mercurial/revset.py

context: add a no-op _prestatus method

This patch adds a private _prestatus method so that certain contexts, such as
workingctx, can add custom pre-processing to status.

# revset.py - revision set queries for mercurial
#
# Copyright 2010 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.

import re
import parser, util, error, discovery, hbisect, phases
import node
import heapq
import match as matchmod
import ancestor as ancestormod
from i18n import _
import encoding
import obsolete as obsmod
import pathutil
import repoview

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

    def iterate():
        revqueue, revsnode = None, None
        h = []

        revs.descending()
        revqueue = util.deque(revs)
        if revqueue:
            revsnode = revqueue.popleft()
            heapq.heappush(h, -revsnode)

        seen = set([node.nullrev])
        while h:
            current = -heapq.heappop(h)
            if current not in seen:
                if revsnode and current == revsnode:
                    if revqueue:
                        revsnode = revqueue.popleft()
                        heapq.heappush(h, -revsnode)
                seen.add(current)
                yield current
                for parent in cl.parentrevs(current)[:cut]:
                    if parent != node.nullrev:
                        heapq.heappush(h, -parent)

    return _descgeneratorset(iterate())

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

    def iterate():
        cl = repo.changelog
        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 _ascgeneratorset(iterate())

def _revsbetween(repo, roots, heads):
    """Return all paths between roots and heads, inclusive of both endpoint
    sets."""
    if not roots:
        return baseset([])
    parentrevs = repo.changelog.parentrevs
    visit = baseset(heads)
    reachable = set()
    seen = {}
    minroot = min(roots)
    roots = set(roots)
    # open-code the post-order traversal due to the tiny size of
    # sys.getrecursionlimit()
    while visit:
        rev = visit.pop()
        if rev in roots:
            reachable.add(rev)
        parents = parentrevs(rev)
        seen[rev] = parents
        for parent in parents:
            if parent >= minroot and parent not in seen:
                visit.append(parent)
    if not reachable:
        return baseset([])
    for rev in sorted(seen):
        for parent in seen[rev]:
            if parent in reachable:
                reachable.add(rev)
    return baseset(sorted(reachable))

elements = {
    "(": (20, ("group", 1, ")"), ("func", 1, ")")),
    "~": (18, None, ("ancestor", 18)),
    "^": (18, None, ("parent", 18), ("parentpost", 18)),
    "-": (5, ("negate", 19), ("minus", 5)),
    "::": (17, ("dagrangepre", 17), ("dagrange", 17),
           ("dagrangepost", 17)),
    "..": (17, ("dagrangepre", 17), ("dagrange", 17),
           ("dagrangepost", 17)),
    ":": (15, ("rangepre", 15), ("range", 15), ("rangepost", 15)),
    "not": (10, ("not", 10)),
    "!": (10, ("not", 10)),
    "and": (5, None, ("and", 5)),
    "&": (5, None, ("and", 5)),
    "or": (4, None, ("or", 4)),
    "|": (4, None, ("or", 4)),
    "+": (4, None, ("or", 4)),
    ",": (2, None, ("list", 2)),
    ")": (0, None, None),
    "symbol": (0, ("symbol",), None),
    "string": (0, ("string",), None),
    "end": (0, None, None),
}

keywords = set(['and', 'or', 'not'])

def tokenize(program, lookup=None):
    '''
    Parse a revset statement into a stream of tokens

    Check that @ is a valid unquoted token character (issue3686):
    >>> list(tokenize("@::"))
    [('symbol', '@', 0), ('::', None, 1), ('end', None, 3)]

    '''

    pos, l = 0, len(program)
    while pos < l:
        c = program[pos]
        if c.isspace(): # skip inter-token whitespace
            pass
        elif c == ':' and program[pos:pos + 2] == '::': # look ahead carefully
            yield ('::', None, pos)
            pos += 1 # skip ahead
        elif c == '.' and program[pos:pos + 2] == '..': # look ahead carefully
            yield ('..', None, pos)
            pos += 1 # skip ahead
        elif c in "():,-|&+!~^": # handle simple operators
            yield (c, None, pos)
        elif (c in '"\'' or c == 'r' and
              program[pos:pos + 2] in ("r'", 'r"')): # handle quoted strings
            if c == 'r':
                pos += 1
                c = program[pos]
                decode = lambda x: x
            else:
                decode = lambda x: x.decode('string-escape')
            pos += 1
            s = pos
            while pos < l: # find closing quote
                d = program[pos]
                if d == '\\': # skip over escaped characters
                    pos += 2
                    continue
                if d == c:
                    yield ('string', decode(program[s:pos]), s)
                    break
                pos += 1
            else:
                raise error.ParseError(_("unterminated string"), s)
        # gather up a symbol/keyword
        elif c.isalnum() or c in '._@' or ord(c) > 127:
            s = pos
            pos += 1
            while pos < l: # find end of symbol
                d = program[pos]
                if not (d.isalnum() or d in "-._/@" or ord(d) > 127):
                    break
                if d == '.' and program[pos - 1] == '.': # special case for ..
                    pos -= 1
                    break
                pos += 1
            sym = program[s:pos]
            if sym in keywords: # operator keywords
                yield (sym, None, s)
            elif '-' in sym:
                # some jerk gave us foo-bar-baz, try to check if it's a symbol
                if lookup and lookup(sym):
                    # looks like a real symbol
                    yield ('symbol', sym, s)
                else:
                    # looks like an expression
                    parts = sym.split('-')
                    for p in parts[:-1]:
                        if p: # possible consecutive -
                            yield ('symbol', p, s)
                        s += len(p)
                        yield ('-', None, pos)
                        s += 1
                    if parts[-1]: # possible trailing -
                        yield ('symbol', parts[-1], s)
            else:
                yield ('symbol', sym, s)
            pos -= 1
        else:
            raise error.ParseError(_("syntax error"), pos)
        pos += 1
    yield ('end', None, pos)

# helpers

def getstring(x, err):
    if x and (x[0] == 'string' or x[0] == 'symbol'):
        return x[1]
    raise error.ParseError(err)

def getlist(x):
    if not x:
        return []
    if x[0] == 'list':
        return getlist(x[1]) + [x[2]]
    return [x]

def getargs(x, min, max, err):
    l = getlist(x)
    if len(l) < min or (max >= 0 and len(l) > max):
        raise error.ParseError(err)
    return l

def getset(repo, subset, x):
    if not x:
        raise error.ParseError(_("missing argument"))
    s = methods[x[0]](repo, subset, *x[1:])
    if util.safehasattr(s, 'set'):
        return s
    return baseset(s)

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 = repo[x].rev()
    if x == -1 and len(subset) == len(repo):
        return baseset([-1])
    if len(subset) == len(repo) or x in subset:
        return baseset([x])
    return baseset([])

def symbolset(repo, subset, x):
    if x in symbols:
        raise error.ParseError(_("can't use %s here") % x)
    return stringset(repo, subset, x)

def rangeset(repo, subset, x, y):
    cl = baseset(repo.changelog)
    m = getset(repo, cl, x)
    n = getset(repo, cl, y)

    if not m or not n:
        return baseset([])
    m, n = m[0], n[-1]

    if m < n:
        r = spanset(repo, m, n + 1)
    else:
        r = spanset(repo, m, n - 1)
    return r & subset

def dagrange(repo, subset, x, y):
    r = spanset(repo)
    xs = _revsbetween(repo, getset(repo, r, x), getset(repo, r, y))
    s = subset.set()
    return xs.filter(s.__contains__)

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

def orset(repo, subset, x, y):
    xl = getset(repo, subset, x)
    yl = getset(repo, subset - xl, y)
    return xl + yl

