view tests/hghave.py @ 40021:c537144fdbef

wireprotov2: support response caching

One of the things I've learned from managing VCS servers over the
years is that they are hard to scale. It is well known that some
companies have very beefy (read: very expensive) servers to power
their VCS needs. It is also known that specialized servers for
various VCS exist in order to facilitate scaling servers. (Mercurial
is in this boat.)

One of the aspects that make a VCS server hard to scale is the
high CPU load incurred by constant client clone/pull operations.

To alleviate the scaling pain associated with data retrieval
operations, I want to integrate caching into the Mercurial wire
protocol server as robustly as possible such that servers can
aggressively cache responses and defer as much server load as
possible.

This commit represents the initial implementation of a general
caching layer in wire protocol version 2.

We define a new interface and behavior for a wire protocol cacher
in repository.py. (This is probably where a reviewer should look
first to understand what is going on.)

The bulk of the added code is in wireprotov2server.py, where we
define how a command can opt in to being cached and integrate
caching into command dispatching.

From a very high-level:

* A command can declare itself as cacheable by providing a callable
  that can be used to derive a cache key.
* At dispatch time, if a command is cacheable, we attempt to
  construct a cacher and use it for serving the request and/or
  caching the request.
* The dispatch layer handles the bulk of the business logic for
  caching, making cachers mostly "dumb content stores."
* The mechanism for invalidating cached entries (one of the harder
  parts about caching in general) is by varying the cache key when
  state changes. As such, cachers don't need to be concerned with
  cache invalidation.

Initially, we've hooked up support for caching "manifestdata" and
"filedata" commands. These are the simplest to cache, as they should
be immutable over time. Caching of commands related to changeset
data is a bit harder (because cache validation is impacted by
changes to bookmarks, phases, etc). This will be implemented later.
(Strictly speaking, censoring a file should invalidate caches. I've
added an inline TODO to track this edge case.)

To prove it works, this commit implements a test-only extension
providing in-memory caching backed by an lrucachedict. A new test
showing this extension behaving properly is added. FWIW, the
cacher is ~50 lines of code, demonstrating the relative ease with
which a cache can be added to a server.

While the test cacher is not suitable for production workloads, just
for kicks I performed a clone of just the changeset and manifest data
for the mozilla-unified repository. With a fully warmed cache (of just
the manifest data since changeset data is not cached), server-side
CPU usage dropped from ~73s to ~28s. That's pretty significant and
demonstrates the potential that response caching has on server
scalability!

Differential Revision: https://phab.mercurial-scm.org/D4773

from __future__ import absolute_import

import errno
import os
import re
import socket
import stat
import subprocess
import sys
import tempfile

tempprefix = 'hg-hghave-'

checks = {
    "true": (lambda: True, "yak shaving"),
    "false": (lambda: False, "nail clipper"),
}

if sys.version_info[0] >= 3:
    def _bytespath(p):
        if p is None:
            return p
        return p.encode('utf-8')

    def _strpath(p):
        if p is None:
            return p
        return p.decode('utf-8')
else:
    def _bytespath(p):
        return p

    _strpath = _bytespath

def check(name, desc):
    """Registers a check function for a feature."""
    def decorator(func):
        checks[name] = (func, desc)
        return func
    return decorator

def checkvers(name, desc, vers):
    """Registers a check function for each of a series of versions.

    vers can be a list or an iterator"""
    def decorator(func):
        def funcv(v):
            def f():
                return func(v)
            return f
        for v in vers:
            v = str(v)
            f = funcv(v)
            checks['%s%s' % (name, v.replace('.', ''))] = (f, desc % v)
        return func
    return decorator

def checkfeatures(features):
    result = {
        'error': [],
        'missing': [],
        'skipped': [],
    }

    for feature in features:
        negate = feature.startswith('no-')
        if negate:
            feature = feature[3:]

        if feature not in checks:
            result['missing'].append(feature)
            continue

        check, desc = checks[feature]
        try:
            available = check()
        except Exception:
            result['error'].append('hghave check failed: %s' % feature)
            continue

        if not negate and not available:
            result['skipped'].append('missing feature: %s' % desc)
        elif negate and available:
            result['skipped'].append('system supports %s' % desc)

    return result

def require(features):
    """Require that features are available, exiting if not."""
    result = checkfeatures(features)

