hgext/git/__init__.py

procutil: always waiting on child processes to prevent zombies with 'hg serve'

When runbgcommand is invoked by an extension with ensurestart=False, we never
called waitpid - which is fine in most cases, except if that's happening on a
command server (e.g. chg), in which case the child defunct process will just
sit there for as long as the server is running.

The actual semantics of SIGCHLD signal handling is a lot more complex than
it seems, and the POSIX standard *seems* to read that it's ignored by default
and everything would just work without the waitpid if we're not listening for
it, but the truth is that it's only ignored if we *explicitly* set it to
SIG_IGN. We further cannot set it to SIG_IGN or to a catch-all handler across
all of 'hg serve', because Python's suprocess.Popen relies on that signal,
and a few specific parts of hg also set custom handlers, so instead we wait
for specific PIDs in dedicated threads.

I did a poor-man's benchmark of the thread creation and it seems to take
about 1ms, which is way better than the 20+ms from ensurestart=True.

Differential Revision: https://phab.mercurial-scm.org/D8497

"""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,
    scmutil,
    store,
    util,
)

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

# 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

    @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._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):
        # 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

        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)
                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)