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

def listset(repo, subset, a, b):
    raise error.ParseError(_("can't use a list in this context"))

def func(repo, subset, a, b):
    if a[0] == 'symbol' and a[1] in symbols:
        return symbols[a[1]](repo, subset, b)
    raise error.ParseError(_("not a function: %s") % a[1])

# functions

def adds(repo, subset, x):
    """``adds(pattern)``
    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)

def ancestor(repo, subset, x):
    """``ancestor(*changeset)``
    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 = spanset(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):
    args = getset(repo, spanset(repo), x)
    if not args:
        return baseset([])
    s = _revancestors(repo, args, followfirst)
    return subset.filter(s.__contains__)

def ancestors(repo, subset, x):
    """``ancestors(set)``
    Changesets that are ancestors of a changeset in set.
    """
    return _ancestors(repo, subset, x)

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):
    """``set~n``
    Changesets that are the Nth ancestor (first parents only) of a changeset
    in set.
    """
    try:
        n = int(n[1])
    except (TypeError, ValueError):
        raise error.ParseError(_("~ expects a number"))
    ps = set()
    cl = repo.changelog
    for r in getset(repo, baseset(cl), x):
        for i in range(n):
            r = cl.parentrevs(r)[0]
        ps.add(r)
    return subset.filter(ps.__contains__)

def author(repo, subset, x):
    """``author(string)``
    Alias for ``user(string)``.
    """
    # i18n: "author" is a keyword
    n = encoding.lower(getstring(x, _("author requires a string")))
    kind, pattern, matcher = _substringmatcher(n)
    return subset.filter(lambda x: matcher(encoding.lower(repo[x].user())))

def only(repo, subset, x):
    """``only(set, [set])``
    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, spanset(repo), args[0]).set()
    if len(args) == 1:
        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, spanset(repo), args[1])

    results = set(ancestormod.missingancestors(include, exclude, cl.parentrevs))
    return lazyset(subset, results.__contains__)

def bisect(repo, subset, x):
    """``bisect(string)``
    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.filter(state.__contains__)

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

def bookmark(repo, subset, x):
    """``bookmark([name])``
    The named bookmark or all bookmarks.

    If `name` starts with `re:`, the remainder of the name is treated as
    a regular expression. To match a bookmark that actually starts with `re:`,
    use the prefix `literal:`.
    """
    # 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 = _stringmatcher(bm)
        if kind == 'literal':
            bmrev = repo._bookmarks.get(bm, None)
            if not bmrev:
                raise util.Abort(_("bookmark '%s' does not exist") % bm)
            bmrev = repo[bmrev].rev()
            return subset.filter(lambda r: r == bmrev)
        else:
            matchrevs = set()
            for name, bmrev in repo._bookmarks.iteritems():
                if matcher(name):
                    matchrevs.add(bmrev)
            if not matchrevs:
                raise util.Abort(_("no bookmarks exist that match '%s'")
                                 % pattern)
            bmrevs = set()
            for bmrev in matchrevs:
                bmrevs.add(repo[bmrev].rev())
            return subset & bmrevs

    bms = set([repo[r].rev()
               for r in repo._bookmarks.values()])
    return subset.filter(bms.__contains__)

def branch(repo, subset, x):
    """``branch(string or set)``
    All changesets belonging to the given branch or the branches of the given
    changesets.

    If `string` starts with `re:`, the remainder of the name is treated as
    a regular expression. To match a branch that actually starts with `re:`,
    use the prefix `literal:`.
    """
    try:
        b = getstring(x, '')
    except error.ParseError:
        # not a string, but another revspec, e.g. tip()
        pass
    else:
        kind, pattern, matcher = _stringmatcher(b)
        if kind == 'literal':
            # note: falls through to the revspec case if no branch with
            # this name exists
            if pattern in repo.branchmap():
                return subset.filter(lambda r: matcher(repo[r].branch()))
        else:
            return subset.filter(lambda r: matcher(repo[r].branch()))

    s = getset(repo, spanset(repo), x)
    b = set()
    for r in s:
        b.add(repo[r].branch())
    s = s.set()
    return subset.filter(lambda r: r in s or repo[r].branch() in b)

def bumped(repo, subset, x):
    """``bumped()``
    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

def bundle(repo, subset, x):
    """``bundle()``
    Changesets in the bundle.

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

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

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

    def matches(x):
        m = None
        fname = None
        c = repo[x]
        if not m or hasset:
            m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=c)
            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)

def _children(repo, narrow, parentset):
    cs = set()
    if not parentset:
        return baseset(cs)
    pr = repo.changelog.parentrevs
    minrev = min(parentset)
    for r in narrow:
        if r <= minrev:
            continue
        for p in pr(r):
            if p in parentset:
                cs.add(r)
    return baseset(cs)

def children(repo, subset, x):
    """``children(set)``
    Child changesets of changesets in set.
    """
    s = getset(repo, baseset(repo), x).set()
    cs = _children(repo, subset, s)
    return subset & cs

def closed(repo, subset, x):
    """``closed()``
    Changeset is closed.
    """
    # i18n: "closed" is a keyword
    getargs(x, 0, 0, _("closed takes no arguments"))
    return subset.filter(lambda r: repo[r].closesbranch())

def contains(repo, subset, x):
    """``contains(pattern)``
    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)

def converted(repo, subset, x):
    """``converted([id])``
    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))

def date(repo, subset, x):
    """``date(interval)``
    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]))

def desc(repo, subset, x):
    """``desc(string)``
    Search commit message for string. The match is case-insensitive.
    """
    # i18n: "desc" is a keyword
    ds = encoding.lower(getstring(x, _("desc requires a string")))

    def matches(x):
        c = repo[x]
        return ds in encoding.lower(c.description())

    return subset.filter(matches)

def _descendants(repo, subset, x, followfirst=False):
    args = getset(repo, spanset(repo), x)
    if not args:
        return baseset([])
    s = _revdescendants(repo, args, followfirst)

    # Both sets need to be ascending in order to lazily return the union
    # in the correct order.
    args.ascending()

    subsetset = subset.set()
    result = (orderedlazyset(s, subsetset.__contains__, ascending=True) +
              orderedlazyset(args, subsetset.__contains__, ascending=True))

    # Wrap result in a lazyset since it's an _addset, which doesn't implement
    # all the necessary functions to be consumed by callers.
    return orderedlazyset(result, lambda r: True, ascending=True)

def descendants(repo, subset, x):
    """``descendants(set)``
    Changesets which are descendants of changesets in set.
    """
    return _descendants(repo, subset, x)

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

def destination(repo, subset, x):
    """``destination([set])``
    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:
        args = getset(repo, spanset(repo), x).set()
    else:
        args = getall(repo, spanset(repo), x).set()

    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 args.
    # Even if the immediate src of r is not in the args, 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 args or src in dests:
                dests.update(lineage)
                break

            r = src
            src = _getrevsource(repo, r)

    return subset.filter(dests.__contains__)

def divergent(repo, subset, x):
    """``divergent()``
    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.filter(divergent.__contains__)

def draft(repo, subset, x):
    """``draft()``
    Changeset in draft phase."""
    # i18n: "draft" is a keyword
    getargs(x, 0, 0, _("draft takes no arguments"))
    pc = repo._phasecache
    return subset.filter(lambda r: pc.phase(repo, r) == phases.draft)

def extinct(repo, subset, x):
    """``extinct()``
    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

def extra(repo, subset, x):
    """``extra(label, [value])``
    Changesets with the given label in the extra metadata, with the given
    optional value.