    for missing in result['missing']:
        sys.stderr.write('skipped: unknown feature: %s\n' % missing)
    for msg in result['skipped']:
        sys.stderr.write('skipped: %s\n' % msg)
    for msg in result['error']:
        sys.stderr.write('%s\n' % msg)

    if result['missing']:
        sys.exit(2)

    if result['skipped'] or result['error']:
        sys.exit(1)

def matchoutput(cmd, regexp, ignorestatus=False):
    """Return the match object if cmd executes successfully and its output
    is matched by the supplied regular expression.
    """
    r = re.compile(regexp)
    try:
        p = subprocess.Popen(
            cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    except OSError as e:
        if e.errno != errno.ENOENT:
            raise
        ret = -1
    s = p.communicate()[0]
    ret = p.returncode
    return (ignorestatus or not ret) and r.search(s)

@check("baz", "GNU Arch baz client")
def has_baz():
    return matchoutput('baz --version 2>&1', br'baz Bazaar version')

@check("bzr", "Canonical's Bazaar client")
def has_bzr():
    try:
        import bzrlib
        import bzrlib.bzrdir
        import bzrlib.errors
        import bzrlib.revision
        import bzrlib.revisionspec
        bzrlib.revisionspec.RevisionSpec
        return bzrlib.__doc__ is not None
    except (AttributeError, ImportError):
        return False

@checkvers("bzr", "Canonical's Bazaar client >= %s", (1.14,))
def has_bzr_range(v):
    major, minor = v.split('.')[0:2]
    try:
        import bzrlib
        return (bzrlib.__doc__ is not None
                and bzrlib.version_info[:2] >= (int(major), int(minor)))
    except ImportError:
        return False

@check("chg", "running with chg")
def has_chg():
    return 'CHGHG' in os.environ

@check("cvs", "cvs client/server")
def has_cvs():
    re = br'Concurrent Versions System.*?server'
    return matchoutput('cvs --version 2>&1', re) and not has_msys()

@check("cvs112", "cvs client/server 1.12.* (not cvsnt)")
def has_cvs112():
    re = br'Concurrent Versions System \(CVS\) 1.12.*?server'
    return matchoutput('cvs --version 2>&1', re) and not has_msys()

@check("cvsnt", "cvsnt client/server")
def has_cvsnt():
    re = br'Concurrent Versions System \(CVSNT\) (\d+).(\d+).*\(client/server\)'
    return matchoutput('cvsnt --version 2>&1', re)

@check("darcs", "darcs client")
def has_darcs():
    return matchoutput('darcs --version', br'\b2\.([2-9]|\d{2})', True)

@check("mtn", "monotone client (>= 1.0)")
def has_mtn():
    return matchoutput('mtn --version', br'monotone', True) and not matchoutput(
        'mtn --version', br'monotone 0\.', True)

@check("eol-in-paths", "end-of-lines in paths")
def has_eol_in_paths():
    try:
        fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix, suffix='\n\r')
        os.close(fd)
        os.remove(path)
        return True
    except (IOError, OSError):
        return False

@check("execbit", "executable bit")
def has_executablebit():
    try:
        EXECFLAGS = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
        fh, fn = tempfile.mkstemp(dir='.', prefix=tempprefix)
        try:
            os.close(fh)
            m = os.stat(fn).st_mode & 0o777
            new_file_has_exec = m & EXECFLAGS
            os.chmod(fn, m ^ EXECFLAGS)
            exec_flags_cannot_flip = ((os.stat(fn).st_mode & 0o777) == m)
        finally:
            os.unlink(fn)
    except (IOError, OSError):
        # we don't care, the user probably won't be able to commit anyway
        return False
    return not (new_file_has_exec or exec_flags_cannot_flip)

@check("icasefs", "case insensitive file system")
def has_icasefs():
    # Stolen from mercurial.util
    fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix)
    os.close(fd)
    try:
        s1 = os.stat(path)
        d, b = os.path.split(path)
        p2 = os.path.join(d, b.upper())
        if path == p2:
            p2 = os.path.join(d, b.lower())
        try:
            s2 = os.stat(p2)
            return s2 == s1
        except OSError:
            return False
    finally:
        os.remove(path)

