revlog: split functionality related to deltas computation in a new module

The revlog module is getting big and this logic is getting more and more
advanced. Moving it to `mercurial.revlogutils.deltas` split a lot off
revlog.py and will help this logic to become less interleaved with revlog.

The code is simply moved without modification (but for namespace changes).
Refactoring and improvement will be made in later changesets.

mercurial/debugcommands.py

@@ -88,6 +88,10 b' from .utils import ('
     stringutil,
 )
 
+from .revlogutils import (
+    deltas as deltautil
+)
+
 release = lockmod.release
 
 command = registrar.command()
@@ -706,7 +710,7 b' def debugdeltachain(ui, repo, file_=None'
             largestblock = 0
             srchunks = 0
 
-            for revschunk in revlog._slicechunk(r, chain):
+            for revschunk in deltautil.slicechunk(r, chain):
                 srchunks += 1
                 blkend = start(revschunk[-1]) + length(revschunk[-1])
                 blksize = blkend - start(revschunk[0])

mercurial/revlog.py

@@ -17,7 +17,6 b' import collections'
 import contextlib
 import errno
 import hashlib
-import heapq
 import os
 import re
 import struct
@@ -39,7 +38,6 b' from .i18n import _'
 from .revlogutils.constants import (
     FLAG_GENERALDELTA,
     FLAG_INLINE_DATA,
-    LIMIT_DELTA2TEXT,
     REVIDX_DEFAULT_FLAGS,
     REVIDX_ELLIPSIS,
     REVIDX_EXTSTORED,
@@ -69,6 +67,9 b' from . import ('
     templatefilters,
     util,
 )
+from .revlogutils import (
+    deltas as deltautil,
+)
 from .utils import (
     interfaceutil,
     stringutil,
@@ -211,610 +212,6 b' def hash(text, p1, p2):'
     s.update(text)
     return s.digest()
 
-class _testrevlog(object):
-    """minimalist fake revlog to use in doctests"""
-
-    def __init__(self, data, density=0.5, mingap=0):
-        """data is an list of revision payload boundaries"""
-        self._data = data
-        self._srdensitythreshold = density
-        self._srmingapsize = mingap
-
-    def start(self, rev):
-        if rev == 0:
-            return 0
-        return self._data[rev - 1]
-
-    def end(self, rev):
-        return self._data[rev]
-
-    def length(self, rev):
-        return self.end(rev) - self.start(rev)
-
-    def __len__(self):
-        return len(self._data)
-
-def _trimchunk(revlog, revs, startidx, endidx=None):
-    """returns revs[startidx:endidx] without empty trailing revs
-
-    Doctest Setup
-    >>> revlog = _testrevlog([
-    ...  5,  #0
-    ...  10, #1
-    ...  12, #2
-    ...  12, #3 (empty)
-    ...  17, #4
-    ...  21, #5
-    ...  21, #6 (empty)
-    ... ])
-
-    Contiguous cases:
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0)
-    [0, 1, 2, 3, 4, 5]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 5)
-    [0, 1, 2, 3, 4]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 4)
-    [0, 1, 2]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 2, 4)
-    [2]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3)
-    [3, 4, 5]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3, 5)
-    [3, 4]
-
-    Discontiguous cases:
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 0)
-    [1, 3, 5]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 0, 2)
-    [1]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 1, 3)
-    [3, 5]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 1)
-    [3, 5]
-    """
-    length = revlog.length
-
-    if endidx is None:
-        endidx = len(revs)
-
-    # If we have a non-emtpy delta candidate, there are nothing to trim
-    if revs[endidx - 1] < len(revlog):
-        # Trim empty revs at the end, except the very first revision of a chain
-        while (endidx > 1
-                and endidx > startidx
-                and length(revs[endidx - 1]) == 0):
-            endidx -= 1
-
-    return revs[startidx:endidx]
-
-def _segmentspan(revlog, revs, deltainfo=None):
-    """Get the byte span of a segment of revisions
-
-    revs is a sorted array of revision numbers
-
-    >>> revlog = _testrevlog([
-    ...  5,  #0
-    ...  10, #1
-    ...  12, #2
-    ...  12, #3 (empty)
-    ...  17, #4
-    ... ])
-
-    >>> _segmentspan(revlog, [0, 1, 2, 3, 4])
-    17
-    >>> _segmentspan(revlog, [0, 4])
-    17
-    >>> _segmentspan(revlog, [3, 4])
-    5
-    >>> _segmentspan(revlog, [1, 2, 3,])
-    7
-    >>> _segmentspan(revlog, [1, 3])
-    7
-    """
-    if not revs:
-        return 0
-    if deltainfo is not None and len(revlog) <= revs[-1]:
-        if len(revs) == 1:
-            return deltainfo.deltalen
-        offset = revlog.end(len(revlog) - 1)
-        end = deltainfo.deltalen + offset
-    else:
-        end = revlog.end(revs[-1])
-    return end - revlog.start(revs[0])
-
-def _slicechunk(revlog, revs, deltainfo=None, targetsize=None):
-    """slice revs to reduce the amount of unrelated data to be read from disk.
-
-    ``revs`` is sliced into groups that should be read in one time.
-    Assume that revs are sorted.
-
-    The initial chunk is sliced until the overall density (payload/chunks-span
-    ratio) is above `revlog._srdensitythreshold`. No gap smaller than
-    `revlog._srmingapsize` is skipped.
-
-    If `targetsize` is set, no chunk larger than `targetsize` will be yield.
-    For consistency with other slicing choice, this limit won't go lower than
-    `revlog._srmingapsize`.
-
-    If individual revisions chunk are larger than this limit, they will still
-    be raised individually.
-
-    >>> revlog = _testrevlog([
-    ...  5,  #00 (5)
-    ...  10, #01 (5)
-    ...  12, #02 (2)
-    ...  12, #03 (empty)
-    ...  27, #04 (15)
-    ...  31, #05 (4)
-    ...  31, #06 (empty)
-    ...  42, #07 (11)
-    ...  47, #08 (5)
-    ...  47, #09 (empty)
-    ...  48, #10 (1)
-    ...  51, #11 (3)
-    ...  74, #12 (23)
-    ...  85, #13 (11)
-    ...  86, #14 (1)
-    ...  91, #15 (5)
-    ... ])
-
-    >>> list(_slicechunk(revlog, list(range(16))))
-    [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]]
-    >>> list(_slicechunk(revlog, [0, 15]))
-    [[0], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 15]))
-    [[0], [11], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15]))
-    [[0], [11, 13, 15]]
-    >>> list(_slicechunk(revlog, [1, 2, 3, 5, 8, 10, 11, 14]))
-    [[1, 2], [5, 8, 10, 11], [14]]
-
-    Slicing with a maximum chunk size
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15], targetsize=15))
-    [[0], [11], [13], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15], targetsize=20))
-    [[0], [11], [13, 15]]
-    """
-    if targetsize is not None:
-        targetsize = max(targetsize, revlog._srmingapsize)
-    # targetsize should not be specified when evaluating delta candidates:
-    # * targetsize is used to ensure we stay within specification when reading,
-    # * deltainfo is used to pick are good delta chain when writing.
-    if not (deltainfo is None or targetsize is None):
-        msg = 'cannot use `targetsize` with a `deltainfo`'
-        raise error.ProgrammingError(msg)
-    for chunk in _slicechunktodensity(revlog, revs,
-                                      deltainfo,
-                                      revlog._srdensitythreshold,
-                                      revlog._srmingapsize):
-        for subchunk in _slicechunktosize(revlog, chunk, targetsize):
-            yield subchunk
-
-def _slicechunktosize(revlog, revs, targetsize=None):
-    """slice revs to match the target size
-
-    This is intended to be used on chunk that density slicing selected by that
-    are still too large compared to the read garantee of revlog. This might
-    happens when "minimal gap size" interrupted the slicing or when chain are
-    built in a way that create large blocks next to each other.
-
-    >>> revlog = _testrevlog([
-    ...  3,  #0 (3)
-    ...  5,  #1 (2)
-    ...  6,  #2 (1)
-    ...  8,  #3 (2)
-    ...  8,  #4 (empty)
-    ...  11, #5 (3)
-    ...  12, #6 (1)
-    ...  13, #7 (1)
-    ...  14, #8 (1)
-    ... ])
-
-    Cases where chunk is already small enough
-    >>> list(_slicechunktosize(revlog, [0], 3))
-    [[0]]
-    >>> list(_slicechunktosize(revlog, [6, 7], 3))
-    [[6, 7]]
-    >>> list(_slicechunktosize(revlog, [0], None))
-    [[0]]
-    >>> list(_slicechunktosize(revlog, [6, 7], None))
-    [[6, 7]]
-
-    cases where we need actual slicing
-    >>> list(_slicechunktosize(revlog, [0, 1], 3))
-    [[0], [1]]
-    >>> list(_slicechunktosize(revlog, [1, 3], 3))
-    [[1], [3]]
-    >>> list(_slicechunktosize(revlog, [1, 2, 3], 3))
-    [[1, 2], [3]]
-    >>> list(_slicechunktosize(revlog, [3, 5], 3))
-    [[3], [5]]
-    >>> list(_slicechunktosize(revlog, [3, 4, 5], 3))
-    [[3], [5]]
-    >>> list(_slicechunktosize(revlog, [5, 6, 7, 8], 3))
-    [[5], [6, 7, 8]]
-    >>> list(_slicechunktosize(revlog, [0, 1, 2, 3, 4, 5, 6, 7, 8], 3))
-    [[0], [1, 2], [3], [5], [6, 7, 8]]
-
-    Case with too large individual chunk (must return valid chunk)
-    >>> list(_slicechunktosize(revlog, [0, 1], 2))
-    [[0], [1]]
-    >>> list(_slicechunktosize(revlog, [1, 3], 1))
-    [[1], [3]]
-    >>> list(_slicechunktosize(revlog, [3, 4, 5], 2))
-    [[3], [5]]
-    """
-    assert targetsize is None or 0 <= targetsize
-    if targetsize is None or _segmentspan(revlog, revs) <= targetsize:
-        yield revs
-        return
-
-    startrevidx = 0
-    startdata = revlog.start(revs[0])
-    endrevidx = 0
-    iterrevs = enumerate(revs)
-    next(iterrevs) # skip first rev.
-    for idx, r in iterrevs:
-        span = revlog.end(r) - startdata
-        if span <= targetsize:
-            endrevidx = idx
-        else:
-            chunk = _trimchunk(revlog, revs, startrevidx, endrevidx + 1)
-            if chunk:
-                yield chunk
-            startrevidx = idx
-            startdata = revlog.start(r)
-            endrevidx = idx
-    yield _trimchunk(revlog, revs, startrevidx)
-
-def _slicechunktodensity(revlog, revs, deltainfo=None, targetdensity=0.5,
-                         mingapsize=0):
-    """slice revs to reduce the amount of unrelated data to be read from disk.
-
-    ``revs`` is sliced into groups that should be read in one time.
-    Assume that revs are sorted.
-
-    ``deltainfo`` is a _deltainfo instance of a revision that we would append
-    to the top of the revlog.
-
-    The initial chunk is sliced until the overall density (payload/chunks-span
-    ratio) is above `targetdensity`. No gap smaller than `mingapsize` is
-    skipped.
-
-    >>> revlog = _testrevlog([
-    ...  5,  #00 (5)
-    ...  10, #01 (5)
-    ...  12, #02 (2)
-    ...  12, #03 (empty)
-    ...  27, #04 (15)
-    ...  31, #05 (4)
-    ...  31, #06 (empty)
-    ...  42, #07 (11)
-    ...  47, #08 (5)
-    ...  47, #09 (empty)
-    ...  48, #10 (1)
-    ...  51, #11 (3)
-    ...  74, #12 (23)
-    ...  85, #13 (11)
-    ...  86, #14 (1)
-    ...  91, #15 (5)
-    ... ])
-
-    >>> list(_slicechunktodensity(revlog, list(range(16))))
-    [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]]
-    >>> list(_slicechunktodensity(revlog, [0, 15]))
-    [[0], [15]]
-    >>> list(_slicechunktodensity(revlog, [0, 11, 15]))
-    [[0], [11], [15]]
-    >>> list(_slicechunktodensity(revlog, [0, 11, 13, 15]))
-    [[0], [11, 13, 15]]
-    >>> list(_slicechunktodensity(revlog, [1, 2, 3, 5, 8, 10, 11, 14]))
-    [[1, 2], [5, 8, 10, 11], [14]]
-    >>> list(_slicechunktodensity(revlog, [1, 2, 3, 5, 8, 10, 11, 14],
-    ...                           mingapsize=20))
-    [[1, 2, 3, 5, 8, 10, 11], [14]]
-    >>> list(_slicechunktodensity(revlog, [1, 2, 3, 5, 8, 10, 11, 14],
-    ...                           targetdensity=0.95))
-    [[1, 2], [5], [8, 10, 11], [14]]
-    >>> list(_slicechunktodensity(revlog, [1, 2, 3, 5, 8, 10, 11, 14],
-    ...                           targetdensity=0.95, mingapsize=12))
-    [[1, 2], [5, 8, 10, 11], [14]]
-    """
-    start = revlog.start
-    length = revlog.length
-
-    if len(revs) <= 1:
-        yield revs
-        return
-
-    nextrev = len(revlog)
-    nextoffset = revlog.end(nextrev - 1)
-
-    if deltainfo is None:
-        deltachainspan = _segmentspan(revlog, revs)
-        chainpayload = sum(length(r) for r in revs)
-    else:
-        deltachainspan = deltainfo.distance
-        chainpayload = deltainfo.compresseddeltalen
-
-    if deltachainspan < mingapsize:
-        yield revs
-        return
-
-    readdata = deltachainspan
-
-    if deltachainspan:
-        density = chainpayload / float(deltachainspan)
-    else:
-        density = 1.0
-
-    if density >= targetdensity:
-        yield revs
-        return
-
-    if deltainfo is not None and deltainfo.deltalen:
-        revs = list(revs)
-        revs.append(nextrev)
-
-    # Store the gaps in a heap to have them sorted by decreasing size
-    gapsheap = []
-    heapq.heapify(gapsheap)
-    prevend = None
-    for i, rev in enumerate(revs):
-        if rev < nextrev:
-            revstart = start(rev)
-            revlen = length(rev)
-        else:
-            revstart = nextoffset
-            revlen = deltainfo.deltalen
-
-        # Skip empty revisions to form larger holes
-        if revlen == 0:
-            continue
-
-        if prevend is not None:
-            gapsize = revstart - prevend
-            # only consider holes that are large enough
-            if gapsize > mingapsize:
-                heapq.heappush(gapsheap, (-gapsize, i))
-
-        prevend = revstart + revlen
-
-    # Collect the indices of the largest holes until the density is acceptable
-    indicesheap = []
-    heapq.heapify(indicesheap)
-    while gapsheap and density < targetdensity:
-        oppgapsize, gapidx = heapq.heappop(gapsheap)
-
-        heapq.heappush(indicesheap, gapidx)
-
-        # the gap sizes are stored as negatives to be sorted decreasingly
-        # by the heap
-        readdata -= (-oppgapsize)
-        if readdata > 0:
-            density = chainpayload / float(readdata)
-        else:
-            density = 1.0
-
-    # Cut the revs at collected indices
-    previdx = 0
-    while indicesheap:
-        idx = heapq.heappop(indicesheap)
-
-        chunk = _trimchunk(revlog, revs, previdx, idx)
-        if chunk:
-            yield chunk
-
-        previdx = idx
-
-    chunk = _trimchunk(revlog, revs, previdx)
-    if chunk:
-        yield chunk
-
-@attr.s(slots=True, frozen=True)
-class _deltainfo(object):
-    distance = attr.ib()
-    deltalen = attr.ib()
-    data = attr.ib()
-    base = attr.ib()
-    chainbase = attr.ib()
-    chainlen = attr.ib()
-    compresseddeltalen = attr.ib()
-    snapshotdepth = attr.ib()
-
-class _deltacomputer(object):
-    def __init__(self, revlog):
-        self.revlog = revlog
-
-    def _getcandidaterevs(self, p1, p2, cachedelta):
-        """
-        Provides revisions that present an interest to be diffed against,
-        grouped by level of easiness.
-        """
-        revlog = self.revlog
-        gdelta = revlog._generaldelta
-        curr = len(revlog)
-        prev = curr - 1
-        p1r, p2r = revlog.rev(p1), revlog.rev(p2)
-
-        # should we try to build a delta?
-        if prev != nullrev and revlog._storedeltachains:
-            tested = set()
-            # This condition is true most of the time when processing
-            # changegroup data into a generaldelta repo. The only time it
-            # isn't true is if this is the first revision in a delta chain
-            # or if ``format.generaldelta=true`` disabled ``lazydeltabase``.
-            if cachedelta and gdelta and revlog._lazydeltabase:
-                # Assume what we received from the server is a good choice
-                # build delta will reuse the cache
-                yield (cachedelta[0],)
-                tested.add(cachedelta[0])
-
-            if gdelta:
-                # exclude already lazy tested base if any
-                parents = [p for p in (p1r, p2r)
-                           if p != nullrev and p not in tested]
-
-                if not revlog._deltabothparents and len(parents) == 2:
-                    parents.sort()
-                    # To minimize the chance of having to build a fulltext,
-                    # pick first whichever parent is closest to us (max rev)
-                    yield (parents[1],)
-                    # then the other one (min rev) if the first did not fit
-                    yield (parents[0],)
-                    tested.update(parents)
-                elif len(parents) > 0:
-                    # Test all parents (1 or 2), and keep the best candidate
-                    yield parents
-                    tested.update(parents)
-
-            if prev not in tested:
-                # other approach failed try against prev to hopefully save us a
-                # fulltext.
-                yield (prev,)
-                tested.add(prev)
-
-    def buildtext(self, revinfo, fh):
-        """Builds a fulltext version of a revision
-
-        revinfo: _revisioninfo instance that contains all needed info
-        fh:      file handle to either the .i or the .d revlog file,
-                 depending on whether it is inlined or not
-        """
-        btext = revinfo.btext
-        if btext[0] is not None:
-            return btext[0]
-
-        revlog = self.revlog
-        cachedelta = revinfo.cachedelta
-        flags = revinfo.flags
-        node = revinfo.node
-
-        baserev = cachedelta[0]
-        delta = cachedelta[1]
-        # special case deltas which replace entire base; no need to decode
-        # base revision. this neatly avoids censored bases, which throw when
-        # they're decoded.
-        hlen = struct.calcsize(">lll")
-        if delta[:hlen] == mdiff.replacediffheader(revlog.rawsize(baserev),
-                                                   len(delta) - hlen):
-            btext[0] = delta[hlen:]
-        else:
-            # deltabase is rawtext before changed by flag processors, which is
-            # equivalent to non-raw text
-            basetext = revlog.revision(baserev, _df=fh, raw=False)
-            btext[0] = mdiff.patch(basetext, delta)
-
-        try:
-            res = revlog._processflags(btext[0], flags, 'read', raw=True)
-            btext[0], validatehash = res
-            if validatehash:
-                revlog.checkhash(btext[0], node, p1=revinfo.p1, p2=revinfo.p2)
-            if flags & REVIDX_ISCENSORED:
-                raise RevlogError(_('node %s is not censored') % node)
-        except CensoredNodeError:
-            # must pass the censored index flag to add censored revisions
-            if not flags & REVIDX_ISCENSORED:
-                raise
-        return btext[0]
-
-    def _builddeltadiff(self, base, revinfo, fh):
-        revlog = self.revlog
-        t = self.buildtext(revinfo, fh)
-        if revlog.iscensored(base):
-            # deltas based on a censored revision must replace the
-            # full content in one patch, so delta works everywhere
-            header = mdiff.replacediffheader(revlog.rawsize(base), len(t))
-            delta = header + t
-        else:
-            ptext = revlog.revision(base, _df=fh, raw=True)
-            delta = mdiff.textdiff(ptext, t)
-
-        return delta
-
-    def _builddeltainfo(self, revinfo, base, fh):
-        # can we use the cached delta?
-        if revinfo.cachedelta and revinfo.cachedelta[0] == base:
-            delta = revinfo.cachedelta[1]
-        else:
-            delta = self._builddeltadiff(base, revinfo, fh)
-        revlog = self.revlog
-        header, data = revlog.compress(delta)
-        deltalen = len(header) + len(data)
-        chainbase = revlog.chainbase(base)
-        offset = revlog.end(len(revlog) - 1)
-        dist = deltalen + offset - revlog.start(chainbase)
-        if revlog._generaldelta:
-            deltabase = base
-        else:
-            deltabase = chainbase
-        chainlen, compresseddeltalen = revlog._chaininfo(base)
-        chainlen += 1
-        compresseddeltalen += deltalen
-
-        revlog = self.revlog
-        snapshotdepth = None
-        if deltabase == nullrev:
-            snapshotdepth = 0
-        elif revlog._sparserevlog and revlog.issnapshot(deltabase):
-            # A delta chain should always be one full snapshot,
-            # zero or more semi-snapshots, and zero or more deltas
-            p1, p2 = revlog.rev(revinfo.p1), revlog.rev(revinfo.p2)
-            if deltabase not in (p1, p2) and revlog.issnapshot(deltabase):
-                snapshotdepth = len(revlog._deltachain(deltabase)[0])
-
-        return _deltainfo(dist, deltalen, (header, data), deltabase,
-                          chainbase, chainlen, compresseddeltalen,
-                          snapshotdepth)
-
-    def finddeltainfo(self, revinfo, fh):
-        """Find an acceptable delta against a candidate revision
-
-        revinfo: information about the revision (instance of _revisioninfo)
-        fh:      file handle to either the .i or the .d revlog file,
-                 depending on whether it is inlined or not
-
-        Returns the first acceptable candidate revision, as ordered by
-        _getcandidaterevs
-        """
-        if not revinfo.textlen:
-            return None # empty file do not need delta
-
-        cachedelta = revinfo.cachedelta
-        p1 = revinfo.p1
-        p2 = revinfo.p2
-        revlog = self.revlog
-
-        deltalength = self.revlog.length
-        deltaparent = self.revlog.deltaparent
-
-        deltainfo = None
-        deltas_limit = revinfo.textlen * LIMIT_DELTA2TEXT
-        for candidaterevs in self._getcandidaterevs(p1, p2, cachedelta):
-            # filter out delta base that will never produce good delta
-            candidaterevs = [r for r in candidaterevs
-                             if self.revlog.length(r) <= deltas_limit]
-            nominateddeltas = []
-            for candidaterev in candidaterevs:
-                # skip over empty delta (no need to include them in a chain)
-                while candidaterev != nullrev and not deltalength(candidaterev):
-                    candidaterev = deltaparent(candidaterev)
-                # no need to try a delta against nullid, this will be handled
-                # by fulltext later.
-                if candidaterev == nullrev:
-                    continue
-                # no delta for rawtext-changing revs (see "candelta" for why)
-                if revlog.flags(candidaterev) & REVIDX_RAWTEXT_CHANGING_FLAGS:
-                    continue
-                candidatedelta = self._builddeltainfo(revinfo, candidaterev, fh)
-                if revlog._isgooddeltainfo(candidatedelta, revinfo):
-                    nominateddeltas.append(candidatedelta)
-            if nominateddeltas:
-                deltainfo = min(nominateddeltas, key=lambda x: x.deltalen)
-                break
-
-        return deltainfo
-
 @attr.s(slots=True, frozen=True)
 class _revisioninfo(object):
     """Information about a revision that allows building its fulltext
@@ -2095,7 +1492,8 b' class revlog(object):'
         if not self._withsparseread:
             slicedchunks = (revs,)
         else:
-            slicedchunks = _slicechunk(self, revs, targetsize=targetsize)
+            slicedchunks = deltautil.slicechunk(self, revs,
+                                                targetsize=targetsize)
 