    If `value` starts with `re:`, the remainder of the value is treated as
    a regular expression. To match a value that actually starts with `re:`,
    use the prefix `literal:`.
    """

    # i18n: "extra" is a keyword
    l = getargs(x, 1, 2, _('extra takes at least 1 and at most 2 arguments'))
    # i18n: "extra" is a keyword
    label = getstring(l[0], _('first argument to extra must be a string'))
    value = None

    if len(l) > 1:
        # i18n: "extra" is a keyword
        value = getstring(l[1], _('second argument to extra must be a string'))
        kind, value, matcher = _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))

def filelog(repo, subset, x):
    """``filelog(pattern)``
    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.
    """

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

    if not matchmod.patkind(pat):
        f = pathutil.canonpath(repo.root, repo.getcwd(), pat)
        fl = repo.file(f)
        for fr in fl:
            s.add(fl.linkrev(fr))
    else:
        m = matchmod.match(repo.root, repo.getcwd(), [pat], ctx=repo[None])
        for f in repo[None]:
            if m(f):
                fl = repo.file(f)
                for fr in fl:
                    s.add(fl.linkrev(fr))

    return subset.filter(s.__contains__)

def first(repo, subset, x):
    """``first(set, [n])``
    An alias for limit().
    """
    return limit(repo, subset, x)

def _follow(repo, subset, x, name, followfirst=False):
    l = getargs(x, 0, 1, _("%s takes no arguments or a filename") % name)
    c = repo['.']
    if l:
        x = getstring(l[0], _("%s expected a filename") % name)
        if x in c:
            cx = c[x]
            s = set(ctx.rev() for ctx in cx.ancestors(followfirst=followfirst))
            # include the revision responsible for the most recent version
            s.add(cx.linkrev())
        else:
            return baseset([])
    else:
        s = _revancestors(repo, baseset([c.rev()]), followfirst)

    return subset.filter(s.__contains__)

def follow(repo, subset, x):
    """``follow([file])``
    An alias for ``::.`` (ancestors of the working copy's first parent).
    If a filename is specified, the history of the given file is followed,
    including copies.
    """
    return _follow(repo, subset, x, 'follow')

def _followfirst(repo, subset, x):
    # ``followfirst([file])``
    # Like ``follow([file])`` but follows only the first parent of
    # every revision or file revision.
    return _follow(repo, subset, x, '_followfirst', followfirst=True)

def getall(repo, subset, x):
    """``all()``
    All changesets, the same as ``0:tip``.
    """
    # i18n: "all" is a keyword
    getargs(x, 0, 0, _("all takes no arguments"))
    return subset

def grep(repo, subset, x):
    """``grep(regex)``
    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, 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)

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.

    # i18n: "_matchfiles" is a keyword
    l = getargs(x, 1, -1, _("_matchfiles requires at least one argument"))
    pats, inc, exc = [], [], []
    hasset = False
    rev, default = None, None
    for arg in l:
        # i18n: "_matchfiles" is a keyword
        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:
                # i18n: "_matchfiles" is a keyword
                raise error.ParseError(_('_matchfiles expected at most one '
                                         'revision'))
            rev = value
        elif prefix == 'd:':
            if default is not None:
                # i18n: "_matchfiles" is a keyword
                raise error.ParseError(_('_matchfiles expected at most one '
                                         'default mode'))
            default = value
        else:
            # i18n: "_matchfiles" is a keyword
            raise error.ParseError(_('invalid _matchfiles prefix: %s') % prefix)
        if not hasset and matchmod.patkind(value) == 'set':
            hasset = True
    if not default:
        default = 'glob'

    def matches(x):
        m = None
        c = repo[x]
        if not m or (hasset and rev is None):
            ctx = c
            if rev is not None:
                ctx = repo[rev or None]
            m = matchmod.match(repo.root, repo.getcwd(), pats, include=inc,
                               exclude=exc, ctx=ctx, default=default)
        for f in c.files():
            if m(f):
                return True
        return False

    return subset.filter(matches)

def hasfile(repo, subset, x):
    """``file(pattern)``
    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))

def head(repo, subset, x):
    """``head()``
    Changeset is a named branch head.
    """
    # i18n: "head" is a keyword
    getargs(x, 0, 0, _("head takes no arguments"))
    hs = set()
    for b, ls in repo.branchmap().iteritems():
        hs.update(repo[h].rev() for h in ls)
    return baseset(hs).filter(subset.__contains__)

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

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

def keyword(repo, subset, x):
    """``keyword(string)``
    Search commit message, user name, and names of changed files for
    string. The match is case-insensitive.
    """
    # i18n: "keyword" is a keyword
    kw = encoding.lower(getstring(x, _("keyword requires a string")))

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

    return subset.filter(matches)

def limit(repo, subset, x):
    """``limit(set, [n])``
    First n members of set, defaulting to 1.
    """
    # i18n: "limit" is a keyword
    l = getargs(x, 1, 2, _("limit requires one or two arguments"))
    try:
        lim = 1
        if len(l) == 2:
            # i18n: "limit" is a keyword
            lim = int(getstring(l[1], _("limit requires a number")))
    except (TypeError, ValueError):
        # i18n: "limit" is a keyword
        raise error.ParseError(_("limit expects a number"))
    ss = subset.set()
    os = getset(repo, spanset(repo), l[0])
    bs = baseset([])
    it = iter(os)
    for x in xrange(lim):
        try:
            y = it.next()
            if y in ss:
                bs.append(y)
        except (StopIteration):
            break
    return bs

def last(repo, subset, x):
    """``last(set, [n])``
    Last n members of set, defaulting to 1.
    """
    # i18n: "last" is a keyword
    l = getargs(x, 1, 2, _("last requires one or two arguments"))
    try:
        lim = 1
        if len(l) == 2:
            # i18n: "last" is a keyword
            lim = int(getstring(l[1], _("last requires a number")))
    except (TypeError, ValueError):
        # i18n: "last" is a keyword
        raise error.ParseError(_("last expects a number"))
    ss = subset.set()
    os = getset(repo, spanset(repo), l[0])
    os.reverse()
    bs = baseset([])
    it = iter(os)
    for x in xrange(lim):
        try:
            y = it.next()
            if y in ss:
                bs.append(y)
        except (StopIteration):
            break
    return bs

def maxrev(repo, subset, x):
    """``max(set)``
    Changeset with highest revision number in set.
    """
    os = getset(repo, spanset(repo), x)
    if os:
        m = os.max()
        if m in subset:
            return baseset([m])
    return baseset([])

def merge(repo, subset, x):
    """``merge()``
    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)

def branchpoint(repo, subset, x):
    """``branchpoint()``
    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([])
    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)

def minrev(repo, subset, x):
    """``min(set)``
    Changeset with lowest revision number in set.
    """
    os = getset(repo, spanset(repo), x)
    if os:
        m = os.min()
        if m in subset:
            return baseset([m])
    return baseset([])

def _missingancestors(repo, subset, x):
    # i18n: "_missingancestors" is a keyword
    revs, bases = getargs(x, 2, 2,
                          _("_missingancestors requires two arguments"))
    rs = baseset(repo)
    revs = getset(repo, rs, revs)
    bases = getset(repo, rs, bases)
    missing = set(repo.changelog.findmissingrevs(bases, revs))
    return baseset([r for r in subset if r in missing])

def modifies(repo, subset, x):
    """``modifies(pattern)``
    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)

def node_(repo, subset, x):
    """``id(string)``
    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:
        rn = repo[n].rev()
    else:
        rn = None
        pm = repo.changelog._partialmatch(n)
        if pm is not None:
            rn = repo.changelog.rev(pm)

    return subset.filter(lambda r: r == rn)

def obsolete(repo, subset, x):
    """``obsolete()``
    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

def origin(repo, subset, x):
    """``origin([set])``
    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:
        args = getset(repo, spanset(repo), x).set()
    else:
        args = getall(repo, spanset(repo), x).set()