@check("fifo", "named pipes")
def has_fifo():
    if getattr(os, "mkfifo", None) is None:
        return False
    name = tempfile.mktemp(dir='.', prefix=tempprefix)
    try:
        os.mkfifo(name)
        os.unlink(name)
        return True
    except OSError:
        return False

@check("killdaemons", 'killdaemons.py support')
def has_killdaemons():
    return True

@check("cacheable", "cacheable filesystem")
def has_cacheable_fs():
    from mercurial import util

    fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix)
    os.close(fd)
    try:
        return util.cachestat(path).cacheable()
    finally:
        os.remove(path)

@check("lsprof", "python lsprof module")
def has_lsprof():
    try:
        import _lsprof
        _lsprof.Profiler # silence unused import warning
        return True
    except ImportError:
        return False

def gethgversion():
    m = matchoutput('hg --version --quiet 2>&1', br'(\d+)\.(\d+)')
    if not m:
        return (0, 0)
    return (int(m.group(1)), int(m.group(2)))

@checkvers("hg", "Mercurial >= %s",
            list([(1.0 * x) / 10 for x in range(9, 99)]))
def has_hg_range(v):
    major, minor = v.split('.')[0:2]
    return gethgversion() >= (int(major), int(minor))

@check("hg08", "Mercurial >= 0.8")
def has_hg08():
    if checks["hg09"][0]():
        return True
    return matchoutput('hg help annotate 2>&1', '--date')

@check("hg07", "Mercurial >= 0.7")
def has_hg07():
    if checks["hg08"][0]():
        return True
    return matchoutput('hg --version --quiet 2>&1', 'Mercurial Distributed SCM')

@check("hg06", "Mercurial >= 0.6")
def has_hg06():
    if checks["hg07"][0]():
        return True
    return matchoutput('hg --version --quiet 2>&1', 'Mercurial version')

@check("gettext", "GNU Gettext (msgfmt)")
def has_gettext():
    return matchoutput('msgfmt --version', br'GNU gettext-tools')

@check("git", "git command line client")
def has_git():
    return matchoutput('git --version 2>&1', br'^git version')

def getgitversion():
    m = matchoutput('git --version 2>&1', br'git version (\d+)\.(\d+)')
    if not m:
        return (0, 0)
    return (int(m.group(1)), int(m.group(2)))

# https://github.com/git-lfs/lfs-test-server
@check("lfs-test-server", "git-lfs test server")
def has_lfsserver():
    exe = 'lfs-test-server'
    if has_windows():
        exe = 'lfs-test-server.exe'
    return any(
        os.access(os.path.join(path, exe), os.X_OK)
        for path in os.environ["PATH"].split(os.pathsep)
    )

@checkvers("git", "git client (with ext::sh support) version >= %s", (1.9,))
def has_git_range(v):
    major, minor = v.split('.')[0:2]
    return getgitversion() >= (int(major), int(minor))

@check("docutils", "Docutils text processing library")
def has_docutils():
    try:
        import docutils.core
        docutils.core.publish_cmdline # silence unused import
        return True
    except ImportError:
        return False

def getsvnversion():
    m = matchoutput('svn --version --quiet 2>&1', br'^(\d+)\.(\d+)')
    if not m:
        return (0, 0)
    return (int(m.group(1)), int(m.group(2)))

@checkvers("svn", "subversion client and admin tools >= %s", (1.3, 1.5))
def has_svn_range(v):
    major, minor = v.split('.')[0:2]
    return getsvnversion() >= (int(major), int(minor))

@check("svn", "subversion client and admin tools")
def has_svn():
    return matchoutput('svn --version 2>&1', br'^svn, version') and \
        matchoutput('svnadmin --version 2>&1', br'^svnadmin, version')

@check("svn-bindings", "subversion python bindings")
def has_svn_bindings():
    try:
        import svn.core
        version = svn.core.SVN_VER_MAJOR, svn.core.SVN_VER_MINOR
        if version < (1, 4):
            return False
        return True
    except ImportError:
        return False

@check("p4", "Perforce server and client")
def has_p4():
    return (matchoutput('p4 -V', br'Rev\. P4/') and
            matchoutput('p4d -V', br'Rev\. P4D/'))

