view mercurial/revlogutils/constants.py @ 51901:f4733654f144

typing: add `from __future__ import annotations` to most files

Now that py36 is no longer supported, we can postpone annotation evaluation.
This means that the quoting is usually optional (for things imported under the
guard of `if typing.TYPE_CHECKING:` to avoid circular imports), and there's less
overhead on startup[1].

There may be some missing here.  I backed out 6000f5b25c9b (which removed the
`from __future__ import ...` that was supporting py2), reverted the changes in
`contrib/`, `doc/`, and `tests/`, and then ran:

    $ hg status -n --change . | \
        xargs sed -i -e 's/from __future__ import .*$/from __future__ import annotations/'

There were some minor tweaks needed when reviewing (mostly making the spacing
around the import consistent, and `mercurial/testing/__init__.py` had a
multiline import that wasn't fully rewritten.

[1] https://docs.python.org/3/whatsnew/3.7.html#pep-563-postponed-evaluation-of-annotations

# revlogdeltas.py - constant used for revlog logic.
#
# Copyright 2005-2007 Olivia 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.
"""Helper class to compute deltas stored inside revlogs"""

from __future__ import annotations

import struct

from ..interfaces import repository
from .. import revlogutils

### Internal utily constants

KIND_CHANGELOG = 1001  # over 256 to not be comparable with a bytes
KIND_MANIFESTLOG = 1002
KIND_FILELOG = 1003
KIND_OTHER = 1004

ALL_KINDS = {
    KIND_CHANGELOG,
    KIND_MANIFESTLOG,
    KIND_FILELOG,
    KIND_OTHER,
}

### Index entry key
#
#
#    Internal details
#    ----------------
#
#    A large part of the revlog logic deals with revisions' "index entries", tuple
#    objects that contains the same "items" whatever the revlog version.
#    Different versions will have different ways of storing these items (sometimes
#    not having them at all), but the tuple will always be the same. New fields
#    are usually added at the end to avoid breaking existing code that relies
#    on the existing order. The field are defined as follows:

#    [0] offset:
#            The byte index of the start of revision data chunk.
#            That value is shifted up by 16 bits. use "offset = field >> 16" to
#            retrieve it.
#
#        flags:
#            A flag field that carries special information or changes the behavior
#            of the revision. (see `REVIDX_*` constants for details)
#            The flag field only occupies the first 16 bits of this field,
#            use "flags = field & 0xFFFF" to retrieve the value.
ENTRY_DATA_OFFSET = 0

#    [1] compressed length:
#            The size, in bytes, of the chunk on disk
ENTRY_DATA_COMPRESSED_LENGTH = 1

#    [2] uncompressed length:
#            The size, in bytes, of the full revision once reconstructed.
ENTRY_DATA_UNCOMPRESSED_LENGTH = 2

#    [3] base rev:
#            Either the base of the revision delta chain (without general
#            delta), or the base of the delta (stored in the data chunk)
#            with general delta.
ENTRY_DELTA_BASE = 3

#    [4] link rev:
#            Changelog revision number of the changeset introducing this
#            revision.
ENTRY_LINK_REV = 4

#    [5] parent 1 rev:
#            Revision number of the first parent
ENTRY_PARENT_1 = 5

#    [6] parent 2 rev:
#            Revision number of the second parent
ENTRY_PARENT_2 = 6

#    [7] node id:
#            The node id of the current revision
ENTRY_NODE_ID = 7

#    [8] sidedata offset:
#            The byte index of the start of the revision's side-data chunk.
ENTRY_SIDEDATA_OFFSET = 8

#    [9] sidedata chunk length:
#            The size, in bytes, of the revision's side-data chunk.
ENTRY_SIDEDATA_COMPRESSED_LENGTH = 9

#    [10] data compression mode:
#            two bits that detail the way the data chunk is compressed on disk.
#            (see "COMP_MODE_*" constants for details). For revlog version 0 and
#            1 this will always be COMP_MODE_INLINE.
ENTRY_DATA_COMPRESSION_MODE = 10

