pattern)
            for bmrev in matchrevs:
                bms.add(repo[bmrev].rev())
    else:
        bms = {repo[r].rev() for r in repo._bookmarks.values()}
    bms -= {node.nullrev}
    return subset & bms

@predicate('branch(string or set)', safe=True)
def branch(repo, subset, x):
    """
    All changesets belonging to the given branch or the branches of the given
    changesets.

    Pattern matching is supported for `string`. See
    :hg:`help revisions.patterns`.
    """
    getbi = repo.revbranchcache().branchinfo
    def getbranch(r):
        try:
            return getbi(r)[0]
        except error.WdirUnsupported:
            return repo[r].branch()

    try:
        b = getstring(x, '')
    except error.ParseError:
        # not a string, but another revspec, e.g. tip()
        pass
    else:
        kind, pattern, matcher = util.stringmatcher(b)
        if kind == 'literal':
            # note: falls through to the revspec case if no branch with
            # this name exists and pattern kind is not specified explicitly
            if pattern in repo.branchmap():
                return subset.filter(lambda r: matcher(getbranch(r)),
                                     condrepr=('<branch %r>', b))
            if b.startswith('literal:'):
                raise error.RepoLookupError(_("branch '%s' does not exist")
                                            % pattern)
        else:
            return subset.filter(lambda r: matcher(getbranch(r)),
                                 condrepr=('<branch %r>', b))

    s = getset(repo, fullreposet(repo), x)
    b = set()
    for r in s:
        b.add(getbranch(r))
    c = s.__contains__
    return subset.filter(lambda r: c(r) or getbranch(r) in b,
                         condrepr=lambda: '<branch %r>' % sorted(b))

@predicate('bumped()', safe=True)
def bumped(repo, subset, x):
    """Mutable changesets marked as successors of public changesets.

    Only non-public and non-obsolete changesets can be `bumped`.
    """
    # i18n: "bumped" is a keyword
    getargs(x, 0, 0, _("bumped takes no arguments"))
    bumped = obsmod.getrevs(repo, 'bumped')
    return subset & bumped

@predicate('bundle()', safe=True)
def bundle(repo, subset, x):
    """Changesets in the bundle.

    Bundle must be specified by the -R option."""

    try:
        bundlerevs = repo.changelog.bundlerevs
    except AttributeError:
        raise error.Abort(_("no bundle provided - specify with -R"))
    return subset & bundlerevs

def checkstatus(repo, subset, pat, field):
    hasset = matchmod.patkind(pat) == 'set'

    mcache = [None]
    def matches(x):
        c = repo[x]
        if not mcache[0] or hasset:
            mcache[0] = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=c)
        m = mcache[0]
        fname = None
        if not m.anypats() and len(m.files()) == 1:
            fname = m.files()[0]
        if fname is not None:
            if fname not in c.files():
                return False
        else:
            for f in c.files():
                if m(f):
                    break
            else:
                return False
        files = repo.status(c.p1().node(), c.node())[field]
        if fname is not None:
            if fname in files:
                return True
        else:
            for f in files:
                if m(f):
                    return True

    return subset.filter(matches, condrepr=('<status[%r] %r>', field, pat))

def _children(repo, subset, parentset):
    if not parentset:
        return baseset()
    cs = set()
    pr = repo.changelog.parentrevs
    minrev = parentset.min()
    nullrev = node.nullrev
    for r in subset:
        if r <= minrev:
            continue
        p1, p2 = pr(r)
        if p1 in parentset:
            cs.add(r)
        if p2 != nullrev and p2 in parentset:
            cs.add(r)
    return baseset(cs)

@predicate('children(set)', safe=True)
def children(repo, subset, x):
    """Child changesets of changesets in set.
    """
    s = getset(repo, fullreposet(repo), x)
    cs = _children(repo, subset, s)
    return subset & cs

@predicate('closed()', safe=True)
def closed(repo, subset, x):
    """Changeset is closed.
    """
    # i18n: "closed" is a keyword
    getargs(x, 0, 0, _("closed takes no arguments"))
    return subset.filter(lambda r: repo[r].closesbranch(),
                         condrepr='<branch closed>')

@predicate('contains(pattern)')
def contains(repo, subset, x):
    """The revision's manifest contains a file matching pattern (but might not
    modify it). See :hg:`help patterns` for information about file patterns.

    The pattern without explicit kind like ``glob:`` is expected to be
    relative to the current directory and match against a file exactly
    for efficiency.
    """
    # i18n: "contains" is a keyword
    pat = getstring(x, _("contains requires a pattern"))

    def matches(x):
        if not matchmod.patkind(pat):
            pats = pathutil.canonpath(repo.root, repo.getcwd(), pat)
            if pats in repo[x]:
                return True
        else:
            c = repo[x]
            m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=c)
            for f in c.manifest():
                if m(f):
                    return True
        return False

    return subset.filter(matches, condrepr=('<contains %r>', pat))

@predicate('converted([id])', safe=True)
def converted(repo, subset, x):
    """Changesets converted from the given identifier in the old repository if
    present, or all converted changesets if no identifier is specified.
    """

    # There is exactly no chance of resolving the revision, so do a simple
    # string compare and hope for the best

    rev = None
    # i18n: "converted" is a keyword
    l = getargs(x, 0, 1, _('converted takes one or no arguments'))
    if l:
        # i18n: "converted" is a keyword
        rev = getstring(l[0], _('converted requires a revision'))

    def _matchvalue(r):
        source = repo[r].extra().get('convert_revision', None)
        return source is not None and (rev is None or source.startswith(rev))

    return subset.filter(lambda r: _matchvalue(r),
                         condrepr=('<converted %r>', rev))

@predicate('date(interval)', safe=True)
def date(repo, subset, x):
    """Changesets within the interval, see :hg:`help dates`.
    """
    # i18n: "date" is a keyword
    ds = getstring(x, _("date requires a string"))
    dm = util.matchdate(ds)
    return subset.filter(lambda x: dm(repo[x].date()[0]),
                         condrepr=('<date %r>', ds))

@predicate('desc(string)', safe=True)
def desc(repo, subset, x):
    """Search commit message for string. The match is case-insensitive.

    Pattern matching is supported for `string`. See
    :hg:`help revisions.patterns`.
    """
    # i18n: "desc" is a keyword
    ds = getstring(x, _("desc requires a string"))

    kind, pattern, matcher = _substringmatcher(ds, casesensitive=False)

    return subset.filter(lambda r: matcher(repo[r].description()),
                         condrepr=('<desc %r>', ds))

def _descendants(repo, subset, x, followfirst=False):
    roots = getset(repo, fullreposet(repo), x)
    if not roots:
        return baseset()
    s = _revdescendants(repo, roots, followfirst)

    # Both sets need to be ascending in order to lazily return the union
    # in the correct order.
    base = subset & roots
    desc = subset & s
    result = base + desc
    if subset.isascending():
        result.sort()
    elif subset.isdescending():
        result.sort(reverse=True)
    else:
        result = subset & result
    return result

@predicate('descendants(set)', safe=True)
def descendants(repo, subset, x):
    """Changesets which are descendants of changesets in set.
    """
    return _descendants(repo, subset, x)

@predicate('_firstdescendants', safe=True)
def _firstdescendants(repo, subset, x):
    # ``_firstdescendants(set)``
    # Like ``descendants(set)`` but follows only the first parents.
    return _descendants(repo, subset, x, followfirst=True)