@check("symlink", "symbolic links")
def has_symlink():
    if getattr(os, "symlink", None) is None:
        return False
    name = tempfile.mktemp(dir='.', prefix=tempprefix)
    try:
        os.symlink(".", name)
        os.unlink(name)
        return True
    except (OSError, AttributeError):
        return False

@check("hardlink", "hardlinks")
def has_hardlink():
    from mercurial import util
    fh, fn = tempfile.mkstemp(dir='.', prefix=tempprefix)
    os.close(fh)
    name = tempfile.mktemp(dir='.', prefix=tempprefix)
    try:
        util.oslink(_bytespath(fn), _bytespath(name))
        os.unlink(name)
        return True
    except OSError:
        return False
    finally:
        os.unlink(fn)

@check("hardlink-whitelisted", "hardlinks on whitelisted filesystems")
def has_hardlink_whitelisted():
    from mercurial import util
    try:
        fstype = util.getfstype(b'.')
    except OSError:
        return False
    return fstype in util._hardlinkfswhitelist

@check("rmcwd", "can remove current working directory")
def has_rmcwd():
    ocwd = os.getcwd()
    temp = tempfile.mkdtemp(dir='.', prefix=tempprefix)
    try:
        os.chdir(temp)
        # On Linux, 'rmdir .' isn't allowed, but the other names are okay.
        # On Solaris and Windows, the cwd can't be removed by any names.
        os.rmdir(os.getcwd())
        return True
    except OSError:
        return False
    finally:
        os.chdir(ocwd)
        # clean up temp dir on platforms where cwd can't be removed
        try:
            os.rmdir(temp)
        except OSError:
            pass

@check("tla", "GNU Arch tla client")
def has_tla():
    return matchoutput('tla --version 2>&1', br'The GNU Arch Revision')

@check("gpg", "gpg client")
def has_gpg():
    return matchoutput('gpg --version 2>&1', br'GnuPG')

@check("gpg2", "gpg client v2")
def has_gpg2():
    return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.')

@check("gpg21", "gpg client v2.1+")
def has_gpg21():
    return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.(?!0)')

@check("unix-permissions", "unix-style permissions")
def has_unix_permissions():
    d = tempfile.mkdtemp(dir='.', prefix=tempprefix)
    try:
        fname = os.path.join(d, 'foo')
        for umask in (0o77, 0o07, 0o22):
            os.umask(umask)
            f = open(fname, 'w')
            f.close()
            mode = os.stat(fname).st_mode
            os.unlink(fname)
            if mode & 0o777 != ~umask & 0o666:
                return False
        return True
    finally:
        os.rmdir(d)

@check("unix-socket", "AF_UNIX socket family")
def has_unix_socket():
    return getattr(socket, 'AF_UNIX', None) is not None

@check("root", "root permissions")
def has_root():
    return getattr(os, 'geteuid', None) and os.geteuid() == 0

@check("pyflakes", "Pyflakes python linter")
def has_pyflakes():
    return matchoutput("sh -c \"echo 'import re' 2>&1 | pyflakes\"",
                       br"<stdin>:1: 're' imported but unused",
                       True)

@check("pylint", "Pylint python linter")
def has_pylint():
    return matchoutput("pylint --help",
                       br"Usage:  pylint",
                       True)

@check("clang-format", "clang-format C code formatter")
def has_clang_format():
    m = matchoutput('clang-format --version', br'clang-format version (\d)')
    # style changed somewhere between 4.x and 6.x
    return m and int(m.group(1)) >= 6

@check("jshint", "JSHint static code analysis tool")
def has_jshint():
    return matchoutput("jshint --version 2>&1", br"jshint v")

@check("pygments", "Pygments source highlighting library")
def has_pygments():
    try:
        import pygments
        pygments.highlight # silence unused import warning
        return True
    except ImportError:
        return False

@check("outer-repo", "outer repo")
def has_outer_repo():
    # failing for other reasons than 'no repo' imply that there is a repo
    return not matchoutput('hg root 2>&1',
                           br'abort: no repository found', True)

@check("ssl", "ssl module available")
def has_ssl():
    try:
        import ssl
        ssl.CERT_NONE
        return True
    except ImportError:
        return False

@check("sslcontext", "python >= 2.7.9 ssl")
def has_sslcontext():
    try:
        import ssl
        ssl.SSLContext
        return True
    except (ImportError, AttributeError):
        return False