         for revschunk in slicedchunks:
             firstrev = revschunk[0]
@@ -2393,7 +1791,7 b' class revlog(object):'
             computed by default as hash(text, p1, p2), however subclasses might
             use different hashing method (and override checkhash() in such case)
         flags - the known flags to set on the revision
-        deltacomputer - an optional _deltacomputer instance shared between
+        deltacomputer - an optional deltacomputer instance shared between
             multiple calls
         """
         if link == nullrev:
@@ -2516,95 +1914,6 b' class revlog(object):'
 
         return compressor.decompress(data)
 
-    def _isgooddeltainfo(self, deltainfo, revinfo):
-        """Returns True if the given delta is good. Good means that it is within
-        the disk span, disk size, and chain length bounds that we know to be
-        performant."""
-        if deltainfo is None:
-            return False
-
-        # - 'deltainfo.distance' is the distance from the base revision --
-        #   bounding it limits the amount of I/O we need to do.
-        # - 'deltainfo.compresseddeltalen' is the sum of the total size of
-        #   deltas we need to apply -- bounding it limits the amount of CPU
-        #   we consume.
-
-        if self._sparserevlog:
-            # As sparse-read will be used, we can consider that the distance,
-            # instead of being the span of the whole chunk,
-            # is the span of the largest read chunk
-            base = deltainfo.base
-
-            if base != nullrev:
-                deltachain = self._deltachain(base)[0]
-            else:
-                deltachain = []
-
-            # search for the first non-snapshot revision
-            for idx, r in enumerate(deltachain):
-                if not self.issnapshot(r):
-                    break
-            deltachain = deltachain[idx:]
-            chunks = _slicechunk(self, deltachain, deltainfo)
-            all_span = [_segmentspan(self, revs, deltainfo) for revs in chunks]
-            distance = max(all_span)
-        else:
-            distance = deltainfo.distance
-
-        textlen = revinfo.textlen
-        defaultmax = textlen * 4
-        maxdist = self._maxdeltachainspan
-        if not maxdist:
-            maxdist = distance # ensure the conditional pass
-        maxdist = max(maxdist, defaultmax)
-        if self._sparserevlog and maxdist < self._srmingapsize:
-            # In multiple place, we are ignoring irrelevant data range below a
-            # certain size. Be also apply this tradeoff here and relax span
-            # constraint for small enought content.
-            maxdist = self._srmingapsize
-
-        # Bad delta from read span:
-        #
-        #   If the span of data read is larger than the maximum allowed.
-        if maxdist < distance:
-            return False
-
-        # Bad delta from new delta size:
-        #
-        #   If the delta size is larger than the target text, storing the
-        #   delta will be inefficient.
-        if textlen < deltainfo.deltalen:
-            return False
-
-        # Bad delta from cumulated payload size:
-        #
-        #   If the sum of delta get larger than K * target text length.
-        if textlen * LIMIT_DELTA2TEXT < deltainfo.compresseddeltalen:
-            return False
-
-        # Bad delta from chain length:
-        #
-        #   If the number of delta in the chain gets too high.
-        if self._maxchainlen and  self._maxchainlen < deltainfo.chainlen:
-            return False
-
-        # bad delta from intermediate snapshot size limit
-        #
-        #   If an intermediate snapshot size is higher than the limit.  The
-        #   limit exist to prevent endless chain of intermediate delta to be
-        #   created.
-        if (deltainfo.snapshotdepth is not None and
-                (textlen >> deltainfo.snapshotdepth) < deltainfo.deltalen):
-            return False
-
-        # bad delta if new intermediate snapshot is larger than the previous
-        # snapshot
-        if (deltainfo.snapshotdepth
-                and self.length(deltainfo.base) < deltainfo.deltalen):
-            return False
-
-        return True
-
     def _addrevision(self, node, rawtext, transaction, link, p1, p2, flags,
                      cachedelta, ifh, dfh, alwayscache=False,
                      deltacomputer=None):
@@ -2652,7 +1961,7 b' class revlog(object):'
             textlen = len(rawtext)
 
         if deltacomputer is None:
-            deltacomputer = _deltacomputer(self)
+            deltacomputer = deltautil.deltacomputer(self)
 
         revinfo = _revisioninfo(node, p1, p2, btext, textlen, cachedelta, flags)
 
@@ -2754,7 +2063,7 b' class revlog(object):'
                 dfh.flush()
             ifh.flush()
         try:
-            deltacomputer = _deltacomputer(self)
+            deltacomputer = deltautil.deltacomputer(self)
             # loop through our set of deltas
             for data in deltas:
                 node, p1, p2, linknode, deltabase, delta, flags = data
@@ -3127,7 +2436,7 b' class revlog(object):'
             populatecachedelta = deltareuse in (self.DELTAREUSEALWAYS,
                                                 self.DELTAREUSESAMEREVS)
 
-            deltacomputer = _deltacomputer(destrevlog)
+            deltacomputer = deltautil.deltacomputer(destrevlog)
             index = self.index
             for rev in self:
                 entry = index[rev]

mercurial/revlogutils/constants.py

@@ -41,6 +41,3 b' REVIDX_FLAGS_ORDER = ['
 REVIDX_KNOWN_FLAGS = util.bitsfrom(REVIDX_FLAGS_ORDER)
 # bitmark for flags that could cause rawdata content change
 REVIDX_RAWTEXT_CHANGING_FLAGS = REVIDX_ISCENSORED | REVIDX_EXTSTORED
-
-# maximum <delta-chain-data>/<revision-text-length> ratio
-LIMIT_DELTA2TEXT = 2

mercurial/revlogutils/deltas.py

@@ -1,215 +1,42 b''
-# revlog.py - storage back-end for mercurial
+# revlogdeltas.py - Logic around delta computation for revlog
 #
 # Copyright 2005-2007 Matt Mackall <[e-mail]>
+# Copyright 2018 Octobus <[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.
-
-"""Storage back-end for Mercurial.
-
-This provides efficient delta storage with O(1) retrieve and append
-and O(changes) merge between branches.
-"""
+"""Helper class to compute deltas stored inside revlogs"""
 
 from __future__ import absolute_import
 
-import collections
-import contextlib
-import errno
-import hashlib
 import heapq
-import os
-import re
 import struct
-import zlib
 
 # import stuff from node for others to import from revlog
-from .node import (
-    bin,
-    hex,
-    nullhex,
-    nullid,
+from ..node import (
     nullrev,
-    wdirfilenodeids,
-    wdirhex,
-    wdirid,
-    wdirrev,
 )
-from .i18n import _
-from .revlogutils.constants import (
-    FLAG_GENERALDELTA,
-    FLAG_INLINE_DATA,
-    LIMIT_DELTA2TEXT,
-    REVIDX_DEFAULT_FLAGS,
-    REVIDX_ELLIPSIS,
-    REVIDX_EXTSTORED,
-    REVIDX_FLAGS_ORDER,
+from ..i18n import _
+
+from .constants import (
     REVIDX_ISCENSORED,
-    REVIDX_KNOWN_FLAGS,
     REVIDX_RAWTEXT_CHANGING_FLAGS,
-    REVLOGV0,
-    REVLOGV1,
-    REVLOGV1_FLAGS,
-    REVLOGV2,
-    REVLOGV2_FLAGS,
-    REVLOG_DEFAULT_FLAGS,
-    REVLOG_DEFAULT_FORMAT,
-    REVLOG_DEFAULT_VERSION,
 )
-from .thirdparty import (
+
+from ..thirdparty import (
     attr,
 )
-from . import (
-    ancestor,
+
+from .. import (
     error,
     mdiff,
-    policy,
-    pycompat,
-    repository,
-    templatefilters,
-    util,
 )
-from .utils import (
-    interfaceutil,
-    stringutil,
-)
-
-# blanked usage of all the name to prevent pyflakes constraints
-# We need these name available in the module for extensions.
-REVLOGV0
-REVLOGV1
-REVLOGV2
-FLAG_INLINE_DATA
-FLAG_GENERALDELTA
-REVLOG_DEFAULT_FLAGS
-REVLOG_DEFAULT_FORMAT
-REVLOG_DEFAULT_VERSION
-REVLOGV1_FLAGS
-REVLOGV2_FLAGS
-REVIDX_ISCENSORED
-REVIDX_ELLIPSIS
-REVIDX_EXTSTORED
-REVIDX_DEFAULT_FLAGS
-REVIDX_FLAGS_ORDER
-REVIDX_KNOWN_FLAGS
-REVIDX_RAWTEXT_CHANGING_FLAGS
-
-parsers = policy.importmod(r'parsers')
-
-# Aliased for performance.
-_zlibdecompress = zlib.decompress
-
-# max size of revlog with inline data
-_maxinline = 131072
-_chunksize = 1048576
 
 RevlogError = error.RevlogError
-LookupError = error.LookupError
-AmbiguousPrefixLookupError = error.AmbiguousPrefixLookupError
 CensoredNodeError = error.CensoredNodeError
-ProgrammingError = error.ProgrammingError
-
-# Store flag processors (cf. 'addflagprocessor()' to register)
-_flagprocessors = {
-    REVIDX_ISCENSORED: None,
-}
-
-_mdre = re.compile('\1\n')
-def parsemeta(text):
-    """return (metadatadict, metadatasize)"""
-    # text can be buffer, so we can't use .startswith or .index
-    if text[:2] != '\1\n':
-        return None, None
-    s = _mdre.search(text, 2).start()
-    mtext = text[2:s]
-    meta = {}
-    for l in mtext.splitlines():
-        k, v = l.split(": ", 1)
-        meta[k] = v
-    return meta, (s + 2)
-
-def packmeta(meta, text):
-    keys = sorted(meta)
-    metatext = "".join("%s: %s\n" % (k, meta[k]) for k in keys)
-    return "\1\n%s\1\n%s" % (metatext, text)
-
-def _censoredtext(text):
-    m, offs = parsemeta(text)
-    return m and "censored" in m
-
-def addflagprocessor(flag, processor):
-    """Register a flag processor on a revision data flag.
 