@predicate('destination([set])', safe=True)
def destination(repo, subset, x):
    """Changesets that were created by a graft, transplant or rebase operation,
    with the given revisions specified as the source.  Omitting the optional set
    is the same as passing all().
    """
    if x is not None:
        sources = getset(repo, fullreposet(repo), x)
    else:
        sources = fullreposet(repo)

    dests = set()

    # subset contains all of the possible destinations that can be returned, so
    # iterate over them and see if their source(s) were provided in the arg set.
    # Even if the immediate src of r is not in the arg set, src's source (or
    # further back) may be.  Scanning back further than the immediate src allows
    # transitive transplants and rebases to yield the same results as transitive
    # grafts.
    for r in subset:
        src = _getrevsource(repo, r)
        lineage = None

        while src is not None:
            if lineage is None:
                lineage = list()

            lineage.append(r)

            # The visited lineage is a match if the current source is in the arg
            # set.  Since every candidate dest is visited by way of iterating
            # subset, any dests further back in the lineage will be tested by a
            # different iteration over subset.  Likewise, if the src was already
            # selected, the current lineage can be selected without going back
            # further.
            if src in sources or src in dests:
                dests.update(lineage)
                break

            r = src
            src = _getrevsource(repo, r)

    return subset.filter(dests.__contains__,
                         condrepr=lambda: '<destination %r>' % sorted(dests))

@predicate('divergent()', safe=True)
def divergent(repo, subset, x):
    """
    Final successors of changesets with an alternative set of final successors.
    """
    # i18n: "divergent" is a keyword
    getargs(x, 0, 0, _("divergent takes no arguments"))
    divergent = obsmod.getrevs(repo, 'divergent')
    return subset & divergent

@predicate('extinct()', safe=True)
def extinct(repo, subset, x):
    """Obsolete changesets with obsolete descendants only.
    """
    # i18n: "extinct" is a keyword
    getargs(x, 0, 0, _("extinct takes no arguments"))
    extincts = obsmod.getrevs(repo, 'extinct')
    return subset & extincts

@predicate('extra(label, [value])', safe=True)
def extra(repo, subset, x):
    """Changesets with the given label in the extra metadata, with the given
    optional value.

    Pattern matching is supported for `value`. See
    :hg:`help revisions.patterns`.
    """
    args = getargsdict(x, 'extra', 'label value')
    if 'label' not in args:
        # i18n: "extra" is a keyword
        raise error.ParseError(_('extra takes at least 1 argument'))
    # i18n: "extra" is a keyword
    label = getstring(args['label'], _('first argument to extra must be '
                                       'a string'))
    value = None

    if 'value' in args:
        # i18n: "extra" is a keyword
        value = getstring(args['value'], _('second argument to extra must be '
                                           'a string'))
        kind, value, matcher = util.stringmatcher(value)

    def _matchvalue(r):
        extra = repo[r].extra()
        return label in extra and (value is None or matcher(extra[label]))

    return subset.filter(lambda r: _matchvalue(r),
                         condrepr=('<extra[%r] %r>', label, value))

@predicate('filelog(pattern)', safe=True)
def filelog(repo, subset, x):
    """Changesets connected to the specified filelog.

    For performance reasons, visits only revisions mentioned in the file-level
    filelog, rather than filtering through all changesets (much faster, but
    doesn't include deletes or duplicate changes). For a slower, more accurate
    result, use ``file()``.

    The pattern without explicit kind like ``glob:`` is expected to be
    relative to the current directory and match against a file exactly
    for efficiency.

    If some linkrev points to revisions filtered by the current repoview, we'll
    work around it to return a non-filtered value.
    """

    # i18n: "filelog" is a keyword
    pat = getstring(x, _("filelog requires a pattern"))
    s = set()
    cl = repo.changelog

    if not matchmod.patkind(pat):
        f = pathutil.canonpath(repo.root, repo.getcwd(), pat)
        files = [f]
    else:
        m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=repo[None])
        files = (f for f in repo[None] if m(f))

    for f in files:
        fl = repo.file(f)
        known = {}
        scanpos = 0
        for fr in list(fl):
            fn = fl.node(fr)
            if fn in known:
                s.add(known[fn])
                continue

            lr = fl.linkrev(fr)
            if lr in cl:
                s.add(lr)
            elif scanpos is not None:
                # lowest matching changeset is filtered, scan further
                # ahead in changelog
                start = max(lr, scanpos) + 1
                scanpos = None
                for r in cl.revs(start):
                    # minimize parsing of non-matching entries
                    if f in cl.revision(r) and f in cl.readfiles(r):
                        try:
                            # try to use manifest delta fastpath
                            n = repo[r].filenode(f)
                            if n not in known:
                                if n == fn:
                                    s.add(r)
                                    scanpos = r
                                    break
                                else:
                                    known[n] = r
                        except error.ManifestLookupError:
                            # deletion in changelog
                            continue

    return subset & s

@predicate('first(set, [n])', safe=True)
def first(repo, subset, x):
    """An alias for limit().
    """
    return limit(repo, subset, x)

def _follow(repo, subset, x, name, followfirst=False):
    l = getargs(x, 0, 2, _("%s takes no arguments or a pattern "
                           "and an optional revset") % name)
    c = repo['.']
    if l:
        x = getstring(l[0], _("%s expected a pattern") % name)
        rev = None
        if len(l) >= 2:
            revs = getset(repo, fullreposet(repo), l[1])
            if len(revs) != 1:
                raise error.RepoLookupError(
                        _("%s expected one starting revision") % name)
            rev = revs.last()
            c = repo[rev]
        matcher = matchmod.match(repo.root, repo.getcwd(), [x],
                                 ctx=repo[rev], default='path')

        files = c.manifest().walk(matcher)

        s = set()
        for fname in files:
            fctx = c[fname]
            s = s.union(set(c.rev() for c in fctx.ancestors(followfirst)))
            # include the revision responsible for the most recent version
            s.add(fctx.introrev())
    else:
        s = _revancestors(repo, baseset([c.rev()]), followfirst)

    return subset & s

@predicate('follow([pattern[, startrev]])', safe=True)
def follow(repo, subset, x):
    """
    An alias for ``::.`` (ancestors of the working directory's first parent).
    If pattern is specified, the histories of files matching given
    pattern in the revision given by startrev are followed, including copies.
    """
    return _follow(repo, subset, x, 'follow')

@predicate('_followfirst', safe=True)
def _followfirst(repo, subset, x):
    # ``followfirst([pattern[, startrev]])``
    # Like ``follow([pattern[, startrev]])`` but follows only the first parent
    # of every revisions or files revisions.
    return _follow(repo, subset, x, '_followfirst', followfirst=True)

@predicate('followlines(file, fromline:toline[, startrev=., descend=False])',
           safe=True)
def followlines(repo, subset, x):
    """Changesets modifying `file` in line range ('fromline', 'toline').

    Line range corresponds to 'file' content at 'startrev' and should hence be
    consistent with file size. If startrev is not specified, working directory's
    parent is used.