@check("defaultcacerts", "can verify SSL certs by system's CA certs store")
def has_defaultcacerts():
    from mercurial import sslutil, ui as uimod
    ui = uimod.ui.load()
    return sslutil._defaultcacerts(ui) or sslutil._canloaddefaultcerts

@check("defaultcacertsloaded", "detected presence of loaded system CA certs")
def has_defaultcacertsloaded():
    import ssl
    from mercurial import sslutil, ui as uimod

    if not has_defaultcacerts():
        return False
    if not has_sslcontext():
        return False

    ui = uimod.ui.load()
    cafile = sslutil._defaultcacerts(ui)
    ctx = ssl.create_default_context()
    if cafile:
        ctx.load_verify_locations(cafile=cafile)
    else:
        ctx.load_default_certs()

    return len(ctx.get_ca_certs()) > 0

@check("tls1.2", "TLS 1.2 protocol support")
def has_tls1_2():
    from mercurial import sslutil
    return 'tls1.2' in sslutil.supportedprotocols

@check("windows", "Windows")
def has_windows():
    return os.name == 'nt'

@check("system-sh", "system() uses sh")
def has_system_sh():
    return os.name != 'nt'

@check("serve", "platform and python can manage 'hg serve -d'")
def has_serve():
    return True

@check("test-repo", "running tests from repository")
def has_test_repo():
    t = os.environ["TESTDIR"]
    return os.path.isdir(os.path.join(t, "..", ".hg"))

@check("tic", "terminfo compiler and curses module")
def has_tic():
    try:
        import curses
        curses.COLOR_BLUE
        return matchoutput('test -x "`which tic`"', br'')
    except ImportError:
        return False

@check("msys", "Windows with MSYS")
def has_msys():
    return os.getenv('MSYSTEM')

@check("aix", "AIX")
def has_aix():
    return sys.platform.startswith("aix")

@check("osx", "OS X")
def has_osx():
    return sys.platform == 'darwin'

@check("osxpackaging", "OS X packaging tools")
def has_osxpackaging():
    try:
        return (matchoutput('pkgbuild', br'Usage: pkgbuild ', ignorestatus=1)
                and matchoutput(
                    'productbuild', br'Usage: productbuild ',
                    ignorestatus=1)
                and matchoutput('lsbom', br'Usage: lsbom', ignorestatus=1)
                and matchoutput(
                    'xar --help', br'Usage: xar', ignorestatus=1))
    except ImportError:
        return False

@check('linuxormacos', 'Linux or MacOS')
def has_linuxormacos():
    # This isn't a perfect test for MacOS. But it is sufficient for our needs.
    return sys.platform.startswith(('linux', 'darwin'))

@check("docker", "docker support")
def has_docker():
    pat = br'A self-sufficient runtime for'
    if matchoutput('docker --help', pat):
        if 'linux' not in sys.platform:
            # TODO: in theory we should be able to test docker-based
            # package creation on non-linux using boot2docker, but in
            # practice that requires extra coordination to make sure
            # $TESTTEMP is going to be visible at the same path to the
            # boot2docker VM. If we figure out how to verify that, we
            # can use the following instead of just saying False:
            # return 'DOCKER_HOST' in os.environ
            return False

        return True
    return False

@check("debhelper", "debian packaging tools")
def has_debhelper():
    # Some versions of dpkg say `dpkg', some say 'dpkg' (` vs ' on the first
    # quote), so just accept anything in that spot.
    dpkg = matchoutput('dpkg --version',
                       br"Debian .dpkg' package management program")
    dh = matchoutput('dh --help',
                     br'dh is a part of debhelper.', ignorestatus=True)
    dh_py2 = matchoutput('dh_python2 --help',
                         br'other supported Python versions')
    # debuild comes from the 'devscripts' package, though you might want
    # the 'build-debs' package instead, which has a dependency on devscripts.
    debuild = matchoutput('debuild --help',
                          br'to run debian/rules with given parameter')
    return dpkg and dh and dh_py2 and debuild

@check("debdeps",
       "debian build dependencies (run dpkg-checkbuilddeps in contrib/)")
def has_debdeps():
    # just check exit status (ignoring output)
    path = '%s/../contrib/packaging/debian/control' % os.environ['TESTDIR']
    return matchoutput('dpkg-checkbuilddeps %s' % path, br'')