-    Invariant:
-    - Flags need to be defined in REVIDX_KNOWN_FLAGS and REVIDX_FLAGS_ORDER,
-      and REVIDX_RAWTEXT_CHANGING_FLAGS if they can alter rawtext.
-    - Only one flag processor can be registered on a specific flag.
-    - flagprocessors must be 3-tuples of functions (read, write, raw) with the
-      following signatures:
-          - (read)  f(self, rawtext) -> text, bool
-          - (write) f(self, text) -> rawtext, bool
-          - (raw)   f(self, rawtext) -> bool
-      "text" is presented to the user. "rawtext" is stored in revlog data, not
-      directly visible to the user.
-      The boolean returned by these transforms is used to determine whether
-      the returned text can be used for hash integrity checking. For example,
-      if "write" returns False, then "text" is used to generate hash. If
-      "write" returns True, that basically means "rawtext" returned by "write"
-      should be used to generate hash. Usually, "write" and "read" return
-      different booleans. And "raw" returns a same boolean as "write".
-
-      Note: The 'raw' transform is used for changegroup generation and in some
-      debug commands. In this case the transform only indicates whether the
-      contents can be used for hash integrity checks.
-    """
-    if not flag & REVIDX_KNOWN_FLAGS:
-        msg = _("cannot register processor on unknown flag '%#x'.") % (flag)
-        raise ProgrammingError(msg)
-    if flag not in REVIDX_FLAGS_ORDER:
-        msg = _("flag '%#x' undefined in REVIDX_FLAGS_ORDER.") % (flag)
-        raise ProgrammingError(msg)
-    if flag in _flagprocessors:
-        msg = _("cannot register multiple processors on flag '%#x'.") % (flag)
-        raise error.Abort(msg)
-    _flagprocessors[flag] = processor
-
-def getoffset(q):
-    return int(q >> 16)
-
-def gettype(q):
-    return int(q & 0xFFFF)
-
-def offset_type(offset, type):
-    if (type & ~REVIDX_KNOWN_FLAGS) != 0:
-        raise ValueError('unknown revlog index flags')
-    return int(int(offset) << 16 | type)
-
-_nullhash = hashlib.sha1(nullid)
-
-def hash(text, p1, p2):
-    """generate a hash from the given text and its parent hashes
-
-    This hash combines both the current file contents and its history
-    in a manner that makes it easy to distinguish nodes with the same
-    content in the revision graph.
-    """
-    # As of now, if one of the parent node is null, p2 is null
-    if p2 == nullid:
-        # deep copy of a hash is faster than creating one
-        s = _nullhash.copy()
-        s.update(p1)
-    else:
-        # none of the parent nodes are nullid
-        if p1 < p2:
-            a = p1
-            b = p2
-        else:
-            a = p2
-            b = p1
-        s = hashlib.sha1(a)
-        s.update(b)
-    s.update(text)
-    return s.digest()
+# maximum <delta-chain-data>/<revision-text-length> ratio
+LIMIT_DELTA2TEXT = 2
 
 class _testrevlog(object):
     """minimalist fake revlog to use in doctests"""
@@ -234,95 +61,7 b' class _testrevlog(object):'
     def __len__(self):
         return len(self._data)
 
-def _trimchunk(revlog, revs, startidx, endidx=None):
-    """returns revs[startidx:endidx] without empty trailing revs
-
-    Doctest Setup
-    >>> revlog = _testrevlog([
-    ...  5,  #0
-    ...  10, #1
-    ...  12, #2
-    ...  12, #3 (empty)
-    ...  17, #4
-    ...  21, #5
-    ...  21, #6 (empty)
-    ... ])
-
-    Contiguous cases:
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0)
-    [0, 1, 2, 3, 4, 5]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 5)
-    [0, 1, 2, 3, 4]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 4)
-    [0, 1, 2]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 2, 4)
-    [2]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3)
-    [3, 4, 5]
-    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3, 5)
-    [3, 4]
-
-    Discontiguous cases:
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 0)
-    [1, 3, 5]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 0, 2)
-    [1]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 1, 3)
-    [3, 5]
-    >>> _trimchunk(revlog, [1, 3, 5, 6], 1)
-    [3, 5]
-    """
-    length = revlog.length
-
-    if endidx is None:
-        endidx = len(revs)
-
-    # If we have a non-emtpy delta candidate, there are nothing to trim
-    if revs[endidx - 1] < len(revlog):
-        # Trim empty revs at the end, except the very first revision of a chain
-        while (endidx > 1
-                and endidx > startidx
-                and length(revs[endidx - 1]) == 0):
-            endidx -= 1
-
-    return revs[startidx:endidx]
-
-def _segmentspan(revlog, revs, deltainfo=None):
-    """Get the byte span of a segment of revisions
-
-    revs is a sorted array of revision numbers
-
-    >>> revlog = _testrevlog([
-    ...  5,  #0
-    ...  10, #1
-    ...  12, #2
-    ...  12, #3 (empty)
-    ...  17, #4
-    ... ])
-
-    >>> _segmentspan(revlog, [0, 1, 2, 3, 4])
-    17
-    >>> _segmentspan(revlog, [0, 4])
-    17
-    >>> _segmentspan(revlog, [3, 4])
-    5
-    >>> _segmentspan(revlog, [1, 2, 3,])
-    7
-    >>> _segmentspan(revlog, [1, 3])
-    7
-    """
-    if not revs:
-        return 0
-    if deltainfo is not None and len(revlog) <= revs[-1]:
-        if len(revs) == 1:
-            return deltainfo.deltalen
-        offset = revlog.end(len(revlog) - 1)
-        end = deltainfo.deltalen + offset
-    else:
-        end = revlog.end(revs[-1])
-    return end - revlog.start(revs[0])
-
-def _slicechunk(revlog, revs, deltainfo=None, targetsize=None):
+def slicechunk(revlog, revs, deltainfo=None, targetsize=None):
     """slice revs to reduce the amount of unrelated data to be read from disk.
 
     ``revs`` is sliced into groups that should be read in one time.
@@ -358,21 +97,21 b' def _slicechunk(revlog, revs, deltainfo='
     ...  91, #15 (5)
     ... ])
 
-    >>> list(_slicechunk(revlog, list(range(16))))
+    >>> list(slicechunk(revlog, list(range(16))))
     [[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]]
-    >>> list(_slicechunk(revlog, [0, 15]))
+    >>> list(slicechunk(revlog, [0, 15]))
     [[0], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 15]))
+    >>> list(slicechunk(revlog, [0, 11, 15]))
     [[0], [11], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15]))
+    >>> list(slicechunk(revlog, [0, 11, 13, 15]))
     [[0], [11, 13, 15]]
-    >>> list(_slicechunk(revlog, [1, 2, 3, 5, 8, 10, 11, 14]))
+    >>> list(slicechunk(revlog, [1, 2, 3, 5, 8, 10, 11, 14]))
     [[1, 2], [5, 8, 10, 11], [14]]
 
     Slicing with a maximum chunk size
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15], targetsize=15))
+    >>> list(slicechunk(revlog, [0, 11, 13, 15], targetsize=15))
     [[0], [11], [13], [15]]
-    >>> list(_slicechunk(revlog, [0, 11, 13, 15], targetsize=20))
+    >>> list(slicechunk(revlog, [0, 11, 13, 15], targetsize=20))
     [[0], [11], [13, 15]]
     """
     if targetsize is not None:
@@ -445,7 +184,7 b' def _slicechunktosize(revlog, revs, targ'
     [[3], [5]]
     """
     assert targetsize is None or 0 <= targetsize
-    if targetsize is None or _segmentspan(revlog, revs) <= targetsize:
+    if targetsize is None or segmentspan(revlog, revs) <= targetsize:
         yield revs
         return
 
@@ -531,7 +270,7 b' def _slicechunktodensity(revlog, revs, d'
     nextoffset = revlog.end(nextrev - 1)
 
     if deltainfo is None:
-        deltachainspan = _segmentspan(revlog, revs)
+        deltachainspan = segmentspan(revlog, revs)
         chainpayload = sum(length(r) for r in revs)
     else:
         deltachainspan = deltainfo.distance
@@ -611,6 +350,94 b' def _slicechunktodensity(revlog, revs, d'
     if chunk:
         yield chunk
 
+def _trimchunk(revlog, revs, startidx, endidx=None):
+    """returns revs[startidx:endidx] without empty trailing revs
+
+    Doctest Setup
+    >>> revlog = _testrevlog([
+    ...  5,  #0
+    ...  10, #1
+    ...  12, #2
+    ...  12, #3 (empty)
+    ...  17, #4
+    ...  21, #5
+    ...  21, #6 (empty)
+    ... ])
+
+    Contiguous cases:
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0)
+    [0, 1, 2, 3, 4, 5]
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 5)
+    [0, 1, 2, 3, 4]
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 0, 4)
+    [0, 1, 2]
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 2, 4)
+    [2]
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3)
+    [3, 4, 5]
+    >>> _trimchunk(revlog, [0, 1, 2, 3, 4, 5, 6], 3, 5)
+    [3, 4]
+
+    Discontiguous cases:
+    >>> _trimchunk(revlog, [1, 3, 5, 6], 0)
+    [1, 3, 5]
+    >>> _trimchunk(revlog, [1, 3, 5, 6], 0, 2)
+    [1]
+    >>> _trimchunk(revlog, [1, 3, 5, 6], 1, 3)
+    [3, 5]
+    >>> _trimchunk(revlog, [1, 3, 5, 6], 1)
+    [3, 5]
+    """
+    length = revlog.length
+
+    if endidx is None:
+        endidx = len(revs)
+
+    # If we have a non-emtpy delta candidate, there are nothing to trim
+    if revs[endidx - 1] < len(revlog):
+        # Trim empty revs at the end, except the very first revision of a chain
+        while (endidx > 1
+                and endidx > startidx
+                and length(revs[endidx - 1]) == 0):
+            endidx -= 1
+
+    return revs[startidx:endidx]
+
+def segmentspan(revlog, revs, deltainfo=None):
+    """Get the byte span of a segment of revisions
+
+    revs is a sorted array of revision numbers
+
+    >>> revlog = _testrevlog([
+    ...  5,  #0
+    ...  10, #1
+    ...  12, #2
+    ...  12, #3 (empty)
+    ...  17, #4
+    ... ])
+
+    >>> segmentspan(revlog, [0, 1, 2, 3, 4])
+    17
+    >>> segmentspan(revlog, [0, 4])
+    17
+    >>> segmentspan(revlog, [3, 4])
+    5
+    >>> segmentspan(revlog, [1, 2, 3,])
+    7
+    >>> segmentspan(revlog, [1, 3])
+    7
+    """
+    if not revs:
+        return 0
+    if deltainfo is not None and len(revlog) <= revs[-1]:
+        if len(revs) == 1:
+            return deltainfo.deltalen
+        offset = revlog.end(len(revlog) - 1)
+        end = deltainfo.deltalen + offset
+    else:
+        end = revlog.end(revs[-1])
+    return end - revlog.start(revs[0])
+
 @attr.s(slots=True, frozen=True)
 class _deltainfo(object):
     distance = attr.ib()
@@ -622,7 +449,98 b' class _deltainfo(object):'
     compresseddeltalen = attr.ib()
     snapshotdepth = attr.ib()
 
-class _deltacomputer(object):
+def isgooddeltainfo(revlog, deltainfo, revinfo):
+    """Returns True if the given delta is good. Good means that it is within
+    the disk span, disk size, and chain length bounds that we know to be
+    performant."""
+    if deltainfo is None:
+        return False
+
+    # - 'deltainfo.distance' is the distance from the base revision --
+    #   bounding it limits the amount of I/O we need to do.
+    # - 'deltainfo.compresseddeltalen' is the sum of the total size of
+    #   deltas we need to apply -- bounding it limits the amount of CPU
+    #   we consume.
+
+    if revlog._sparserevlog:
+        # As sparse-read will be used, we can consider that the distance,
+        # instead of being the span of the whole chunk,
+        # is the span of the largest read chunk
+        base = deltainfo.base
+
+        if base != nullrev:
+            deltachain = revlog._deltachain(base)[0]
+        else:
+            deltachain = []
+
+        # search for the first non-snapshot revision
+        for idx, r in enumerate(deltachain):
+            if not revlog.issnapshot(r):
+                break
+        deltachain = deltachain[idx:]
+        chunks = slicechunk(revlog, deltachain, deltainfo)
+        all_span = [segmentspan(revlog, revs, deltainfo)
+                    for revs in chunks]
+        distance = max(all_span)
+    else:
+        distance = deltainfo.distance
+
+    textlen = revinfo.textlen
+    defaultmax = textlen * 4
+    maxdist = revlog._maxdeltachainspan
+    if not maxdist:
+        maxdist = distance # ensure the conditional pass
+    maxdist = max(maxdist, defaultmax)
+    if revlog._sparserevlog and maxdist < revlog._srmingapsize:
+        # In multiple place, we are ignoring irrelevant data range below a
+        # certain size. Be also apply this tradeoff here and relax span
+        # constraint for small enought content.
+        maxdist = revlog._srmingapsize
+
+    # Bad delta from read span:
+    #
+    #   If the span of data read is larger than the maximum allowed.
+    if maxdist < distance:
+        return False
+
+    # Bad delta from new delta size:
+    #
+    #   If the delta size is larger than the target text, storing the
+    #   delta will be inefficient.
+    if textlen < deltainfo.deltalen:
+        return False
+
+    # Bad delta from cumulated payload size:
+    #
+    #   If the sum of delta get larger than K * target text length.
+    if textlen * LIMIT_DELTA2TEXT < deltainfo.compresseddeltalen:
+        return False
+
+    # Bad delta from chain length:
+    #
+    #   If the number of delta in the chain gets too high.
+    if (revlog._maxchainlen
+            and revlog._maxchainlen < deltainfo.chainlen):
+        return False
+
+    # bad delta from intermediate snapshot size limit
+    #
+    #   If an intermediate snapshot size is higher than the limit.  The
+    #   limit exist to prevent endless chain of intermediate delta to be
+    #   created.
+    if (deltainfo.snapshotdepth is not None and
+            (textlen >> deltainfo.snapshotdepth) < deltainfo.deltalen):
+        return False
+
+    # bad delta if new intermediate snapshot is larger than the previous
+    # snapshot
+    if (deltainfo.snapshotdepth
+            and revlog.length(deltainfo.base) < deltainfo.deltalen):
+        return False
+
+    return True
+
+class deltacomputer(object):
     def __init__(self, revlog):
         self.revlog = revlog
 
