view mercurial/revlogutils/flagutil.py @ 42877:5bb68fb72df2

flagutil: introduce a flagprocessorsmixin class

To avoid code duplication, we will provide a simple "ready to use" mixin that
carry the appropriate logic. First we use it in standard revlog, we'll remove
code duplication in later changesets.

Differential Revision: https://phab.mercurial-scm.org/D6796

# flagutils.py - code to deal with revlog flags and their processors
#
# Copyright 2016 Remi Chaintron <[e-mail]>
# Copyright 2016-2019 Pierre-Yves David <[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 absolute_import

from ..i18n import _

from .constants import (
    REVIDX_DEFAULT_FLAGS,
    REVIDX_ELLIPSIS,
    REVIDX_EXTSTORED,
    REVIDX_FLAGS_ORDER,
    REVIDX_ISCENSORED,
    REVIDX_RAWTEXT_CHANGING_FLAGS,
)

from .. import (
    error,
    util
)

# blanked usage of all the name to prevent pyflakes constraints
# We need these name available in the module for extensions.
REVIDX_ISCENSORED
REVIDX_ELLIPSIS
REVIDX_EXTSTORED
REVIDX_DEFAULT_FLAGS
REVIDX_FLAGS_ORDER
REVIDX_RAWTEXT_CHANGING_FLAGS

REVIDX_KNOWN_FLAGS = util.bitsfrom(REVIDX_FLAGS_ORDER)

# Store flag processors (cf. 'addflagprocessor()' to register)
flagprocessors = {
    REVIDX_ISCENSORED: None,
}

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.
    """
    insertflagprocessor(flag, processor, flagprocessors)

def insertflagprocessor(flag, processor, flagprocessors):
    if not flag & REVIDX_KNOWN_FLAGS:
        msg = _("cannot register processor on unknown flag '%#x'.") % (flag)
        raise error.ProgrammingError(msg)
    if flag not in REVIDX_FLAGS_ORDER:
        msg = _("flag '%#x' undefined in REVIDX_FLAGS_ORDER.") % (flag)
        raise error.ProgrammingError(msg)
    if flag in flagprocessors:
        msg = _("cannot register multiple processors on flag '%#x'.") % (flag)
        raise error.Abort(msg)
    flagprocessors[flag] = processor

class flagprocessorsmixin(object):
    """basic mixin to support revlog flag processing

    Make sure the `_flagprocessors` attribute is set at ``__init__`` time.

    See the documentation of the ``_processflags`` method for details.
    """

    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 error.ProgrammingError(_("invalid '%s' operation") %
                                         operation)
        # Check all flags are known.
        if flags & ~REVIDX_KNOWN_FLAGS:
            raise error.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 self._flagprocessors:
                    message = _("missing processor for flag '%#x'") % (flag)
                    raise error.RevlogError(message)

                processor = self._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