view hg @ 34413:014d467f9d08

effectflag: store an empty effect flag for the moment

The idea behind effect flag is to store additional information in obs-markers
about what changed between a changeset and its successor(s). It's a low-level
information that comes without guarantees.

This information can be computed a posteriori, but only if we have all
changesets locally. This is not the case with distributed workflows where you
work with several people or on several computers (eg: laptop + build server).

Storing the effect-flag as a bitfield has several advantages:

- It's compact, we are using one byte per obs-marker at most for the effect-
  flag.
- It's compoundable, the obsfate log approach needs to display evolve history
  that could spans several obs-markers. Computing the effect-flag between a
  changeset and its grand-grand-grand-successor is simple thanks to the
  bitfield.

The effect-flag design has also some limitations:

- Evolving a changeset and reverting these changes just after would lead to
  two obs-markers with the same effect-flag without information that the first
  and third changesets are the same.

The effect-flag current design is a trade-off between compactness and
usefulness.

Storing this information helps commands to display a more complete and
understandable evolve history. For example, obslog (an Evolve command) use it
to improve its output:

x  62206adfd571 (34302) obscache: skip updating outdated obscache...
|    rewritten(parent) by Matthieu Laneuville <matthieu.laneuville@octobus...
|    rewritten(content) by Boris Feld <[e-mail]>

The effect flag is stored in obs-markers metadata while we iterate on the
information we want to store. We plan to extend the existing obsmarkers
bit-field when the effect flag design will be stabilized.

It's different from the CommitCustody concept, effect-flag are not signed and
can be forged. It's also different from the operation metadata as the command
name (for example: amend) could alter a changeset in different ways (changing
the content with hg amend, changing the description with hg amend -e, changing
the user with hg amend -U). Also it's compatible with every custom command
that writes obs-markers without needing to be updated.

The effect-flag is placed behind an experimental flag set to off by default.

Hook the saving of effect flag in create markers, but store only an empty one
for the moment, I will refine the values in effect flag in following patches.

For more information, see:

  https://www.mercurial-scm.org/wiki/ChangesetEvolutionDevel#Record_types_of_operation

Differential Revision: https://phab.mercurial-scm.org/D533

#!/usr/bin/env python
#
# mercurial - scalable distributed SCM
#
# Copyright 2005-2007 Matt Mackall <[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

import os
import sys

if os.environ.get('HGUNICODEPEDANTRY', False):
    try:
        reload(sys)
        sys.setdefaultencoding("undefined")
    except NameError:
        pass

libdir = '@LIBDIR@'

if libdir != '@' 'LIBDIR' '@':
    if not os.path.isabs(libdir):
        libdir = os.path.join(os.path.dirname(os.path.realpath(__file__)),
                              libdir)
        libdir = os.path.abspath(libdir)
    sys.path.insert(0, libdir)

# enable importing on demand to reduce startup time
try:
    if sys.version_info[0] < 3 or sys.version_info >= (3, 6):
        import hgdemandimport; hgdemandimport.enable()
except ImportError:
    sys.stderr.write("abort: couldn't find mercurial libraries in [%s]\n" %
                     ' '.join(sys.path))
    sys.stderr.write("(check your install and PYTHONPATH)\n")
    sys.exit(-1)

from mercurial import (
    dispatch,
    util,
)
for fp in (sys.stdin, sys.stdout, sys.stderr):
    util.setbinary(fp)

dispatch.run()