mercurial/utils/repoviewutil.py

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

# repoviewutil.py - constaints data relevant to repoview.py and other module
#
# Copyright 2012 Pierre-Yves David <[e-mail]>
#                Logilab SA        <[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

from .. import error

### Nearest subset relation
# Nearest subset of filter X is a filter Y so that:
# * Y is included in X,
# * X - Y is as small as possible.
# This create and ordering used for branchmap purpose.
# the ordering may be partial
subsettable = {
    None: b'visible',
    b'visible-hidden': b'visible',
    b'visible': b'served',
    b'served.hidden': b'served',
    b'served': b'immutable',
    b'immutable': b'base',
}


def get_ordered_subset():
    """return a list of subset name from dependencies to dependents"""
    _unfinalized = set(subsettable.values())
    ordered = []

    # the subset table is expected to be small so we do the stupid N² version
    # of the algorithm
    while _unfinalized:
        this_level = []
        for candidate in _unfinalized:
            dependency = subsettable.get(candidate)
            if dependency not in _unfinalized:
                this_level.append(candidate)

        if not this_level:
            msg = "cyclic dependencies in repoview subset %r"
            msg %= subsettable
            raise error.ProgrammingError(msg)

        this_level.sort(key=lambda x: x if x is not None else '')

        ordered.extend(this_level)
        _unfinalized.difference_update(this_level)

    return ordered