mercurial/revlogutils/rewrite.py

interfaces: introduce and use a protocol class for the `mpatch` module

See f2832de2a46c for details when this was done for the `bdiff` module.

Two things worth pointing out-

  1) The `cffi` module "inherits" the `pure` implementation of `patchedsize()`
     because of its wildcard import.
  2) It's odd that the `mpatchError` lives in both `pure` and `cext` modules.

I initially thought to move the exception into the new class, and make the
existing class name an alias to the class in the new location, but the exception
is created in C code by the `cext` module, so that won't work.  I don't think a
protocol class is approriate, because there's nothing special about the class to
distinguish from any other `Exception`.  Fortunately, nobody is catching this
exception in core, so we can kick the can down the road.

# censor code related to censoring revision
# coding: utf8
#
# Copyright 2021 Pierre-Yves David <[e-mail]>
# Copyright 2015 Google, Inc <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.

from __future__ import annotations

import binascii
import contextlib
import os
import struct

from ..node import (
    nullrev,
)
from .constants import (
    COMP_MODE_PLAIN,
    ENTRY_DATA_COMPRESSED_LENGTH,
    ENTRY_DATA_COMPRESSION_MODE,
    ENTRY_DATA_OFFSET,
    ENTRY_DATA_UNCOMPRESSED_LENGTH,
    ENTRY_DELTA_BASE,
    ENTRY_LINK_REV,
    ENTRY_NODE_ID,
    ENTRY_PARENT_1,
    ENTRY_PARENT_2,
    ENTRY_SIDEDATA_COMPRESSED_LENGTH,
    ENTRY_SIDEDATA_COMPRESSION_MODE,
    ENTRY_SIDEDATA_OFFSET,
    REVIDX_ISCENSORED,
    REVLOGV0,
    REVLOGV1,
)
from ..i18n import _

from .. import (
    error,
    mdiff,
    pycompat,
    revlogutils,
    util,
)
from ..utils import (
    storageutil,
)
from . import (
    constants,
    deltas,
)


def v1_censor(rl, tr, censor_nodes, tombstone=b''):
    """censors a revision in a "version 1" revlog"""
    assert rl._format_version == constants.REVLOGV1, rl._format_version

    # avoid cycle
    from .. import revlog

    censor_revs = set(rl.rev(node) for node in censor_nodes)
    tombstone = storageutil.packmeta({b'censored': tombstone}, b'')

    # Rewriting the revlog in place is hard. Our strategy for censoring is
    # to create a new revlog, copy all revisions to it, then replace the
    # revlogs on transaction close.
    #
    # This is a bit dangerous. We could easily have a mismatch of state.
    newrl = revlog.revlog(
        rl.opener,
        target=rl.target,
        radix=rl.radix,
        postfix=b'tmpcensored',
        censorable=True,
        data_config=rl.data_config,
        delta_config=rl.delta_config,
        feature_config=rl.feature_config,
        may_inline=rl._inline,
    )
    # inline splitting will prepare some transaction work that will get
    # confused by the final file move. So if there is a risk of not being
    # inline at the end, we prevent the new revlog to be inline in the first
    # place.
    assert not (newrl._inline and not rl._inline)

    for rev in rl.revs():
        node = rl.node(rev)
        p1, p2 = rl.parents(node)

        if rev in censor_revs:
            newrl.addrawrevision(
                tombstone,
                tr,
                rl.linkrev(rev),
                p1,
                p2,
                node,
                constants.REVIDX_ISCENSORED,
            )

            if newrl.deltaparent(rev) != nullrev:
                m = _(b'censored revision stored as delta; cannot censor')
                h = _(
                    b'censoring of revlogs is not fully implemented;'
                    b' please report this bug'
                )
                raise error.Abort(m, hint=h)
            continue

        if rl.iscensored(rev):
            if rl.deltaparent(rev) != nullrev:
                m = _(
                    b'cannot censor due to censored '
                    b'revision having delta stored'
                )
                raise error.Abort(m)
            rawtext = rl._inner._chunk(rev)
        else:
            rawtext = rl.rawdata(rev)

        newrl.addrawrevision(
            rawtext, tr, rl.linkrev(rev), p1, p2, node, rl.flags(rev)
        )

