obsolete: introduction of obsolete markers

Markers are stored as binary records in a log structured file in
.hg/store/obsstore.

mercurial/obsolete.py

@@ -0,0 +1,175 b''
+# 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
+from mercurial import util
+from i18n import _
+
+_pack = struct.pack
+_unpack = struct.unpack
+
+
+
+# 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')
+                             % (len(metadata), mdsize))
+        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 obsstore(object):
+    """Store obsolete markers
+
+    Markers can be accessed with two mappings:
+    - precursors: old -> set(new)
+    - successors: new -> set(old)
+    """
+
+    def __init__(self):
+        self._all = []
+        # new markers to serialize
+        self._new = []
+        self.precursors = {}
+        self.successors = {}
+
+    def add(self, marker):
+        """Add a new marker to the store
+
+        This marker still needs to be written to disk"""
+        self._new.append(marker)
+        self._load(marker)
+
+    def loadmarkers(self, data):
+        """Load all markers in data, mark them as known."""
+        for marker in _readmarkers(data):
+            self._load(marker)
+
+    def flushmarkers(self, stream):
+        """Write all markers to a stream
+
+        After this operation, "new" markers are considered "known"."""
+        self._writemarkers(stream)
+        self._new[:] = []
+
+    def _load(self, marker):
+        self._all.append(marker)
+        pre, sucs = marker[:2]
+        self.precursors.setdefault(pre, set()).add(marker)
+        for suc in sucs:
+            self.successors.setdefault(suc, set()).add(marker)
+
+    def _writemarkers(self, stream):
+        # Kept separate from flushmarkers(), it will be reused for
+        # markers exchange.
+        stream.write(_pack('>B', _fmversion))
+        for marker in self._all:
+            pre, sucs, flags, metadata = marker
+            nbsuc = len(sucs)
+            format = _fmfixed + (_fmnode * nbsuc)
+            data = [nbsuc, len(metadata), flags, pre]
+            data.extend(sucs)
+            stream.write(_pack(format, *data))
+            stream.write(metadata)

mercurial/localrepo.py

@@ -7,7 +7,7 b''
 
 from node import bin, hex, nullid, nullrev, short
 from i18n import _
-import repo, changegroup, subrepo, discovery, pushkey
+import repo, changegroup, subrepo, discovery, pushkey, obsolete
 import changelog, dirstate, filelog, manifest, context, bookmarks, phases
 import lock, transaction, store, encoding
 import scmutil, util, extensions, hook, error, revset
@@ -192,6 +192,14 b' class localrepository(repo.repository):'
     def _phasecache(self):
         return phases.phasecache(self, self._phasedefaults)
 
+    @storecache('obsstore')
+    def obsstore(self):
+        store = obsolete.obsstore()
+        data = self.sopener.tryread('obsstore')
+        if data:
+            store.loadmarkers(data)
+        return store
+
     @storecache('00changelog.i')
     def changelog(self):
         c = changelog.changelog(self.sopener)
@@ -983,6 +991,16 b' class localrepository(repo.repository):'
             self.store.write()
             if '_phasecache' in vars(self):
                 self._phasecache.write()
+            if 'obsstore' in vars(self) and self.obsstore._new:
+                # XXX: transaction logic should be used here. But for
+                # now rewriting the whole file is good enough.
+                f = self.sopener('obsstore', 'wb', atomictemp=True)
+                try:
+                    self.obsstore.flushmarkers(f)
+                    f.close()
+                except: # re-raises
+                    f.discard()
+                    raise
             for k, ce in self._filecache.items():
                 if k == 'dirstate':
                     continue