mercurial/manifest.py

# manifest.py - manifest revision class for mercurial
#
# Copyright 2005-2007 Matt Mackall <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from i18n import _
import mdiff, parsers, error, revlog, util
import array, struct
import os
import heapq

propertycache = util.propertycache

def _parsev1(data):
    # This method does a little bit of excessive-looking
    # precondition checking. This is so that the behavior of this
    # class exactly matches its C counterpart to try and help
    # prevent surprise breakage for anyone that develops against
    # the pure version.
    if data and data[-1] != '\n':
        raise ValueError('Manifest did not end in a newline.')
    prev = None
    for l in data.splitlines():
        if prev is not None and prev > l:
            raise ValueError('Manifest lines not in sorted order.')
        prev = l
        f, n = l.split('\0')
        if len(n) > 40:
            yield f, revlog.bin(n[:40]), n[40:]
        else:
            yield f, revlog.bin(n), ''

def _parsev2(data):
    metadataend = data.find('\n')
    # Just ignore metadata for now
    pos = metadataend + 1
    prevf = ''
    while pos < len(data):
        end = data.find('\n', pos + 1) # +1 to skip stem length byte
        if end == -1:
            raise ValueError('Manifest ended with incomplete file entry.')
        stemlen = ord(data[pos])
        items = data[pos + 1:end].split('\0')
        f = prevf[:stemlen] + items[0]
        if prevf > f:
            raise ValueError('Manifest entries not in sorted order.')
        fl = items[1]
        # Just ignore metadata (items[2:] for now)
        n = data[end + 1:end + 21]
        yield f, n, fl
        pos = end + 22
        prevf = f

def _parse(data):
    """Generates (path, node, flags) tuples from a manifest text"""
    if data.startswith('\0'):
        return iter(_parsev2(data))
    else:
        return iter(_parsev1(data))

def _text(it, usemanifestv2):
    """Given an iterator over (path, node, flags) tuples, returns a manifest
    text"""
    if usemanifestv2:
        return _textv2(it)
    else:
        return _textv1(it)

def _textv1(it):
    files = []
    lines = []
    _hex = revlog.hex
    for f, n, fl in it:
        files.append(f)
        # if this is changed to support newlines in filenames,
        # be sure to check the templates/ dir again (especially *-raw.tmpl)
        lines.append("%s\0%s%s\n" % (f, _hex(n), fl))

    _checkforbidden(files)
    return ''.join(lines)

def _textv2(it):
    files = []
    lines = ['\0\n']
    prevf = ''
    for f, n, fl in it:
        files.append(f)
        stem = os.path.commonprefix([prevf, f])
        stemlen = min(len(stem), 255)
        lines.append("%c%s\0%s\n%s\n" % (stemlen, f[stemlen:], fl, n))
        prevf = f
    _checkforbidden(files)
    return ''.join(lines)

class _lazymanifest(dict):
    """This is the pure implementation of lazymanifest.

    It has not been optimized *at all* and is not lazy.
    """

    def __init__(self, data):
        dict.__init__(self)
        for f, n, fl in _parse(data):
            self[f] = n, fl

    def __setitem__(self, k, v):
        node, flag = v
        assert node is not None
        if len(node) > 21:
            node = node[:21] # match c implementation behavior
        dict.__setitem__(self, k, (node, flag))

    def __iter__(self):
        return iter(sorted(dict.keys(self)))

    def iterkeys(self):
        return iter(sorted(dict.keys(self)))

    def iterentries(self):
        return ((f, e[0], e[1]) for f, e in sorted(self.iteritems()))

    def copy(self):
        c = _lazymanifest('')
        c.update(self)
        return c

    def diff(self, m2, clean=False):
        '''Finds changes between the current manifest and m2.'''
        diff = {}

        for fn, e1 in self.iteritems():
            if fn not in m2:
                diff[fn] = e1, (None, '')
            else:
                e2 = m2[fn]
                if e1 != e2:
                    diff[fn] = e1, e2
                elif clean:
                    diff[fn] = None

        for fn, e2 in m2.iteritems():
            if fn not in self:
                diff[fn] = (None, ''), e2