    tr.addbackup(rl._indexfile, location=b'store')
    if not rl._inline:
        tr.addbackup(rl._datafile, location=b'store')

    rl.opener.rename(newrl._indexfile, rl._indexfile)
    if newrl._inline:
        assert rl._inline
    else:
        assert not rl._inline
        rl.opener.rename(newrl._datafile, rl._datafile)

    rl.clearcaches()
    chunk_cache = rl._loadindex()
    rl._load_inner(chunk_cache)


def v2_censor(revlog, tr, censor_nodes, tombstone=b''):
    """censors a revision in a "version 2" revlog"""
    assert revlog._format_version != REVLOGV0, revlog._format_version
    assert revlog._format_version != REVLOGV1, revlog._format_version

    censor_revs = {revlog.rev(node) for node in censor_nodes}
    _rewrite_v2(revlog, tr, censor_revs, tombstone)


def _rewrite_v2(revlog, tr, censor_revs, tombstone=b''):
    """rewrite a revlog to censor some of its content

    General principle

    We create new revlog files (index/data/sidedata) to copy the content of
    the existing data without the censored data.

    We need to recompute new delta for any revision that used the censored
    revision as delta base. As the cumulative size of the new delta may be
    large, we store them in a temporary file until they are stored in their
    final destination.

    All data before the censored data can be blindly copied. The rest needs
    to be copied as we go and the associated index entry needs adjustement.
    """
    assert revlog._format_version != REVLOGV0, revlog._format_version
    assert revlog._format_version != REVLOGV1, revlog._format_version

    old_index = revlog.index
    docket = revlog._docket

    tombstone = storageutil.packmeta({b'censored': tombstone}, b'')

    first_excl_rev = min(censor_revs)

    first_excl_entry = revlog.index[first_excl_rev]
    index_cutoff = revlog.index.entry_size * first_excl_rev
    data_cutoff = first_excl_entry[ENTRY_DATA_OFFSET] >> 16
    sidedata_cutoff = revlog.sidedata_cut_off(first_excl_rev)

    with pycompat.unnamedtempfile(mode=b"w+b") as tmp_storage:
        # rev → (new_base, data_start, data_end, compression_mode)
        rewritten_entries = _precompute_rewritten_delta(
            revlog,
            old_index,
            censor_revs,
            tmp_storage,
        )

        all_files = _setup_new_files(
            revlog,
            index_cutoff,
            data_cutoff,
            sidedata_cutoff,
        )

        # we dont need to open the old index file since its content already
        # exist in a usable form in `old_index`.
        with all_files() as open_files:
            (
                old_data_file,
                old_sidedata_file,
                new_index_file,
                new_data_file,
                new_sidedata_file,
            ) = open_files

            # writing the censored revision

            # Writing all subsequent revisions
            for rev in range(first_excl_rev, len(old_index)):
                if rev in censor_revs:
                    _rewrite_censor(
                        revlog,
                        old_index,
                        open_files,
                        rev,
                        tombstone,
                    )
                else:
                    _rewrite_simple(
                        revlog,
                        old_index,
                        open_files,
                        rev,
                        rewritten_entries,
                        tmp_storage,
                    )
    docket.write(transaction=None, stripping=True)


def _precompute_rewritten_delta(
    revlog,
    old_index,
    excluded_revs,
    tmp_storage,
):
    """Compute new delta for revisions whose delta is based on revision that
    will not survive as is.

    Return a mapping: {rev → (new_base, data_start, data_end, compression_mode)}
    """
    dc = deltas.deltacomputer(revlog)
    rewritten_entries = {}
    first_excl_rev = min(excluded_revs)
    with revlog.reading():
        for rev in range(first_excl_rev, len(old_index)):
            if rev in excluded_revs:
                # this revision will be preserved as is, so we don't need to
                # consider recomputing a delta.
                continue
            entry = old_index[rev]
            if entry[ENTRY_DELTA_BASE] not in excluded_revs:
                continue
            # This is a revision that use the censored revision as the base
            # for its delta. We need a need new deltas
            if entry[ENTRY_DATA_UNCOMPRESSED_LENGTH] == 0:
                # this revision is empty, we can delta against nullrev
                rewritten_entries[rev] = (nullrev, 0, 0, COMP_MODE_PLAIN)
            else:
                text = revlog.rawdata(rev)
                info = revlogutils.revisioninfo(
                    node=entry[ENTRY_NODE_ID],
                    p1=revlog.node(entry[ENTRY_PARENT_1]),
                    p2=revlog.node(entry[ENTRY_PARENT_2]),
                    btext=[text],
                    textlen=len(text),
                    cachedelta=None,
                    flags=entry[ENTRY_DATA_OFFSET] & 0xFFFF,
                )
                d = dc.finddeltainfo(
                    info, excluded_bases=excluded_revs, target_rev=rev
                )
                default_comp = revlog._docket.default_compression_header
                comp_mode, d = deltas.delta_compression(default_comp, d)
                # using `tell` is a bit lazy, but we are not here for speed
                start = tmp_storage.tell()
                tmp_storage.write(d.data[1])
                end = tmp_storage.tell()
                rewritten_entries[rev] = (d.base, start, end, comp_mode)
    return rewritten_entries