    By default, ancestors of 'startrev' are returned. If 'descend' is True,
    descendants of 'startrev' are returned though renames are (currently) not
    followed in this direction.
    """
    from . import context  # avoid circular import issues

    args = getargsdict(x, 'followlines', 'file *lines startrev descend')
    if len(args['lines']) != 1:
        raise error.ParseError(_("followlines requires a line range"))

    rev = '.'
    if 'startrev' in args:
        revs = getset(repo, fullreposet(repo), args['startrev'])
        if len(revs) != 1:
            raise error.ParseError(
                # i18n: "followlines" is a keyword
                _("followlines expects exactly one revision"))
        rev = revs.last()

    pat = getstring(args['file'], _("followlines requires a pattern"))
    if not matchmod.patkind(pat):
        fname = pathutil.canonpath(repo.root, repo.getcwd(), pat)
    else:
        m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=repo[rev])
        files = [f for f in repo[rev] if m(f)]
        if len(files) != 1:
            # i18n: "followlines" is a keyword
            raise error.ParseError(_("followlines expects exactly one file"))
        fname = files[0]

    # i18n: "followlines" is a keyword
    lr = getrange(args['lines'][0], _("followlines expects a line range"))
    fromline, toline = [getinteger(a, _("line range bounds must be integers"))
                        for a in lr]
    fromline, toline = util.processlinerange(fromline, toline)

    fctx = repo[rev].filectx(fname)
    descend = False
    if 'descend' in args:
        descend = getboolean(args['descend'],
                             # i18n: "descend" is a keyword
                             _("descend argument must be a boolean"))
    if descend:
        rs = generatorset(
            (c.rev() for c, _linerange
             in context.blockdescendants(fctx, fromline, toline)),
            iterasc=True)
    else:
        rs = generatorset(
            (c.rev() for c, _linerange
             in context.blockancestors(fctx, fromline, toline)),
            iterasc=False)
    return subset & rs

@predicate('all()', safe=True)
def getall(repo, subset, x):
    """All changesets, the same as ``0:tip``.
    """
    # i18n: "all" is a keyword
    getargs(x, 0, 0, _("all takes no arguments"))
    return subset & spanset(repo)  # drop "null" if any

@predicate('grep(regex)')
def grep(repo, subset, x):
    """Like ``keyword(string)`` but accepts a regex. Use ``grep(r'...')``
    to ensure special escape characters are handled correctly. Unlike
    ``keyword(string)``, the match is case-sensitive.
    """
    try:
        # i18n: "grep" is a keyword
        gr = re.compile(getstring(x, _("grep requires a string")))
    except re.error as e:
        raise error.ParseError(_('invalid match pattern: %s') % e)

    def matches(x):
        c = repo[x]
        for e in c.files() + [c.user(), c.description()]:
            if gr.search(e):
                return True
        return False

    return subset.filter(matches, condrepr=('<grep %r>', gr.pattern))

@predicate('_matchfiles', safe=True)
def _matchfiles(repo, subset, x):
    # _matchfiles takes a revset list of prefixed arguments:
    #
    #   [p:foo, i:bar, x:baz]
    #
    # builds a match object from them and filters subset. Allowed
    # prefixes are 'p:' for regular patterns, 'i:' for include
    # patterns and 'x:' for exclude patterns. Use 'r:' prefix to pass
    # a revision identifier, or the empty string to reference the
    # working directory, from which the match object is
    # initialized. Use 'd:' to set the default matching mode, default
    # to 'glob'. At most one 'r:' and 'd:' argument can be passed.

    l = getargs(x, 1, -1, "_matchfiles requires at least one argument")
    pats, inc, exc = [], [], []
    rev, default = None, None
    for arg in l:
        s = getstring(arg, "_matchfiles requires string arguments")
        prefix, value = s[:2], s[2:]
        if prefix == 'p:':
            pats.append(value)
        elif prefix == 'i:':
            inc.append(value)
        elif prefix == 'x:':
            exc.append(value)
        elif prefix == 'r:':
            if rev is not None:
                raise error.ParseError('_matchfiles expected at most one '
                                       'revision')
            if value != '': # empty means working directory; leave rev as None
                rev = value
        elif prefix == 'd:':
            if default is not None:
                raise error.ParseError('_matchfiles expected at most one '
                                       'default mode')
            default = value
        else:
            raise error.ParseError('invalid _matchfiles prefix: %s' % prefix)
    if not default:
        default = 'glob'

    m = matchmod.match(repo.root, repo.getcwd(), pats, include=inc,
                       exclude=exc, ctx=repo[rev], default=default)

    # This directly read the changelog data as creating changectx for all
    # revisions is quite expensive.
    getfiles = repo.changelog.readfiles
    wdirrev = node.wdirrev
    def matches(x):
        if x == wdirrev:
            files = repo[x].files()
        else:
            files = getfiles(x)
        for f in files:
            if m(f):
                return True
        return False

    return subset.filter(matches,
                         condrepr=('<matchfiles patterns=%r, include=%r '
                                   'exclude=%r, default=%r, rev=%r>',
                                   pats, inc, exc, default, rev))

@predicate('file(pattern)', safe=True)
def hasfile(repo, subset, x):
    """Changesets affecting files matched by pattern.

    For a faster but less accurate result, consider using ``filelog()``
    instead.

    This predicate uses ``glob:`` as the default kind of pattern.
    """
    # i18n: "file" is a keyword
    pat = getstring(x, _("file requires a pattern"))
    return _matchfiles(repo, subset, ('string', 'p:' + pat))

@predicate('head()', safe=True)
def head(repo, subset, x):
    """Changeset is a named branch head.
    """
    # i18n: "head" is a keyword
    getargs(x, 0, 0, _("head takes no arguments"))
    hs = set()
    cl = repo.changelog
    for ls in repo.branchmap().itervalues():
        hs.update(cl.rev(h) for h in ls)
    return subset & baseset(hs)

@predicate('heads(set)', safe=True)
def heads(repo, subset, x):
    """Members of set with no children in set.
    """
    s = getset(repo, subset, x)
    ps = parents(repo, subset, x)
    return s - ps

@predicate('hidden()', safe=True)
def hidden(repo, subset, x):
    """Hidden changesets.
    """
    # i18n: "hidden" is a keyword
    getargs(x, 0, 0, _("hidden takes no arguments"))
    hiddenrevs = repoview.filterrevs(repo, 'visible')
    return subset & hiddenrevs

@predicate('keyword(string)', safe=True)
def keyword(repo, subset, x):
    """Search commit message, user name, and names of changed files for
    string. The match is case-insensitive.

    For a regular expression or case sensitive search of these fields, use
    ``grep(regex)``.
    """
    # i18n: "keyword" is a keyword
    kw = encoding.lower(getstring(x, _("keyword requires a string")))

    def matches(r):
        c = repo[r]
        return any(kw in encoding.lower(t)
                   for t in c.files() + [c.user(), c.description()])

    return subset.filter(matches, condrepr=('<keyword %r>', kw))

@predicate('limit(set[, n[, offset]])', safe=True)
def limit(repo, subset, x):
    """First n members of set, defaulting to 1, starting from offset.
    """
    args = getargsdict(x, 'limit', 'set n offset')
    if 'set' not in args:
        # i18n: "limit" is a keyword
        raise error.ParseError(_("limit requires one to three arguments"))
    # i18n: "limit" is a keyword
    lim = getinteger(args.get('n'), _("limit expects a number"), default=1)
    # i18n: "limit" is a keyword
    ofs = getinteger(args.get('offset'), _("limit expects a number"), default=0)
    if ofs < 0:
        raise error.ParseError(_("negative offset"))
    os = getset(repo, fullreposet(repo), args['set'])
    result = []
    it = iter(os)
    for x in xrange(ofs):
        y = next(it, None)
        if y is None:
            break
    for x in xrange(lim):
        y = next(it, None)
        if y is None:
            break
        elif y in subset:
            result.append(y)
    return baseset(result, datarepr=('<limit n=%d, offset=%d, %r, %r>',
                                     lim, ofs, subset, os))