@@ -807,2374 +725,10 b' class _deltacomputer(object):'
                 if revlog.flags(candidaterev) & REVIDX_RAWTEXT_CHANGING_FLAGS:
                     continue
                 candidatedelta = self._builddeltainfo(revinfo, candidaterev, fh)
-                if revlog._isgooddeltainfo(candidatedelta, revinfo):
+                if isgooddeltainfo(self.revlog, candidatedelta, revinfo):
                     nominateddeltas.append(candidatedelta)
             if nominateddeltas:
                 deltainfo = min(nominateddeltas, key=lambda x: x.deltalen)
                 break
 
         return deltainfo
-
-@attr.s(slots=True, frozen=True)
-class _revisioninfo(object):
-    """Information about a revision that allows building its fulltext
-    node:       expected hash of the revision
-    p1, p2:     parent revs of the revision
-    btext:      built text cache consisting of a one-element list
-    cachedelta: (baserev, uncompressed_delta) or None
-    flags:      flags associated to the revision storage
-
-    One of btext[0] or cachedelta must be set.
-    """
-    node = attr.ib()
-    p1 = attr.ib()
-    p2 = attr.ib()
-    btext = attr.ib()
-    textlen = attr.ib()
-    cachedelta = attr.ib()
-    flags = attr.ib()
-
[e-mail](repository.irevisiondelta)
-@attr.s(slots=True, frozen=True)
-class revlogrevisiondelta(object):
-    node = attr.ib()
-    p1node = attr.ib()
-    p2node = attr.ib()
-    basenode = attr.ib()
-    linknode = attr.ib()
-    flags = attr.ib()
-    baserevisionsize = attr.ib()
-    revision = attr.ib()
-    delta = attr.ib()
-
-# index v0:
-#  4 bytes: offset
-#  4 bytes: compressed length
-#  4 bytes: base rev
-#  4 bytes: link rev
-# 20 bytes: parent 1 nodeid
-# 20 bytes: parent 2 nodeid
-# 20 bytes: nodeid
-indexformatv0 = struct.Struct(">4l20s20s20s")
-indexformatv0_pack = indexformatv0.pack
-indexformatv0_unpack = indexformatv0.unpack
-
-class revlogoldindex(list):
-    def __getitem__(self, i):
-        if i == -1:
-            return (0, 0, 0, -1, -1, -1, -1, nullid)
-        return list.__getitem__(self, i)
-
-class revlogoldio(object):
-    def __init__(self):
-        self.size = indexformatv0.size
-
-    def parseindex(self, data, inline):
-        s = self.size
-        index = []
-        nodemap = {nullid: nullrev}
-        n = off = 0
-        l = len(data)
-        while off + s <= l:
-            cur = data[off:off + s]
-            off += s
-            e = indexformatv0_unpack(cur)
-            # transform to revlogv1 format
-            e2 = (offset_type(e[0], 0), e[1], -1, e[2], e[3],
-                  nodemap.get(e[4], nullrev), nodemap.get(e[5], nullrev), e[6])
-            index.append(e2)
-            nodemap[e[6]] = n
-            n += 1
-
-        return revlogoldindex(index), nodemap, None
-
-    def packentry(self, entry, node, version, rev):
-        if gettype(entry[0]):
-            raise RevlogError(_('index entry flags need revlog version 1'))
-        e2 = (getoffset(entry[0]), entry[1], entry[3], entry[4],
-              node(entry[5]), node(entry[6]), entry[7])
-        return indexformatv0_pack(*e2)
-
-# index ng:
-#  6 bytes: offset
-#  2 bytes: flags
-#  4 bytes: compressed length
-#  4 bytes: uncompressed length
-#  4 bytes: base rev
-#  4 bytes: link rev
-#  4 bytes: parent 1 rev
-#  4 bytes: parent 2 rev
-# 32 bytes: nodeid
-indexformatng = struct.Struct(">Qiiiiii20s12x")
-indexformatng_pack = indexformatng.pack
-versionformat = struct.Struct(">I")
-versionformat_pack = versionformat.pack
-versionformat_unpack = versionformat.unpack
-
-# corresponds to uncompressed length of indexformatng (2 gigs, 4-byte
-# signed integer)
-_maxentrysize = 0x7fffffff
-
-class revlogio(object):
-    def __init__(self):
-        self.size = indexformatng.size
-
-    def parseindex(self, data, inline):
-        # call the C implementation to parse the index data
-        index, cache = parsers.parse_index2(data, inline)
-        return index, getattr(index, 'nodemap', None), cache
-
-    def packentry(self, entry, node, version, rev):
-        p = indexformatng_pack(*entry)
-        if rev == 0:
-            p = versionformat_pack(version) + p[4:]
-        return p
-
-class revlog(object):
-    """
-    the underlying revision storage object
-
-    A revlog consists of two parts, an index and the revision data.
-
-    The index is a file with a fixed record size containing
-    information on each revision, including its nodeid (hash), the
-    nodeids of its parents, the position and offset of its data within
-    the data file, and the revision it's based on. Finally, each entry
-    contains a linkrev entry that can serve as a pointer to external
-    data.
-
-    The revision data itself is a linear collection of data chunks.
-    Each chunk represents a revision and is usually represented as a
-    delta against the previous chunk. To bound lookup time, runs of
-    deltas are limited to about 2 times the length of the original
-    version data. This makes retrieval of a version proportional to
-    its size, or O(1) relative to the number of revisions.
-
-    Both pieces of the revlog are written to in an append-only
-    fashion, which means we never need to rewrite a file to insert or
-    remove data, and can use some simple techniques to avoid the need
-    for locking while reading.
-
-    If checkambig, indexfile is opened with checkambig=True at
-    writing, to avoid file stat ambiguity.
-
-    If mmaplargeindex is True, and an mmapindexthreshold is set, the
-    index will be mmapped rather than read if it is larger than the
-    configured threshold.
-
-    If censorable is True, the revlog can have censored revisions.
-    """
-    def __init__(self, opener, indexfile, datafile=None, checkambig=False,
-                 mmaplargeindex=False, censorable=False):
-        """
-        create a revlog object
-
-        opener is a function that abstracts the file opening operation
-        and can be used to implement COW semantics or the like.
-        """
-        self.indexfile = indexfile
-        self.datafile = datafile or (indexfile[:-2] + ".d")
-        self.opener = opener
-        #  When True, indexfile is opened with checkambig=True at writing, to
-        #  avoid file stat ambiguity.
-        self._checkambig = checkambig
-        self._censorable = censorable
-        # 3-tuple of (node, rev, text) for a raw revision.
-        self._cache = None
-        # Maps rev to chain base rev.
-        self._chainbasecache = util.lrucachedict(100)
-        # 2-tuple of (offset, data) of raw data from the revlog at an offset.
-        self._chunkcache = (0, '')
-        # How much data to read and cache into the raw revlog data cache.
-        self._chunkcachesize = 65536
-        self._maxchainlen = None
-        self._deltabothparents = True
-        self.index = []
-        # Mapping of partial identifiers to full nodes.
-        self._pcache = {}
-        # Mapping of revision integer to full node.
-        self._nodecache = {nullid: nullrev}
-        self._nodepos = None
-        self._compengine = 'zlib'
-        self._maxdeltachainspan = -1
-        self._withsparseread = False
-        self._sparserevlog = False
-        self._srdensitythreshold = 0.50
-        self._srmingapsize = 262144
-
-        mmapindexthreshold = None
-        v = REVLOG_DEFAULT_VERSION
-        opts = getattr(opener, 'options', None)
-        if opts is not None:
-            if 'revlogv2' in opts:
-                # version 2 revlogs always use generaldelta.
-                v = REVLOGV2 | FLAG_GENERALDELTA | FLAG_INLINE_DATA
-            elif 'revlogv1' in opts:
-                if 'generaldelta' in opts:
-                    v |= FLAG_GENERALDELTA
-            else:
-                v = 0
-            if 'chunkcachesize' in opts:
-                self._chunkcachesize = opts['chunkcachesize']
-            if 'maxchainlen' in opts:
-                self._maxchainlen = opts['maxchainlen']
-            if 'deltabothparents' in opts:
-                self._deltabothparents = opts['deltabothparents']
-            self._lazydeltabase = bool(opts.get('lazydeltabase', False))
-            if 'compengine' in opts:
-                self._compengine = opts['compengine']
-            if 'maxdeltachainspan' in opts:
-                self._maxdeltachainspan = opts['maxdeltachainspan']
-            if mmaplargeindex and 'mmapindexthreshold' in opts:
-                mmapindexthreshold = opts['mmapindexthreshold']
-            self._sparserevlog = bool(opts.get('sparse-revlog', False))
-            withsparseread = bool(opts.get('with-sparse-read', False))
-            # sparse-revlog forces sparse-read
-            self._withsparseread = self._sparserevlog or withsparseread
-            if 'sparse-read-density-threshold' in opts:
-                self._srdensitythreshold = opts['sparse-read-density-threshold']
-            if 'sparse-read-min-gap-size' in opts:
-                self._srmingapsize = opts['sparse-read-min-gap-size']
-
-        if self._chunkcachesize <= 0:
-            raise RevlogError(_('revlog chunk cache size %r is not greater '
-                                'than 0') % self._chunkcachesize)
-        elif self._chunkcachesize & (self._chunkcachesize - 1):
-            raise RevlogError(_('revlog chunk cache size %r is not a power '
-                                'of 2') % self._chunkcachesize)
-
-        indexdata = ''
-        self._initempty = True
-        try:
-            with self._indexfp() as f:
-                if (mmapindexthreshold is not None and
-                        self.opener.fstat(f).st_size >= mmapindexthreshold):
-                    indexdata = util.buffer(util.mmapread(f))
-                else:
-                    indexdata = f.read()
-            if len(indexdata) > 0:
-                v = versionformat_unpack(indexdata[:4])[0]
-                self._initempty = False
-        except IOError as inst:
-            if inst.errno != errno.ENOENT:
-                raise
-
-        self.version = v
-        self._inline = v & FLAG_INLINE_DATA
-        self._generaldelta = v & FLAG_GENERALDELTA
-        flags = v & ~0xFFFF
-        fmt = v & 0xFFFF
-        if fmt == REVLOGV0:
-            if flags:
-                raise RevlogError(_('unknown flags (%#04x) in version %d '
-                                    'revlog %s') %
-                                  (flags >> 16, fmt, self.indexfile))
-        elif fmt == REVLOGV1:
-            if flags & ~REVLOGV1_FLAGS:
-                raise RevlogError(_('unknown flags (%#04x) in version %d '
-                                    'revlog %s') %
-                                  (flags >> 16, fmt, self.indexfile))
-        elif fmt == REVLOGV2:
-            if flags & ~REVLOGV2_FLAGS:
-                raise RevlogError(_('unknown flags (%#04x) in version %d '
-                                    'revlog %s') %
-                                  (flags >> 16, fmt, self.indexfile))
-        else:
-            raise RevlogError(_('unknown version (%d) in revlog %s') %
-                              (fmt, self.indexfile))
-
-        self._storedeltachains = True
-
-        self._io = revlogio()
-        if self.version == REVLOGV0:
-            self._io = revlogoldio()
-        try:
-            d = self._io.parseindex(indexdata, self._inline)
-        except (ValueError, IndexError):
-            raise RevlogError(_("index %s is corrupted") % (self.indexfile))
-        self.index, nodemap, self._chunkcache = d
-        if nodemap is not None:
-            self.nodemap = self._nodecache = nodemap
-        if not self._chunkcache:
-            self._chunkclear()
-        # revnum -> (chain-length, sum-delta-length)
-        self._chaininfocache = {}
-        # revlog header -> revlog compressor
-        self._decompressors = {}
-
-    @util.propertycache
-    def _compressor(self):
-        return util.compengines[self._compengine].revlogcompressor()
-
-    def _indexfp(self, mode='r'):
-        """file object for the revlog's index file"""
-        args = {r'mode': mode}
-        if mode != 'r':
-            args[r'checkambig'] = self._checkambig
-        if mode == 'w':
-            args[r'atomictemp'] = True
-        return self.opener(self.indexfile, **args)
-
-    def _datafp(self, mode='r'):
-        """file object for the revlog's data file"""
-        return self.opener(self.datafile, mode=mode)
-
-    @contextlib.contextmanager
-    def _datareadfp(self, existingfp=None):
-        """file object suitable to read data"""
-        if existingfp is not None:
-            yield existingfp
-        else:
-            if self._inline:
-                func = self._indexfp
-            else:
-                func = self._datafp
-            with func() as fp:
-                yield fp
-
-    def tip(self):
-        return self.node(len(self.index) - 1)
-    def __contains__(self, rev):
-        return 0 <= rev < len(self)
-    def __len__(self):
-        return len(self.index)
-    def __iter__(self):
-        return iter(pycompat.xrange(len(self)))
-    def revs(self, start=0, stop=None):
-        """iterate over all rev in this revlog (from start to stop)"""
-        step = 1
-        length = len(self)
-        if stop is not None:
-            if start > stop:
-                step = -1
-            stop += step
-            if stop > length:
-                stop = length
-        else:
-            stop = length
-        return pycompat.xrange(start, stop, step)
-
-    @util.propertycache
-    def nodemap(self):
-        if self.index:
-            # populate mapping down to the initial node
-            node0 = self.index[0][7]  # get around changelog filtering
-            self.rev(node0)
-        return self._nodecache
-
-    def hasnode(self, node):
-        try:
-            self.rev(node)
-            return True
-        except KeyError:
-            return False
-
-    def candelta(self, baserev, rev):
-        """whether two revisions (baserev, rev) can be delta-ed or not"""
-        # Disable delta if either rev requires a content-changing flag
-        # processor (ex. LFS). This is because such flag processor can alter
-        # the rawtext content that the delta will be based on, and two clients
-        # could have a same revlog node with different flags (i.e. different
-        # rawtext contents) and the delta could be incompatible.
-        if ((self.flags(baserev) & REVIDX_RAWTEXT_CHANGING_FLAGS)
-            or (self.flags(rev) & REVIDX_RAWTEXT_CHANGING_FLAGS)):
-            return False
-        return True
-
-    def clearcaches(self):
-        self._cache = None
-        self._chainbasecache.clear()
-        self._chunkcache = (0, '')
-        self._pcache = {}
-
-        try:
-            self._nodecache.clearcaches()
-        except AttributeError:
-            self._nodecache = {nullid: nullrev}
-            self._nodepos = None
-
-    def rev(self, node):
-        try:
-            return self._nodecache[node]
-        except TypeError:
-            raise
-        except RevlogError:
-            # parsers.c radix tree lookup failed
-            if node == wdirid or node in wdirfilenodeids:
-                raise error.WdirUnsupported
-            raise LookupError(node, self.indexfile, _('no node'))
-        except KeyError:
-            # pure python cache lookup failed
-            n = self._nodecache
-            i = self.index
-            p = self._nodepos
-            if p is None:
-                p = len(i) - 1
-            else:
-                assert p < len(i)
-            for r in pycompat.xrange(p, -1, -1):
-                v = i[r][7]
-                n[v] = r
-                if v == node:
-                    self._nodepos = r - 1
-                    return r
-            if node == wdirid or node in wdirfilenodeids:
-                raise error.WdirUnsupported
-            raise LookupError(node, self.indexfile, _('no node'))
-
-    # Accessors for index entries.
-
-    # First tuple entry is 8 bytes. First 6 bytes are offset. Last 2 bytes
-    # are flags.
-    def start(self, rev):
-        return int(self.index[rev][0] >> 16)
-
-    def flags(self, rev):
-        return self.index[rev][0] & 0xFFFF
-
-    def length(self, rev):
-        return self.index[rev][1]
-
-    def rawsize(self, rev):
-        """return the length of the uncompressed text for a given revision"""
-        l = self.index[rev][2]
-        if l >= 0:
-            return l
-
-        t = self.revision(rev, raw=True)
-        return len(t)
-
-    def size(self, rev):
-        """length of non-raw text (processed by a "read" flag processor)"""
-        # fast path: if no "read" flag processor could change the content,
-        # size is rawsize. note: ELLIPSIS is known to not change the content.
-        flags = self.flags(rev)
-        if flags & (REVIDX_KNOWN_FLAGS ^ REVIDX_ELLIPSIS) == 0:
-            return self.rawsize(rev)
-
-        return len(self.revision(rev, raw=False))
-
-    def chainbase(self, rev):
-        base = self._chainbasecache.get(rev)
-        if base is not None:
-            return base
-
-        index = self.index
-        iterrev = rev
-        base = index[iterrev][3]
-        while base != iterrev:
-            iterrev = base
-            base = index[iterrev][3]
-
-        self._chainbasecache[rev] = base
-        return base
-
-    def linkrev(self, rev):
-        return self.index[rev][4]
-
-    def parentrevs(self, rev):
-        try:
-            entry = self.index[rev]
-        except IndexError:
-            if rev == wdirrev:
-                raise error.WdirUnsupported
-            raise
-
-        return entry[5], entry[6]
-
-    def node(self, rev):
-        try:
-            return self.index[rev][7]
-        except IndexError:
-            if rev == wdirrev:
-                raise error.WdirUnsupported
-            raise
-
-    # Derived from index values.
-
-    def end(self, rev):
-        return self.start(rev) + self.length(rev)
-
-    def parents(self, node):
-        i = self.index
-        d = i[self.rev(node)]
-        return i[d[5]][7], i[d[6]][7] # map revisions to nodes inline
-
-    def chainlen(self, rev):