def _setup_new_files(
    revlog,
    index_cutoff,
    data_cutoff,
    sidedata_cutoff,
):
    """

    return a context manager to open all the relevant files:
    - old_data_file,
    - old_sidedata_file,
    - new_index_file,
    - new_data_file,
    - new_sidedata_file,

    The old_index_file is not here because it is accessed through the
    `old_index` object if the caller function.
    """
    docket = revlog._docket
    old_index_filepath = revlog.opener.join(docket.index_filepath())
    old_data_filepath = revlog.opener.join(docket.data_filepath())
    old_sidedata_filepath = revlog.opener.join(docket.sidedata_filepath())

    new_index_filepath = revlog.opener.join(docket.new_index_file())
    new_data_filepath = revlog.opener.join(docket.new_data_file())
    new_sidedata_filepath = revlog.opener.join(docket.new_sidedata_file())

    util.copyfile(old_index_filepath, new_index_filepath, nb_bytes=index_cutoff)
    util.copyfile(old_data_filepath, new_data_filepath, nb_bytes=data_cutoff)
    util.copyfile(
        old_sidedata_filepath,
        new_sidedata_filepath,
        nb_bytes=sidedata_cutoff,
    )
    revlog.opener.register_file(docket.index_filepath())
    revlog.opener.register_file(docket.data_filepath())
    revlog.opener.register_file(docket.sidedata_filepath())

    docket.index_end = index_cutoff
    docket.data_end = data_cutoff
    docket.sidedata_end = sidedata_cutoff

    # reload the revlog internal information
    revlog.clearcaches()
    revlog._loadindex(docket=docket)

    @contextlib.contextmanager
    def all_files_opener():
        # hide opening in an helper function to please check-code, black
        # and various python version at the same time
        with open(old_data_filepath, 'rb') as old_data_file:
            with open(old_sidedata_filepath, 'rb') as old_sidedata_file:
                with open(new_index_filepath, 'r+b') as new_index_file:
                    with open(new_data_filepath, 'r+b') as new_data_file:
                        with open(
                            new_sidedata_filepath, 'r+b'
                        ) as new_sidedata_file:
                            new_index_file.seek(0, os.SEEK_END)
                            assert new_index_file.tell() == index_cutoff
                            new_data_file.seek(0, os.SEEK_END)
                            assert new_data_file.tell() == data_cutoff
                            new_sidedata_file.seek(0, os.SEEK_END)
                            assert new_sidedata_file.tell() == sidedata_cutoff
                            yield (
                                old_data_file,
                                old_sidedata_file,
                                new_index_file,
                                new_data_file,
                                new_sidedata_file,
                            )

    return all_files_opener


def _rewrite_simple(
    revlog,
    old_index,
    all_files,
    rev,
    rewritten_entries,
    tmp_storage,
):
    """append a normal revision to the index after the rewritten one(s)"""
    (
        old_data_file,
        old_sidedata_file,
        new_index_file,
        new_data_file,
        new_sidedata_file,
    ) = all_files
    entry = old_index[rev]
    flags = entry[ENTRY_DATA_OFFSET] & 0xFFFF
    old_data_offset = entry[ENTRY_DATA_OFFSET] >> 16

    if rev not in rewritten_entries:
        old_data_file.seek(old_data_offset)
        new_data_size = entry[ENTRY_DATA_COMPRESSED_LENGTH]
        new_data = old_data_file.read(new_data_size)
        data_delta_base = entry[ENTRY_DELTA_BASE]
        d_comp_mode = entry[ENTRY_DATA_COMPRESSION_MODE]
    else:
        (
            data_delta_base,
            start,
            end,
            d_comp_mode,
        ) = rewritten_entries[rev]
        new_data_size = end - start
        tmp_storage.seek(start)
        new_data = tmp_storage.read(new_data_size)