        return diff

    def filtercopy(self, filterfn):
        c = _lazymanifest('')
        for f, n, fl in self.iterentries():
            if filterfn(f):
                c[f] = n, fl
        return c

    def text(self):
        """Get the full data of this manifest as a bytestring."""
        return _textv1(self.iterentries())

try:
    _lazymanifest = parsers.lazymanifest
except AttributeError:
    pass

class manifestdict(object):
    def __init__(self, data=''):
        if data.startswith('\0'):
            #_lazymanifest can not parse v2
            self._lm = _lazymanifest('')
            for f, n, fl in _parsev2(data):
                self._lm[f] = n, fl
        else:
            self._lm = _lazymanifest(data)

    def __getitem__(self, key):
        return self._lm[key][0]

    def find(self, key):
        return self._lm[key]

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

    def __setitem__(self, key, node):
        self._lm[key] = node, self.flags(key, '')

    def __contains__(self, key):
        return key in self._lm

    def __delitem__(self, key):
        del self._lm[key]

    def __iter__(self):
        return self._lm.__iter__()

    def iterkeys(self):
        return self._lm.iterkeys()

    def keys(self):
        return list(self.iterkeys())

    def filesnotin(self, m2):
        '''Set of files in this manifest that are not in the other'''
        files = set(self)
        files.difference_update(m2)
        return files

    @propertycache
    def _dirs(self):
        return util.dirs(self)

    def dirs(self):
        return self._dirs

    def hasdir(self, dir):
        return dir in self._dirs

    def _filesfastpath(self, match):
        '''Checks whether we can correctly and quickly iterate over matcher
        files instead of over manifest files.'''
        files = match.files()
        return (len(files) < 100 and (match.isexact() or
            (match.prefix() and all(fn in self for fn in files))))

    def walk(self, match):
        '''Generates matching file names.

        Equivalent to manifest.matches(match).iterkeys(), but without creating
        an entirely new manifest.

        It also reports nonexistent files by marking them bad with match.bad().
        '''
        if match.always():
            for f in iter(self):
                yield f
            return

        fset = set(match.files())

        # avoid the entire walk if we're only looking for specific files
        if self._filesfastpath(match):
            for fn in sorted(fset):
                yield fn
            return

        for fn in self:
            if fn in fset:
                # specified pattern is the exact name
                fset.remove(fn)
            if match(fn):
                yield fn

        # for dirstate.walk, files=['.'] means "walk the whole tree".
        # follow that here, too
        fset.discard('.')

        for fn in sorted(fset):
            if not self.hasdir(fn):
                match.bad(fn, None)

    def matches(self, match):
        '''generate a new manifest filtered by the match argument'''
        if match.always():
            return self.copy()

        if self._filesfastpath(match):
            m = manifestdict()
            lm = self._lm
            for fn in match.files():
                if fn in lm:
                    m._lm[fn] = lm[fn]
            return m

        m = manifestdict()
        m._lm = self._lm.filtercopy(match)
        return m

    def diff(self, m2, clean=False):
        '''Finds changes between the current manifest and m2.

        Args:
          m2: the manifest to which this manifest should be compared.
          clean: if true, include files unchanged between these manifests
                 with a None value in the returned dictionary.

        The result is returned as a dict with filename as key and
        values of the form ((n1,fl1),(n2,fl2)), where n1/n2 is the
        nodeid in the current/other manifest and fl1/fl2 is the flag
        in the current/other manifest. Where the file does not exist,
        the nodeid will be None and the flags will be the empty
        string.
        '''
        return self._lm.diff(m2._lm, clean)

    def setflag(self, key, flag):
        self._lm[key] = self[key], flag

    def get(self, key, default=None):
        try:
            return self._lm[key][0]
        except KeyError:
            return default

    def flags(self, key, default=''):
        try:
            return self._lm[key][1]
        except KeyError:
            return default

    def copy(self):
        c = manifestdict()
        c._lm = self._lm.copy()
        return c

    def iteritems(self):
        return (x[:2] for x in self._lm.iterentries())

    def text(self, usemanifestv2=False):
        if usemanifestv2:
            return _textv2(self._lm.iterentries())
        else:
            # use (probably) native version for v1
            return self._lm.text()

    def fastdelta(self, base, changes):
        """Given a base manifest text as an array.array and a list of changes
        relative to that text, compute a delta that can be used by revlog.
        """
        delta = []
        dstart = None
        dend = None
        dline = [""]
        start = 0
        # zero copy representation of base as a buffer
        addbuf = util.buffer(base)