    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 = set([_firstsrc(r) for r in args])
    return subset.filter(o.__contains__)

def outgoing(repo, subset, x):
    """``outgoing([path])``
    Changesets not found in the specified destination repository, or the
    default push location.
    """
    import hg # avoid start-up nasties
    # 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 = set([cl.rev(r) for r in outgoing.missing])
    return subset.filter(o.__contains__)

def p1(repo, subset, x):
    """``p1([set])``
    First parent of changesets in set, or the working directory.
    """
    if x is None:
        p = repo[x].p1().rev()
        return subset.filter(lambda r: r == p)

    ps = set()
    cl = repo.changelog
    for r in getset(repo, spanset(repo), x):
        ps.add(cl.parentrevs(r)[0])
    return subset & ps

def p2(repo, subset, x):
    """``p2([set])``
    Second parent of changesets in set, or the working directory.
    """
    if x is None:
        ps = repo[x].parents()
        try:
            p = ps[1].rev()
            return subset.filter(lambda r: r == p)
        except IndexError:
            return baseset([])

    ps = set()
    cl = repo.changelog
    for r in getset(repo, spanset(repo), x):
        ps.add(cl.parentrevs(r)[1])
    return subset & ps

def parents(repo, subset, x):
    """``parents([set])``
    The set of all parents for all changesets in set, or the working directory.
    """
    if x is None:
        ps = tuple(p.rev() for p in repo[x].parents())
        return subset & ps

    ps = set()
    cl = repo.changelog
    for r in getset(repo, spanset(repo), x):
        ps.update(cl.parentrevs(r))
    return subset & ps

def parentspec(repo, subset, x, n):
    """``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, baseset(cl), x):
        if n == 0:
            ps.add(r)
        elif n == 1:
            ps.add(cl.parentrevs(r)[0])
        elif n == 2:
            parents = cl.parentrevs(r)
            if len(parents) > 1:
                ps.add(parents[1])
    return subset & ps

def present(repo, subset, x):
    """``present(set)``
    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([])

def public(repo, subset, x):
    """``public()``
    Changeset in public phase."""
    # i18n: "public" is a keyword
    getargs(x, 0, 0, _("public takes no arguments"))
    pc = repo._phasecache
    return subset.filter(lambda r: pc.phase(repo, r) == phases.public)

def remote(repo, subset, x):
    """``remote([id [,path]])``
    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.
    """

    import hg # avoid start-up nasties
    # i18n: "remote" is a keyword
    l = getargs(x, 0, 2, _("remote takes one, two or no 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([])

def removes(repo, subset, x):
    """``removes(pattern)``
    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)

def rev(repo, subset, x):
    """``rev(number)``
    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"))
    return subset.filter(lambda r: r == l)

def matching(repo, subset, x):
    """``matching(revision [, field])``
    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, baseset(repo.changelog), 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)

def reverse(repo, subset, x):
    """``reverse(set)``
    Reverse order of set.
    """
    l = getset(repo, subset, x)
    l.reverse()
    return l

def roots(repo, subset, x):
    """``roots(set)``
    Changesets in set with no parent changeset in set.
    """
    s = getset(repo, spanset(repo), x).set()
    subset = baseset([r for r in s if r in subset.set()])
    cs = _children(repo, subset, s)
    return subset - cs

def secret(repo, subset, x):
    """``secret()``
    Changeset in secret phase."""
    # i18n: "secret" is a keyword
    getargs(x, 0, 0, _("secret takes no arguments"))
    pc = repo._phasecache
    return subset.filter(lambda x: pc.phase(repo, x) == phases.secret)

def sort(repo, subset, x):
    """``sort(set[, [-]key...])``
    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
    """
    # i18n: "sort" is a keyword
    l = getargs(x, 1, 2, _("sort requires one or two arguments"))
    keys = "rev"
    if len(l) == 2:
        # i18n: "sort" is a keyword
        keys = getstring(l[1], _("sort spec must be a string"))

    s = l[0]
    keys = keys.split()
    l = []
    def invert(s):
        return "".join(chr(255 - ord(c)) for c in s)
    revs = getset(repo, subset, s)
    if keys == ["rev"]:
        revs.sort()
        return revs
    elif keys == ["-rev"]:
        revs.sort(reverse=True)
        return revs
    for r in revs:
        c = repo[r]
        e = []
        for k in keys:
            if k == 'rev':
                e.append(r)
            elif k == '-rev':
                e.append(-r)
            elif k == 'branch':
                e.append(c.branch())
            elif k == '-branch':
                e.append(invert(c.branch()))
            elif k == 'desc':
                e.append(c.description())
            elif k == '-desc':
                e.append(invert(c.description()))
            elif k in 'user author':
                e.append(c.user())
            elif k in '-user -author':
                e.append(invert(c.user()))
            elif k == 'date':
                e.append(c.date()[0])
            elif k == '-date':
                e.append(-c.date()[0])
            else:
                raise error.ParseError(_("unknown sort key %r") % k)
        e.append(r)
        l.append(e)
    l.sort()
    return baseset([e[-1] for e in l])

def _stringmatcher(pattern):
    """
    accepts a string, possibly starting with 're:' or 'literal:' prefix.
    returns the matcher name, pattern, and matcher function.
    missing or unknown prefixes are treated as literal matches.

    helper for tests:
    >>> def test(pattern, *tests):
    ...     kind, pattern, matcher = _stringmatcher(pattern)
    ...     return (kind, pattern, [bool(matcher(t)) for t in tests])

    exact matching (no prefix):
    >>> test('abcdefg', 'abc', 'def', 'abcdefg')
    ('literal', 'abcdefg', [False, False, True])

    regex matching ('re:' prefix)
    >>> test('re:a.+b', 'nomatch', 'fooadef', 'fooadefbar')
    ('re', 'a.+b', [False, False, True])

    force exact matches ('literal:' prefix)
    >>> test('literal:re:foobar', 'foobar', 're:foobar')
    ('literal', 're:foobar', [False, True])

    unknown prefixes are ignored and treated as literals
    >>> test('foo:bar', 'foo', 'bar', 'foo:bar')
    ('literal', 'foo:bar', [False, False, True])
    """
    if pattern.startswith('re:'):
        pattern = pattern[3:]
        try:
            regex = re.compile(pattern)
        except re.error, e:
            raise error.ParseError(_('invalid regular expression: %s')
                                   % e)
        return 're', pattern, regex.search
    elif pattern.startswith('literal:'):
        pattern = pattern[8:]
    return 'literal', pattern, pattern.__eq__

def _substringmatcher(pattern):
    kind, pattern, matcher = _stringmatcher(pattern)
    if kind == 'literal':
        matcher = lambda s: pattern in s
    return kind, pattern, matcher

def tag(repo, subset, x):
    """``tag([name])``
    The specified tag by name, or all tagged revisions if no name is given.

    If `name` starts with `re:`, the remainder of the name is treated as
    a regular expression. To match a tag that actually starts with `re:`,
    use the prefix `literal:`.
    """
    # 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 = _stringmatcher(pattern)
        if kind == 'literal':
            # avoid resolving all tags
            tn = repo._tagscache.tags.get(pattern, None)
            if tn is None:
                raise util.Abort(_("tag '%s' does not exist") % pattern)
            s = set([repo[tn].rev()])
        else:
            s = set([cl.rev(n) for t, n in repo.tagslist() if matcher(t)])
    else:
        s = set([cl.rev(n) for t, n in repo.tagslist() if t != 'tip'])
    return subset & s

def tagged(repo, subset, x):
    return tag(repo, subset, x)

def unstable(repo, subset, x):
    """``unstable()``
    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


def user(repo, subset, x):
    """``user(string)``
    User name contains string. The match is case-insensitive.

