view mercurial/dirstateutils/timestamp.py @ 48262:68bb472aee9c

dirstate: ignore sub-second component when either is zero in mtime

When comparing mtimes for equality.

Some APIs simply return zero when more precision is not available.
When comparing values from different sources, if only one is truncated in
that way, doing a simple comparison would cause many false negatives.

Differential Revision: https://phab.mercurial-scm.org/D11701

# Copyright Mercurial Contributors
#
# 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 functools
import stat


rangemask = 0x7FFFFFFF


@functools.total_ordering
class timestamp(tuple):
    """
    A Unix timestamp with optional nanoseconds precision,
    modulo 2**31 seconds.

    A 2-tuple containing:

    `truncated_seconds`: seconds since the Unix epoch,
    truncated to its lower 31 bits

    `subsecond_nanoseconds`: number of nanoseconds since `truncated_seconds`.
    When this is zero, the sub-second precision is considered unknown.
    """

    def __new__(cls, value):
        truncated_seconds, subsec_nanos = value
        value = (truncated_seconds & rangemask, subsec_nanos)
        return super(timestamp, cls).__new__(cls, value)

    def __eq__(self, other):
        self_secs, self_subsec_nanos = self
        other_secs, other_subsec_nanos = other
        return self_secs == other_secs and (
            self_subsec_nanos == other_subsec_nanos
            or self_subsec_nanos == 0
            or other_subsec_nanos == 0
        )

    def __gt__(self, other):
        self_secs, self_subsec_nanos = self
        other_secs, other_subsec_nanos = other
        if self_secs > other_secs:
            return True
        if self_secs < other_secs:
            return False
        if self_subsec_nanos == 0 or other_subsec_nanos == 0:
            # they are considered equal, so not "greater than"
            return False
        return self_subsec_nanos > other_subsec_nanos


def zero():
    """
    Returns the `timestamp` at the Unix epoch.
    """
    return tuple.__new__(timestamp, (0, 0))


def mtime_of(stat_result):
    """
    Takes an `os.stat_result`-like object and returns a `timestamp` object
    for its modification time.
    """
    # https://docs.python.org/2/library/os.html#os.stat_float_times
    # "For compatibility with older Python versions,
    #  accessing stat_result as a tuple always returns integers."
    secs = stat_result[stat.ST_MTIME]

    # For now
    subsec_nanos = 0

    return timestamp((secs, subsec_nanos))