        # start with a readonly loop that finds the offset of
        # each line and creates the deltas
        for f, todelete in changes:
            # bs will either be the index of the item or the insert point
            start, end = _msearch(addbuf, f, start)
            if not todelete:
                h, fl = self._lm[f]
                l = "%s\0%s%s\n" % (f, revlog.hex(h), fl)
            else:
                if start == end:
                    # item we want to delete was not found, error out
                    raise AssertionError(
                            _("failed to remove %s from manifest") % f)
                l = ""
            if dstart is not None and dstart <= start and dend >= start:
                if dend < end:
                    dend = end
                if l:
                    dline.append(l)
            else:
                if dstart is not None:
                    delta.append([dstart, dend, "".join(dline)])
                dstart = start
                dend = end
                dline = [l]

        if dstart is not None:
            delta.append([dstart, dend, "".join(dline)])
        # apply the delta to the base, and get a delta for addrevision
        deltatext, arraytext = _addlistdelta(base, delta)
        return arraytext, deltatext

def _msearch(m, s, lo=0, hi=None):
    '''return a tuple (start, end) that says where to find s within m.

    If the string is found m[start:end] are the line containing
    that string.  If start == end the string was not found and
    they indicate the proper sorted insertion point.

    m should be a buffer or a string
    s is a string'''
    def advance(i, c):
        while i < lenm and m[i] != c:
            i += 1
        return i
    if not s:
        return (lo, lo)
    lenm = len(m)
    if not hi:
        hi = lenm
    while lo < hi:
        mid = (lo + hi) // 2
        start = mid
        while start > 0 and m[start - 1] != '\n':
            start -= 1
        end = advance(start, '\0')
        if m[start:end] < s:
            # we know that after the null there are 40 bytes of sha1
            # this translates to the bisect lo = mid + 1
            lo = advance(end + 40, '\n') + 1
        else:
            # this translates to the bisect hi = mid
            hi = start
    end = advance(lo, '\0')
    found = m[lo:end]
    if s == found:
        # we know that after the null there are 40 bytes of sha1
        end = advance(end + 40, '\n')
        return (lo, end + 1)
    else:
        return (lo, lo)

def _checkforbidden(l):
    """Check filenames for illegal characters."""
    for f in l:
        if '\n' in f or '\r' in f:
            raise error.RevlogError(
                _("'\\n' and '\\r' disallowed in filenames: %r") % f)


# apply the changes collected during the bisect loop to our addlist
# return a delta suitable for addrevision
def _addlistdelta(addlist, x):
    # for large addlist arrays, building a new array is cheaper
    # than repeatedly modifying the existing one
    currentposition = 0
    newaddlist = array.array('c')

    for start, end, content in x:
        newaddlist += addlist[currentposition:start]
        if content:
            newaddlist += array.array('c', content)

        currentposition = end

    newaddlist += addlist[currentposition:]

    deltatext = "".join(struct.pack(">lll", start, end, len(content))
                   + content for start, end, content in x)
    return deltatext, newaddlist

def _splittopdir(f):
    if '/' in f:
        dir, subpath = f.split('/', 1)
        return dir + '/', subpath
    else:
        return '', f

_noop = lambda: None

class treemanifest(object):
    def __init__(self, dir='', text=''):
        self._dir = dir
        self._node = revlog.nullid
        self._load = _noop
        self._dirty = False
        self._dirs = {}
        # Using _lazymanifest here is a little slower than plain old dicts
        self._files = {}
        self._flags = {}
        if text:
            def readsubtree(subdir, subm):
                raise AssertionError('treemanifest constructor only accepts '
                                     'flat manifests')
            self.parse(text, readsubtree)
            self._dirty = True # Mark flat manifest dirty after parsing