#    [11] side-data compression mode:
#            two bits that detail the way the sidedata chunk is compressed on disk.
#            (see "COMP_MODE_*" constants for details)
ENTRY_SIDEDATA_COMPRESSION_MODE = 11

#    [12] Revision rank:
#            The number of revision under this one.
#
#            Formally this is defined as : rank(X) = len(ancestors(X) + X)
#
#            If rank == -1; then we do not have this information available.
#            Only `null` has a rank of 0.
ENTRY_RANK = 12

RANK_UNKNOWN = -1

### main revlog header

# We cannot rely on  Struct.format is inconsistent for python <=3.6 versus above
INDEX_HEADER_FMT = b">I"
INDEX_HEADER = struct.Struct(INDEX_HEADER_FMT)

## revlog version
REVLOGV0 = 0
REVLOGV1 = 1
# Dummy value until file format is finalized.
REVLOGV2 = 0xDEAD
# Dummy value until file format is finalized.
CHANGELOGV2 = 0xD34D

##  global revlog header flags
# Shared across v1 and v2.
FLAG_INLINE_DATA = 1 << 16
# Only used by v1, implied by v2.
FLAG_GENERALDELTA = 1 << 17
REVLOG_DEFAULT_FLAGS = FLAG_INLINE_DATA
REVLOG_DEFAULT_FORMAT = REVLOGV1
REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_FORMAT | REVLOG_DEFAULT_FLAGS
REVLOGV0_FLAGS = 0
REVLOGV1_FLAGS = FLAG_INLINE_DATA | FLAG_GENERALDELTA
REVLOGV2_FLAGS = FLAG_INLINE_DATA
CHANGELOGV2_FLAGS = 0

### individual entry

## 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
INDEX_ENTRY_V0 = struct.Struct(b">4l20s20s20s")

## index v1
#  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
INDEX_ENTRY_V1 = struct.Struct(b">Qiiiiii20s12x")
assert INDEX_ENTRY_V1.size == 32 * 2

#  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
#  8 bytes: sidedata offset
#  4 bytes: sidedata compressed length
#  1 bytes: compression mode (2 lower bit are data_compression_mode)
#  19 bytes: Padding to align to 96 bytes (see RevlogV2Plan wiki page)
INDEX_ENTRY_V2 = struct.Struct(b">Qiiiiii20s12xQiB19x")
assert INDEX_ENTRY_V2.size == 32 * 3, INDEX_ENTRY_V2.size

#  6 bytes: offset
#  2 bytes: flags
#  4 bytes: compressed length
#  4 bytes: uncompressed length
#  4 bytes: parent 1 rev
#  4 bytes: parent 2 rev
# 32 bytes: nodeid
#  8 bytes: sidedata offset
#  4 bytes: sidedata compressed length
#  1 bytes: compression mode (2 lower bit are data_compression_mode)
#  4 bytes: changeset rank (i.e. `len(::REV)`)
#  23 bytes: Padding to align to 96 bytes (see RevlogV2Plan wiki page)
INDEX_ENTRY_CL_V2 = struct.Struct(b">Qiiii20s12xQiBi23x")
assert INDEX_ENTRY_CL_V2.size == 32 * 3, INDEX_ENTRY_CL_V2.size
INDEX_ENTRY_V2_IDX_OFFSET = 0
INDEX_ENTRY_V2_IDX_COMPRESSED_LENGTH = 1
INDEX_ENTRY_V2_IDX_UNCOMPRESSED_LENGTH = 2
INDEX_ENTRY_V2_IDX_PARENT_1 = 3
INDEX_ENTRY_V2_IDX_PARENT_2 = 4
INDEX_ENTRY_V2_IDX_NODEID = 5
INDEX_ENTRY_V2_IDX_SIDEDATA_OFFSET = 6
INDEX_ENTRY_V2_IDX_SIDEDATA_COMPRESSED_LENGTH = 7
INDEX_ENTRY_V2_IDX_COMPRESSION_MODE = 8
INDEX_ENTRY_V2_IDX_RANK = 9

# revlog index flags

# For historical reasons, revlog's internal flags were exposed via the
# wire protocol and are even exposed in parts of the storage APIs.