    If `string` starts with `re:`, the remainder of the string is treated as
    a regular expression. To match a user that actually contains `re:`, use
    the prefix `literal:`.
    """
    return author(repo, subset, x)

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

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

# for internal use
def _hexlist(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.set()
    return baseset([r for r in ls if r in s])

symbols = {
    "adds": adds,
    "all": getall,
    "ancestor": ancestor,
    "ancestors": ancestors,
    "_firstancestors": _firstancestors,
    "author": author,
    "only": only,
    "bisect": bisect,
    "bisected": bisected,
    "bookmark": bookmark,
    "branch": branch,
    "branchpoint": branchpoint,
    "bumped": bumped,
    "bundle": bundle,
    "children": children,
    "closed": closed,
    "contains": contains,
    "converted": converted,
    "date": date,
    "desc": desc,
    "descendants": descendants,
    "_firstdescendants": _firstdescendants,
    "destination": destination,
    "divergent": divergent,
    "draft": draft,
    "extinct": extinct,
    "extra": extra,
    "file": hasfile,
    "filelog": filelog,
    "first": first,
    "follow": follow,
    "_followfirst": _followfirst,
    "grep": grep,
    "head": head,
    "heads": heads,
    "hidden": hidden,
    "id": node_,
    "keyword": keyword,
    "last": last,
    "limit": limit,
    "_matchfiles": _matchfiles,
    "max": maxrev,
    "merge": merge,
    "min": minrev,
    "_missingancestors": _missingancestors,
    "modifies": modifies,
    "obsolete": obsolete,
    "origin": origin,
    "outgoing": outgoing,
    "p1": p1,
    "p2": p2,
    "parents": parents,
    "present": present,
    "public": public,
    "remote": remote,
    "removes": removes,
    "rev": rev,
    "reverse": reverse,
    "roots": roots,
    "sort": sort,
    "secret": secret,
    "matching": matching,
    "tag": tag,
    "tagged": tagged,
    "user": user,
    "unstable": unstable,
    "_list": _list,
    "_intlist": _intlist,
    "_hexlist": _hexlist,
}

# 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([
    "adds",
    "all",
    "ancestor",
    "ancestors",
    "_firstancestors",
    "author",
    "bisect",
    "bisected",
    "bookmark",
    "branch",
    "branchpoint",
    "bumped",
    "bundle",
    "children",
    "closed",
    "converted",
    "date",
    "desc",
    "descendants",
    "_firstdescendants",
    "destination",
    "divergent",
    "draft",
    "extinct",
    "extra",
    "file",
    "filelog",
    "first",
    "follow",
    "_followfirst",
    "head",
    "heads",
    "hidden",
    "id",
    "keyword",
    "last",
    "limit",
    "_matchfiles",
    "max",
    "merge",
    "min",
    "_missingancestors",
    "modifies",
    "obsolete",
    "origin",
    "outgoing",
    "p1",
    "p2",
    "parents",
    "present",
    "public",
    "remote",
    "removes",
    "rev",
    "reverse",
    "roots",
    "sort",
    "secret",
    "matching",
    "tag",
    "tagged",
    "user",
    "unstable",
    "_list",
    "_intlist",
    "_hexlist",
])

methods = {
    "range": rangeset,
    "dagrange": dagrange,
    "string": stringset,
    "symbol": symbolset,
    "and": andset,
    "or": orset,
    "not": notset,
    "list": listset,
    "func": func,
    "ancestor": ancestorspec,
    "parent": parentspec,
    "parentpost": p1,
}

def optimize(x, small):
    if x is None:
        return 0, x

    smallbonus = 1
    if small:
        smallbonus = .5

    op = x[0]
    if op == 'minus':
        return optimize(('and', x[1], ('not', x[2])), small)
    elif op == 'dagrangepre':
        return optimize(('func', ('symbol', 'ancestors'), x[1]), small)
    elif op == 'dagrangepost':
        return optimize(('func', ('symbol', 'descendants'), x[1]), small)
    elif op == 'rangepre':
        return optimize(('range', ('string', '0'), x[1]), small)
    elif op == 'rangepost':
        return optimize(('range', x[1], ('string', 'tip')), small)
    elif op == 'negate':
        return optimize(('string',
                         '-' + getstring(x[1], _("can't negate that"))), small)
    elif op in 'string symbol negate':
        return smallbonus, x # single revisions are small
    elif op == 'and':
        wa, ta = optimize(x[1], True)
        wb, tb = optimize(x[2], True)

        # (::x and not ::y)/(not ::y and ::x) have a fast path
        def ismissingancestors(revs, bases):
            return (
                revs[0] == 'func'
                and getstring(revs[1], _('not a symbol')) == 'ancestors'
                and bases[0] == 'not'
                and bases[1][0] == 'func'
                and getstring(bases[1][1], _('not a symbol')) == 'ancestors')

        w = min(wa, wb)
        if ismissingancestors(ta, tb):
            return w, ('func', ('symbol', '_missingancestors'),
                       ('list', ta[2], tb[1][2]))
        if ismissingancestors(tb, ta):
            return w, ('func', ('symbol', '_missingancestors'),
                       ('list', tb[2], ta[1][2]))

        if wa > wb:
            return w, (op, tb, ta)
        return w, (op, ta, tb)
    elif op == 'or':
        wa, ta = optimize(x[1], False)
        wb, tb = optimize(x[2], False)
        if wb < wa:
            wb, wa = wa, wb
        return max(wa, wb), (op, ta, tb)
    elif op == 'not':
        o = optimize(x[1], not small)
        return o[0], (op, o[1])
    elif op == 'parentpost':
        o = optimize(x[1], small)
        return o[0], (op, o[1])
    elif op == 'group':
        return optimize(x[1], small)
    elif op in 'dagrange range list parent ancestorspec':
        if op == 'parent':
            # x^:y means (x^) : y, not x ^ (:y)
            post = ('parentpost', x[1])
            if x[2][0] == 'dagrangepre':
                return optimize(('dagrange', post, x[2][1]), small)
            elif x[2][0] == 'rangepre':
                return optimize(('range', post, x[2][1]), small)

        wa, ta = optimize(x[1], small)
        wb, tb = optimize(x[2], small)
        return wa + wb, (op, ta, tb)
    elif op == 'func':
        f = getstring(x[1], _("not a symbol"))
        wa, ta = optimize(x[2], small)
        if f in ("author branch closed date desc file grep keyword "
                 "outgoing user"):
            w = 10 # slow
        elif f in "modifies adds removes":
            w = 30 # slower
        elif f == "contains":
            w = 100 # very slow
        elif f == "ancestor":
            w = 1 * smallbonus
        elif f in "reverse limit first":
            w = 0
        elif f in "sort":
            w = 10 # assume most sorts look at changelog
        else:
            w = 1
        return w + wa, (op, x[1], ta)
    return 1, x