    def _subpath(self, path):
        return self._dir + path

    def __len__(self):
        self._load()
        size = len(self._files)
        for m in self._dirs.values():
            size += m.__len__()
        return size

    def _isempty(self):
        self._load() # for consistency; already loaded by all callers
        return (not self._files and (not self._dirs or
                all(m._isempty() for m in self._dirs.values())))

    def __str__(self):
        return ('<treemanifest dir=%s, node=%s, loaded=%s, dirty=%s>' %
                (self._dir, revlog.hex(self._node),
                 bool(self._load is _noop),
                 self._dirty))

    def dir(self):
        '''The directory that this tree manifest represents, including a
        trailing '/'. Empty string for the repo root directory.'''
        return self._dir

    def node(self):
        '''This node of this instance. nullid for unsaved instances. Should
        be updated when the instance is read or written from a revlog.
        '''
        assert not self._dirty
        return self._node

    def setnode(self, node):
        self._node = node
        self._dirty = False

    def iteritems(self):
        self._load()
        for p, n in sorted(self._dirs.items() + self._files.items()):
            if p in self._files:
                yield self._subpath(p), n
            else:
                for f, sn in n.iteritems():
                    yield f, sn

    def iterkeys(self):
        self._load()
        for p in sorted(self._dirs.keys() + self._files.keys()):
            if p in self._files:
                yield self._subpath(p)
            else:
                for f in self._dirs[p].iterkeys():
                    yield f

    def keys(self):
        return list(self.iterkeys())

    def __iter__(self):
        return self.iterkeys()

    def __contains__(self, f):
        if f is None:
            return False
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            if dir not in self._dirs:
                return False
            return self._dirs[dir].__contains__(subpath)
        else:
            return f in self._files

    def get(self, f, default=None):
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            if dir not in self._dirs:
                return default
            return self._dirs[dir].get(subpath, default)
        else:
            return self._files.get(f, default)

    def __getitem__(self, f):
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            return self._dirs[dir].__getitem__(subpath)
        else:
            return self._files[f]

    def flags(self, f):
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            if dir not in self._dirs:
                return ''
            return self._dirs[dir].flags(subpath)
        else:
            if f in self._dirs:
                return ''
            return self._flags.get(f, '')

    def find(self, f):
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            return self._dirs[dir].find(subpath)
        else:
            return self._files[f], self._flags.get(f, '')

    def __delitem__(self, f):
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            self._dirs[dir].__delitem__(subpath)
            # If the directory is now empty, remove it
            if self._dirs[dir]._isempty():
                del self._dirs[dir]
        else:
            del self._files[f]
            if f in self._flags:
                del self._flags[f]
        self._dirty = True

    def __setitem__(self, f, n):
        assert n is not None
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            if dir not in self._dirs:
                self._dirs[dir] = treemanifest(self._subpath(dir))
            self._dirs[dir].__setitem__(subpath, n)
        else:
            self._files[f] = n[:21] # to match manifestdict's behavior
        self._dirty = True

    def setflag(self, f, flags):
        """Set the flags (symlink, executable) for path f."""
        assert 'd' not in flags
        self._load()
        dir, subpath = _splittopdir(f)
        if dir:
            if dir not in self._dirs:
                self._dirs[dir] = treemanifest(self._subpath(dir))
            self._dirs[dir].setflag(subpath, flags)
        else:
            self._flags[f] = flags
        self._dirty = True

    def copy(self):
        copy = treemanifest(self._dir)
        copy._node = self._node
        copy._dirty = self._dirty
        def _load():
            self._load()
            for d in self._dirs:
                copy._dirs[d] = self._dirs[d].copy()
            copy._files = dict.copy(self._files)
            copy._flags = dict.copy(self._flags)
            copy._load = _noop
        copy._load = _load
        if self._load == _noop:
            # Chaining _load if it's _noop is functionally correct, but the
            # chain may end up excessively long (stack overflow), and
            # will prevent garbage collection of 'self'.
            copy._load()
        return copy

    def filesnotin(self, m2):
        '''Set of files in this manifest that are not in the other'''
        files = set()
        def _filesnotin(t1, t2):
            if t1._node == t2._node and not t1._dirty and not t2._dirty:
                return
            t1._load()
            t2._load()
            for d, m1 in t1._dirs.iteritems():
                if d in t2._dirs:
                    m2 = t2._dirs[d]
                    _filesnotin(m1, m2)
                else:
                    files.update(m1.iterkeys())

            for fn in t1._files.iterkeys():
                if fn not in t2._files:
                    files.add(t1._subpath(fn))

