annotate mercurial/obsolete.py @ 17774:0496d4f73cf4

obsolete: cheap detection of nullid as successors

Nullid as successors create multiple issues:

- Nullid revnum is -1, confusing algorithm that use revnum unless you add
  special handling in all of them.
- Nullid confuses "divergent" changeset detection and resolution. As you can't
  add any successors to Nullid without being in even more troubles

Fortunately, there is no good reason to use nullid as a successor. The only
sensible meaning of "succeed by nullid" is "dropped" and this meaning is already
covered by obsolescence marker with empty successors set.

However, letting some nullid successors to slip in may cause terrible damage in
such algorithm difficult to debug. So I prefer to perform and clear detection of
of such pathological changeset. We could be much smarter by cleaning up nullid
successors on the fly but it would be much for expensive. As core Mercurial does
not create any such changeset, I think it is fine to just abort when suspicious
situation is detected.

Earlier experimental version created such changesets, so there are some out
there.  The evolve extension added the necessary logic to clean up its mess.

# obsolete.py - obsolete markers handling
#
# Copyright 2012 Pierre-Yves David <[e-mail]>
#                Logilab SA        <[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.

"""Obsolete markers handling

An obsolete marker maps an old changeset to a list of new
changesets. If the list of new changesets is empty, the old changeset
is said to be "killed". Otherwise, the old changeset is being
"replaced" by the new changesets.

Obsolete markers can be used to record and distribute changeset graph
transformations performed by history rewriting operations, and help
building new tools to reconciliate conflicting rewriting actions. To
facilitate conflicts resolution, markers include various annotations
besides old and news changeset identifiers, such as creation date or
author name.


Format
------

Markers are stored in an append-only file stored in
'.hg/store/obsstore'.

The file starts with a version header:

- 1 unsigned byte: version number, starting at zero.


The header is followed by the markers. Each marker is made of:

- 1 unsigned byte: number of new changesets "R", could be zero.

- 1 unsigned 32-bits integer: metadata size "M" in bytes.

- 1 byte: a bit field. It is reserved for flags used in obsolete
  markers common operations, to avoid repeated decoding of metadata
  entries.

- 20 bytes: obsoleted changeset identifier.

- N*20 bytes: new changesets identifiers.

- M bytes: metadata as a sequence of nul-terminated strings. Each
  string contains a key and a value, separated by a color ':', without
  additional encoding. Keys cannot contain '\0' or ':' and values
  cannot contain '\0'.
"""
import struct
import util, base85, node
from i18n import _

_pack = struct.pack
_unpack = struct.unpack

_SEEK_END = 2 # os.SEEK_END was introduced in Python 2.5

# the obsolete feature is not mature enough to be enabled by default.
# you have to rely on third party extension extension to enable this.
_enabled = False

# data used for parsing and writing
_fmversion = 0
_fmfixed   = '>BIB20s'
_fmnode = '20s'
_fmfsize = struct.calcsize(_fmfixed)
_fnodesize = struct.calcsize(_fmnode)

def _readmarkers(data):
    """Read and enumerate markers from raw data"""
    off = 0
    diskversion = _unpack('>B', data[off:off + 1])[0]
    off += 1
    if diskversion != _fmversion:
        raise util.Abort(_('parsing obsolete marker: unknown version %r')
                         % diskversion)

    # Loop on markers
    l = len(data)
    while off + _fmfsize <= l:
        # read fixed part
        cur = data[off:off + _fmfsize]
        off += _fmfsize
        nbsuc, mdsize, flags, pre = _unpack(_fmfixed, cur)
        # read replacement
        sucs = ()
        if nbsuc:
            s = (_fnodesize * nbsuc)
            cur = data[off:off + s]
            sucs = _unpack(_fmnode * nbsuc, cur)
            off += s
        # read metadata
        # (metadata will be decoded on demand)
        metadata = data[off:off + mdsize]
        if len(metadata) != mdsize:
            raise util.Abort(_('parsing obsolete marker: metadata is too '
                               'short, %d bytes expected, got %d')
                             % (mdsize, len(metadata)))
        off += mdsize
        yield (pre, sucs, flags, metadata)

def encodemeta(meta):
    """Return encoded metadata string to string mapping.