-        return self._chaininfo(rev)[0]
-
-    def _chaininfo(self, rev):
-        chaininfocache = self._chaininfocache
-        if rev in chaininfocache:
-            return chaininfocache[rev]
-        index = self.index
-        generaldelta = self._generaldelta
-        iterrev = rev
-        e = index[iterrev]
-        clen = 0
-        compresseddeltalen = 0
-        while iterrev != e[3]:
-            clen += 1
-            compresseddeltalen += e[1]
-            if generaldelta:
-                iterrev = e[3]
-            else:
-                iterrev -= 1
-            if iterrev in chaininfocache:
-                t = chaininfocache[iterrev]
-                clen += t[0]
-                compresseddeltalen += t[1]
-                break
-            e = index[iterrev]
-        else:
-            # Add text length of base since decompressing that also takes
-            # work. For cache hits the length is already included.
-            compresseddeltalen += e[1]
-        r = (clen, compresseddeltalen)
-        chaininfocache[rev] = r
-        return r
-
-    def _deltachain(self, rev, stoprev=None):
-        """Obtain the delta chain for a revision.
-
-        ``stoprev`` specifies a revision to stop at. If not specified, we
-        stop at the base of the chain.
-
-        Returns a 2-tuple of (chain, stopped) where ``chain`` is a list of
-        revs in ascending order and ``stopped`` is a bool indicating whether
-        ``stoprev`` was hit.
-        """
-        # Try C implementation.
-        try:
-            return self.index.deltachain(rev, stoprev, self._generaldelta)
-        except AttributeError:
-            pass
-
-        chain = []
-
-        # Alias to prevent attribute lookup in tight loop.
-        index = self.index
-        generaldelta = self._generaldelta
-
-        iterrev = rev
-        e = index[iterrev]
-        while iterrev != e[3] and iterrev != stoprev:
-            chain.append(iterrev)
-            if generaldelta:
-                iterrev = e[3]
-            else:
-                iterrev -= 1
-            e = index[iterrev]
-
-        if iterrev == stoprev:
-            stopped = True
-        else:
-            chain.append(iterrev)
-            stopped = False
-
-        chain.reverse()
-        return chain, stopped
-
-    def ancestors(self, revs, stoprev=0, inclusive=False):
-        """Generate the ancestors of 'revs' in reverse topological order.
-        Does not generate revs lower than stoprev.
-
-        See the documentation for ancestor.lazyancestors for more details."""
-
-        return ancestor.lazyancestors(self.parentrevs, revs, stoprev=stoprev,
-                                      inclusive=inclusive)
-
-    def descendants(self, revs):
-        """Generate the descendants of 'revs' in revision order.
-
-        Yield a sequence of revision numbers starting with a child of
-        some rev in revs, i.e., each revision is *not* considered a
-        descendant of itself.  Results are ordered by revision number (a
-        topological sort)."""
-        first = min(revs)
-        if first == nullrev:
-            for i in self:
-                yield i
-            return
-
-        seen = set(revs)
-        for i in self.revs(start=first + 1):
-            for x in self.parentrevs(i):
-                if x != nullrev and x in seen:
-                    seen.add(i)
-                    yield i
-                    break
-
-    def findcommonmissing(self, common=None, heads=None):
-        """Return a tuple of the ancestors of common and the ancestors of heads
-        that are not ancestors of common. In revset terminology, we return the
-        tuple:
-
-          ::common, (::heads) - (::common)
-
-        The list is sorted by revision number, meaning it is
-        topologically sorted.
-
-        'heads' and 'common' are both lists of node IDs.  If heads is
-        not supplied, uses all of the revlog's heads.  If common is not
-        supplied, uses nullid."""
-        if common is None:
-            common = [nullid]
-        if heads is None:
-            heads = self.heads()
-
-        common = [self.rev(n) for n in common]
-        heads = [self.rev(n) for n in heads]
-
-        # we want the ancestors, but inclusive
-        class lazyset(object):
-            def __init__(self, lazyvalues):
-                self.addedvalues = set()
-                self.lazyvalues = lazyvalues
-
-            def __contains__(self, value):
-                return value in self.addedvalues or value in self.lazyvalues
-
-            def __iter__(self):
-                added = self.addedvalues
-                for r in added:
-                    yield r
-                for r in self.lazyvalues:
-                    if not r in added:
-                        yield r
-
-            def add(self, value):
-                self.addedvalues.add(value)
-
-            def update(self, values):
-                self.addedvalues.update(values)
-
-        has = lazyset(self.ancestors(common))
-        has.add(nullrev)
-        has.update(common)
-
-        # take all ancestors from heads that aren't in has
-        missing = set()
-        visit = collections.deque(r for r in heads if r not in has)
-        while visit:
-            r = visit.popleft()
-            if r in missing:
-                continue
-            else:
-                missing.add(r)
-                for p in self.parentrevs(r):
-                    if p not in has:
-                        visit.append(p)
-        missing = list(missing)
-        missing.sort()
-        return has, [self.node(miss) for miss in missing]
-
-    def incrementalmissingrevs(self, common=None):
-        """Return an object that can be used to incrementally compute the
-        revision numbers of the ancestors of arbitrary sets that are not
-        ancestors of common. This is an ancestor.incrementalmissingancestors
-        object.
-
-        'common' is a list of revision numbers. If common is not supplied, uses
-        nullrev.
-        """
-        if common is None:
-            common = [nullrev]
-
-        return ancestor.incrementalmissingancestors(self.parentrevs, common)
-
-    def findmissingrevs(self, common=None, heads=None):
-        """Return the revision numbers of the ancestors of heads that
-        are not ancestors of common.
-
-        More specifically, return a list of revision numbers corresponding to
-        nodes N such that every N satisfies the following constraints:
-
-          1. N is an ancestor of some node in 'heads'
-          2. N is not an ancestor of any node in 'common'
-
-        The list is sorted by revision number, meaning it is
-        topologically sorted.
-
-        'heads' and 'common' are both lists of revision numbers.  If heads is
-        not supplied, uses all of the revlog's heads.  If common is not
-        supplied, uses nullid."""
-        if common is None:
-            common = [nullrev]
-        if heads is None:
-            heads = self.headrevs()
-
-        inc = self.incrementalmissingrevs(common=common)
-        return inc.missingancestors(heads)
-
-    def findmissing(self, common=None, heads=None):
-        """Return the ancestors of heads that are not ancestors of common.
-
-        More specifically, return a list of nodes N such that every N
-        satisfies the following constraints:
-
-          1. N is an ancestor of some node in 'heads'
-          2. N is not an ancestor of any node in 'common'
-
-        The list is sorted by revision number, meaning it is
-        topologically sorted.
-
-        'heads' and 'common' are both lists of node IDs.  If heads is
-        not supplied, uses all of the revlog's heads.  If common is not
-        supplied, uses nullid."""
-        if common is None:
-            common = [nullid]
-        if heads is None:
-            heads = self.heads()
-
-        common = [self.rev(n) for n in common]
-        heads = [self.rev(n) for n in heads]
-
-        inc = self.incrementalmissingrevs(common=common)
-        return [self.node(r) for r in inc.missingancestors(heads)]
-
-    def nodesbetween(self, roots=None, heads=None):
-        """Return a topological path from 'roots' to 'heads'.
-
-        Return a tuple (nodes, outroots, outheads) where 'nodes' is a
-        topologically sorted list of all nodes N that satisfy both of
-        these constraints:
-
-          1. N is a descendant of some node in 'roots'
-          2. N is an ancestor of some node in 'heads'
-
-        Every node is considered to be both a descendant and an ancestor
-        of itself, so every reachable node in 'roots' and 'heads' will be
-        included in 'nodes'.
-
-        'outroots' is the list of reachable nodes in 'roots', i.e., the
-        subset of 'roots' that is returned in 'nodes'.  Likewise,
-        'outheads' is the subset of 'heads' that is also in 'nodes'.
-
-        'roots' and 'heads' are both lists of node IDs.  If 'roots' is
-        unspecified, uses nullid as the only root.  If 'heads' is
-        unspecified, uses list of all of the revlog's heads."""
-        nonodes = ([], [], [])
-        if roots is not None:
-            roots = list(roots)
-            if not roots:
-                return nonodes
-            lowestrev = min([self.rev(n) for n in roots])
-        else:
-            roots = [nullid] # Everybody's a descendant of nullid
-            lowestrev = nullrev
-        if (lowestrev == nullrev) and (heads is None):
-            # We want _all_ the nodes!
-            return ([self.node(r) for r in self], [nullid], list(self.heads()))
-        if heads is None:
-            # All nodes are ancestors, so the latest ancestor is the last
-            # node.
-            highestrev = len(self) - 1
-            # Set ancestors to None to signal that every node is an ancestor.
-            ancestors = None
-            # Set heads to an empty dictionary for later discovery of heads
-            heads = {}
-        else:
-            heads = list(heads)
-            if not heads:
-                return nonodes
-            ancestors = set()
-            # Turn heads into a dictionary so we can remove 'fake' heads.
-            # Also, later we will be using it to filter out the heads we can't
-            # find from roots.
-            heads = dict.fromkeys(heads, False)
-            # Start at the top and keep marking parents until we're done.
-            nodestotag = set(heads)
-            # Remember where the top was so we can use it as a limit later.
-            highestrev = max([self.rev(n) for n in nodestotag])
-            while nodestotag:
-                # grab a node to tag
-                n = nodestotag.pop()
-                # Never tag nullid
-                if n == nullid:
-                    continue
-                # A node's revision number represents its place in a
-                # topologically sorted list of nodes.
-                r = self.rev(n)
-                if r >= lowestrev:
-                    if n not in ancestors:
-                        # If we are possibly a descendant of one of the roots
-                        # and we haven't already been marked as an ancestor
-                        ancestors.add(n) # Mark as ancestor
-                        # Add non-nullid parents to list of nodes to tag.
-                        nodestotag.update([p for p in self.parents(n) if
-                                           p != nullid])
-                    elif n in heads: # We've seen it before, is it a fake head?
-                        # So it is, real heads should not be the ancestors of
-                        # any other heads.
-                        heads.pop(n)
-            if not ancestors:
-                return nonodes
-            # Now that we have our set of ancestors, we want to remove any
-            # roots that are not ancestors.
-
-            # If one of the roots was nullid, everything is included anyway.
-            if lowestrev > nullrev:
-                # But, since we weren't, let's recompute the lowest rev to not
-                # include roots that aren't ancestors.
-
-                # Filter out roots that aren't ancestors of heads
-                roots = [root for root in roots if root in ancestors]
-                # Recompute the lowest revision
-                if roots:
-                    lowestrev = min([self.rev(root) for root in roots])
-                else:
-                    # No more roots?  Return empty list
-                    return nonodes
-            else:
-                # We are descending from nullid, and don't need to care about
-                # any other roots.
-                lowestrev = nullrev
-                roots = [nullid]
-        # Transform our roots list into a set.
-        descendants = set(roots)
-        # Also, keep the original roots so we can filter out roots that aren't
-        # 'real' roots (i.e. are descended from other roots).
-        roots = descendants.copy()
-        # Our topologically sorted list of output nodes.
-        orderedout = []
-        # Don't start at nullid since we don't want nullid in our output list,
-        # and if nullid shows up in descendants, empty parents will look like
-        # they're descendants.
-        for r in self.revs(start=max(lowestrev, 0), stop=highestrev + 1):
-            n = self.node(r)
-            isdescendant = False
-            if lowestrev == nullrev:  # Everybody is a descendant of nullid
-                isdescendant = True
-            elif n in descendants:
-                # n is already a descendant
-                isdescendant = True
-                # This check only needs to be done here because all the roots
-                # will start being marked is descendants before the loop.
-                if n in roots:
-                    # If n was a root, check if it's a 'real' root.
-                    p = tuple(self.parents(n))
-                    # If any of its parents are descendants, it's not a root.
-                    if (p[0] in descendants) or (p[1] in descendants):
-                        roots.remove(n)
-            else:
-                p = tuple(self.parents(n))
-                # A node is a descendant if either of its parents are
-                # descendants.  (We seeded the dependents list with the roots
-                # up there, remember?)
-                if (p[0] in descendants) or (p[1] in descendants):
-                    descendants.add(n)
-                    isdescendant = True
-            if isdescendant and ((ancestors is None) or (n in ancestors)):
-                # Only include nodes that are both descendants and ancestors.
-                orderedout.append(n)
-                if (ancestors is not None) and (n in heads):
-                    # We're trying to figure out which heads are reachable
-                    # from roots.
-                    # Mark this head as having been reached
-                    heads[n] = True
-                elif ancestors is None:
-                    # Otherwise, we're trying to discover the heads.
-                    # Assume this is a head because if it isn't, the next step
-                    # will eventually remove it.
-                    heads[n] = True
-                    # But, obviously its parents aren't.
-                    for p in self.parents(n):
-                        heads.pop(p, None)
-        heads = [head for head, flag in heads.iteritems() if flag]
-        roots = list(roots)
-        assert orderedout
-        assert roots
-        assert heads
-        return (orderedout, roots, heads)
-
-    def headrevs(self):
-        try:
-            return self.index.headrevs()
-        except AttributeError:
-            return self._headrevs()
-
-    def computephases(self, roots):
-        return self.index.computephasesmapsets(roots)
-
-    def _headrevs(self):
-        count = len(self)
-        if not count:
-            return [nullrev]
-        # we won't iter over filtered rev so nobody is a head at start
-        ishead = [0] * (count + 1)
-        index = self.index
-        for r in self:
-            ishead[r] = 1  # I may be an head
-            e = index[r]
-            ishead[e[5]] = ishead[e[6]] = 0  # my parent are not
-        return [r for r, val in enumerate(ishead) if val]
-
-    def heads(self, start=None, stop=None):
-        """return the list of all nodes that have no children
-
-        if start is specified, only heads that are descendants of
-        start will be returned
-        if stop is specified, it will consider all the revs from stop
-        as if they had no children
-        """
-        if start is None and stop is None:
-            if not len(self):
-                return [nullid]
-            return [self.node(r) for r in self.headrevs()]
-
-        if start is None:
-            start = nullid
-        if stop is None:
-            stop = []
-        stoprevs = set([self.rev(n) for n in stop])
-        startrev = self.rev(start)
-        reachable = {startrev}
-        heads = {startrev}
-
-        parentrevs = self.parentrevs
-        for r in self.revs(start=startrev + 1):
-            for p in parentrevs(r):
-                if p in reachable:
-                    if r not in stoprevs:
-                        reachable.add(r)
-                    heads.add(r)
-                if p in heads and p not in stoprevs:
-                    heads.remove(p)
-
-        return [self.node(r) for r in heads]
-
-    def children(self, node):
-        """find the children of a given node"""
-        c = []
-        p = self.rev(node)
-        for r in self.revs(start=p + 1):
-            prevs = [pr for pr in self.parentrevs(r) if pr != nullrev]
-            if prevs:
-                for pr in prevs:
-                    if pr == p:
-                        c.append(self.node(r))
-            elif p == nullrev:
-                c.append(self.node(r))
-        return c
-
-    def commonancestorsheads(self, a, b):
-        """calculate all the heads of the common ancestors of nodes a and b"""
-        a, b = self.rev(a), self.rev(b)
-        ancs = self._commonancestorsheads(a, b)