        _filesnotin(self, m2)
        return files

    @propertycache
    def _alldirs(self):
        return util.dirs(self)

    def dirs(self):
        return self._alldirs

    def hasdir(self, dir):
        self._load()
        topdir, subdir = _splittopdir(dir)
        if topdir:
            if topdir in self._dirs:
                return self._dirs[topdir].hasdir(subdir)
            return False
        return (dir + '/') in self._dirs

    def walk(self, match):
        '''Generates matching file names.

        Equivalent to manifest.matches(match).iterkeys(), but without creating
        an entirely new manifest.

        It also reports nonexistent files by marking them bad with match.bad().
        '''
        if match.always():
            for f in iter(self):
                yield f
            return

        fset = set(match.files())

        for fn in self._walk(match):
            if fn in fset:
                # specified pattern is the exact name
                fset.remove(fn)
            yield fn

        # for dirstate.walk, files=['.'] means "walk the whole tree".
        # follow that here, too
        fset.discard('.')

        for fn in sorted(fset):
            if not self.hasdir(fn):
                match.bad(fn, None)

    def _walk(self, match):
        '''Recursively generates matching file names for walk().'''
        if not match.visitdir(self._dir[:-1] or '.'):
            return

        # yield this dir's files and walk its submanifests
        self._load()
        for p in sorted(self._dirs.keys() + self._files.keys()):
            if p in self._files:
                fullp = self._subpath(p)
                if match(fullp):
                    yield fullp
            else:
                for f in self._dirs[p]._walk(match):
                    yield f

    def matches(self, match):
        '''generate a new manifest filtered by the match argument'''
        if match.always():
            return self.copy()

        return self._matches(match)

    def _matches(self, match):
        '''recursively generate a new manifest filtered by the match argument.
        '''
        ret = treemanifest(self._dir)

        if not match.visitdir(self._dir[:-1] or '.'):
            return ret

        self._load()
        for fn in self._files:
            fullp = self._subpath(fn)
            if not match(fullp):
                continue
            ret._files[fn] = self._files[fn]
            if fn in self._flags:
                ret._flags[fn] = self._flags[fn]

        for dir, subm in self._dirs.iteritems():
            m = subm._matches(match)
            if not m._isempty():
                ret._dirs[dir] = m

        if not ret._isempty():
            ret._dirty = True
        return ret

    def diff(self, m2, clean=False):
        '''Finds changes between the current manifest and m2.

        Args:
          m2: the manifest to which this manifest should be compared.
          clean: if true, include files unchanged between these manifests
                 with a None value in the returned dictionary.

        The result is returned as a dict with filename as key and
        values of the form ((n1,fl1),(n2,fl2)), where n1/n2 is the
        nodeid in the current/other manifest and fl1/fl2 is the flag
        in the current/other manifest. Where the file does not exist,
        the nodeid will be None and the flags will be the empty
        string.
        '''
        result = {}
        emptytree = treemanifest()
        def _diff(t1, t2):
            if t1._node == t2._node and not t1._dirty and not t2._dirty:
                return
            t1._load()
            t2._load()
            for d, m1 in t1._dirs.iteritems():
                m2 = t2._dirs.get(d, emptytree)
                _diff(m1, m2)

            for d, m2 in t2._dirs.iteritems():
                if d not in t1._dirs:
                    _diff(emptytree, m2)

            for fn, n1 in t1._files.iteritems():
                fl1 = t1._flags.get(fn, '')
                n2 = t2._files.get(fn, None)
                fl2 = t2._flags.get(fn, '')
                if n1 != n2 or fl1 != fl2:
                    result[t1._subpath(fn)] = ((n1, fl1), (n2, fl2))
                elif clean:
                    result[t1._subpath(fn)] = None

            for fn, n2 in t2._files.iteritems():
                if fn not in t1._files:
                    fl2 = t2._flags.get(fn, '')
                    result[t2._subpath(fn)] = ((None, ''), (n2, fl2))

