mercurial/obsolete.py

# 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.

The old obsoleted changeset is called "precursor" and possible replacements are
called "successors".  Markers that used changeset X as a precursors are called
"successor markers of X" because they hold information about the successors of
X. Markers that use changeset Y as a successors are call "precursor markers of
Y" because they hold information about the precursors of Y.

Examples:

- When changeset A is replacement by a changeset A', one marker is stored:

    (A, (A'))

- When changesets A and B are folded into a new changeset C two markers are
  stored:

    (A, (C,)) and (B, (C,))

- When changeset A is simply "pruned" from the graph, a marker in create:

    (A, ())

- When changeset A is split into B and C, a single marker are used:

    (A, (C, C))

  We use a single marker to distinct the "split" case from the "divergence"
  case. If two independants operation rewrite the same changeset A in to A' and
  A'' when have an error case: divergent rewriting. We can detect it because
  two markers will be created independently:

  (A, (B,)) and (A, (C,))

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)

### obsolescence marker flag

## bumpedfix flag
#
# When a changeset A' succeed to a changeset A which became public, we call A'
# "bumped" because it's a successors of a public changesets
#
# o    A' (bumped)
# |`:
# | o  A
# |/
# o    Z
#
# The way to solve this situation is to create a new changeset Ad as children
# of A. This changeset have the same content than A'. So the diff from A to A'
# is the same than the diff from A to Ad. Ad is marked as a successors of A'
#
# o   Ad
# |`:
# | x A'
# |'|
# o | A
# |/
# o Z
#
# But by transitivity Ad is also a successors of A. To avoid having Ad marked
# as bumped too, we add the `bumpedfix` flag to the marker. <A', (Ad,)>.
# This flag mean that the successors are an interdiff that fix the bumped
# situation, breaking the transitivity of "bumped" here.
bumpedfix = 1

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[x] -> set(markers on precursors edges of x)
    - successors[x] -> set(markers on successors edges of x)
    """

    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.successors.setdefault(pre, set()).add(mark)
            for suc in sucs:
                self.precursors.setdefault(suc, set()).add(mark)
        if node.nullid in self.precursors:
            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 marking this changeset as a successors"""
    for data in ctx._repo.obsstore.precursors.get(ctx.node(), ()):
        yield marker(ctx._repo, data)

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

def allsuccessors(obsstore, nodes, ignoreflags=0):
    """Yield node for every successor of <nodes>.

    Some successors may be unknown locally.

    This is a linear yield unsuited to detecting split changesets."""
    remaining = set(nodes)
    seen = set(remaining)
    while remaining:
        current = remaining.pop()
        yield current
        for mark in obsstore.successors.get(current, ()):
            # ignore marker flagged with with specified flag
            if mark[2] & ignoreflags:
                continue
            for suc in mark[1]:
                if suc not in seen:
                    seen.add(suc)
                    remaining.add(suc)

def _knownrevs(repo, nodes):
    """yield revision numbers of known nodes passed in parameters

    Unknown revisions are silently ignored."""
    torev = repo.changelog.nodemap.get
    for n in nodes:
        rev = torev(n)
        if rev is not None:
            yield rev

# mapping of 'set-name' -> <function to compute 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 getrevs(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 node in repo.obsstore.successors:
        rev = nm.get(node)
        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()'))


@cachefor('bumped')
def _computebumpedset(repo):
    """the set of revs trying to obsolete public revisions"""
    # get all possible bumped changesets
    tonode = repo.changelog.node
    publicnodes = (tonode(r) for r in repo.revs('public()'))
    successors = allsuccessors(repo.obsstore, publicnodes,
                               ignoreflags=bumpedfix)
    # revision public or already obsolete don't count as bumped
    query = '%ld - obsolete() - public()'
    return set(repo.revs(query, _knownrevs(repo, successors)))

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()