    Assume no ':' in key and no '\0' in both key and value."""
    for key, value in meta.iteritems():
        if ':' in key or '\0' in key:
            raise ValueError("':' and '\0' are forbidden in metadata key'")
        if '\0' in value:
            raise ValueError("':' are forbidden in metadata value'")
    return '\0'.join(['%s:%s' % (k, meta[k]) for k in sorted(meta)])

def decodemeta(data):
    """Return string to string dictionary from encoded version."""
    d = {}
    for l in data.split('\0'):
        if l:
            key, value = l.split(':')
            d[key] = value
    return d

class marker(object):
    """Wrap obsolete marker raw data"""

    def __init__(self, repo, data):
        # the repo argument will be used to create changectx in later version
        self._repo = repo
        self._data = data
        self._decodedmeta = None

    def precnode(self):
        """Precursor changeset node identifier"""
        return self._data[0]

    def succnodes(self):
        """List of successor changesets node identifiers"""
        return self._data[1]

    def metadata(self):
        """Decoded metadata dictionary"""
        if self._decodedmeta is None:
            self._decodedmeta = decodemeta(self._data[3])
        return self._decodedmeta

    def date(self):
        """Creation date as (unixtime, offset)"""
        parts = self.metadata()['date'].split(' ')
        return (float(parts[0]), int(parts[1]))

class obsstore(object):
    """Store obsolete markers

    Markers can be accessed with two mappings:
    - precursors: old -> set(new)
    - successors: new -> set(old)
    """

    def __init__(self, sopener):
        # caches for various obsolescence related cache
        self.caches = {}
        self._all = []
        # new markers to serialize
        self.precursors = {}
        self.successors = {}
        self.sopener = sopener
        data = sopener.tryread('obsstore')
        if data:
            self._load(_readmarkers(data))

    def __iter__(self):
        return iter(self._all)

    def __nonzero__(self):
        return bool(self._all)

    def create(self, transaction, prec, succs=(), flag=0, metadata=None):
        """obsolete: add a new obsolete marker

        * ensuring it is hashable
        * check mandatory metadata
        * encode metadata
        """
        if metadata is None:
            metadata = {}
        if len(prec) != 20:
            raise ValueError(prec)
        for succ in succs:
            if len(succ) != 20:
                raise ValueError(succ)
        marker = (str(prec), tuple(succs), int(flag), encodemeta(metadata))
        self.add(transaction, [marker])

    def add(self, transaction, markers):
        """Add new markers to the store

        Take care of filtering duplicate.
        Return the number of new marker."""
        if not _enabled:
            raise util.Abort('obsolete feature is not enabled on this repo')
        new = [m for m in markers if m not in self._all]
        if new:
            f = self.sopener('obsstore', 'ab')
            try:
                # Whether the file's current position is at the begin or at
                # the end after opening a file for appending is implementation
                # defined. So we must seek to the end before calling tell(),
                # or we may get a zero offset for non-zero sized files on
                # some platforms (issue3543).
                f.seek(0, _SEEK_END)
                offset = f.tell()
                transaction.add('obsstore', offset)
                # offset == 0: new file - add the version header
                for bytes in _encodemarkers(new, offset == 0):
                    f.write(bytes)
            finally:
                # XXX: f.close() == filecache invalidation == obsstore rebuilt.
                # call 'filecacheentry.refresh()'  here
                f.close()
            self._load(new)
            # new marker *may* have changed several set. invalidate the cache.
            self.caches.clear()
        return len(new)

    def mergemarkers(self, transaction, data):
        markers = _readmarkers(data)
        self.add(transaction, markers)

    def _load(self, markers):
        for mark in markers:
            self._all.append(mark)
            pre, sucs = mark[:2]
            self.precursors.setdefault(pre, set()).add(mark)
            for suc in sucs:
                self.successors.setdefault(suc, set()).add(mark)
        if node.nullid in self.successors:
            raise util.Abort(_('bad obsolescence marker detected: '
                               'invalid successors nullid'))

def _encodemarkers(markers, addheader=False):
    # Kept separate from flushmarkers(), it will be reused for
    # markers exchange.
    if addheader:
        yield _pack('>B', _fmversion)
    for marker in markers:
        yield _encodeonemarker(marker)


def _encodeonemarker(marker):
    pre, sucs, flags, metadata = marker
    nbsuc = len(sucs)
    format = _fmfixed + (_fmnode * nbsuc)
    data = [nbsuc, len(metadata), flags, pre]
    data.extend(sucs)
    return _pack(format, *data) + metadata

# arbitrary picked to fit into 8K limit from HTTP server
# you have to take in account:
# - the version header
# - the base85 encoding
_maxpayload = 5300

def listmarkers(repo):
    """List markers over pushkey"""
    if not repo.obsstore:
        return {}
    keys = {}
    parts = []
    currentlen = _maxpayload * 2  # ensure we create a new part
    for marker in  repo.obsstore:
        nextdata = _encodeonemarker(marker)
        if (len(nextdata) + currentlen > _maxpayload):
            currentpart = []
            currentlen = 0
            parts.append(currentpart)
        currentpart.append(nextdata)
        currentlen += len(nextdata)
    for idx, part in enumerate(reversed(parts)):
        data = ''.join([_pack('>B', _fmversion)] + part)
        keys['dump%i' % idx] = base85.b85encode(data)
    return keys