        _diff(self, m2)
        return result

    def unmodifiedsince(self, m2):
        return not self._dirty and not m2._dirty and self._node == m2._node

    def parse(self, text, readsubtree):
        for f, n, fl in _parse(text):
            if fl == 'd':
                f = f + '/'
                self._dirs[f] = readsubtree(self._subpath(f), n)
            elif '/' in f:
                # This is a flat manifest, so use __setitem__ and setflag rather
                # than assigning directly to _files and _flags, so we can
                # assign a path in a subdirectory, and to mark dirty (compared
                # to nullid).
                self[f] = n
                if fl:
                    self.setflag(f, fl)
            else:
                # Assigning to _files and _flags avoids marking as dirty,
                # and should be a little faster.
                self._files[f] = n
                if fl:
                    self._flags[f] = fl

    def text(self, usemanifestv2=False):
        """Get the full data of this manifest as a bytestring."""
        self._load()
        flags = self.flags
        return _text(((f, self[f], flags(f)) for f in self.keys()),
                     usemanifestv2)

    def dirtext(self, usemanifestv2=False):
        """Get the full data of this directory as a bytestring. Make sure that
        any submanifests have been written first, so their nodeids are correct.
        """
        self._load()
        flags = self.flags
        dirs = [(d[:-1], self._dirs[d]._node, 'd') for d in self._dirs]
        files = [(f, self._files[f], flags(f)) for f in self._files]
        return _text(sorted(dirs + files), usemanifestv2)

    def read(self, gettext, readsubtree):
        def _load():
            # Mark as loaded already here, so __setitem__ and setflag() don't
            # cause infinite loops when they try to load.
            self._load = _noop
            self.parse(gettext(), readsubtree)
            self._dirty = False
        self._load = _load

    def writesubtrees(self, m1, m2, writesubtree):
        self._load() # for consistency; should never have any effect here
        emptytree = treemanifest()
        for d, subm in self._dirs.iteritems():
            subp1 = m1._dirs.get(d, emptytree)._node
            subp2 = m2._dirs.get(d, emptytree)._node
            if subp1 == revlog.nullid:
                subp1, subp2 = subp2, subp1
            writesubtree(subm, subp1, subp2)

class manifest(revlog.revlog):
    def __init__(self, opener, dir='', dirlogcache=None):
        '''The 'dir' and 'dirlogcache' arguments are for internal use by
        manifest.manifest only. External users should create a root manifest
        log with manifest.manifest(opener) and call dirlog() on it.
        '''
        # During normal operations, we expect to deal with not more than four
        # revs at a time (such as during commit --amend). When rebasing large
        # stacks of commits, the number can go up, hence the config knob below.
        cachesize = 4
        usetreemanifest = False
        usemanifestv2 = False
        opts = getattr(opener, 'options', None)
        if opts is not None:
            cachesize = opts.get('manifestcachesize', cachesize)
            usetreemanifest = opts.get('treemanifest', usetreemanifest)
            usemanifestv2 = opts.get('manifestv2', usemanifestv2)
        self._mancache = util.lrucachedict(cachesize)
        self._treeinmem = usetreemanifest
        self._treeondisk = usetreemanifest
        self._usemanifestv2 = usemanifestv2
        indexfile = "00manifest.i"
        if dir:
            assert self._treeondisk
            if not dir.endswith('/'):
                dir = dir + '/'
            indexfile = "meta/" + dir + "00manifest.i"
        revlog.revlog.__init__(self, opener, indexfile)
        self._dir = dir
        # The dirlogcache is kept on the root manifest log
        if dir:
            self._dirlogcache = dirlogcache
        else:
            self._dirlogcache = {'': self}

    def _newmanifest(self, data=''):
        if self._treeinmem:
            return treemanifest(self._dir, data)
        return manifestdict(data)

    def dirlog(self, dir):
        assert self._treeondisk
        if dir not in self._dirlogcache:
            self._dirlogcache[dir] = manifest(self.opener, dir,
                                              self._dirlogcache)
        return self._dirlogcache[dir]