# revision has censor metadata, must be verified
REVIDX_ISCENSORED = repository.REVISION_FLAG_CENSORED
# revision hash does not match data (narrowhg)
REVIDX_ELLIPSIS = repository.REVISION_FLAG_ELLIPSIS
# revision data is stored externally
REVIDX_EXTSTORED = repository.REVISION_FLAG_EXTSTORED
# revision changes files in a way that could affect copy tracing.
REVIDX_HASCOPIESINFO = repository.REVISION_FLAG_HASCOPIESINFO
REVIDX_DEFAULT_FLAGS = 0
# stable order in which flags need to be processed and their processors applied
REVIDX_FLAGS_ORDER = [
    REVIDX_ISCENSORED,
    REVIDX_ELLIPSIS,
    REVIDX_EXTSTORED,
    REVIDX_HASCOPIESINFO,
]

# bitmark for flags that could cause rawdata content change
REVIDX_RAWTEXT_CHANGING_FLAGS = REVIDX_ISCENSORED | REVIDX_EXTSTORED

## chunk compression mode constants:
# These constants are used in revlog version >=2 to denote the compression used
# for a chunk.

# Chunk use no compression, the data stored on disk can be directly use as
# chunk value. Without any header information prefixed.
COMP_MODE_PLAIN = 0

# Chunk use the "default compression" for the revlog (usually defined in the
# revlog docket). A header is still used.
#
# XXX: keeping a header is probably not useful and we should probably drop it.
#
# XXX: The value of allow mixed type of compression in the revlog is unclear
#      and we should consider making PLAIN/DEFAULT the only available mode for
#      revlog v2, disallowing INLINE mode.
COMP_MODE_DEFAULT = 1

# Chunk use a compression mode stored "inline" at the start of the chunk
# itself.  This is the mode always used for revlog version "0" and "1"
COMP_MODE_INLINE = revlogutils.COMP_MODE_INLINE

SUPPORTED_FLAGS = {
    REVLOGV0: REVLOGV0_FLAGS,
    REVLOGV1: REVLOGV1_FLAGS,
    REVLOGV2: REVLOGV2_FLAGS,
    CHANGELOGV2: CHANGELOGV2_FLAGS,
}

_no = lambda flags: False
_yes = lambda flags: True


def _from_flag(flag):
    return lambda flags: bool(flags & flag)


FEATURES_BY_VERSION = {
    REVLOGV0: {
        b'inline': _no,
        b'generaldelta': _no,
        b'sidedata': False,
        b'docket': False,
    },
    REVLOGV1: {
        b'inline': _from_flag(FLAG_INLINE_DATA),
        b'generaldelta': _from_flag(FLAG_GENERALDELTA),
        b'sidedata': False,
        b'docket': False,
    },
    REVLOGV2: {
        # The point of inline-revlog is to reduce the number of files used in
        # the store. Using a docket defeat this purpose. So we needs other
        # means to reduce the number of files for revlogv2.
        b'inline': _no,
        b'generaldelta': _yes,
        b'sidedata': True,
        b'docket': True,
    },
    CHANGELOGV2: {
        b'inline': _no,
        # General delta is useless for changelog since we don't do any delta
        b'generaldelta': _no,
        b'sidedata': True,
        b'docket': True,
    },
}


SPARSE_REVLOG_MAX_CHAIN_LENGTH = 1000

### What should be done with a cached delta and its base ?

# Ignore the cache when considering candidates.
#
# The cached delta might be used, but the delta base will not be scheduled for
# usage earlier than in "normal" order.
DELTA_BASE_REUSE_NO = 0

# Prioritize trying the cached delta base
#
# The delta base will be tested for validy first. So that the cached deltas get
# used when possible.
DELTA_BASE_REUSE_TRY = 1
DELTA_BASE_REUSE_FORCE = 2