view mercurial/scmwindows.py @ 49000:dd6b67d5c256 stable

rust: fix unsound `OwningDirstateMap`

As per the previous patch, `OwningDirstateMap` is unsound. Self-referential
structs are difficult to implement correctly in Rust since the compiler is
free to move structs around as much as it wants to. They are also very rarely
needed in practice, so the state-of-the-art on how they should be done within
the Rust rules is still a bit new.

The crate `ouroboros` is an attempt at providing a safe way (in the Rust sense)
of declaring self-referential structs. It is getting a lot attention and was
improved very quickly when soundness issues were found in the past: rather than
relying on our own (limited) review circle, we might as well use the de-facto
common crate to fix this problem. This will give us a much better chance of
finding issues should any new ones be discovered as well as the benefit of
fewer `unsafe` APIs of our own.

I was starting to think about how I would present a safe API to the old struct
but soon realized that the callback-based approach was already done in
`ouroboros`, along with a lot more care towards refusing incorrect structs.

In short: we don't return a mutable reference to the `DirstateMap` anymore, we
expect users of its API to pass a `FnOnce` that takes the map as an argument.
This allows our `OwningDirstateMap` to control the input and output lifetimes
of the code that modifies it to prevent such issues.

Changing to `ouroboros` meant changing every API with it, but it is relatively
low churn in the end. It correctly identified the example buggy modification of
`copy_map_insert` outlined in the previous patch as violating the borrow rules.

Differential Revision: https://phab.mercurial-scm.org/D12429

from __future__ import absolute_import

import os

from . import (
    encoding,
    pycompat,
    util,
    win32,
)

try:
    import _winreg as winreg  # pytype: disable=import-error

    winreg.CloseKey
except ImportError:
    # py2 only
    import winreg  # pytype: disable=import-error

# MS-DOS 'more' is the only pager available by default on Windows.
fallbackpager = b'more'


def systemrcpath():
    '''return default os-specific hgrc search path'''
    rcpath = []
    filename = win32.executablepath()
    # Use mercurial.ini found in directory with hg.exe
    progrc = os.path.join(os.path.dirname(filename), b'mercurial.ini')
    rcpath.append(progrc)

    def _processdir(progrcd):
        if os.path.isdir(progrcd):
            for f, kind in sorted(util.listdir(progrcd)):
                if f.endswith(b'.rc'):
                    rcpath.append(os.path.join(progrcd, f))

    # Use hgrc.d found in directory with hg.exe
    _processdir(os.path.join(os.path.dirname(filename), b'hgrc.d'))

    # treat a PROGRAMDATA directory as equivalent to /etc/mercurial
    programdata = encoding.environ.get(b'PROGRAMDATA')
    if programdata:
        programdata = os.path.join(programdata, b'Mercurial')
        _processdir(os.path.join(programdata, b'hgrc.d'))

        ini = os.path.join(programdata, b'mercurial.ini')
        if os.path.isfile(ini):
            rcpath.append(ini)

        ini = os.path.join(programdata, b'hgrc')
        if os.path.isfile(ini):
            rcpath.append(ini)

    # next look for a system rcpath in the registry
    value = util.lookupreg(
        b'SOFTWARE\\Mercurial', None, winreg.HKEY_LOCAL_MACHINE
    )
    if value and isinstance(value, bytes):
        value = util.localpath(value)
        for p in value.split(pycompat.ospathsep):
            if p.lower().endswith(b'mercurial.ini'):
                rcpath.append(p)
            else:
                _processdir(p)
    return rcpath


def userrcpath():
    '''return os-specific hgrc search path to the user dir'''
    home = _legacy_expanduser(b'~')
    path = [os.path.join(home, b'mercurial.ini'), os.path.join(home, b'.hgrc')]
    userprofile = encoding.environ.get(b'USERPROFILE')
    if userprofile and userprofile != home:
        path.append(os.path.join(userprofile, b'mercurial.ini'))
        path.append(os.path.join(userprofile, b'.hgrc'))
    return path


def _legacy_expanduser(path):
    """Expand ~ and ~user constructs in the pre 3.8 style"""

    # Python 3.8+ changed the expansion of '~' from HOME to USERPROFILE.  See
    # https://bugs.python.org/issue36264.  It also seems to capitalize the drive
    # letter, as though it was processed through os.path.realpath().
    if not path.startswith(b'~'):
        return path

    i, n = 1, len(path)
    while i < n and path[i] not in b'\\/':
        i += 1

    if b'HOME' in encoding.environ:
        userhome = encoding.environ[b'HOME']
    elif b'USERPROFILE' in encoding.environ:
        userhome = encoding.environ[b'USERPROFILE']
    elif b'HOMEPATH' not in encoding.environ:
        return path
    else:
        try:
            drive = encoding.environ[b'HOMEDRIVE']
        except KeyError:
            drive = b''
        userhome = os.path.join(drive, encoding.environ[b'HOMEPATH'])

    if i != 1:  # ~user
        userhome = os.path.join(os.path.dirname(userhome), path[1:i])

    return userhome + path[i:]


def termsize(ui):
    return win32.termsize()