_aliasarg = ('func', ('symbol', '_aliasarg'))
def _getaliasarg(tree):
    """If tree matches ('func', ('symbol', '_aliasarg'), ('string', X))
    return X, None otherwise.
    """
    if (len(tree) == 3 and tree[:2] == _aliasarg
        and tree[2][0] == 'string'):
        return tree[2][1]
    return None

def _checkaliasarg(tree, known=None):
    """Check tree contains no _aliasarg construct or only ones which
    value is in known. Used to avoid alias placeholders injection.
    """
    if isinstance(tree, tuple):
        arg = _getaliasarg(tree)
        if arg is not None and (not known or arg not in known):
            raise error.ParseError(_("not a function: %s") % '_aliasarg')
        for t in tree:
            _checkaliasarg(t, known)

class revsetalias(object):
    funcre = re.compile('^([^(]+)\(([^)]+)\)$')
    args = None

    def __init__(self, name, value):
        '''Aliases like:

        h = heads(default)
        b($1) = ancestors($1) - ancestors(default)
        '''
        m = self.funcre.search(name)
        if m:
            self.name = m.group(1)
            self.tree = ('func', ('symbol', m.group(1)))
            self.args = [x.strip() for x in m.group(2).split(',')]
            for arg in self.args:
                # _aliasarg() is an unknown symbol only used separate
                # alias argument placeholders from regular strings.
                value = value.replace(arg, '_aliasarg(%r)' % (arg,))
        else:
            self.name = name
            self.tree = ('symbol', name)

        self.replacement, pos = parse(value)
        if pos != len(value):
            raise error.ParseError(_('invalid token'), pos)
        # Check for placeholder injection
        _checkaliasarg(self.replacement, self.args)

def _getalias(aliases, tree):
    """If tree looks like an unexpanded alias, return it. Return None
    otherwise.
    """
    if isinstance(tree, tuple) and tree:
        if tree[0] == 'symbol' and len(tree) == 2:
            name = tree[1]
            alias = aliases.get(name)
            if alias and alias.args is None and alias.tree == tree:
                return alias
        if tree[0] == 'func' and len(tree) > 1:
            if tree[1][0] == 'symbol' and len(tree[1]) == 2:
                name = tree[1][1]
                alias = aliases.get(name)
                if alias and alias.args is not None and alias.tree == tree[:2]:
                    return alias
    return None

def _expandargs(tree, args):
    """Replace _aliasarg instances with the substitution value of the
    same name in args, recursively.
    """
    if not tree or not isinstance(tree, tuple):
        return tree
    arg = _getaliasarg(tree)
    if arg is not None:
        return args[arg]
    return tuple(_expandargs(t, args) for t in tree)

def _expandaliases(aliases, tree, expanding, cache):
    """Expand aliases in tree, recursively.

    'aliases' is a dictionary mapping user defined aliases to
    revsetalias objects.
    """
    if not isinstance(tree, tuple):
        # Do not expand raw strings
        return tree
    alias = _getalias(aliases, tree)
    if alias is not None:
        if alias in expanding:
            raise error.ParseError(_('infinite expansion of revset alias "%s" '
                                     'detected') % alias.name)
        expanding.append(alias)
        if alias.name not in cache:
            cache[alias.name] = _expandaliases(aliases, alias.replacement,
                                               expanding, cache)
        result = cache[alias.name]
        expanding.pop()
        if alias.args is not None:
            l = getlist(tree[2])
            if len(l) != len(alias.args):
                raise error.ParseError(
                    _('invalid number of arguments: %s') % len(l))
            l = [_expandaliases(aliases, a, [], cache) for a in l]
            result = _expandargs(result, dict(zip(alias.args, l)))
    else:
        result = tuple(_expandaliases(aliases, t, expanding, cache)
                       for t in tree)
    return result

def findaliases(ui, tree):
    _checkaliasarg(tree)
    aliases = {}
    for k, v in ui.configitems('revsetalias'):
        alias = revsetalias(k, v)
        aliases[alias.name] = alias
    return _expandaliases(aliases, tree, [], {})

def parse(spec, lookup=None):
    p = parser.parser(tokenize, elements)
    return p.parse(spec, lookup=lookup)

def match(ui, spec, repo=None):
    if not spec:
        raise error.ParseError(_("empty query"))
    lookup = None
    if repo:
        lookup = repo.__contains__
    tree, pos = parse(spec, lookup)
    if (pos != len(spec)):
        raise error.ParseError(_("invalid token"), pos)
    if ui:
        tree = findaliases(ui, tree)
    weight, tree = optimize(tree, True)
    def mfunc(repo, subset):
        if util.safehasattr(subset, 'set'):
            return getset(repo, subset, tree)
        return getset(repo, baseset(subset), tree)
    return mfunc

def formatspec(expr, *args):
    '''
    This is a convenience function for using revsets internally, and
    escapes arguments appropriately. Aliases are intentionally ignored
    so that intended expression behavior isn't accidentally subverted.

    Supported arguments:

    %r = revset expression, parenthesized
    %d = int(arg), no quoting
    %s = string(arg), escaped and single-quoted
    %b = arg.branch(), escaped and single-quoted
    %n = hex(arg), single-quoted
    %% = a literal '%'

    Prefixing the type with 'l' specifies a parenthesized list of that type.

    >>> formatspec('%r:: and %lr', '10 or 11', ("this()", "that()"))
    '(10 or 11):: and ((this()) or (that()))'
    >>> formatspec('%d:: and not %d::', 10, 20)
    '10:: and not 20::'
    >>> formatspec('%ld or %ld', [], [1])
    "_list('') or 1"
    >>> formatspec('keyword(%s)', 'foo\\xe9')
    "keyword('foo\\\\xe9')"
    >>> b = lambda: 'default'
    >>> b.branch = b
    >>> formatspec('branch(%b)', b)
    "branch('default')"
    >>> formatspec('root(%ls)', ['a', 'b', 'c', 'd'])
    "root(_list('a\\x00b\\x00c\\x00d'))"
    '''

    def quote(s):
        return repr(str(s))

    def argtype(c, arg):
        if c == 'd':
            return str(int(arg))
        elif c == 's':
            return quote(arg)
        elif c == 'r':
            parse(arg) # make sure syntax errors are confined
            return '(%s)' % arg
        elif c == 'n':
            return quote(node.hex(arg))
        elif c == 'b':
            return quote(arg.branch())

    def listexp(s, t):
        l = len(s)
        if l == 0:
            return "_list('')"
        elif l == 1:
            return argtype(t, s[0])
        elif t == 'd':
            return "_intlist('%s')" % "\0".join(str(int(a)) for a in s)
        elif t == 's':
            return "_list('%s')" % "\0".join(s)
        elif t == 'n':
            return "_hexlist('%s')" % "\0".join(node.hex(a) for a in s)
        elif t == 'b':
            return "_list('%s')" % "\0".join(a.branch() for a in s)

        m = l // 2
        return '(%s or %s)' % (listexp(s[:m], t), listexp(s[m:], t))

    ret = ''
    pos = 0
    arg = 0
    while pos < len(expr):
        c = expr[pos]
        if c == '%':
            pos += 1
            d = expr[pos]
            if d == '%':
                ret += d
            elif d in 'dsnbr':
                ret += argtype(d, args[arg])
                arg += 1
            elif d == 'l':
                # a list of some type
                pos += 1
                d = expr[pos]
                ret += listexp(list(args[arg]), d)
                arg += 1
            else:
                raise util.Abort('unexpected revspec format character %s' % d)
        else:
            ret += c
        pos += 1

    return ret

def prettyformat(tree):
    def _prettyformat(tree, level, lines):
        if not isinstance(tree, tuple) or tree[0] in ('string', 'symbol'):
            lines.append((level, str(tree)))
        else:
            lines.append((level, '(%s' % tree[0]))
            for s in tree[1:]:
                _prettyformat(s, level + 1, lines)
            lines[-1:] = [(lines[-1][0], lines[-1][1] + ')')]

    lines = []
    _prettyformat(tree, 0, lines)
    output = '\n'.join(('  '*l + s) for l, s in lines)
    return output

def depth(tree):
    if isinstance(tree, tuple):
        return max(map(depth, tree)) + 1
    else:
        return 0

def funcsused(tree):
    if not isinstance(tree, tuple) or tree[0] in ('string', 'symbol'):
        return set()
    else:
        funcs = set()
        for s in tree[1:]:
            funcs |= funcsused(s)
        if tree[0] == 'func':
            funcs.add(tree[1][1])
        return funcs

class baseset(list):
    """Basic data structure that represents a revset and contains the basic
    operation that it should be able to perform.