@predicate('last(set, [n])', safe=True)
def last(repo, subset, x):
    """Last n members of set, defaulting to 1.
    """
    # i18n: "last" is a keyword
    l = getargs(x, 1, 2, _("last requires one or two arguments"))
    lim = 1
    if len(l) == 2:
        # i18n: "last" is a keyword
        lim = getinteger(l[1], _("last expects a number"))
    os = getset(repo, fullreposet(repo), l[0])
    os.reverse()
    result = []
    it = iter(os)
    for x in xrange(lim):
        y = next(it, None)
        if y is None:
            break
        elif y in subset:
            result.append(y)
    return baseset(result, datarepr=('<last n=%d, %r, %r>', lim, subset, os))

@predicate('max(set)', safe=True)
def maxrev(repo, subset, x):
    """Changeset with highest revision number in set.
    """
    os = getset(repo, fullreposet(repo), x)
    try:
        m = os.max()
        if m in subset:
            return baseset([m], datarepr=('<max %r, %r>', subset, os))
    except ValueError:
        # os.max() throws a ValueError when the collection is empty.
        # Same as python's max().
        pass
    return baseset(datarepr=('<max %r, %r>', subset, os))

@predicate('merge()', safe=True)
def merge(repo, subset, x):
    """Changeset is a merge changeset.
    """
    # i18n: "merge" is a keyword
    getargs(x, 0, 0, _("merge takes no arguments"))
    cl = repo.changelog
    return subset.filter(lambda r: cl.parentrevs(r)[1] != -1,
                         condrepr='<merge>')

@predicate('branchpoint()', safe=True)
def branchpoint(repo, subset, x):
    """Changesets with more than one child.
    """
    # i18n: "branchpoint" is a keyword
    getargs(x, 0, 0, _("branchpoint takes no arguments"))
    cl = repo.changelog
    if not subset:
        return baseset()
    # XXX this should be 'parentset.min()' assuming 'parentset' is a smartset
    # (and if it is not, it should.)
    baserev = min(subset)
    parentscount = [0]*(len(repo) - baserev)
    for r in cl.revs(start=baserev + 1):
        for p in cl.parentrevs(r):
            if p >= baserev:
                parentscount[p - baserev] += 1
    return subset.filter(lambda r: parentscount[r - baserev] > 1,
                         condrepr='<branchpoint>')

@predicate('min(set)', safe=True)
def minrev(repo, subset, x):
    """Changeset with lowest revision number in set.
    """
    os = getset(repo, fullreposet(repo), x)
    try:
        m = os.min()
        if m in subset:
            return baseset([m], datarepr=('<min %r, %r>', subset, os))
    except ValueError:
        # os.min() throws a ValueError when the collection is empty.
        # Same as python's min().
        pass
    return baseset(datarepr=('<min %r, %r>', subset, os))

@predicate('modifies(pattern)', safe=True)
def modifies(repo, subset, x):
    """Changesets modifying files matched by pattern.

    The pattern without explicit kind like ``glob:`` is expected to be
    relative to the current directory and match against a file or a
    directory.
    """
    # i18n: "modifies" is a keyword
    pat = getstring(x, _("modifies requires a pattern"))
    return checkstatus(repo, subset, pat, 0)

@predicate('named(namespace)')
def named(repo, subset, x):
    """The changesets in a given namespace.

    Pattern matching is supported for `namespace`. See
    :hg:`help revisions.patterns`.
    """
    # i18n: "named" is a keyword
    args = getargs(x, 1, 1, _('named requires a namespace argument'))

    ns = getstring(args[0],
                   # i18n: "named" is a keyword
                   _('the argument to named must be a string'))
    kind, pattern, matcher = util.stringmatcher(ns)
    namespaces = set()
    if kind == 'literal':
        if pattern not in repo.names:
            raise error.RepoLookupError(_("namespace '%s' does not exist")
                                        % ns)
        namespaces.add(repo.names[pattern])
    else:
        for name, ns in repo.names.iteritems():
            if matcher(name):
                namespaces.add(ns)
        if not namespaces:
            raise error.RepoLookupError(_("no namespace exists"
                                          " that match '%s'") % pattern)

    names = set()
    for ns in namespaces:
        for name in ns.listnames(repo):
            if name not in ns.deprecated:
                names.update(repo[n].rev() for n in ns.nodes(repo, name))

    names -= {node.nullrev}
    return subset & names

@predicate('id(string)', safe=True)
def node_(repo, subset, x):
    """Revision non-ambiguously specified by the given hex string prefix.
    """
    # i18n: "id" is a keyword
    l = getargs(x, 1, 1, _("id requires one argument"))
    # i18n: "id" is a keyword
    n = getstring(l[0], _("id requires a string"))
    if len(n) == 40:
        try:
            rn = repo.changelog.rev(node.bin(n))
        except error.WdirUnsupported:
            rn = node.wdirrev
        except (LookupError, TypeError):
            rn = None
    else:
        rn = None
        try:
            pm = repo.changelog._partialmatch(n)
            if pm is not None:
                rn = repo.changelog.rev(pm)
        except error.WdirUnsupported:
            rn = node.wdirrev

    if rn is None:
        return baseset()
    result = baseset([rn])
    return result & subset

@predicate('obsolete()', safe=True)
def obsolete(repo, subset, x):
    """Mutable changeset with a newer version."""
    # i18n: "obsolete" is a keyword
    getargs(x, 0, 0, _("obsolete takes no arguments"))
    obsoletes = obsmod.getrevs(repo, 'obsolete')
    return subset & obsoletes

@predicate('only(set, [set])', safe=True)
def only(repo, subset, x):
    """Changesets that are ancestors of the first set that are not ancestors
    of any other head in the repo. If a second set is specified, the result
    is ancestors of the first set that are not ancestors of the second set
    (i.e. ::<set1> - ::<set2>).
    """
    cl = repo.changelog
    # i18n: "only" is a keyword
    args = getargs(x, 1, 2, _('only takes one or two arguments'))
    include = getset(repo, fullreposet(repo), args[0])
    if len(args) == 1:
        if not include:
            return baseset()

        descendants = set(_revdescendants(repo, include, False))
        exclude = [rev for rev in cl.headrevs()
            if not rev in descendants and not rev in include]
    else:
        exclude = getset(repo, fullreposet(repo), args[1])

    results = set(cl.findmissingrevs(common=exclude, heads=include))
    # XXX we should turn this into a baseset instead of a set, smartset may do
    # some optimizations from the fact this is a baseset.
    return subset & results

@predicate('origin([set])', safe=True)
def origin(repo, subset, x):
    """
    Changesets that were specified as a source for the grafts, transplants or
    rebases that created the given revisions.  Omitting the optional set is the
    same as passing all().  If a changeset created by these operations is itself
    specified as a source for one of these operations, only the source changeset
    for the first operation is selected.
    """
    if x is not None:
        dests = getset(repo, fullreposet(repo), x)
    else:
        dests = fullreposet(repo)

    def _firstsrc(rev):
        src = _getrevsource(repo, rev)
        if src is None:
            return None

        while True:
            prev = _getrevsource(repo, src)

            if prev is None:
                return src
            src = prev

    o = {_firstsrc(r) for r in dests}
    o -= {None}
    # XXX we should turn this into a baseset instead of a set, smartset may do
    # some optimizations from the fact this is a baseset.
    return subset & o

