view hgext/git/__init__.py @ 46607:e9901d01d135

revlog: add a mechanism to verify expected file position before appending

If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.

The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)

When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.

For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.

This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.

Differential Revision: https://phab.mercurial-scm.org/D9952

"""grant Mercurial the ability to operate on Git repositories. (EXPERIMENTAL)

This is currently super experimental. It probably will consume your
firstborn a la Rumpelstiltskin, etc.
"""

from __future__ import absolute_import

import os

from mercurial.i18n import _

from mercurial import (
    commands,
    error,
    extensions,
    localrepo,
    pycompat,
    registrar,
    scmutil,
    store,
    util,
)

from . import (
    dirstate,
    gitlog,
    gitutil,
    index,
)

# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
# be specifying the version(s) of Mercurial they are tested with, or
# leave the attribute unspecified.
testedwith = b'ships-with-hg-core'

configtable = {}
configitem = registrar.configitem(configtable)
# git.log-index-cache-miss: internal knob for testing
configitem(
    b"git",
    b"log-index-cache-miss",
    default=False,
)

getversion = gitutil.pygit2_version


# TODO: extract an interface for this in core
class gitstore(object):  # store.basicstore):
    def __init__(self, path, vfstype):
        self.vfs = vfstype(path)
        self.path = self.vfs.base
        self.createmode = store._calcmode(self.vfs)
        # above lines should go away in favor of:
        # super(gitstore, self).__init__(path, vfstype)

        self.git = gitutil.get_pygit2().Repository(
            os.path.normpath(os.path.join(path, b'..', b'.git'))
        )
        self._progress_factory = lambda *args, **kwargs: None
        self._logfn = lambda x: None

    @util.propertycache
    def _db(self):
        # We lazy-create the database because we want to thread a
        # progress callback down to the indexing process if it's
        # required, and we don't have a ui handle in makestore().
        return index.get_index(self.git, self._logfn, self._progress_factory)

    def join(self, f):
        """Fake store.join method for git repositories.

        For the most part, store.join is used for @storecache
        decorators to invalidate caches when various files
        change. We'll map the ones we care about, and ignore the rest.
        """
        if f in (b'00changelog.i', b'00manifest.i'):
            # This is close enough: in order for the changelog cache
            # to be invalidated, HEAD will have to change.
            return os.path.join(self.path, b'HEAD')
        elif f == b'lock':
            # TODO: we probably want to map this to a git lock, I
            # suspect index.lock. We should figure out what the
            # most-alike file is in git-land. For now we're risking
            # bad concurrency errors if another git client is used.
            return os.path.join(self.path, b'hgit-bogus-lock')
        elif f in (b'obsstore', b'phaseroots', b'narrowspec', b'bookmarks'):
            return os.path.join(self.path, b'..', b'.hg', f)
        raise NotImplementedError(b'Need to pick file for %s.' % f)

    def changelog(self, trypending, concurrencychecker):
        # TODO we don't have a plan for trypending in hg's git support yet
        return gitlog.changelog(self.git, self._db)

    def manifestlog(self, repo, storenarrowmatch):
        # TODO handle storenarrowmatch and figure out if we need the repo arg
        return gitlog.manifestlog(self.git, self._db)

    def invalidatecaches(self):
        pass

    def write(self, tr=None):
        # normally this handles things like fncache writes, which we don't have
        pass


def _makestore(orig, requirements, storebasepath, vfstype):
    if b'git' in requirements:
        if not os.path.exists(os.path.join(storebasepath, b'..', b'.git')):
            raise error.Abort(
                _(
                    b'repository specified git format in '
                    b'.hg/requires but has no .git directory'
                )
            )
        # Check for presence of pygit2 only here. The assumption is that we'll
        # run this code iff we'll later need pygit2.
        if gitutil.get_pygit2() is None:
            raise error.Abort(
                _(
                    b'the git extension requires the Python '
                    b'pygit2 library to be installed'
                )
            )

        return gitstore(storebasepath, vfstype)
    return orig(requirements, storebasepath, vfstype)


class gitfilestorage(object):
    def file(self, path):
        if path[0:1] == b'/':
            path = path[1:]
        return gitlog.filelog(self.store.git, self.store._db, path)


def _makefilestorage(orig, requirements, features, **kwargs):
    store = kwargs['store']
    if isinstance(store, gitstore):
        return gitfilestorage
    return orig(requirements, features, **kwargs)


def _setupdothg(ui, path):
    dothg = os.path.join(path, b'.hg')
    if os.path.exists(dothg):
        ui.warn(_(b'git repo already initialized for hg\n'))
    else:
        os.mkdir(os.path.join(path, b'.hg'))
        # TODO is it ok to extend .git/info/exclude like this?
        with open(
            os.path.join(path, b'.git', b'info', b'exclude'), 'ab'
        ) as exclude:
            exclude.write(b'\n.hg\n')
    with open(os.path.join(dothg, b'requires'), 'wb') as f:
        f.write(b'git\n')