    # It might be faster to group continuous read/write operation,
    # however, this is censor, an operation that is not focussed
    # around stellar performance. So I have not written this
    # optimisation yet.
    new_data_offset = new_data_file.tell()
    new_data_file.write(new_data)

    sidedata_size = entry[ENTRY_SIDEDATA_COMPRESSED_LENGTH]
    new_sidedata_offset = new_sidedata_file.tell()
    if 0 < sidedata_size:
        old_sidedata_offset = entry[ENTRY_SIDEDATA_OFFSET]
        old_sidedata_file.seek(old_sidedata_offset)
        new_sidedata = old_sidedata_file.read(sidedata_size)
        new_sidedata_file.write(new_sidedata)

    data_uncompressed_length = entry[ENTRY_DATA_UNCOMPRESSED_LENGTH]
    sd_com_mode = entry[ENTRY_SIDEDATA_COMPRESSION_MODE]
    assert data_delta_base <= rev, (data_delta_base, rev)

    new_entry = revlogutils.entry(
        flags=flags,
        data_offset=new_data_offset,
        data_compressed_length=new_data_size,
        data_uncompressed_length=data_uncompressed_length,
        data_delta_base=data_delta_base,
        link_rev=entry[ENTRY_LINK_REV],
        parent_rev_1=entry[ENTRY_PARENT_1],
        parent_rev_2=entry[ENTRY_PARENT_2],
        node_id=entry[ENTRY_NODE_ID],
        sidedata_offset=new_sidedata_offset,
        sidedata_compressed_length=sidedata_size,
        data_compression_mode=d_comp_mode,
        sidedata_compression_mode=sd_com_mode,
    )
    revlog.index.append(new_entry)
    entry_bin = revlog.index.entry_binary(rev)
    new_index_file.write(entry_bin)

    revlog._docket.index_end = new_index_file.tell()
    revlog._docket.data_end = new_data_file.tell()
    revlog._docket.sidedata_end = new_sidedata_file.tell()


def _rewrite_censor(
    revlog,
    old_index,
    all_files,
    rev,
    tombstone,
):
    """rewrite and append a censored revision"""
    (
        old_data_file,
        old_sidedata_file,
        new_index_file,
        new_data_file,
        new_sidedata_file,
    ) = all_files
    entry = old_index[rev]

    # XXX consider trying the default compression too
    new_data_size = len(tombstone)
    new_data_offset = new_data_file.tell()
    new_data_file.write(tombstone)

    # we are not adding any sidedata as they might leak info about the censored version

    link_rev = entry[ENTRY_LINK_REV]

    p1 = entry[ENTRY_PARENT_1]
    p2 = entry[ENTRY_PARENT_2]

    new_entry = revlogutils.entry(
        flags=constants.REVIDX_ISCENSORED,
        data_offset=new_data_offset,
        data_compressed_length=new_data_size,
        data_uncompressed_length=new_data_size,
        data_delta_base=rev,
        link_rev=link_rev,
        parent_rev_1=p1,
        parent_rev_2=p2,
        node_id=entry[ENTRY_NODE_ID],
        sidedata_offset=0,
        sidedata_compressed_length=0,
        data_compression_mode=COMP_MODE_PLAIN,
        sidedata_compression_mode=COMP_MODE_PLAIN,
    )
    revlog.index.append(new_entry)
    entry_bin = revlog.index.entry_binary(rev)
    new_index_file.write(entry_bin)
    revlog._docket.index_end = new_index_file.tell()
    revlog._docket.data_end = new_data_file.tell()


def _get_filename_from_filelog_index(path):
    # Drop the extension and the `data/` prefix
    path_part = path.rsplit(b'.', 1)[0].split(b'/', 1)
    if len(path_part) < 2:
        msg = _(b"cannot recognize filelog from filename: '%s'")
        msg %= path
        raise error.Abort(msg)