@predicate('outgoing([path])', safe=False)
def outgoing(repo, subset, x):
    """Changesets not found in the specified destination repository, or the
    default push location.
    """
    # Avoid cycles.
    from . import (
        discovery,
        hg,
    )
    # i18n: "outgoing" is a keyword
    l = getargs(x, 0, 1, _("outgoing takes one or no arguments"))
    # i18n: "outgoing" is a keyword
    dest = l and getstring(l[0], _("outgoing requires a repository path")) or ''
    dest = repo.ui.expandpath(dest or 'default-push', dest or 'default')
    dest, branches = hg.parseurl(dest)
    revs, checkout = hg.addbranchrevs(repo, repo, branches, [])
    if revs:
        revs = [repo.lookup(rev) for rev in revs]
    other = hg.peer(repo, {}, dest)
    repo.ui.pushbuffer()
    outgoing = discovery.findcommonoutgoing(repo, other, onlyheads=revs)
    repo.ui.popbuffer()
    cl = repo.changelog
    o = {cl.rev(r) for r in outgoing.missing}
    return subset & o

@predicate('p1([set])', safe=True)
def p1(repo, subset, x):
    """First parent of changesets in set, or the working directory.
    """
    if x is None:
        p = repo[x].p1().rev()
        if p >= 0:
            return subset & baseset([p])
        return baseset()

    ps = set()
    cl = repo.changelog
    for r in getset(repo, fullreposet(repo), x):
        try:
            ps.add(cl.parentrevs(r)[0])
        except error.WdirUnsupported:
            ps.add(repo[r].parents()[0].rev())
    ps -= {node.nullrev}
    # XXX we should turn this into a baseset instead of a set, smartset may do
    # some optimizations from the fact this is a baseset.
    return subset & ps

@predicate('p2([set])', safe=True)
def p2(repo, subset, x):
    """Second parent of changesets in set, or the working directory.
    """
    if x is None:
        ps = repo[x].parents()
        try:
            p = ps[1].rev()
            if p >= 0:
                return subset & baseset([p])
            return baseset()
        except IndexError:
            return baseset()

    ps = set()
    cl = repo.changelog
    for r in getset(repo, fullreposet(repo), x):
        try:
            ps.add(cl.parentrevs(r)[1])
        except error.WdirUnsupported:
            parents = repo[r].parents()
            if len(parents) == 2:
                ps.add(parents[1])
    ps -= {node.nullrev}
    # XXX we should turn this into a baseset instead of a set, smartset may do
    # some optimizations from the fact this is a baseset.
    return subset & ps

def parentpost(repo, subset, x, order):
    return p1(repo, subset, x)

@predicate('parents([set])', safe=True)
def parents(repo, subset, x):
    """
    The set of all parents for all changesets in set, or the working directory.
    """
    if x is None:
        ps = set(p.rev() for p in repo[x].parents())
    else:
        ps = set()
        cl = repo.changelog
        up = ps.update
        parentrevs = cl.parentrevs
        for r in getset(repo, fullreposet(repo), x):
            try:
                up(parentrevs(r))
            except error.WdirUnsupported:
                up(p.rev() for p in repo[r].parents())
    ps -= {node.nullrev}
    return subset & ps

def _phase(repo, subset, *targets):
    """helper to select all rev in <targets> phases"""
    s = repo._phasecache.getrevset(repo, targets)
    return subset & s

@predicate('draft()', safe=True)
def draft(repo, subset, x):
    """Changeset in draft phase."""
    # i18n: "draft" is a keyword
    getargs(x, 0, 0, _("draft takes no arguments"))
    target = phases.draft
    return _phase(repo, subset, target)

@predicate('secret()', safe=True)
def secret(repo, subset, x):
    """Changeset in secret phase."""
    # i18n: "secret" is a keyword
    getargs(x, 0, 0, _("secret takes no arguments"))
    target = phases.secret
    return _phase(repo, subset, target)

def parentspec(repo, subset, x, n, order):
    """``set^0``
    The set.
    ``set^1`` (or ``set^``), ``set^2``
    First or second parent, respectively, of all changesets in set.
    """
    try:
        n = int(n[1])
        if n not in (0, 1, 2):
            raise ValueError
    except (TypeError, ValueError):
        raise error.ParseError(_("^ expects a number 0, 1, or 2"))
    ps = set()
    cl = repo.changelog
    for r in getset(repo, fullreposet(repo), x):
        if n == 0:
            ps.add(r)
        elif n == 1:
            try:
                ps.add(cl.parentrevs(r)[0])
            except error.WdirUnsupported:
                ps.add(repo[r].parents()[0].rev())
        else:
            try:
                parents = cl.parentrevs(r)
                if parents[1] != node.nullrev:
                    ps.add(parents[1])
            except error.WdirUnsupported:
                parents = repo[r].parents()
                if len(parents) == 2:
                    ps.add(parents[1].rev())
    return subset & ps

@predicate('present(set)', safe=True)
def present(repo, subset, x):
    """An empty set, if any revision in set isn't found; otherwise,
    all revisions in set.

    If any of specified revisions is not present in the local repository,
    the query is normally aborted. But this predicate allows the query
    to continue even in such cases.
    """
    try:
        return getset(repo, subset, x)
    except error.RepoLookupError:
        return baseset()

# for internal use
@predicate('_notpublic', safe=True)
def _notpublic(repo, subset, x):
    getargs(x, 0, 0, "_notpublic takes no arguments")
    return _phase(repo, subset, phases.draft, phases.secret)

@predicate('public()', safe=True)
def public(repo, subset, x):
    """Changeset in public phase."""
    # i18n: "public" is a keyword
    getargs(x, 0, 0, _("public takes no arguments"))
    phase = repo._phasecache.phase
    target = phases.public
    condition = lambda r: phase(repo, r) == target
    return subset.filter(condition, condrepr=('<phase %r>', target),
                         cache=False)

@predicate('remote([id [,path]])', safe=False)
def remote(repo, subset, x):
    """Local revision that corresponds to the given identifier in a
    remote repository, if present. Here, the '.' identifier is a
    synonym for the current local branch.
    """

    from . import hg # avoid start-up nasties
    # i18n: "remote" is a keyword
    l = getargs(x, 0, 2, _("remote takes zero, one, or two arguments"))

    q = '.'
    if len(l) > 0:
    # i18n: "remote" is a keyword
        q = getstring(l[0], _("remote requires a string id"))
    if q == '.':
        q = repo['.'].branch()

    dest = ''
    if len(l) > 1:
        # i18n: "remote" is a keyword
        dest = getstring(l[1], _("remote requires a repository path"))
    dest = repo.ui.expandpath(dest or 'default')
    dest, branches = hg.parseurl(dest)
    revs, checkout = hg.addbranchrevs(repo, repo, branches, [])
    if revs:
        revs = [repo.lookup(rev) for rev in revs]
    other = hg.peer(repo, {}, dest)
    n = other.lookup(q)
    if n in repo:
        r = repo[n].rev()
        if r in subset:
            return baseset([r])
    return baseset()

@predicate('removes(pattern)', safe=True)
def removes(repo, subset, x):
    """Changesets which remove files matching pattern.

    The pattern without explicit kind like ``glob:`` is expected to be
    relative to the current directory and match against a file or a
    directory.
    """
    # i18n: "removes" is a keyword
    pat = getstring(x, _("removes requires a pattern"))
    return checkstatus(repo, subset, pat, 2)

@predicate('rev(number)', safe=True)
def rev(repo, subset, x):
    """Revision with the given numeric identifier.
    """
    # i18n: "rev" is a keyword
    l = getargs(x, 1, 1, _("rev requires one argument"))
    try:
        # i18n: "rev" is a keyword
        l = int(getstring(l[0], _("rev requires a number")))
    except (TypeError, ValueError):
        # i18n: "rev" is a keyword
        raise error.ParseError(_("rev expects a number"))
    if l not in repo.changelog and l not in (node.nullrev, node.wdirrev):
        return baseset()
    return subset & baseset([l])

@predicate('matching(revision [, field])', safe=True)
def matching(repo, subset, x):
    """Changesets in which a given set of fields match the set of fields in the
    selected revision or set.

