mercurial/state.py

narrow: add server logic to send cg while widening without ellipsis

Before this patch, if you try to widen a narrow clone without ellipsis enabled,
it will be broken and the exchange.pull() done by tracked command to widen the
clone will be no-op because no custom logic exists for this and server sees that
we have all csets and it says `no changes found`.

The widening with ellipsis send KILL for existing changegroups and send new
changegroups because of the change in ellipsis hash, but we can prevent that in
non-ellipsis cases.

This patch adds server side logic to send the changegroups for the changesets
which are on the client again with filelogs and manifests for the new includes.
This is a very starting implementation and we send changegroups and manifests
too while we can prevent them.

Following things can definitely be improved in the logic this patch adds:

  1) Send just the filelogs and treemanifests
  2) Send the filelogs only for the additions in the include

I tried 1) here but the code is coupled tightly and the way I was able to do
that was hacking into the changegroup generation code in a very dirty way, like
adding conditionals and preventing the yield.

This patch also adds a 'widen' kwarg to prevent other commands except widening
to go through that codepath.

The test changes demonstrate that the new implementation is correct and fixes
things.

Differential Revision: https://phab.mercurial-scm.org/D4383

# state.py - writing and reading state files in Mercurial
#
# Copyright 2018 Pulkit Goyal <[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.

"""
This file contains class to wrap the state for commands and other
related logic.

All the data related to the command state is stored as dictionary in the object.
The class has methods using which the data can be stored to disk in a file under
.hg/ directory.

We store the data on disk in cbor, for which we use the third party cbor library
to serialize and deserialize data.
"""

from __future__ import absolute_import

from .thirdparty import cbor

from . import (
    error,
    util,
)

class cmdstate(object):
    """a wrapper class to store the state of commands like `rebase`, `graft`,
    `histedit`, `shelve` etc. Extensions can also use this to write state files.

    All the data for the state is stored in the form of key-value pairs in a
    dictionary.

    The class object can write all the data to a file in .hg/ directory and
    can populate the object data reading that file.

    Uses cbor to serialize and deserialize data while writing and reading from
    disk.
    """

    def __init__(self, repo, fname):
        """ repo is the repo object
        fname is the file name in which data should be stored in .hg directory
        """
        self._repo = repo
        self.fname = fname

    def read(self):
        """read the existing state file and return a dict of data stored"""
        return self._read()

    def save(self, version, data):
        """write all the state data stored to .hg/<filename> file

        we use third-party library cbor to serialize data to write in the file.
        """
        if not isinstance(version, int):
            raise error.ProgrammingError("version of state file should be"
                                         " an integer")

        with self._repo.vfs(self.fname, 'wb', atomictemp=True) as fp:
            fp.write('%d\n' % version)
            cbor.dump(data, fp, canonical=True)

    def _read(self):
        """reads the state file and returns a dictionary which contain
        data in the same format as it was before storing"""
        with self._repo.vfs(self.fname, 'rb') as fp:
            try:
                int(fp.readline())
            except ValueError:
                raise error.CorruptedState("unknown version of state file"
                                           " found")
            return cbor.load(fp)

    def delete(self):
        """drop the state file if exists"""
        util.unlinkpath(self._repo.vfs.join(self.fname), ignoremissing=True)

    def exists(self):
        """check whether the state file exists or not"""
        return self._repo.vfs.exists(self.fname)