    return path_part[1]


def _filelog_from_filename(repo, path):
    """Returns the filelog for the given `path`. Stolen from `engine.py`"""

    from .. import filelog  # avoid cycle

    fl = filelog.filelog(repo.svfs, path)
    return fl


def _write_swapped_parents(repo, rl, rev, offset, fp):
    """Swaps p1 and p2 and overwrites the revlog entry for `rev` in `fp`"""
    from ..pure import parsers  # avoid cycle

    if repo._currentlock(repo._lockref) is None:
        # Let's be paranoid about it
        msg = "repo needs to be locked to rewrite parents"
        raise error.ProgrammingError(msg)

    index_format = parsers.IndexObject.index_format
    entry = rl.index[rev]
    new_entry = list(entry)
    new_entry[5], new_entry[6] = entry[6], entry[5]
    packed = index_format.pack(*new_entry[:8])
    fp.seek(offset)
    fp.write(packed)


def _reorder_filelog_parents(repo, fl, to_fix):
    """
    Swaps p1 and p2 for all `to_fix` revisions of filelog `fl` and writes the
    new version to disk, overwriting the old one with a rename.
    """
    from ..pure import parsers  # avoid cycle

    ui = repo.ui
    assert len(to_fix) > 0
    rl = fl._revlog
    if rl._format_version != constants.REVLOGV1:
        msg = "expected version 1 revlog, got version '%d'" % rl._format_version
        raise error.ProgrammingError(msg)

    index_file = rl._indexfile
    new_file_path = index_file + b'.tmp-parents-fix'
    repaired_msg = _(b"repaired revision %d of 'filelog %s'\n")

    with ui.uninterruptible():
        try:
            util.copyfile(
                rl.opener.join(index_file),
                rl.opener.join(new_file_path),
                checkambig=rl.data_config.check_ambig,
            )

            with rl.opener(new_file_path, mode=b"r+") as fp:
                if rl._inline:
                    index = parsers.InlinedIndexObject(fp.read())
                    for rev in fl.revs():
                        if rev in to_fix:
                            offset = index._calculate_index(rev)
                            _write_swapped_parents(repo, rl, rev, offset, fp)
                            ui.write(repaired_msg % (rev, index_file))
                else:
                    index_format = parsers.IndexObject.index_format
                    for rev in to_fix:
                        offset = rev * index_format.size
                        _write_swapped_parents(repo, rl, rev, offset, fp)
                        ui.write(repaired_msg % (rev, index_file))

            rl.opener.rename(new_file_path, index_file)
            rl.clearcaches()
            rl._loadindex()
        finally:
            util.tryunlink(new_file_path)


def _is_revision_affected(fl, filerev, metadata_cache=None):
    full_text = lambda: fl._revlog.rawdata(filerev)
    parent_revs = lambda: fl._revlog.parentrevs(filerev)
    return _is_revision_affected_inner(
        full_text, parent_revs, filerev, metadata_cache
    )


def _is_revision_affected_inner(
    full_text,
    parents_revs,
    filerev,
    metadata_cache=None,
):
    """Mercurial currently (5.9rc0) uses `p1 == nullrev and p2 != nullrev` as a
    special meaning compared to the reverse in the context of filelog-based
    copytracing. issue6528 exists because new code assumed that parent ordering
    didn't matter, so this detects if the revision contains metadata (since
    it's only used for filelog-based copytracing) and its parents are in the
    "wrong" order."""
    try:
        raw_text = full_text()
    except error.CensoredNodeError:
        # We don't care about censored nodes as they never carry metadata
        return False

    # raw text can be a `memoryview`, which doesn't implement `startswith`
    has_meta = bytes(raw_text[:2]) == b'\x01\n'
    if metadata_cache is not None:
        metadata_cache[filerev] = has_meta
    if has_meta:
        (p1, p2) = parents_revs()
        if p1 != nullrev and p2 == nullrev:
            return True
    return False