    def _slowreaddelta(self, node):
        r0 = self.deltaparent(self.rev(node))
        m0 = self.read(self.node(r0))
        m1 = self.read(node)
        md = self._newmanifest()
        for f, ((n0, fl0), (n1, fl1)) in m0.diff(m1).iteritems():
            if n1:
                md[f] = n1
                if fl1:
                    md.setflag(f, fl1)
        return md

    def readdelta(self, node):
        if self._usemanifestv2 or self._treeondisk:
            return self._slowreaddelta(node)
        r = self.rev(node)
        d = mdiff.patchtext(self.revdiff(self.deltaparent(r), r))
        return self._newmanifest(d)

    def readfast(self, node):
        '''use the faster of readdelta or read

        This will return a manifest which is either only the files
        added/modified relative to p1, or all files in the
        manifest. Which one is returned depends on the codepath used
        to retrieve the data.
        '''
        r = self.rev(node)
        deltaparent = self.deltaparent(r)
        if deltaparent != revlog.nullrev and deltaparent in self.parentrevs(r):
            return self.readdelta(node)
        return self.read(node)

    def read(self, node):
        if node == revlog.nullid:
            return self._newmanifest() # don't upset local cache
        if node in self._mancache:
            return self._mancache[node][0]
        if self._treeondisk:
            def gettext():
                return self.revision(node)
            def readsubtree(dir, subm):
                return self.dirlog(dir).read(subm)
            m = self._newmanifest()
            m.read(gettext, readsubtree)
            m.setnode(node)
            arraytext = None
        else:
            text = self.revision(node)
            m = self._newmanifest(text)
            arraytext = array.array('c', text)
        self._mancache[node] = (m, arraytext)
        return m

    def find(self, node, f):
        '''look up entry for a single file efficiently.
        return (node, flags) pair if found, (None, None) if not.'''
        m = self.read(node)
        try:
            return m.find(f)
        except KeyError:
            return None, None

    def add(self, m, transaction, link, p1, p2, added, removed):
        if (p1 in self._mancache and not self._treeinmem
            and not self._usemanifestv2):
            # If our first parent is in the manifest cache, we can
            # compute a delta here using properties we know about the
            # manifest up-front, which may save time later for the
            # revlog layer.

            _checkforbidden(added)
            # combine the changed lists into one sorted iterator
            work = heapq.merge([(x, False) for x in added],
                               [(x, True) for x in removed])

            arraytext, deltatext = m.fastdelta(self._mancache[p1][1], work)
            cachedelta = self.rev(p1), deltatext
            text = util.buffer(arraytext)
            n = self.addrevision(text, transaction, link, p1, p2, cachedelta)
        else:
            # The first parent manifest isn't already loaded, so we'll
            # just encode a fulltext of the manifest and pass that
            # through to the revlog layer, and let it handle the delta
            # process.
            if self._treeondisk:
                m1 = self.read(p1)
                m2 = self.read(p2)
                n = self._addtree(m, transaction, link, m1, m2)
                arraytext = None
            else:
                text = m.text(self._usemanifestv2)
                n = self.addrevision(text, transaction, link, p1, p2)
                arraytext = array.array('c', text)

        self._mancache[n] = (m, arraytext)

        return n

    def _addtree(self, m, transaction, link, m1, m2):
        # If the manifest is unchanged compared to one parent,
        # don't write a new revision
        if m.unmodifiedsince(m1) or m.unmodifiedsince(m2):
            return m.node()
        def writesubtree(subm, subp1, subp2):
            sublog = self.dirlog(subm.dir())
            sublog.add(subm, transaction, link, subp1, subp2, None, None)
        m.writesubtrees(m1, m2, writesubtree)
        text = m.dirtext(self._usemanifestv2)
        # Double-check whether contents are unchanged to one parent
        if text == m1.dirtext(self._usemanifestv2):
            n = m1.node()
        elif text == m2.dirtext(self._usemanifestv2):
            n = m2.node()
        else:
            n = self.addrevision(text, transaction, link, m1.node(), m2.node())
        # Save nodeid so parent manifest can calculate its nodeid
        m.setnode(n)
        return n