def pushmarker(repo, key, old, new):
    """Push markers over pushkey"""
    if not key.startswith('dump'):
        repo.ui.warn(_('unknown key: %r') % key)
        return 0
    if old:
        repo.ui.warn(_('unexpected old value') % key)
        return 0
    data = base85.b85decode(new)
    lock = repo.lock()
    try:
        tr = repo.transaction('pushkey: obsolete markers')
        try:
            repo.obsstore.mergemarkers(tr, data)
            tr.close()
            return 1
        finally:
            tr.release()
    finally:
        lock.release()

def allmarkers(repo):
    """all obsolete markers known in a repository"""
    for markerdata in repo.obsstore:
        yield marker(repo, markerdata)

def precursormarkers(ctx):
    """obsolete marker making this changeset obsolete"""
    for data in ctx._repo.obsstore.precursors.get(ctx.node(), ()):
        yield marker(ctx._repo, data)

def successormarkers(ctx):
    """obsolete marker marking this changeset as a successors"""
    for data in ctx._repo.obsstore.successors.get(ctx.node(), ()):
        yield marker(ctx._repo, data)

def anysuccessors(obsstore, node):
    """Yield every successor of <node>

    This is a linear yield unsuited to detecting split changesets."""
    remaining = set([node])
    seen = set(remaining)
    while remaining:
        current = remaining.pop()
        yield current
        for mark in obsstore.precursors.get(current, ()):
            for suc in mark[1]:
                if suc not in seen:
                    seen.add(suc)
                    remaining.add(suc)

# mapping of 'set-name' -> <function to computer this set>
cachefuncs = {}
def cachefor(name):
    """Decorator to register a function as computing the cache for a set"""
    def decorator(func):
        assert name not in cachefuncs
        cachefuncs[name] = func
        return func
    return decorator

def getobscache(repo, name):
    """Return the set of revision that belong to the <name> set

    Such access may compute the set and cache it for future use"""
    if not repo.obsstore:
        return ()
    if name not in repo.obsstore.caches:
        repo.obsstore.caches[name] = cachefuncs[name](repo)
    return repo.obsstore.caches[name]

# To be simple we need to invalidate obsolescence cache when:
#
# - new changeset is added:
# - public phase is changed
# - obsolescence marker are added
# - strip is used a repo
def clearobscaches(repo):
    """Remove all obsolescence related cache from a repo

    This remove all cache in obsstore is the obsstore already exist on the
    repo.

    (We could be smarter here given the exact event that trigger the cache
    clearing)"""
    # only clear cache is there is obsstore data in this repo
    if 'obsstore' in repo._filecache:
        repo.obsstore.caches.clear()

@cachefor('obsolete')
def _computeobsoleteset(repo):
    """the set of obsolete revisions"""
    obs = set()
    nm = repo.changelog.nodemap
    for prec in repo.obsstore.precursors:
        rev = nm.get(prec)
        if rev is not None:
            obs.add(rev)
    return set(repo.revs('%ld - public()', obs))

@cachefor('unstable')
def _computeunstableset(repo):
    """the set of non obsolete revisions with obsolete parents"""
    return set(repo.revs('(obsolete()::) - obsolete()'))

@cachefor('suspended')
def _computesuspendedset(repo):
    """the set of obsolete parents with non obsolete descendants"""
    return set(repo.revs('obsolete() and obsolete()::unstable()'))

@cachefor('extinct')
def _computeextinctset(repo):
    """the set of obsolete parents without non obsolete descendants"""
    return set(repo.revs('obsolete() - obsolete()::unstable()'))

def createmarkers(repo, relations, flag=0, metadata=None):
    """Add obsolete markers between changesets in a repo

    <relations> must be an iterable of (<old>, (<new>, ...)) tuple.
    `old` and `news` are changectx.

    Trying to obsolete a public changeset will raise an exception.

    Current user and date are used except if specified otherwise in the
    metadata attribute.

    This function operates within a transaction of its own, but does
    not take any lock on the repo.
    """
    # prepare metadata
    if metadata is None:
        metadata = {}
    if 'date' not in metadata:
        metadata['date'] = '%i %i' % util.makedate()
    if 'user' not in metadata:
        metadata['user'] = repo.ui.username()
    tr = repo.transaction('add-obsolescence-marker')
    try:
        for prec, sucs in relations:
            if not prec.mutable():
                raise util.Abort("cannot obsolete immutable changeset: %s"
                                 % prec)
            nprec = prec.node()
            nsucs = tuple(s.node() for s in sucs)
            if nprec in nsucs:
                raise util.Abort("changeset %s cannot obsolete itself" % prec)
            repo.obsstore.create(tr, nprec, nsucs, flag, metadata)
        tr.close()
    finally:
        tr.release()