    Every method in this class should be implemented by any smartset class.
    """
    def __init__(self, data=()):
        super(baseset, self).__init__(data)
        self._set = None

    def ascending(self):
        """Sorts the set in ascending order (in place).

        This is part of the mandatory API for smartset."""
        self.sort()

    def descending(self):
        """Sorts the set in descending order (in place).

        This is part of the mandatory API for smartset."""
        self.sort(reverse=True)

    def min(self):
        return min(self)

    def max(self):
        return max(self)

    def set(self):
        """Returns a set or a smartset containing all the elements.

        The returned structure should be the fastest option for membership
        testing.

        This is part of the mandatory API for smartset."""
        if not self._set:
            self._set = set(self)
        return self._set

    def __sub__(self, other):
        """Returns a new object with the substraction of the two collections.

        This is part of the mandatory API for smartset."""
        if isinstance(other, baseset):
            s = other.set()
        else:
            s = set(other)
        return baseset(self.set() - s)

    def __and__(self, other):
        """Returns a new object with the intersection of the two collections.

        This is part of the mandatory API for smartset."""
        if isinstance(other, baseset):
            other = other.set()
        return baseset([y for y in self if y in other])

    def __add__(self, other):
        """Returns a new object with the union of the two collections.

        This is part of the mandatory API for smartset."""
        s = self.set()
        l = [r for r in other if r not in s]
        return baseset(list(self) + l)

    def isascending(self):
        """Returns True if the collection is ascending order, False if not.

        This is part of the mandatory API for smartset."""
        return False

    def isdescending(self):
        """Returns True if the collection is descending order, False if not.

        This is part of the mandatory API for smartset."""
        return False

    def filter(self, condition):
        """Returns this smartset filtered by condition as a new smartset.

        `condition` is a callable which takes a revision number and returns a
        boolean.

        This is part of the mandatory API for smartset."""
        return lazyset(self, condition)

class _orderedsetmixin(object):
    """Mixin class with utility methods for smartsets

    This should be extended by smartsets which have the isascending(),
    isdescending() and reverse() methods"""

    def _first(self):
        """return the first revision in the set"""
        for r in self:
            return r
        raise ValueError('arg is an empty sequence')

    def _last(self):
        """return the last revision in the set"""
        self.reverse()
        m = self._first()
        self.reverse()
        return m

    def min(self):
        """return the smallest element in the set"""
        if self.isascending():
            return self._first()
        return self._last()

    def max(self):
        """return the largest element in the set"""
        if self.isascending():
            return self._last()
        return self._first()

class lazyset(object):
    """Duck type for baseset class which iterates lazily over the revisions in
    the subset and contains a function which tests for membership in the
    revset
    """
    def __init__(self, subset, condition=lambda x: True):
        """
        condition: a function that decide whether a revision in the subset
                   belongs to the revset or not.
        """
        self._subset = subset
        self._condition = condition
        self._cache = {}

    def ascending(self):
        self._subset.sort()

    def descending(self):
        self._subset.sort(reverse=True)

    def min(self):
        return min(self)

    def max(self):
        return max(self)

    def __contains__(self, x):
        c = self._cache
        if x not in c:
            c[x] = x in self._subset and self._condition(x)
        return c[x]

    def __iter__(self):
        cond = self._condition
        for x in self._subset:
            if cond(x):
                yield x

    def __and__(self, x):
        return lazyset(self, x.__contains__)

    def __sub__(self, x):
        return lazyset(self, lambda r: r not in x)

    def __add__(self, x):
        return _addset(self, x)

    def __nonzero__(self):
        for r in self:
            return True
        return False

    def __len__(self):
        # Basic implementation to be changed in future patches.
        l = baseset([r for r in self])
        return len(l)

    def __getitem__(self, x):
        # Basic implementation to be changed in future patches.
        l = baseset([r for r in self])
        return l[x]

    def sort(self, reverse=False):
        if not util.safehasattr(self._subset, 'sort'):
            self._subset = baseset(self._subset)
        self._subset.sort(reverse=reverse)

    def reverse(self):
        self._subset.reverse()

    def set(self):
        return set([r for r in self])

    def isascending(self):
        return False

    def isdescending(self):
        return False

    def filter(self, l):
        return lazyset(self, l)

class orderedlazyset(_orderedsetmixin, lazyset):
    """Subclass of lazyset which subset can be ordered either ascending or
    descendingly
    """
    def __init__(self, subset, condition, ascending=True):
        super(orderedlazyset, self).__init__(subset, condition)
        self._ascending = ascending

    def filter(self, l):
        return orderedlazyset(self, l, ascending=self._ascending)

    def ascending(self):
        if not self._ascending:
            self.reverse()

    def descending(self):
        if self._ascending:
            self.reverse()

    def __and__(self, x):
        return orderedlazyset(self, x.__contains__,
                ascending=self._ascending)

    def __sub__(self, x):
        return orderedlazyset(self, lambda r: r not in x,
                ascending=self._ascending)

    def __add__(self, x):
        kwargs = {}
        if self.isascending() and x.isascending():
            kwargs['ascending'] = True
        if self.isdescending() and x.isdescending():
            kwargs['ascending'] = False
        return _addset(self, x, **kwargs)

    def sort(self, reverse=False):
        if reverse:
            if self._ascending:
                self._subset.sort(reverse=reverse)
        else:
            if not self._ascending:
                self._subset.sort(reverse=reverse)
        self._ascending = not reverse

    def isascending(self):
        return self._ascending

    def isdescending(self):
        return not self._ascending

    def reverse(self):
        self._subset.reverse()
        self._ascending = not self._ascending

class _addset(_orderedsetmixin):
    """Represent the addition of two sets

    Wrapper structure for lazily adding two structures without losing much
    performance on the __contains__ method

    If the ascending attribute is set, that means the two structures are
    ordered in either an ascending or descending way. Therefore, we can add
    them maintaining the order by iterating over both at the same time

    This class does not duck-type baseset and it's only supposed to be used
    internally
    """
    def __init__(self, revs1, revs2, ascending=None):
        self._r1 = revs1
        self._r2 = revs2
        self._iter = None
        self._ascending = ascending
        self._genlist = None

    def __len__(self):
        return len(self._list)

    @util.propertycache
    def _list(self):
        if not self._genlist:
            self._genlist = baseset(self._iterator())
        return self._genlist

    def filter(self, condition):
        if self._ascending is not None:
            return orderedlazyset(self, condition, ascending=self._ascending)
        return lazyset(self, condition)

    def ascending(self):
        if self._ascending is None:
            self.sort()
            self._ascending = True
        else:
            if not self._ascending:
                self.reverse()

    def descending(self):
        if self._ascending is None:
            self.sort(reverse=True)
            self._ascending = False
        else:
            if self._ascending:
                self.reverse()

    def __and__(self, other):
        filterfunc = other.__contains__
        if self._ascending is not None:
            return orderedlazyset(self, filterfunc, ascending=self._ascending)
        return lazyset(self, filterfunc)

    def __sub__(self, other):
        filterfunc = lambda r: r not in other
        if self._ascending is not None:
            return orderedlazyset(self, filterfunc, ascending=self._ascending)
        return lazyset(self, filterfunc)

    def __add__(self, other):
        """When both collections are ascending or descending, preserve the order
        """
        kwargs = {}
        if self._ascending is not None:
            if self.isascending() and other.isascending():
                kwargs['ascending'] = True
            if self.isdescending() and other.isdescending():
                kwargs['ascending'] = False
        return _addset(self, other, **kwargs)

    def _iterator(self):
        """Iterate over both collections without repeating elements

        If the ascending attribute is not set, iterate over the first one and
        then over the second one checking for membership on the first one so we
        dont yield any duplicates.