    To match more than one field pass the list of fields to match separated
    by spaces (e.g. ``author description``).

    Valid fields are most regular revision fields and some special fields.

    Regular revision fields are ``description``, ``author``, ``branch``,
    ``date``, ``files``, ``phase``, ``parents``, ``substate``, ``user``
    and ``diff``.
    Note that ``author`` and ``user`` are synonyms. ``diff`` refers to the
    contents of the revision. Two revisions matching their ``diff`` will
    also match their ``files``.

    Special fields are ``summary`` and ``metadata``:
    ``summary`` matches the first line of the description.
    ``metadata`` is equivalent to matching ``description user date``
    (i.e. it matches the main metadata fields).

    ``metadata`` is the default field which is used when no fields are
    specified. You can match more than one field at a time.
    """
    # i18n: "matching" is a keyword
    l = getargs(x, 1, 2, _("matching takes 1 or 2 arguments"))

    revs = getset(repo, fullreposet(repo), l[0])

    fieldlist = ['metadata']
    if len(l) > 1:
            fieldlist = getstring(l[1],
                # i18n: "matching" is a keyword
                _("matching requires a string "
                "as its second argument")).split()

    # Make sure that there are no repeated fields,
    # expand the 'special' 'metadata' field type
    # and check the 'files' whenever we check the 'diff'
    fields = []
    for field in fieldlist:
        if field == 'metadata':
            fields += ['user', 'description', 'date']
        elif field == 'diff':
            # a revision matching the diff must also match the files
            # since matching the diff is very costly, make sure to
            # also match the files first
            fields += ['files', 'diff']
        else:
            if field == 'author':
                field = 'user'
            fields.append(field)
    fields = set(fields)
    if 'summary' in fields and 'description' in fields:
        # If a revision matches its description it also matches its summary
        fields.discard('summary')

    # We may want to match more than one field
    # Not all fields take the same amount of time to be matched
    # Sort the selected fields in order of increasing matching cost
    fieldorder = ['phase', 'parents', 'user', 'date', 'branch', 'summary',
        'files', 'description', 'substate', 'diff']
    def fieldkeyfunc(f):
        try:
            return fieldorder.index(f)
        except ValueError:
            # assume an unknown field is very costly
            return len(fieldorder)
    fields = list(fields)
    fields.sort(key=fieldkeyfunc)

    # Each field will be matched with its own "getfield" function
    # which will be added to the getfieldfuncs array of functions
    getfieldfuncs = []
    _funcs = {
        'user': lambda r: repo[r].user(),
        'branch': lambda r: repo[r].branch(),
        'date': lambda r: repo[r].date(),
        'description': lambda r: repo[r].description(),
        'files': lambda r: repo[r].files(),
        'parents': lambda r: repo[r].parents(),
        'phase': lambda r: repo[r].phase(),
        'substate': lambda r: repo[r].substate,
        'summary': lambda r: repo[r].description().splitlines()[0],
        'diff': lambda r: list(repo[r].diff(git=True),)
    }
    for info in fields:
        getfield = _funcs.get(info, None)
        if getfield is None:
            raise error.ParseError(
                # i18n: "matching" is a keyword
                _("unexpected field name passed to matching: %s") % info)
        getfieldfuncs.append(getfield)
    # convert the getfield array of functions into a "getinfo" function
    # which returns an array of field values (or a single value if there
    # is only one field to match)
    getinfo = lambda r: [f(r) for f in getfieldfuncs]

    def matches(x):
        for rev in revs:
            target = getinfo(rev)
            match = True
            for n, f in enumerate(getfieldfuncs):
                if target[n] != f(x):
                    match = False
            if match:
                return True
        return False

    return subset.filter(matches, condrepr=('<matching%r %r>', fields, revs))

@predicate('reverse(set)', safe=True, takeorder=True)
def reverse(repo, subset, x, order):
    """Reverse order of set.
    """
    l = getset(repo, subset, x)
    if order == defineorder:
        l.reverse()
    return l

@predicate('roots(set)', safe=True)
def roots(repo, subset, x):
    """Changesets in set with no parent changeset in set.
    """
    s = getset(repo, fullreposet(repo), x)
    parents = repo.changelog.parentrevs
    def filter(r):
        for p in parents(r):
            if 0 <= p and p in s:
                return False
        return True
    return subset & s.filter(filter, condrepr='<roots>')

_sortkeyfuncs = {
    'rev': lambda c: c.rev(),
    'branch': lambda c: c.branch(),
    'desc': lambda c: c.description(),
    'user': lambda c: c.user(),
    'author': lambda c: c.user(),
    'date': lambda c: c.date()[0],
}

def _getsortargs(x):
    """Parse sort options into (set, [(key, reverse)], opts)"""
    args = getargsdict(x, 'sort', 'set keys topo.firstbranch')
    if 'set' not in args:
        # i18n: "sort" is a keyword
        raise error.ParseError(_('sort requires one or two arguments'))
    keys = "rev"
    if 'keys' in args:
        # i18n: "sort" is a keyword
        keys = getstring(args['keys'], _("sort spec must be a string"))

    keyflags = []
    for k in keys.split():
        fk = k
        reverse = (k[0] == '-')
        if reverse:
            k = k[1:]
        if k not in _sortkeyfuncs and k != 'topo':
            raise error.ParseError(_("unknown sort key %r") % fk)
        keyflags.append((k, reverse))

    if len(keyflags) > 1 and any(k == 'topo' for k, reverse in keyflags):
        # i18n: "topo" is a keyword
        raise error.ParseError(_('topo sort order cannot be combined '
                                 'with other sort keys'))

    opts = {}
    if 'topo.firstbranch' in args:
        if any(k == 'topo' for k, reverse in keyflags):
            opts['topo.firstbranch'] = args['topo.firstbranch']
        else:
            # i18n: "topo" and "topo.firstbranch" are keywords
            raise error.ParseError(_('topo.firstbranch can only be used '
                                     'when using the topo sort key'))

    return args['set'], keyflags, opts

@predicate('sort(set[, [-]key... [, ...]])', safe=True, takeorder=True)
def sort(repo, subset, x, order):
    """Sort set by keys. The default sort order is ascending, specify a key
    as ``-key`` to sort in descending order.

    The keys can be:

    - ``rev`` for the revision number,
    - ``branch`` for the branch name,
    - ``desc`` for the commit message (description),
    - ``user`` for user name (``author`` can be used as an alias),
    - ``date`` for the commit date
    - ``topo`` for a reverse topographical sort

    The ``topo`` sort order cannot be combined with other sort keys. This sort
    takes one optional argument, ``topo.firstbranch``, which takes a revset that
    specifies what topographical branches to prioritize in the sort.

    """
    s, keyflags, opts = _getsortargs(x)
    revs = getset(repo, subset, s)

    if not keyflags or order != defineorder:
        return revs
    if len(keyflags) == 1 and keyflags[0][0] == "rev":
        revs.sort(reverse=keyflags[0][1])
        return revs
    elif keyflags[0][0] == "topo":
        firstbranch = ()
        if 'topo.firstbranch' in opts:
            firstbranch = getset(repo, subset, opts['topo.firstbranch'])
        revs = baseset(_toposort(revs, repo.changelog.parentrevs, firstbranch),
                       istopo=True)
        if keyflags[0][1]:
            revs.reverse()
        return revs

    # sort() is guaranteed to be stable
    ctxs = [repo[r] for r in revs]
    for k, reverse in reversed(keyflags):
        ctxs.sort(key=_sortkeyfuncs[k], reverse=reverse)
    return baseset([c.rev() for c in ctxs])

def _toposort(revs, parentsfunc, firstbranch=()):
    """Yield revisions from heads to roots one (topo) branch at a time.