def _is_revision_affected_fast(repo, fl, filerev, metadata_cache):
    rl = fl._revlog
    is_censored = lambda: rl.iscensored(filerev)
    delta_base = lambda: rl.deltaparent(filerev)
    delta = lambda: rl._inner._chunk(filerev)
    full_text = lambda: rl.rawdata(filerev)
    parent_revs = lambda: rl.parentrevs(filerev)
    # This function is used by repair_issue6528, but not by
    # filter_delta_issue6528. As such, we do not want to trust
    # parent revisions of the delta base to decide whether
    # the delta base has metadata.
    return _is_revision_affected_fast_inner(
        is_censored,
        delta_base,
        delta,
        full_text,
        parent_revs,
        None,  # don't trust the parent revisions
        filerev,
        metadata_cache,
    )


def _is_revision_affected_fast_inner(
    is_censored,
    delta_base,
    delta,
    full_text,
    parent_revs,
    deltabase_parentrevs,
    filerev,
    metadata_cache,
):
    """Optimization fast-path for `_is_revision_affected`.

    `metadata_cache` is a dict of `{rev: has_metadata}` which allows any
    revision to check if its base has metadata, saving computation of the full
    text, instead looking at the current delta.

    This optimization only works if the revisions are looked at in order."""

    if is_censored():
        # Censored revisions don't contain metadata, so they cannot be affected
        metadata_cache[filerev] = False
        return False

    p1, p2 = parent_revs()
    if p1 == nullrev or p2 != nullrev:
        metadata_cache[filerev] = True
        return False

    delta_parent = delta_base()
    parent_has_metadata = metadata_cache.get(delta_parent)
    if parent_has_metadata is None:
        if deltabase_parentrevs is not None:
            deltabase_parentrevs = deltabase_parentrevs()
            if deltabase_parentrevs == (nullrev, nullrev):
                # Need to check the content itself as there is no flag.
                parent_has_metadata = None
            elif deltabase_parentrevs[0] == nullrev:
                # Second parent is !null, assume repository is correct
                # and has flagged this file revision as having metadata.
                parent_has_metadata = True
            elif deltabase_parentrevs[1] == nullrev:
                # First parent is !null, so assume it has no metadata.
                parent_has_metadata = False
        if parent_has_metadata is None:
            return _is_revision_affected_inner(
                full_text,
                parent_revs,
                filerev,
                metadata_cache,
            )

    chunk = delta()
    if not len(chunk):
        # No diff for this revision
        metadata_cache[filerev] = parent_has_metadata
        return parent_has_metadata

    header_length = 12
    if len(chunk) < header_length:
        raise error.Abort(_(b"patch cannot be decoded"))

    start, _end, _length = struct.unpack(b">lll", chunk[:header_length])

    if start < 2:  # len(b'\x01\n') == 2
        # This delta does *something* to the metadata marker (if any).
        # Check it the slow way
        is_affected = _is_revision_affected_inner(
            full_text,
            parent_revs,
            filerev,
            metadata_cache,
        )
        return is_affected

    # The diff did not remove or add the metadata header, it's then in the same
    # situation as its parent
    metadata_cache[filerev] = parent_has_metadata
    return parent_has_metadata


def _from_report(ui, repo, context, from_report, dry_run):
    """
    Fix the revisions given in the `from_report` file, but still checks if the
    revisions are indeed affected to prevent an unfortunate cyclic situation
    where we'd swap well-ordered parents again.

    See the doc for `debug_fix_issue6528` for the format documentation.
    """
    ui.write(_(b"loading report file '%s'\n") % from_report)

    with context(), open(from_report, mode='rb') as f:
        for line in f.read().split(b'\n'):
            if not line:
                continue
            filenodes, filename = line.split(b' ', 1)
            fl = _filelog_from_filename(repo, filename)
            to_fix = set(
                fl.rev(binascii.unhexlify(n)) for n in filenodes.split(b',')
            )
            excluded = set()

            for filerev in to_fix:
                if _is_revision_affected(fl, filerev):
                    msg = b"found affected revision %d for filelog '%s'\n"
                    ui.warn(msg % (filerev, filename))
                else:
                    msg = _(b"revision %s of file '%s' is not affected\n")
                    msg %= (binascii.hexlify(fl.node(filerev)), filename)
                    ui.warn(msg)
                    excluded.add(filerev)

            to_fix = to_fix - excluded
            if not to_fix:
                msg = _(b"no affected revisions were found for '%s'\n")
                ui.write(msg % filename)
                continue
            if not dry_run:
                _reorder_filelog_parents(repo, fl, sorted(to_fix))