-        return pycompat.maplist(self.node, ancs)
-
-    def _commonancestorsheads(self, *revs):
-        """calculate all the heads of the common ancestors of revs"""
-        try:
-            ancs = self.index.commonancestorsheads(*revs)
-        except (AttributeError, OverflowError): # C implementation failed
-            ancs = ancestor.commonancestorsheads(self.parentrevs, *revs)
-        return ancs
-
-    def isancestor(self, a, b):
-        """return True if node a is an ancestor of node b
-
-        A revision is considered an ancestor of itself."""
-        a, b = self.rev(a), self.rev(b)
-        return self.isancestorrev(a, b)
-
-    def isancestorrev(self, a, b):
-        """return True if revision a is an ancestor of revision b
-
-        A revision is considered an ancestor of itself.
-
-        The implementation of this is trivial but the use of
-        commonancestorsheads is not."""
-        if a == nullrev:
-            return True
-        elif a == b:
-            return True
-        elif a > b:
-            return False
-        return a in self._commonancestorsheads(a, b)
-
-    def ancestor(self, a, b):
-        """calculate the "best" common ancestor of nodes a and b"""
-
-        a, b = self.rev(a), self.rev(b)
-        try:
-            ancs = self.index.ancestors(a, b)
-        except (AttributeError, OverflowError):
-            ancs = ancestor.ancestors(self.parentrevs, a, b)
-        if ancs:
-            # choose a consistent winner when there's a tie
-            return min(map(self.node, ancs))
-        return nullid
-
-    def _match(self, id):
-        if isinstance(id, int):
-            # rev
-            return self.node(id)
-        if len(id) == 20:
-            # possibly a binary node
-            # odds of a binary node being all hex in ASCII are 1 in 10**25
-            try:
-                node = id
-                self.rev(node) # quick search the index
-                return node
-            except LookupError:
-                pass # may be partial hex id
-        try:
-            # str(rev)
-            rev = int(id)
-            if "%d" % rev != id:
-                raise ValueError
-            if rev < 0:
-                rev = len(self) + rev
-            if rev < 0 or rev >= len(self):
-                raise ValueError
-            return self.node(rev)
-        except (ValueError, OverflowError):
-            pass
-        if len(id) == 40:
-            try:
-                # a full hex nodeid?
-                node = bin(id)
-                self.rev(node)
-                return node
-            except (TypeError, LookupError):
-                pass
-
-    def _partialmatch(self, id):
-        # we don't care wdirfilenodeids as they should be always full hash
-        maybewdir = wdirhex.startswith(id)
-        try:
-            partial = self.index.partialmatch(id)
-            if partial and self.hasnode(partial):
-                if maybewdir:
-                    # single 'ff...' match in radix tree, ambiguous with wdir
-                    raise RevlogError
-                return partial
-            if maybewdir:
-                # no 'ff...' match in radix tree, wdir identified
-                raise error.WdirUnsupported
-            return None
-        except RevlogError:
-            # parsers.c radix tree lookup gave multiple matches
-            # fast path: for unfiltered changelog, radix tree is accurate
-            if not getattr(self, 'filteredrevs', None):
-                raise AmbiguousPrefixLookupError(id, self.indexfile,
-                                                 _('ambiguous identifier'))
-            # fall through to slow path that filters hidden revisions
-        except (AttributeError, ValueError):
-            # we are pure python, or key was too short to search radix tree
-            pass
-
-        if id in self._pcache:
-            return self._pcache[id]
-
-        if len(id) <= 40:
-            try:
-                # hex(node)[:...]
-                l = len(id) // 2  # grab an even number of digits
-                prefix = bin(id[:l * 2])
-                nl = [e[7] for e in self.index if e[7].startswith(prefix)]
-                nl = [n for n in nl if hex(n).startswith(id) and
-                      self.hasnode(n)]
-                if nullhex.startswith(id):
-                    nl.append(nullid)
-                if len(nl) > 0:
-                    if len(nl) == 1 and not maybewdir:
-                        self._pcache[id] = nl[0]
-                        return nl[0]
-                    raise AmbiguousPrefixLookupError(id, self.indexfile,
-                                                     _('ambiguous identifier'))
-                if maybewdir:
-                    raise error.WdirUnsupported
-                return None
-            except TypeError:
-                pass
-
-    def lookup(self, id):
-        """locate a node based on:
-            - revision number or str(revision number)
-            - nodeid or subset of hex nodeid
-        """
-        n = self._match(id)
-        if n is not None:
-            return n
-        n = self._partialmatch(id)
-        if n:
-            return n
-
-        raise LookupError(id, self.indexfile, _('no match found'))
-
-    def shortest(self, node, minlength=1):
-        """Find the shortest unambiguous prefix that matches node."""
-        def isvalid(prefix):
-            try:
-                node = self._partialmatch(prefix)
-            except error.RevlogError:
-                return False
-            except error.WdirUnsupported:
-                # single 'ff...' match
-                return True
-            if node is None:
-                raise LookupError(node, self.indexfile, _('no node'))
-            return True
-
-        def maybewdir(prefix):
-            return all(c == 'f' for c in prefix)
-
-        hexnode = hex(node)
-
-        def disambiguate(hexnode, minlength):
-            """Disambiguate against wdirid."""
-            for length in range(minlength, 41):
-                prefix = hexnode[:length]
-                if not maybewdir(prefix):
-                    return prefix
-
-        if not getattr(self, 'filteredrevs', None):
-            try:
-                length = max(self.index.shortest(node), minlength)
-                return disambiguate(hexnode, length)
-            except RevlogError:
-                if node != wdirid:
-                    raise LookupError(node, self.indexfile, _('no node'))
-            except AttributeError:
-                # Fall through to pure code
-                pass
-
-        if node == wdirid:
-            for length in range(minlength, 41):
-                prefix = hexnode[:length]
-                if isvalid(prefix):
-                    return prefix
-
-        for length in range(minlength, 41):
-            prefix = hexnode[:length]
-            if isvalid(prefix):
-                return disambiguate(hexnode, length)
-
-    def cmp(self, node, text):
-        """compare text with a given file revision
-
-        returns True if text is different than what is stored.
-        """
-        p1, p2 = self.parents(node)
-        return hash(text, p1, p2) != node
-
-    def _cachesegment(self, offset, data):
-        """Add a segment to the revlog cache.
-
-        Accepts an absolute offset and the data that is at that location.
-        """
-        o, d = self._chunkcache
-        # try to add to existing cache
-        if o + len(d) == offset and len(d) + len(data) < _chunksize:
-            self._chunkcache = o, d + data
-        else:
-            self._chunkcache = offset, data
-
-    def _readsegment(self, offset, length, df=None):
-        """Load a segment of raw data from the revlog.
-
-        Accepts an absolute offset, length to read, and an optional existing
-        file handle to read from.
-
-        If an existing file handle is passed, it will be seeked and the
-        original seek position will NOT be restored.
-
-        Returns a str or buffer of raw byte data.
-        """
-        # Cache data both forward and backward around the requested
-        # data, in a fixed size window. This helps speed up operations
-        # involving reading the revlog backwards.
-        cachesize = self._chunkcachesize
-        realoffset = offset & ~(cachesize - 1)
-        reallength = (((offset + length + cachesize) & ~(cachesize - 1))
-                      - realoffset)
-        with self._datareadfp(df) as df:
-            df.seek(realoffset)
-            d = df.read(reallength)
-        self._cachesegment(realoffset, d)
-        if offset != realoffset or reallength != length:
-            return util.buffer(d, offset - realoffset, length)
-        return d
-
-    def _getsegment(self, offset, length, df=None):
-        """Obtain a segment of raw data from the revlog.
-
-        Accepts an absolute offset, length of bytes to obtain, and an
-        optional file handle to the already-opened revlog. If the file
-        handle is used, it's original seek position will not be preserved.
-
-        Requests for data may be returned from a cache.
-
-        Returns a str or a buffer instance of raw byte data.
-        """
-        o, d = self._chunkcache
-        l = len(d)
-
-        # is it in the cache?
-        cachestart = offset - o
-        cacheend = cachestart + length
-        if cachestart >= 0 and cacheend <= l:
-            if cachestart == 0 and cacheend == l:
-                return d # avoid a copy
-            return util.buffer(d, cachestart, cacheend - cachestart)
-
-        return self._readsegment(offset, length, df=df)
-
-    def _getsegmentforrevs(self, startrev, endrev, df=None):
-        """Obtain a segment of raw data corresponding to a range of revisions.
-
-        Accepts the start and end revisions and an optional already-open
-        file handle to be used for reading. If the file handle is read, its
-        seek position will not be preserved.
-
-        Requests for data may be satisfied by a cache.
-
-        Returns a 2-tuple of (offset, data) for the requested range of
-        revisions. Offset is the integer offset from the beginning of the
-        revlog and data is a str or buffer of the raw byte data.
-
-        Callers will need to call ``self.start(rev)`` and ``self.length(rev)``
-        to determine where each revision's data begins and ends.
-        """
-        # Inlined self.start(startrev) & self.end(endrev) for perf reasons
-        # (functions are expensive).
-        index = self.index
-        istart = index[startrev]
-        start = int(istart[0] >> 16)
-        if startrev == endrev:
-            end = start + istart[1]
-        else:
-            iend = index[endrev]
-            end = int(iend[0] >> 16) + iend[1]
-
-        if self._inline:
-            start += (startrev + 1) * self._io.size
-            end += (endrev + 1) * self._io.size
-        length = end - start
-
-        return start, self._getsegment(start, length, df=df)
-
-    def _chunk(self, rev, df=None):
-        """Obtain a single decompressed chunk for a revision.
-
-        Accepts an integer revision and an optional already-open file handle
-        to be used for reading. If used, the seek position of the file will not
-        be preserved.
-
-        Returns a str holding uncompressed data for the requested revision.
-        """
-        return self.decompress(self._getsegmentforrevs(rev, rev, df=df)[1])
-
-    def _chunks(self, revs, df=None, targetsize=None):
-        """Obtain decompressed chunks for the specified revisions.
-
-        Accepts an iterable of numeric revisions that are assumed to be in
-        ascending order. Also accepts an optional already-open file handle
-        to be used for reading. If used, the seek position of the file will
-        not be preserved.
-
-        This function is similar to calling ``self._chunk()`` multiple times,
-        but is faster.
-
-        Returns a list with decompressed data for each requested revision.
-        """
-        if not revs:
-            return []
-        start = self.start
-        length = self.length
-        inline = self._inline
-        iosize = self._io.size
-        buffer = util.buffer
-
-        l = []
-        ladd = l.append
-
-        if not self._withsparseread:
-            slicedchunks = (revs,)
-        else:
-            slicedchunks = _slicechunk(self, revs, targetsize=targetsize)
-
-        for revschunk in slicedchunks:
-            firstrev = revschunk[0]
-            # Skip trailing revisions with empty diff
-            for lastrev in revschunk[::-1]:
-                if length(lastrev) != 0:
-                    break
-
-            try:
-                offset, data = self._getsegmentforrevs(firstrev, lastrev, df=df)
-            except OverflowError:
-                # issue4215 - we can't cache a run of chunks greater than
-                # 2G on Windows
-                return [self._chunk(rev, df=df) for rev in revschunk]
-
-            decomp = self.decompress
-            for rev in revschunk:
-                chunkstart = start(rev)
-                if inline:
-                    chunkstart += (rev + 1) * iosize
-                chunklength = length(rev)
-                ladd(decomp(buffer(data, chunkstart - offset, chunklength)))
-
-        return l
-
-    def _chunkclear(self):
-        """Clear the raw chunk cache."""
-        self._chunkcache = (0, '')
-
-    def deltaparent(self, rev):
-        """return deltaparent of the given revision"""
-        base = self.index[rev][3]
-        if base == rev:
-            return nullrev
-        elif self._generaldelta:
-            return base
-        else:
-            return rev - 1
-
-    def issnapshot(self, rev):
-        """tells whether rev is a snapshot
-        """
-        if rev == nullrev:
-            return True
-        deltap = self.deltaparent(rev)
-        if deltap == nullrev:
-            return True
-        p1, p2 = self.parentrevs(rev)
-        if deltap in (p1, p2):
-            return False
-        return self.issnapshot(deltap)
-
-    def snapshotdepth(self, rev):
-        """number of snapshot in the chain before this one"""
-        if not self.issnapshot(rev):
-            raise ProgrammingError('revision %d not a snapshot')
-        return len(self._deltachain(rev)[0]) - 1
-
-    def revdiff(self, rev1, rev2):
-        """return or calculate a delta between two revisions
-
-        The delta calculated is in binary form and is intended to be written to
-        revlog data directly. So this function needs raw revision data.
-        """
-        if rev1 != nullrev and self.deltaparent(rev2) == rev1:
-            return bytes(self._chunk(rev2))
-
-        return mdiff.textdiff(self.revision(rev1, raw=True),
-                              self.revision(rev2, raw=True))
-
-    def revision(self, nodeorrev, _df=None, raw=False):
-        """return an uncompressed revision of a given node or revision
-        number.
-
-        _df - an existing file handle to read from. (internal-only)
-        raw - an optional argument specifying if the revision data is to be
-        treated as raw data when applying flag transforms. 'raw' should be set
-        to True when generating changegroups or in debug commands.
-        """
-        if isinstance(nodeorrev, int):
-            rev = nodeorrev
-            node = self.node(rev)
-        else:
-            node = nodeorrev
-            rev = None
-
-        cachedrev = None
-        flags = None
-        rawtext = None
-        if node == nullid:
-            return ""
-        if self._cache:
-            if self._cache[0] == node:
-                # _cache only stores rawtext
-                if raw:
-                    return self._cache[2]
-                # duplicated, but good for perf
-                if rev is None:
-                    rev = self.rev(node)
-                if flags is None:
-                    flags = self.flags(rev)
-                # no extra flags set, no flag processor runs, text = rawtext
-                if flags == REVIDX_DEFAULT_FLAGS:
-                    return self._cache[2]
-                # rawtext is reusable. need to run flag processor
-                rawtext = self._cache[2]
-
-            cachedrev = self._cache[1]
-
-        # look up what we need to read
-        if rawtext is None:
-            if rev is None:
-                rev = self.rev(node)
-
-            chain, stopped = self._deltachain(rev, stoprev=cachedrev)
-            if stopped:
-                rawtext = self._cache[2]
-
-            # drop cache to save memory
-            self._cache = None
-
-            targetsize = None
-            rawsize = self.index[rev][2]
-            if 0 <= rawsize:
-                targetsize = 4 * rawsize
-
-            bins = self._chunks(chain, df=_df, targetsize=targetsize)
-            if rawtext is None:
-                rawtext = bytes(bins[0])
-                bins = bins[1:]
-
-            rawtext = mdiff.patches(rawtext, bins)
-            self._cache = (node, rev, rawtext)
-
-        if flags is None:
-            if rev is None:
-                rev = self.rev(node)
-            flags = self.flags(rev)
-
-        text, validatehash = self._processflags(rawtext, flags, 'read', raw=raw)
-        if validatehash:
-            self.checkhash(text, node, rev=rev)
-
-        return text
-
-    def hash(self, text, p1, p2):
-        """Compute a node hash.
-
-        Available as a function so that subclasses can replace the hash
-        as needed.
-        """
-        return hash(text, p1, p2)
-
-    def _processflags(self, text, flags, operation, raw=False):
-        """Inspect revision data flags and applies transforms defined by
-        registered flag processors.
-
-        ``text`` - the revision data to process
-        ``flags`` - the revision flags
-        ``operation`` - the operation being performed (read or write)
-        ``raw`` - an optional argument describing if the raw transform should be
-        applied.
-
-        This method processes the flags in the order (or reverse order if