    This function aims to be used by a graph generator that wishes to minimize
    the number of parallel branches and their interleaving.

    Example iteration order (numbers show the "true" order in a changelog):

      o  4
      |
      o  1
      |
      | o  3
      | |
      | o  2
      |/
      o  0

    Note that the ancestors of merges are understood by the current
    algorithm to be on the same branch. This means no reordering will
    occur behind a merge.
    """

    ### Quick summary of the algorithm
    #
    # This function is based around a "retention" principle. We keep revisions
    # in memory until we are ready to emit a whole branch that immediately
    # "merges" into an existing one. This reduces the number of parallel
    # branches with interleaved revisions.
    #
    # During iteration revs are split into two groups:
    # A) revision already emitted
    # B) revision in "retention". They are stored as different subgroups.
    #
    # for each REV, we do the following logic:
    #
    #   1) if REV is a parent of (A), we will emit it. If there is a
    #   retention group ((B) above) that is blocked on REV being
    #   available, we emit all the revisions out of that retention
    #   group first.
    #
    #   2) else, we'll search for a subgroup in (B) awaiting for REV to be
    #   available, if such subgroup exist, we add REV to it and the subgroup is
    #   now awaiting for REV.parents() to be available.
    #
    #   3) finally if no such group existed in (B), we create a new subgroup.
    #
    #
    # To bootstrap the algorithm, we emit the tipmost revision (which
    # puts it in group (A) from above).

    revs.sort(reverse=True)

    # Set of parents of revision that have been emitted. They can be considered
    # unblocked as the graph generator is already aware of them so there is no
    # need to delay the revisions that reference them.
    #
    # If someone wants to prioritize a branch over the others, pre-filling this
    # set will force all other branches to wait until this branch is ready to be
    # emitted.
    unblocked = set(firstbranch)

    # list of groups waiting to be displayed, each group is defined by:
    #
    #   (revs:    lists of revs waiting to be displayed,
    #    blocked: set of that cannot be displayed before those in 'revs')
    #
    # The second value ('blocked') correspond to parents of any revision in the
    # group ('revs') that is not itself contained in the group. The main idea
    # of this algorithm is to delay as much as possible the emission of any
    # revision.  This means waiting for the moment we are about to display
    # these parents to display the revs in a group.
    #
    # This first implementation is smart until it encounters a merge: it will
    # emit revs as soon as any parent is about to be emitted and can grow an
    # arbitrary number of revs in 'blocked'. In practice this mean we properly
    # retains new branches but gives up on any special ordering for ancestors
    # of merges. The implementation can be improved to handle this better.
    #
    # The first subgroup is special. It corresponds to all the revision that
    # were already emitted. The 'revs' lists is expected to be empty and the
    # 'blocked' set contains the parents revisions of already emitted revision.
    #
    # You could pre-seed the <parents> set of groups[0] to a specific
    # changesets to select what the first emitted branch should be.
    groups = [([], unblocked)]
    pendingheap = []
    pendingset = set()

    heapq.heapify(pendingheap)
    heappop = heapq.heappop
    heappush = heapq.heappush
    for currentrev in revs:
        # Heap works with smallest element, we want highest so we invert
        if currentrev not in pendingset:
            heappush(pendingheap, -currentrev)
            pendingset.add(currentrev)
        # iterates on pending rev until after the current rev have been
        # processed.
        rev = None
        while rev != currentrev:
            rev = -heappop(pendingheap)
            pendingset.remove(rev)

            # Seek for a subgroup blocked, waiting for the current revision.
            matching = [i for i, g in enumerate(groups) if rev in g[1]]

            if matching:
                # The main idea is to gather together all sets that are blocked
                # on the same revision.
                #
                # Groups are merged when a common blocking ancestor is
                # observed. For example, given two groups:
                #
                # revs [5, 4] waiting for 1
                # revs [3, 2] waiting for 1
                #
                # These two groups will be merged when we process
                # 1. In theory, we could have merged the groups when
                # we added 2 to the group it is now in (we could have
                # noticed the groups were both blocked on 1 then), but
                # the way it works now makes the algorithm simpler.
                #
                # We also always keep the oldest subgroup first. We can
                # probably improve the behavior by having the longest set
                # first. That way, graph algorithms could minimise the length
                # of parallel lines their drawing. This is currently not done.
                targetidx = matching.pop(0)
                trevs, tparents = groups[targetidx]
                for i in matching:
                    gr = groups[i]
                    trevs.extend(gr[0])
                    tparents |= gr[1]
                # delete all merged subgroups (except the one we kept)
                # (starting from the last subgroup for performance and
                # sanity reasons)
                for i in reversed(matching):
                    del groups[i]
            else:
                # This is a new head. We create a new subgroup for it.
                targetidx = len(groups)
                groups.append(([], {rev}))

            gr = groups[targetidx]

            # We now add the current nodes to this subgroups. This is done
            # after the subgroup merging because all elements from a subgroup
            # that relied on this rev must precede it.
            #
            # we also update the <parents> set to include the parents of the
            # new nodes.
            if rev == currentrev: # only display stuff in rev
                gr[0].append(rev)
            gr[1].remove(rev)
            parents = [p for p in parentsfunc(rev) if p > node.nullrev]
            gr[1].update(parents)
            for p in parents:
                if p not in pendingset:
                    pendingset.add(p)
                    heappush(pendingheap, -p)

            # Look for a subgroup to display
            #
            # When unblocked is empty (if clause), we were not waiting for any
            # revisions during the first iteration (if no priority was given) or
            # if we emitted a whole disconnected set of the graph (reached a
            # root).  In that case we arbitrarily take the oldest known
            # subgroup. The heuristic could probably be better.
            #
            # Otherwise (elif clause) if the subgroup is blocked on
            # a revision we just emitted, we can safely emit it as
            # well.
            if not unblocked:
                if len(groups) > 1:  # display other subset
                    targetidx = 1
                    gr = groups[1]
            elif not gr[1] & unblocked:
                gr = None

            if gr is not None:
                # update the set of awaited revisions with the one from the
                # subgroup
                unblocked |= gr[1]
                # output all revisions in the subgroup
                for r in gr[0]:
                    yield r
                # delete the subgroup that you just output
                # unless it is groups[0] in which case you just empty it.
                if targetidx:
                    del groups[targetidx]
                else:
                    gr[0][:] = []
    # Check if we have some subgroup waiting for revisions we are not going to
    # iterate over
    for g in groups:
        for r in g[0]:
            yield r