def filter_delta_issue6528(revlog, deltas_iter):
    """filter incomind deltas to repaire issue 6528 on the fly"""
    metadata_cache = {nullrev: False}

    deltacomputer = deltas.deltacomputer(revlog)

    for rev, d in enumerate(deltas_iter, len(revlog)):
        (
            node,
            p1_node,
            p2_node,
            linknode,
            deltabase,
            delta,
            flags,
            sidedata,
        ) = d

        if not revlog.index.has_node(deltabase):
            raise error.LookupError(
                deltabase, revlog.radix, _(b'unknown parent')
            )
        base_rev = revlog.rev(deltabase)
        if not revlog.index.has_node(p1_node):
            raise error.LookupError(p1_node, revlog.radix, _(b'unknown parent'))
        p1_rev = revlog.rev(p1_node)
        if not revlog.index.has_node(p2_node):
            raise error.LookupError(p2_node, revlog.radix, _(b'unknown parent'))
        p2_rev = revlog.rev(p2_node)

        is_censored = lambda: bool(flags & REVIDX_ISCENSORED)
        delta_base = lambda: base_rev
        parent_revs = lambda: (p1_rev, p2_rev)
        deltabase_parentrevs = lambda: revlog.parentrevs(base_rev)

        def full_text():
            # note: being able to reuse the full text computation in the
            # underlying addrevision would be useful however this is a bit too
            # intrusive the for the "quick" issue6528 we are writing before the
            # 5.8 release
            textlen = mdiff.patchedsize(revlog.size(base_rev), delta)

            revinfo = revlogutils.revisioninfo(
                node,
                p1_node,
                p2_node,
                [None],
                textlen,
                (base_rev, delta),
                flags,
            )
            return deltacomputer.buildtext(revinfo)

        is_affected = _is_revision_affected_fast_inner(
            is_censored,
            delta_base,
            lambda: delta,
            full_text,
            parent_revs,
            deltabase_parentrevs,
            rev,
            metadata_cache,
        )
        if is_affected:
            d = (
                node,
                p2_node,
                p1_node,
                linknode,
                deltabase,
                delta,
                flags,
                sidedata,
            )
        yield d


def repair_issue6528(
    ui, repo, dry_run=False, to_report=None, from_report=None, paranoid=False
):
    @contextlib.contextmanager
    def context():
        if dry_run or to_report:  # No need for locking
            yield
        else:
            with repo.wlock(), repo.lock():
                yield

    if from_report:
        return _from_report(ui, repo, context, from_report, dry_run)

    report_entries = []

    with context():
        files = list(
            entry
            for entry in repo.store.data_entries()
            if entry.is_revlog and entry.is_filelog
        )

        progress = ui.makeprogress(
            _(b"looking for affected revisions"),
            unit=_(b"filelogs"),
            total=len(files),
        )
        found_nothing = True

        for entry in files:
            progress.increment()
            filename = entry.target_id
            fl = _filelog_from_filename(repo, entry.target_id)

            # Set of filerevs (or hex filenodes if `to_report`) that need fixing
            to_fix = set()
            metadata_cache = {nullrev: False}
            for filerev in fl.revs():
                affected = _is_revision_affected_fast(
                    repo, fl, filerev, metadata_cache
                )
                if paranoid:
                    slow = _is_revision_affected(fl, filerev)
                    if slow != affected:
                        msg = _(b"paranoid check failed for '%s' at node %s")
                        node = binascii.hexlify(fl.node(filerev))
                        raise error.Abort(msg % (filename, node))
                if affected:
                    msg = b"found affected revision %d for file '%s'\n"
                    ui.warn(msg % (filerev, filename))
                    found_nothing = False
                    if not dry_run:
                        if to_report:
                            to_fix.add(binascii.hexlify(fl.node(filerev)))
                        else:
                            to_fix.add(filerev)

            if to_fix:
                to_fix = sorted(to_fix)
                if to_report:
                    report_entries.append((filename, to_fix))
                else:
                    _reorder_filelog_parents(repo, fl, to_fix)

        if found_nothing:
            ui.write(_(b"no affected revisions were found\n"))

        if to_report and report_entries:
            with open(to_report, mode="wb") as f:
                for path, to_fix in report_entries:
                    f.write(b"%s %s\n" % (b",".join(to_fix), path))

        progress.complete()