-        ``operation`` is 'write') defined by REVIDX_FLAGS_ORDER, applying the
-        flag processors registered for present flags. The order of flags defined
-        in REVIDX_FLAGS_ORDER needs to be stable to allow non-commutativity.
-
-        Returns a 2-tuple of ``(text, validatehash)`` where ``text`` is the
-        processed text and ``validatehash`` is a bool indicating whether the
-        returned text should be checked for hash integrity.
-
-        Note: If the ``raw`` argument is set, it has precedence over the
-        operation and will only update the value of ``validatehash``.
-        """
-        # fast path: no flag processors will run
-        if flags == 0:
-            return text, True
-        if not operation in ('read', 'write'):
-            raise ProgrammingError(_("invalid '%s' operation ") % (operation))
-        # Check all flags are known.
-        if flags & ~REVIDX_KNOWN_FLAGS:
-            raise RevlogError(_("incompatible revision flag '%#x'") %
-                              (flags & ~REVIDX_KNOWN_FLAGS))
-        validatehash = True
-        # Depending on the operation (read or write), the order might be
-        # reversed due to non-commutative transforms.
-        orderedflags = REVIDX_FLAGS_ORDER
-        if operation == 'write':
-            orderedflags = reversed(orderedflags)
-
-        for flag in orderedflags:
-            # If a flagprocessor has been registered for a known flag, apply the
-            # related operation transform and update result tuple.
-            if flag & flags:
-                vhash = True
-
-                if flag not in _flagprocessors:
-                    message = _("missing processor for flag '%#x'") % (flag)
-                    raise RevlogError(message)
-
-                processor = _flagprocessors[flag]
-                if processor is not None:
-                    readtransform, writetransform, rawtransform = processor
-
-                    if raw:
-                        vhash = rawtransform(self, text)
-                    elif operation == 'read':
-                        text, vhash = readtransform(self, text)
-                    else: # write operation
-                        text, vhash = writetransform(self, text)
-                validatehash = validatehash and vhash
-
-        return text, validatehash
-
-    def checkhash(self, text, node, p1=None, p2=None, rev=None):
-        """Check node hash integrity.
-
-        Available as a function so that subclasses can extend hash mismatch
-        behaviors as needed.
-        """
-        try:
-            if p1 is None and p2 is None:
-                p1, p2 = self.parents(node)
-            if node != self.hash(text, p1, p2):
-                revornode = rev
-                if revornode is None:
-                    revornode = templatefilters.short(hex(node))
-                raise RevlogError(_("integrity check failed on %s:%s")
-                    % (self.indexfile, pycompat.bytestr(revornode)))
-        except RevlogError:
-            if self._censorable and _censoredtext(text):
-                raise error.CensoredNodeError(self.indexfile, node, text)
-            raise
-
-    def _enforceinlinesize(self, tr, fp=None):
-        """Check if the revlog is too big for inline and convert if so.
-
-        This should be called after revisions are added to the revlog. If the
-        revlog has grown too large to be an inline revlog, it will convert it
-        to use multiple index and data files.
-        """
-        tiprev = len(self) - 1
-        if (not self._inline or
-            (self.start(tiprev) + self.length(tiprev)) < _maxinline):
-            return
-
-        trinfo = tr.find(self.indexfile)
-        if trinfo is None:
-            raise RevlogError(_("%s not found in the transaction")
-                              % self.indexfile)
-
-        trindex = trinfo[2]
-        if trindex is not None:
-            dataoff = self.start(trindex)
-        else:
-            # revlog was stripped at start of transaction, use all leftover data
-            trindex = len(self) - 1
-            dataoff = self.end(tiprev)
-
-        tr.add(self.datafile, dataoff)
-
-        if fp:
-            fp.flush()
-            fp.close()
-
-        with self._datafp('w') as df:
-            for r in self:
-                df.write(self._getsegmentforrevs(r, r)[1])
-
-        with self._indexfp('w') as fp:
-            self.version &= ~FLAG_INLINE_DATA
-            self._inline = False
-            io = self._io
-            for i in self:
-                e = io.packentry(self.index[i], self.node, self.version, i)
-                fp.write(e)
-
-            # the temp file replace the real index when we exit the context
-            # manager
-
-        tr.replace(self.indexfile, trindex * self._io.size)
-        self._chunkclear()
-
-    def addrevision(self, text, transaction, link, p1, p2, cachedelta=None,
-                    node=None, flags=REVIDX_DEFAULT_FLAGS, deltacomputer=None):
-        """add a revision to the log
-
-        text - the revision data to add
-        transaction - the transaction object used for rollback
-        link - the linkrev data to add
-        p1, p2 - the parent nodeids of the revision
-        cachedelta - an optional precomputed delta
-        node - nodeid of revision; typically node is not specified, and it is
-            computed by default as hash(text, p1, p2), however subclasses might
-            use different hashing method (and override checkhash() in such case)
-        flags - the known flags to set on the revision
-        deltacomputer - an optional _deltacomputer instance shared between
-            multiple calls
-        """
-        if link == nullrev:
-            raise RevlogError(_("attempted to add linkrev -1 to %s")
-                              % self.indexfile)
-
-        if flags:
-            node = node or self.hash(text, p1, p2)
-
-        rawtext, validatehash = self._processflags(text, flags, 'write')
-
-        # If the flag processor modifies the revision data, ignore any provided
-        # cachedelta.
-        if rawtext != text:
-            cachedelta = None
-
-        if len(rawtext) > _maxentrysize:
-            raise RevlogError(
-                _("%s: size of %d bytes exceeds maximum revlog storage of 2GiB")
-                % (self.indexfile, len(rawtext)))
-
-        node = node or self.hash(rawtext, p1, p2)
-        if node in self.nodemap:
-            return node
-
-        if validatehash:
-            self.checkhash(rawtext, node, p1=p1, p2=p2)
-
-        return self.addrawrevision(rawtext, transaction, link, p1, p2, node,
-                                   flags, cachedelta=cachedelta,
-                                   deltacomputer=deltacomputer)
-
-    def addrawrevision(self, rawtext, transaction, link, p1, p2, node, flags,
-                       cachedelta=None, deltacomputer=None):
-        """add a raw revision with known flags, node and parents
-        useful when reusing a revision not stored in this revlog (ex: received
-        over wire, or read from an external bundle).
-        """
-        dfh = None
-        if not self._inline:
-            dfh = self._datafp("a+")
-        ifh = self._indexfp("a+")
-        try:
-            return self._addrevision(node, rawtext, transaction, link, p1, p2,
-                                     flags, cachedelta, ifh, dfh,
-                                     deltacomputer=deltacomputer)
-        finally:
-            if dfh:
-                dfh.close()
-            ifh.close()
-
-    def compress(self, data):
-        """Generate a possibly-compressed representation of data."""
-        if not data:
-            return '', data
-
-        compressed = self._compressor.compress(data)
-
-        if compressed:
-            # The revlog compressor added the header in the returned data.
-            return '', compressed
-
-        if data[0:1] == '\0':
-            return '', data
-        return 'u', data
-
-    def decompress(self, data):
-        """Decompress a revlog chunk.
-
-        The chunk is expected to begin with a header identifying the
-        format type so it can be routed to an appropriate decompressor.
-        """
-        if not data:
-            return data
-
-        # Revlogs are read much more frequently than they are written and many
-        # chunks only take microseconds to decompress, so performance is
-        # important here.
-        #
-        # We can make a few assumptions about revlogs:
-        #
-        # 1) the majority of chunks will be compressed (as opposed to inline
-        #    raw data).
-        # 2) decompressing *any* data will likely by at least 10x slower than
-        #    returning raw inline data.
-        # 3) we want to prioritize common and officially supported compression
-        #    engines
-        #
-        # It follows that we want to optimize for "decompress compressed data
-        # when encoded with common and officially supported compression engines"
-        # case over "raw data" and "data encoded by less common or non-official
-        # compression engines." That is why we have the inline lookup first
-        # followed by the compengines lookup.
-        #
-        # According to `hg perfrevlogchunks`, this is ~0.5% faster for zlib
-        # compressed chunks. And this matters for changelog and manifest reads.
-        t = data[0:1]
-
-        if t == 'x':
-            try:
-                return _zlibdecompress(data)
-            except zlib.error as e:
-                raise RevlogError(_('revlog decompress error: %s') %
-                                  stringutil.forcebytestr(e))
-        # '\0' is more common than 'u' so it goes first.
-        elif t == '\0':
-            return data
-        elif t == 'u':
-            return util.buffer(data, 1)
-
-        try:
-            compressor = self._decompressors[t]
-        except KeyError:
-            try:
-                engine = util.compengines.forrevlogheader(t)
-                compressor = engine.revlogcompressor()
-                self._decompressors[t] = compressor
-            except KeyError:
-                raise RevlogError(_('unknown compression type %r') % t)
-
-        return compressor.decompress(data)
-
-    def _isgooddeltainfo(self, deltainfo, revinfo):
-        """Returns True if the given delta is good. Good means that it is within
-        the disk span, disk size, and chain length bounds that we know to be
-        performant."""
-        if deltainfo is None:
-            return False
-
-        # - 'deltainfo.distance' is the distance from the base revision --
-        #   bounding it limits the amount of I/O we need to do.
-        # - 'deltainfo.compresseddeltalen' is the sum of the total size of
-        #   deltas we need to apply -- bounding it limits the amount of CPU
-        #   we consume.
-
-        if self._sparserevlog:
-            # As sparse-read will be used, we can consider that the distance,
-            # instead of being the span of the whole chunk,
-            # is the span of the largest read chunk
-            base = deltainfo.base
-
-            if base != nullrev:
-                deltachain = self._deltachain(base)[0]
-            else:
-                deltachain = []
-
-            # search for the first non-snapshot revision
-            for idx, r in enumerate(deltachain):
-                if not self.issnapshot(r):
-                    break
-            deltachain = deltachain[idx:]
-            chunks = _slicechunk(self, deltachain, deltainfo)
-            all_span = [_segmentspan(self, revs, deltainfo) for revs in chunks]
-            distance = max(all_span)
-        else:
-            distance = deltainfo.distance
-
-        textlen = revinfo.textlen
-        defaultmax = textlen * 4
-        maxdist = self._maxdeltachainspan
-        if not maxdist:
-            maxdist = distance # ensure the conditional pass
-        maxdist = max(maxdist, defaultmax)
-        if self._sparserevlog and maxdist < self._srmingapsize:
-            # In multiple place, we are ignoring irrelevant data range below a
-            # certain size. Be also apply this tradeoff here and relax span
-            # constraint for small enought content.
-            maxdist = self._srmingapsize
-
-        # Bad delta from read span:
-        #
-        #   If the span of data read is larger than the maximum allowed.
-        if maxdist < distance:
-            return False
-
-        # Bad delta from new delta size:
-        #
-        #   If the delta size is larger than the target text, storing the
-        #   delta will be inefficient.
-        if textlen < deltainfo.deltalen:
-            return False
-
-        # Bad delta from cumulated payload size:
-        #
-        #   If the sum of delta get larger than K * target text length.
-        if textlen * LIMIT_DELTA2TEXT < deltainfo.compresseddeltalen:
-            return False
-
-        # Bad delta from chain length:
-        #
-        #   If the number of delta in the chain gets too high.
-        if self._maxchainlen and  self._maxchainlen < deltainfo.chainlen:
-            return False
-
-        # bad delta from intermediate snapshot size limit
-        #
-        #   If an intermediate snapshot size is higher than the limit.  The
-        #   limit exist to prevent endless chain of intermediate delta to be
-        #   created.
-        if (deltainfo.snapshotdepth is not None and
-                (textlen >> deltainfo.snapshotdepth) < deltainfo.deltalen):
-            return False
-
-        # bad delta if new intermediate snapshot is larger than the previous
-        # snapshot
-        if (deltainfo.snapshotdepth
-                and self.length(deltainfo.base) < deltainfo.deltalen):
-            return False
-
-        return True
-
-    def _addrevision(self, node, rawtext, transaction, link, p1, p2, flags,
-                     cachedelta, ifh, dfh, alwayscache=False,
-                     deltacomputer=None):
-        """internal function to add revisions to the log
-
-        see addrevision for argument descriptions.
-
-        note: "addrevision" takes non-raw text, "_addrevision" takes raw text.
-
-        if "deltacomputer" is not provided or None, a defaultdeltacomputer will
-        be used.
-
-        invariants:
-        - rawtext is optional (can be None); if not set, cachedelta must be set.
-          if both are set, they must correspond to each other.
-        """
-        if node == nullid:
-            raise RevlogError(_("%s: attempt to add null revision") %
-                              (self.indexfile))
-        if node == wdirid or node in wdirfilenodeids:
-            raise RevlogError(_("%s: attempt to add wdir revision") %
-                              (self.indexfile))
-
-        if self._inline:
-            fh = ifh
-        else:
-            fh = dfh
-
-        btext = [rawtext]
-
-        curr = len(self)
-        prev = curr - 1
-        offset = self.end(prev)
-        p1r, p2r = self.rev(p1), self.rev(p2)
-
-        # full versions are inserted when the needed deltas
-        # become comparable to the uncompressed text
-        if rawtext is None:
-            # need rawtext size, before changed by flag processors, which is
-            # the non-raw size. use revlog explicitly to avoid filelog's extra
-            # logic that might remove metadata size.
-            textlen = mdiff.patchedsize(revlog.size(self, cachedelta[0]),
-                                        cachedelta[1])
-        else:
-            textlen = len(rawtext)
-
-        if deltacomputer is None:
-            deltacomputer = _deltacomputer(self)
-
-        revinfo = _revisioninfo(node, p1, p2, btext, textlen, cachedelta, flags)
-
-        # no delta for flag processor revision (see "candelta" for why)
-        # not calling candelta since only one revision needs test, also to
-        # avoid overhead fetching flags again.
-        if flags & REVIDX_RAWTEXT_CHANGING_FLAGS:
-            deltainfo = None
-        else:
-            deltainfo = deltacomputer.finddeltainfo(revinfo, fh)
-
-        if deltainfo is not None:
-            base = deltainfo.base
-            chainbase = deltainfo.chainbase
-            data = deltainfo.data
-            l = deltainfo.deltalen
-        else:
-            rawtext = deltacomputer.buildtext(revinfo, fh)
-            data = self.compress(rawtext)
-            l = len(data[1]) + len(data[0])
-            base = chainbase = curr
-
-        e = (offset_type(offset, flags), l, textlen,
-             base, link, p1r, p2r, node)
-        self.index.append(e)
-        self.nodemap[node] = curr
-
-        entry = self._io.packentry(e, self.node, self.version, curr)
-        self._writeentry(transaction, ifh, dfh, entry, data, link, offset)
-
-        if alwayscache and rawtext is None:
-            rawtext = deltacomputer.buildtext(revinfo, fh)
-
-        if type(rawtext) == bytes: # only accept immutable objects
-            self._cache = (node, curr, rawtext)
-        self._chainbasecache[curr] = chainbase
-        return node
-
-    def _writeentry(self, transaction, ifh, dfh, entry, data, link, offset):
-        # Files opened in a+ mode have inconsistent behavior on various
-        # platforms. Windows requires that a file positioning call be made
-        # when the file handle transitions between reads and writes. See
-        # 3686fa2b8eee and the mixedfilemodewrapper in windows.py. On other
-        # platforms, Python or the platform itself can be buggy. Some versions
-        # of Solaris have been observed to not append at the end of the file
-        # if the file was seeked to before the end. See issue4943 for more.
-        #
-        # We work around this issue by inserting a seek() before writing.
-        # Note: This is likely not necessary on Python 3.
-        ifh.seek(0, os.SEEK_END)
-        if dfh:
-            dfh.seek(0, os.SEEK_END)
-
-        curr = len(self) - 1
-        if not self._inline:
-            transaction.add(self.datafile, offset)
-            transaction.add(self.indexfile, curr * len(entry))
-            if data[0]:
-                dfh.write(data[0])