        If the ascending attribute is set, iterate over both collections at the
        same time, yielding only one value at a time in the given order.
        """
        if not self._iter:
            def gen():
                if self._ascending is None:
                    for r in self._r1:
                        yield r
                    s = self._r1.set()
                    for r in self._r2:
                        if r not in s:
                            yield r
                else:
                    iter1 = iter(self._r1)
                    iter2 = iter(self._r2)

                    val1 = None
                    val2 = None

                    choice = max
                    if self._ascending:
                        choice = min
                    try:
                        # Consume both iterators in an ordered way until one is
                        # empty
                        while True:
                            if val1 is None:
                                val1 = iter1.next()
                            if val2 is None:
                                val2 = iter2.next()
                            next = choice(val1, val2)
                            yield next
                            if val1 == next:
                                val1 = None
                            if val2 == next:
                                val2 = None
                    except StopIteration:
                        # Flush any remaining values and consume the other one
                        it = iter2
                        if val1 is not None:
                            yield val1
                            it = iter1
                        elif val2 is not None:
                            # might have been equality and both are empty
                            yield val2
                        for val in it:
                            yield val

            self._iter = _generatorset(gen())

        return self._iter

    def __iter__(self):
        if self._genlist:
            return iter(self._genlist)
        return iter(self._iterator())

    def __contains__(self, x):
        return x in self._r1 or x in self._r2

    def set(self):
        return self

    def sort(self, reverse=False):
        """Sort the added set

        For this we use the cached list with all the generated values and if we
        know they are ascending or descending we can sort them in a smart way.
        """
        if self._ascending is None:
            self._list.sort(reverse=reverse)
            self._ascending = not reverse
        else:
            if bool(self._ascending) == bool(reverse):
                self.reverse()

    def isascending(self):
        return self._ascending is not None and self._ascending

    def isdescending(self):
        return self._ascending is not None and not self._ascending

    def reverse(self):
        self._list.reverse()
        if self._ascending is not None:
            self._ascending = not self._ascending

class _generatorset(object):
    """Wrap a generator for lazy iteration

    Wrapper structure for generators that provides lazy membership and can
    be iterated more than once.
    When asked for membership it generates values until either it finds the
    requested one or has gone through all the elements in the generator

    This class does not duck-type baseset and it's only supposed to be used
    internally
    """
    def __init__(self, gen):
        """
        gen: a generator producing the values for the generatorset.
        """
        self._gen = gen
        self._cache = {}
        self._genlist = baseset([])
        self._finished = False

    def __contains__(self, x):
        if x in self._cache:
            return self._cache[x]

        # Use new values only, as existing values would be cached.
        for l in self._consumegen():
            if l == x:
                return True

        self._cache[x] = False
        return False

    def __iter__(self):
        if self._finished:
            for x in self._genlist:
                yield x
            return

        i = 0
        genlist = self._genlist
        consume = self._consumegen()
        while True:
            if i < len(genlist):
                yield genlist[i]
            else:
                yield consume.next()
            i += 1

    def _consumegen(self):
        for item in self._gen:
            self._cache[item] = True
            self._genlist.append(item)
            yield item
        self._finished = True

    def set(self):
        return self

    def sort(self, reverse=False):
        if not self._finished:
            for i in self:
                continue
        self._genlist.sort(reverse=reverse)

class _ascgeneratorset(_generatorset):
    """Wrap a generator of ascending elements for lazy iteration

    Same structure as _generatorset but stops iterating after it goes past
    the value when asked for membership and the element is not contained

    This class does not duck-type baseset and it's only supposed to be used
    internally
    """
    def __contains__(self, x):
        if x in self._cache:
            return self._cache[x]

        # Use new values only, as existing values would be cached.
        for l in self._consumegen():
            if l == x:
                return True
            if l > x:
                break

        self._cache[x] = False
        return False

class _descgeneratorset(_generatorset):
    """Wrap a generator of descending elements for lazy iteration

    Same structure as _generatorset but stops iterating after it goes past
    the value when asked for membership and the element is not contained

    This class does not duck-type baseset and it's only supposed to be used
    internally
    """
    def __contains__(self, x):
        if x in self._cache:
            return self._cache[x]

        # Use new values only, as existing values would be cached.
        for l in self._consumegen():
            if l == x:
                return True
            if l < x:
                break

        self._cache[x] = False
        return False

class spanset(_orderedsetmixin):
    """Duck type for baseset class which represents a range of revisions and
    can work lazily and without having all the range in memory

    Note that spanset(x, y) behave almost like xrange(x, y) except for two
    notable points:
    - when x < y it will be automatically descending,
    - revision filtered with this repoview will be skipped.

    """
    def __init__(self, repo, start=0, end=None):
        """
        start: first revision included the set
               (default to 0)
        end:   first revision excluded (last+1)
               (default to len(repo)

        Spanset will be descending if `end` < `start`.
        """
        self._start = start
        if end is not None:
            self._end = end
        else:
            self._end = len(repo)
        self._hiddenrevs = repo.changelog.filteredrevs

    def ascending(self):
        if self._start > self._end:
            self.reverse()

    def descending(self):
        if self._start < self._end:
            self.reverse()

    def __iter__(self):
        if self._start <= self._end:
            iterrange = xrange(self._start, self._end)
        else:
            iterrange = xrange(self._start, self._end, -1)

        if self._hiddenrevs:
            s = self._hiddenrevs
            for r in iterrange:
                if r not in s:
                    yield r
        else:
            for r in iterrange:
                yield r

    def __contains__(self, rev):
        return (((self._end < rev <= self._start)
                  or (self._start <= rev < self._end))
                and not (self._hiddenrevs and rev in self._hiddenrevs))

    def __nonzero__(self):
        for r in self:
            return True
        return False

    def __and__(self, x):
        if isinstance(x, baseset):
            x = x.set()
        if self._start <= self._end:
            return orderedlazyset(self, x.__contains__)
        else:
            return orderedlazyset(self, x.__contains__, ascending=False)

    def __sub__(self, x):
        if isinstance(x, baseset):
            x = x.set()
        if self._start <= self._end:
            return orderedlazyset(self, lambda r: r not in x)
        else:
            return orderedlazyset(self, lambda r: r not in x, ascending=False)

    def __add__(self, x):
        kwargs = {}
        if self.isascending() and x.isascending():
            kwargs['ascending'] = True
        if self.isdescending() and x.isdescending():
            kwargs['ascending'] = False
        return _addset(self, x, **kwargs)

    def __len__(self):
        if not self._hiddenrevs:
            return abs(self._end - self._start)
        else:
            count = 0
            start = self._start
            end = self._end
            for rev in self._hiddenrevs:
                if (end < rev <= start) or (start <= rev < end):
                    count += 1
            return abs(self._end - self._start) - count

    def __getitem__(self, x):
        # Basic implementation to be changed in future patches.
        l = baseset([r for r in self])
        return l[x]

    def sort(self, reverse=False):
        if bool(reverse) != (self._start > self._end):
            self.reverse()

    def reverse(self):
        # Just switch the _start and _end parameters
        if self._start <= self._end:
            self._start, self._end = self._end - 1, self._start - 1
        else:
            self._start, self._end = self._end + 1, self._start + 1

    def set(self):
        return self

    def isascending(self):
        return self._start < self._end

    def isdescending(self):
        return self._start > self._end

    def filter(self, l):
        if self._start <= self._end:
            return orderedlazyset(self, l)
        else:
            return orderedlazyset(self, l, ascending=False)

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