@predicate('subrepo([pattern])')
def subrepo(repo, subset, x):
    """Changesets that add, modify or remove the given subrepo.  If no subrepo
    pattern is named, any subrepo changes are returned.
    """
    # i18n: "subrepo" is a keyword
    args = getargs(x, 0, 1, _('subrepo takes at most one argument'))
    pat = None
    if len(args) != 0:
        pat = getstring(args[0], _("subrepo requires a pattern"))

    m = matchmod.exact(repo.root, repo.root, ['.hgsubstate'])

    def submatches(names):
        k, p, m = util.stringmatcher(pat)
        for name in names:
            if m(name):
                yield name

    def matches(x):
        c = repo[x]
        s = repo.status(c.p1().node(), c.node(), match=m)

        if pat is None:
            return s.added or s.modified or s.removed

        if s.added:
            return any(submatches(c.substate.keys()))

        if s.modified:
            subs = set(c.p1().substate.keys())
            subs.update(c.substate.keys())

            for path in submatches(subs):
                if c.p1().substate.get(path) != c.substate.get(path):
                    return True

        if s.removed:
            return any(submatches(c.p1().substate.keys()))

        return False

    return subset.filter(matches, condrepr=('<subrepo %r>', pat))

def _substringmatcher(pattern, casesensitive=True):
    kind, pattern, matcher = util.stringmatcher(pattern,
                                                casesensitive=casesensitive)
    if kind == 'literal':
        if not casesensitive:
            pattern = encoding.lower(pattern)
            matcher = lambda s: pattern in encoding.lower(s)
        else:
            matcher = lambda s: pattern in s
    return kind, pattern, matcher

@predicate('tag([name])', safe=True)
def tag(repo, subset, x):
    """The specified tag by name, or all tagged revisions if no name is given.

    Pattern matching is supported for `name`. See
    :hg:`help revisions.patterns`.
    """
    # i18n: "tag" is a keyword
    args = getargs(x, 0, 1, _("tag takes one or no arguments"))
    cl = repo.changelog
    if args:
        pattern = getstring(args[0],
                            # i18n: "tag" is a keyword
                            _('the argument to tag must be a string'))
        kind, pattern, matcher = util.stringmatcher(pattern)
        if kind == 'literal':
            # avoid resolving all tags
            tn = repo._tagscache.tags.get(pattern, None)
            if tn is None:
                raise error.RepoLookupError(_("tag '%s' does not exist")
                                            % pattern)
            s = {repo[tn].rev()}
        else:
            s = {cl.rev(n) for t, n in repo.tagslist() if matcher(t)}
    else:
        s = {cl.rev(n) for t, n in repo.tagslist() if t != 'tip'}
    return subset & s

@predicate('tagged', safe=True)
def tagged(repo, subset, x):
    return tag(repo, subset, x)

@predicate('unstable()', safe=True)
def unstable(repo, subset, x):
    """Non-obsolete changesets with obsolete ancestors.
    """
    # i18n: "unstable" is a keyword
    getargs(x, 0, 0, _("unstable takes no arguments"))
    unstables = obsmod.getrevs(repo, 'unstable')
    return subset & unstables


@predicate('user(string)', safe=True)
def user(repo, subset, x):
    """User name contains string. The match is case-insensitive.

    Pattern matching is supported for `string`. See
    :hg:`help revisions.patterns`.
    """
    return author(repo, subset, x)

@predicate('wdir()', safe=True)
def wdir(repo, subset, x):
    """Working directory. (EXPERIMENTAL)"""
    # i18n: "wdir" is a keyword
    getargs(x, 0, 0, _("wdir takes no arguments"))
    if node.wdirrev in subset or isinstance(subset, fullreposet):
        return baseset([node.wdirrev])
    return baseset()

def _orderedlist(repo, subset, x):
    s = getstring(x, "internal error")
    if not s:
        return baseset()
    # remove duplicates here. it's difficult for caller to deduplicate sets
    # because different symbols can point to the same rev.
    cl = repo.changelog
    ls = []
    seen = set()
    for t in s.split('\0'):
        try:
            # fast path for integer revision
            r = int(t)
            if str(r) != t or r not in cl:
                raise ValueError
            revs = [r]
        except ValueError:
            revs = stringset(repo, subset, t)

        for r in revs:
            if r in seen:
                continue
            if (r in subset
                or r == node.nullrev and isinstance(subset, fullreposet)):
                ls.append(r)
            seen.add(r)
    return baseset(ls)

# for internal use
@predicate('_list', safe=True, takeorder=True)
def _list(repo, subset, x, order):
    if order == followorder:
        # slow path to take the subset order
        return subset & _orderedlist(repo, fullreposet(repo), x)
    else:
        return _orderedlist(repo, subset, x)

def _orderedintlist(repo, subset, x):
    s = getstring(x, "internal error")
    if not s:
        return baseset()
    ls = [int(r) for r in s.split('\0')]
    s = subset
    return baseset([r for r in ls if r in s])

# for internal use
@predicate('_intlist', safe=True, takeorder=True)
def _intlist(repo, subset, x, order):
    if order == followorder:
        # slow path to take the subset order
        return subset & _orderedintlist(repo, fullreposet(repo), x)
    else:
        return _orderedintlist(repo, subset, x)

def _orderedhexlist(repo, subset, x):
    s = getstring(x, "internal error")
    if not s:
        return baseset()
    cl = repo.changelog
    ls = [cl.rev(node.bin(r)) for r in s.split('\0')]
    s = subset
    return baseset([r for r in ls if r in s])

# for internal use
@predicate('_hexlist', safe=True, takeorder=True)
def _hexlist(repo, subset, x, order):
    if order == followorder:
        # slow path to take the subset order
        return subset & _orderedhexlist(repo, fullreposet(repo), x)
    else:
        return _orderedhexlist(repo, subset, x)

methods = {
    "range": rangeset,
    "rangeall": rangeall,
    "rangepre": rangepre,
    "rangepost": rangepost,
    "dagrange": dagrange,
    "string": stringset,
    "symbol": stringset,
    "and": andset,
    "or": orset,
    "not": notset,
    "difference": differenceset,
    "list": listset,
    "keyvalue": keyvaluepair,
    "func": func,
    "ancestor": ancestorspec,
    "parent": parentspec,
    "parentpost": parentpost,
}

def posttreebuilthook(tree, repo):
    # hook for extensions to execute code on the optimized tree
    pass

def match(ui, spec, repo=None, order=defineorder):
    """Create a matcher for a single revision spec

    If order=followorder, a matcher takes the ordering specified by the input
    set.
    """
    return matchany(ui, [spec], repo=repo, order=order)

def matchany(ui, specs, repo=None, order=defineorder):
    """Create a matcher that will include any revisions matching one of the
    given specs

    If order=followorder, a matcher takes the ordering specified by the input
    set.
    """
    if not specs:
        def mfunc(repo, subset=None):
            return baseset()
        return mfunc
    if not all(specs):
        raise error.ParseError(_("empty query"))
    lookup = None
    if repo:
        lookup = repo.__contains__
    if len(specs) == 1:
        tree = revsetlang.parse(specs[0], lookup)
    else:
        tree = ('or',
                ('list',) + tuple(revsetlang.parse(s, lookup) for s in specs))

    if ui:
        tree = revsetlang.expandaliases(ui, tree)
    tree = revsetlang.foldconcat(tree)
    tree = revsetlang.analyze(tree, order)
    tree = revsetlang.optimize(tree)
    posttreebuilthook(tree, repo)
    return makematcher(tree)

def makematcher(tree):
    """Create a matcher from an evaluatable tree"""
    def mfunc(repo, subset=None):
        if subset is None:
            subset = fullreposet(repo)
        return getset(repo, subset, tree)
    return mfunc

def loadpredicate(ui, extname, registrarobj):
    """Load revset predicates from specified registrarobj
    """
    for name, func in registrarobj._table.iteritems():
        symbols[name] = func
        if func._safe:
            safesymbols.add(name)

# load built-in predicates explicitly to setup safesymbols
loadpredicate(None, None, predicate)

# tell hggettext to extract docstrings from these functions:
i18nfunctions = symbols.values()