-            dfh.write(data[1])
-            ifh.write(entry)
-        else:
-            offset += curr * self._io.size
-            transaction.add(self.indexfile, offset, curr)
-            ifh.write(entry)
-            ifh.write(data[0])
-            ifh.write(data[1])
-            self._enforceinlinesize(transaction, ifh)
-
-    def addgroup(self, deltas, linkmapper, transaction, addrevisioncb=None):
-        """
-        add a delta group
-
-        given a set of deltas, add them to the revision log. the
-        first delta is against its parent, which should be in our
-        log, the rest are against the previous delta.
-
-        If ``addrevisioncb`` is defined, it will be called with arguments of
-        this revlog and the node that was added.
-        """
-
-        nodes = []
-
-        r = len(self)
-        end = 0
-        if r:
-            end = self.end(r - 1)
-        ifh = self._indexfp("a+")
-        isize = r * self._io.size
-        if self._inline:
-            transaction.add(self.indexfile, end + isize, r)
-            dfh = None
-        else:
-            transaction.add(self.indexfile, isize, r)
-            transaction.add(self.datafile, end)
-            dfh = self._datafp("a+")
-        def flush():
-            if dfh:
-                dfh.flush()
-            ifh.flush()
-        try:
-            deltacomputer = _deltacomputer(self)
-            # loop through our set of deltas
-            for data in deltas:
-                node, p1, p2, linknode, deltabase, delta, flags = data
-                link = linkmapper(linknode)
-                flags = flags or REVIDX_DEFAULT_FLAGS
-
-                nodes.append(node)
-
-                if node in self.nodemap:
-                    # this can happen if two branches make the same change
-                    continue
-
-                for p in (p1, p2):
-                    if p not in self.nodemap:
-                        raise LookupError(p, self.indexfile,
-                                          _('unknown parent'))
-
-                if deltabase not in self.nodemap:
-                    raise LookupError(deltabase, self.indexfile,
-                                      _('unknown delta base'))
-
-                baserev = self.rev(deltabase)
-
-                if baserev != nullrev and self.iscensored(baserev):
-                    # if base is censored, delta must be full replacement in a
-                    # single patch operation
-                    hlen = struct.calcsize(">lll")
-                    oldlen = self.rawsize(baserev)
-                    newlen = len(delta) - hlen
-                    if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):
-                        raise error.CensoredBaseError(self.indexfile,
-                                                      self.node(baserev))
-
-                if not flags and self._peek_iscensored(baserev, delta, flush):
-                    flags |= REVIDX_ISCENSORED
-
-                # We assume consumers of addrevisioncb will want to retrieve
-                # the added revision, which will require a call to
-                # revision(). revision() will fast path if there is a cache
-                # hit. So, we tell _addrevision() to always cache in this case.
-                # We're only using addgroup() in the context of changegroup
-                # generation so the revision data can always be handled as raw
-                # by the flagprocessor.
-                self._addrevision(node, None, transaction, link,
-                                  p1, p2, flags, (baserev, delta),
-                                  ifh, dfh,
-                                  alwayscache=bool(addrevisioncb),
-                                  deltacomputer=deltacomputer)
-
-                if addrevisioncb:
-                    addrevisioncb(self, node)
-
-                if not dfh and not self._inline:
-                    # addrevision switched from inline to conventional
-                    # reopen the index
-                    ifh.close()
-                    dfh = self._datafp("a+")
-                    ifh = self._indexfp("a+")
-        finally:
-            if dfh:
-                dfh.close()
-            ifh.close()
-
-        return nodes
-
-    def iscensored(self, rev):
-        """Check if a file revision is censored."""
-        if not self._censorable:
-            return False
-
-        return self.flags(rev) & REVIDX_ISCENSORED
-
-    def _peek_iscensored(self, baserev, delta, flush):
-        """Quickly check if a delta produces a censored revision."""
-        if not self._censorable:
-            return False
-
-        # Fragile heuristic: unless new file meta keys are added alphabetically
-        # preceding "censored", all censored revisions are prefixed by
-        # "\1\ncensored:". A delta producing such a censored revision must be a
-        # full-replacement delta, so we inspect the first and only patch in the
-        # delta for this prefix.
-        hlen = struct.calcsize(">lll")
-        if len(delta) <= hlen:
-            return False
-
-        oldlen = self.rawsize(baserev)
-        newlen = len(delta) - hlen
-        if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):
-            return False
-
-        add = "\1\ncensored:"
-        addlen = len(add)
-        return newlen >= addlen and delta[hlen:hlen + addlen] == add
-
-    def getstrippoint(self, minlink):
-        """find the minimum rev that must be stripped to strip the linkrev
-
-        Returns a tuple containing the minimum rev and a set of all revs that
-        have linkrevs that will be broken by this strip.
-        """
-        brokenrevs = set()
-        strippoint = len(self)
-
-        heads = {}
-        futurelargelinkrevs = set()
-        for head in self.headrevs():
-            headlinkrev = self.linkrev(head)
-            heads[head] = headlinkrev
-            if headlinkrev >= minlink:
-                futurelargelinkrevs.add(headlinkrev)
-
-        # This algorithm involves walking down the rev graph, starting at the
-        # heads. Since the revs are topologically sorted according to linkrev,
-        # once all head linkrevs are below the minlink, we know there are
-        # no more revs that could have a linkrev greater than minlink.
-        # So we can stop walking.
-        while futurelargelinkrevs:
-            strippoint -= 1
-            linkrev = heads.pop(strippoint)
-
-            if linkrev < minlink:
-                brokenrevs.add(strippoint)
-            else:
-                futurelargelinkrevs.remove(linkrev)
-
-            for p in self.parentrevs(strippoint):
-                if p != nullrev:
-                    plinkrev = self.linkrev(p)
-                    heads[p] = plinkrev
-                    if plinkrev >= minlink:
-                        futurelargelinkrevs.add(plinkrev)
-
-        return strippoint, brokenrevs
-
-    def strip(self, minlink, transaction):
-        """truncate the revlog on the first revision with a linkrev >= minlink
-
-        This function is called when we're stripping revision minlink and
-        its descendants from the repository.
-
-        We have to remove all revisions with linkrev >= minlink, because
-        the equivalent changelog revisions will be renumbered after the
-        strip.
-
-        So we truncate the revlog on the first of these revisions, and
-        trust that the caller has saved the revisions that shouldn't be
-        removed and that it'll re-add them after this truncation.
-        """
-        if len(self) == 0:
-            return
-
-        rev, _ = self.getstrippoint(minlink)
-        if rev == len(self):
-            return
-
-        # first truncate the files on disk
-        end = self.start(rev)
-        if not self._inline:
-            transaction.add(self.datafile, end)
-            end = rev * self._io.size
-        else:
-            end += rev * self._io.size
-
-        transaction.add(self.indexfile, end)
-
-        # then reset internal state in memory to forget those revisions
-        self._cache = None
-        self._chaininfocache = {}
-        self._chunkclear()
-        for x in pycompat.xrange(rev, len(self)):
-            del self.nodemap[self.node(x)]
-
-        del self.index[rev:-1]
-        self._nodepos = None
-
-    def checksize(self):
-        expected = 0
-        if len(self):
-            expected = max(0, self.end(len(self) - 1))
-
-        try:
-            with self._datafp() as f:
-                f.seek(0, 2)
-                actual = f.tell()
-            dd = actual - expected
-        except IOError as inst:
-            if inst.errno != errno.ENOENT:
-                raise
-            dd = 0
-
-        try:
-            f = self.opener(self.indexfile)
-            f.seek(0, 2)
-            actual = f.tell()
-            f.close()
-            s = self._io.size
-            i = max(0, actual // s)
-            di = actual - (i * s)
-            if self._inline:
-                databytes = 0
-                for r in self:
-                    databytes += max(0, self.length(r))
-                dd = 0
-                di = actual - len(self) * s - databytes
-        except IOError as inst:
-            if inst.errno != errno.ENOENT:
-                raise
-            di = 0
-
-        return (dd, di)
-
-    def files(self):
-        res = [self.indexfile]
-        if not self._inline:
-            res.append(self.datafile)
-        return res
-
-    def emitrevisiondeltas(self, requests):
-        frev = self.rev
-
-        prevrev = None
-        for request in requests:
-            node = request.node
-            rev = frev(node)
-
-            if prevrev is None:
-                prevrev = self.index[rev][5]
-
-            # Requesting a full revision.
-            if request.basenode == nullid:
-                baserev = nullrev
-            # Requesting an explicit revision.
-            elif request.basenode is not None:
-                baserev = frev(request.basenode)
-            # Allowing us to choose.
-            else:
-                p1rev, p2rev = self.parentrevs(rev)
-                deltaparentrev = self.deltaparent(rev)
-
-                # Avoid sending full revisions when delta parent is null. Pick
-                # prev in that case. It's tempting to pick p1 in this case, as
-                # p1 will be smaller in the common case. However, computing a
-                # delta against p1 may require resolving the raw text of p1,
-                # which could be expensive. The revlog caches should have prev
-                # cached, meaning less CPU for delta generation. There is
-                # likely room to add a flag and/or config option to control this
-                # behavior.
-                if deltaparentrev == nullrev and self._storedeltachains:
-                    baserev = prevrev
-
-                # Revlog is configured to use full snapshot for a reason.
-                # Stick to full snapshot.
-                elif deltaparentrev == nullrev:
-                    baserev = nullrev
-
-                # Pick previous when we can't be sure the base is available
-                # on consumer.
-                elif deltaparentrev not in (p1rev, p2rev, prevrev):
-                    baserev = prevrev
-                else:
-                    baserev = deltaparentrev
-
-                if baserev != nullrev and not self.candelta(baserev, rev):
-                    baserev = nullrev
-
-            revision = None
-            delta = None
-            baserevisionsize = None
-
-            if self.iscensored(baserev) or self.iscensored(rev):
-                try:
-                    revision = self.revision(node, raw=True)
-                except error.CensoredNodeError as e:
-                    revision = e.tombstone
-
-                if baserev != nullrev:
-                    baserevisionsize = self.rawsize(baserev)
-
-            elif baserev == nullrev:
-                revision = self.revision(node, raw=True)
-            else:
-                delta = self.revdiff(baserev, rev)
-
-            extraflags = REVIDX_ELLIPSIS if request.ellipsis else 0
-
-            yield revlogrevisiondelta(
-                node=node,
-                p1node=request.p1node,
-                p2node=request.p2node,
-                linknode=request.linknode,
-                basenode=self.node(baserev),
-                flags=self.flags(rev) | extraflags,
-                baserevisionsize=baserevisionsize,
-                revision=revision,
-                delta=delta)
-
-            prevrev = rev
-
-    DELTAREUSEALWAYS = 'always'
-    DELTAREUSESAMEREVS = 'samerevs'
-    DELTAREUSENEVER = 'never'
-
-    DELTAREUSEFULLADD = 'fulladd'
-
-    DELTAREUSEALL = {'always', 'samerevs', 'never', 'fulladd'}
-
-    def clone(self, tr, destrevlog, addrevisioncb=None,
-              deltareuse=DELTAREUSESAMEREVS, deltabothparents=None):
-        """Copy this revlog to another, possibly with format changes.
-
-        The destination revlog will contain the same revisions and nodes.
-        However, it may not be bit-for-bit identical due to e.g. delta encoding
-        differences.
-
-        The ``deltareuse`` argument control how deltas from the existing revlog
-        are preserved in the destination revlog. The argument can have the
-        following values:
-
-        DELTAREUSEALWAYS
-           Deltas will always be reused (if possible), even if the destination
-           revlog would not select the same revisions for the delta. This is the
-           fastest mode of operation.
-        DELTAREUSESAMEREVS
-           Deltas will be reused if the destination revlog would pick the same
-           revisions for the delta. This mode strikes a balance between speed
-           and optimization.
-        DELTAREUSENEVER
-           Deltas will never be reused. This is the slowest mode of execution.
-           This mode can be used to recompute deltas (e.g. if the diff/delta
-           algorithm changes).
-
-        Delta computation can be slow, so the choice of delta reuse policy can
-        significantly affect run time.
-
-        The default policy (``DELTAREUSESAMEREVS``) strikes a balance between
-        two extremes. Deltas will be reused if they are appropriate. But if the
-        delta could choose a better revision, it will do so. This means if you
-        are converting a non-generaldelta revlog to a generaldelta revlog,
-        deltas will be recomputed if the delta's parent isn't a parent of the
-        revision.
-
-        In addition to the delta policy, the ``deltabothparents`` argument
-        controls whether to compute deltas against both parents for merges.
-        By default, the current default is used.
-        """
-        if deltareuse not in self.DELTAREUSEALL:
-            raise ValueError(_('value for deltareuse invalid: %s') % deltareuse)
-
-        if len(destrevlog):
-            raise ValueError(_('destination revlog is not empty'))
-
-        if getattr(self, 'filteredrevs', None):
-            raise ValueError(_('source revlog has filtered revisions'))
-        if getattr(destrevlog, 'filteredrevs', None):
-            raise ValueError(_('destination revlog has filtered revisions'))
-
-        # lazydeltabase controls whether to reuse a cached delta, if possible.
-        oldlazydeltabase = destrevlog._lazydeltabase
-        oldamd = destrevlog._deltabothparents
-
-        try:
-            if deltareuse == self.DELTAREUSEALWAYS:
-                destrevlog._lazydeltabase = True
-            elif deltareuse == self.DELTAREUSESAMEREVS:
-                destrevlog._lazydeltabase = False
-
-            destrevlog._deltabothparents = deltabothparents or oldamd
-
-            populatecachedelta = deltareuse in (self.DELTAREUSEALWAYS,
-                                                self.DELTAREUSESAMEREVS)
-
-            deltacomputer = _deltacomputer(destrevlog)
-            index = self.index
-            for rev in self:
-                entry = index[rev]
-
-                # Some classes override linkrev to take filtered revs into
-                # account. Use raw entry from index.
-                flags = entry[0] & 0xffff
-                linkrev = entry[4]
-                p1 = index[entry[5]][7]
-                p2 = index[entry[6]][7]
-                node = entry[7]
-
-                # (Possibly) reuse the delta from the revlog if allowed and
-                # the revlog chunk is a delta.
-                cachedelta = None
-                rawtext = None
-                if populatecachedelta:
-                    dp = self.deltaparent(rev)
-                    if dp != nullrev:
-                        cachedelta = (dp, bytes(self._chunk(rev)))
-
-                if not cachedelta:
-                    rawtext = self.revision(rev, raw=True)
-
-
-                if deltareuse == self.DELTAREUSEFULLADD:
-                    destrevlog.addrevision(rawtext, tr, linkrev, p1, p2,
-                                           cachedelta=cachedelta,
-                                           node=node, flags=flags,
-                                           deltacomputer=deltacomputer)
-                else:
-                    ifh = destrevlog.opener(destrevlog.indexfile, 'a+',
-                                            checkambig=False)
-                    dfh = None
-                    if not destrevlog._inline:
-                        dfh = destrevlog.opener(destrevlog.datafile, 'a+')
-                    try:
-                        destrevlog._addrevision(node, rawtext, tr, linkrev, p1,
-                                                p2, flags, cachedelta, ifh, dfh,
-                                                deltacomputer=deltacomputer)
-                    finally:
-                        if dfh:
-                            dfh.close()
-                        ifh.close()
-
-                if addrevisioncb:
-                    addrevisioncb(self, rev, node)
-        finally:
-            destrevlog._lazydeltabase = oldlazydeltabase
-            destrevlog._deltabothparents = oldamd