_BMS_PREFIX = 'refs/heads/'


class gitbmstore(object):
    def __init__(self, gitrepo):
        self.gitrepo = gitrepo
        self._aclean = True
        self._active = gitrepo.references['HEAD']  # git head, not mark

    def __contains__(self, name):
        return (
            _BMS_PREFIX + pycompat.fsdecode(name)
        ) in self.gitrepo.references

    def __iter__(self):
        for r in self.gitrepo.listall_references():
            if r.startswith(_BMS_PREFIX):
                yield pycompat.fsencode(r[len(_BMS_PREFIX) :])

    def __getitem__(self, k):
        return (
            self.gitrepo.references[_BMS_PREFIX + pycompat.fsdecode(k)]
            .peel()
            .id.raw
        )

    def get(self, k, default=None):
        try:
            if k in self:
                return self[k]
            return default
        except gitutil.get_pygit2().InvalidSpecError:
            return default

    @property
    def active(self):
        h = self.gitrepo.references['HEAD']
        if not isinstance(h.target, str) or not h.target.startswith(
            _BMS_PREFIX
        ):
            return None
        return pycompat.fsencode(h.target[len(_BMS_PREFIX) :])

    @active.setter
    def active(self, mark):
        githead = mark is not None and (_BMS_PREFIX + mark) or None
        if githead is not None and githead not in self.gitrepo.references:
            raise AssertionError(b'bookmark %s does not exist!' % mark)

        self._active = githead
        self._aclean = False

    def _writeactive(self):
        if self._aclean:
            return
        self.gitrepo.references.create('HEAD', self._active, True)
        self._aclean = True

    def names(self, node):
        r = []
        for ref in self.gitrepo.listall_references():
            if not ref.startswith(_BMS_PREFIX):
                continue
            if self.gitrepo.references[ref].peel().id.raw != node:
                continue
            r.append(pycompat.fsencode(ref[len(_BMS_PREFIX) :]))
        return r

    # Cleanup opportunity: this is *identical* to core's bookmarks store.
    def expandname(self, bname):
        if bname == b'.':
            if self.active:
                return self.active
            raise error.RepoLookupError(_(b"no active bookmark"))
        return bname

    def applychanges(self, repo, tr, changes):
        """Apply a list of changes to bookmarks"""
        # TODO: this should respect transactions, but that's going to
        # require enlarging the gitbmstore to know how to do in-memory
        # temporary writes and read those back prior to transaction
        # finalization.
        for name, node in changes:
            if node is None:
                self.gitrepo.references.delete(
                    _BMS_PREFIX + pycompat.fsdecode(name)
                )
            else:
                self.gitrepo.references.create(
                    _BMS_PREFIX + pycompat.fsdecode(name),
                    gitutil.togitnode(node),
                    force=True,
                )

    def checkconflict(self, mark, force=False, target=None):
        githead = _BMS_PREFIX + mark
        cur = self.gitrepo.references['HEAD']
        if githead in self.gitrepo.references and not force:
            if target:
                if self.gitrepo.references[githead] == target and target == cur:
                    # re-activating a bookmark
                    return []
                # moving a bookmark - forward?
                raise NotImplementedError
            raise error.Abort(
                _(b"bookmark '%s' already exists (use -f to force)") % mark
            )
        if len(mark) > 3 and not force:
            try:
                shadowhash = scmutil.isrevsymbol(self._repo, mark)
            except error.LookupError:  # ambiguous identifier
                shadowhash = False
            if shadowhash:
                self._repo.ui.warn(
                    _(
                        b"bookmark %s matches a changeset hash\n"
                        b"(did you leave a -r out of an 'hg bookmark' "
                        b"command?)\n"
                    )
                    % mark
                )
        return []


def init(orig, ui, dest=b'.', **opts):
    if opts.get('git', False):
        path = os.path.abspath(dest)
        # TODO: walk up looking for the git repo
        _setupdothg(ui, path)
        return 0
    return orig(ui, dest=dest, **opts)


def reposetup(ui, repo):
    if repo.local() and isinstance(repo.store, gitstore):
        orig = repo.__class__
        repo.store._progress_factory = repo.ui.makeprogress
        if ui.configbool(b'git', b'log-index-cache-miss'):
            repo.store._logfn = repo.ui.warn

        class gitlocalrepo(orig):
            def _makedirstate(self):
                # TODO narrow support here
                return dirstate.gitdirstate(
                    self.ui, self.vfs.base, self.store.git
                )

            def commit(self, *args, **kwargs):
                ret = orig.commit(self, *args, **kwargs)
                if ret is None:
                    # there was nothing to commit, so we should skip
                    # the index fixup logic we'd otherwise do.
                    return None
                tid = self.store.git[gitutil.togitnode(ret)].tree.id
                # DANGER! This will flush any writes staged to the
                # index in Git, but we're sidestepping the index in a
                # way that confuses git when we commit. Alas.
                self.store.git.index.read_tree(tid)
                self.store.git.index.write()
                return ret

            @property
            def _bookmarks(self):
                return gitbmstore(self.store.git)

        repo.__class__ = gitlocalrepo
    return repo


def _featuresetup(ui, supported):
    # don't die on seeing a repo with the git requirement
    supported |= {b'git'}


def extsetup(ui):
    extensions.wrapfunction(localrepo, b'makestore', _makestore)
    extensions.wrapfunction(localrepo, b'makefilestorage', _makefilestorage)
    # Inject --git flag for `hg init`
    entry = extensions.wrapcommand(commands.table, b'init', init)
    entry[1].extend(
        [(b'', b'git', None, b'setup up a git repository instead of hg')]
    )
    localrepo.featuresetupfuncs.add(_featuresetup)