@check("demandimport", "demandimport enabled")
def has_demandimport():
    # chg disables demandimport intentionally for performance wins.
    return ((not has_chg()) and os.environ.get('HGDEMANDIMPORT') != 'disable')

@check("py3k", "running with Python 3.x")
def has_py3k():
    return 3 == sys.version_info[0]

@check("py3exe", "a Python 3.x interpreter is available")
def has_python3exe():
    return matchoutput('python3 -V', br'^Python 3.(5|6|7|8|9)')

@check("pure", "running with pure Python code")
def has_pure():
    return any([
        os.environ.get("HGMODULEPOLICY") == "py",
        os.environ.get("HGTEST_RUN_TESTS_PURE") == "--pure",
    ])

@check("slow", "allow slow tests (use --allow-slow-tests)")
def has_slow():
    return os.environ.get('HGTEST_SLOW') == 'slow'

@check("hypothesis", "Hypothesis automated test generation")
def has_hypothesis():
    try:
        import hypothesis
        hypothesis.given
        return True
    except ImportError:
        return False

@check("unziplinks", "unzip(1) understands and extracts symlinks")
def unzip_understands_symlinks():
    return matchoutput('unzip --help', br'Info-ZIP')

@check("zstd", "zstd Python module available")
def has_zstd():
    try:
        import mercurial.zstd
        mercurial.zstd.__version__
        return True
    except ImportError:
        return False

@check("devfull", "/dev/full special file")
def has_dev_full():
    return os.path.exists('/dev/full')

@check("virtualenv", "Python virtualenv support")
def has_virtualenv():
    try:
        import virtualenv
        virtualenv.ACTIVATE_SH
        return True
    except ImportError:
        return False

@check("fsmonitor", "running tests with fsmonitor")
def has_fsmonitor():
    return 'HGFSMONITOR_TESTS' in os.environ

@check("fuzzywuzzy", "Fuzzy string matching library")
def has_fuzzywuzzy():
    try:
        import fuzzywuzzy
        fuzzywuzzy.__version__
        return True
    except ImportError:
        return False

@check("clang-libfuzzer", "clang new enough to include libfuzzer")
def has_clang_libfuzzer():
    mat = matchoutput('clang --version', b'clang version (\d)')
    if mat:
        # libfuzzer is new in clang 6
        return int(mat.group(1)) > 5
    return False

@check("clang-6.0", "clang 6.0 with version suffix (libfuzzer included)")
def has_clang60():
    return matchoutput('clang-6.0 --version', b'clang version 6\.')

@check("xdiff", "xdiff algorithm")
def has_xdiff():
    try:
        from mercurial import policy
        bdiff = policy.importmod('bdiff')
        return bdiff.xdiffblocks(b'', b'') == [(0, 0, 0, 0)]
    except (ImportError, AttributeError):
        return False

@check('extraextensions', 'whether tests are running with extra extensions')
def has_extraextensions():
    return 'HGTESTEXTRAEXTENSIONS' in os.environ

def getrepofeatures():
    """Obtain set of repository features in use.

    HGREPOFEATURES can be used to define or remove features. It contains
    a space-delimited list of feature strings. Strings beginning with ``-``
    mean to remove.
    """
    # Default list provided by core.
    features = {
        'bundlerepo',
        'revlogstore',
        'fncache',
    }

    # Features that imply other features.
    implies = {
        'simplestore': ['-revlogstore', '-bundlerepo', '-fncache'],
    }

    for override in os.environ.get('HGREPOFEATURES', '').split(' '):
        if not override:
            continue

        if override.startswith('-'):
            if override[1:] in features:
                features.remove(override[1:])
        else:
            features.add(override)

            for imply in implies.get(override, []):
                if imply.startswith('-'):
                    if imply[1:] in features:
                        features.remove(imply[1:])
                else:
                    features.add(imply)

    return features

@check('reporevlogstore', 'repository using the default revlog store')
def has_reporevlogstore():
    return 'revlogstore' in getrepofeatures()

@check('reposimplestore', 'repository using simple storage extension')
def has_reposimplestore():
    return 'simplestore' in getrepofeatures()

@check('repobundlerepo', 'whether we can open bundle files as repos')
def has_repobundlerepo():
    return 'bundlerepo' in getrepofeatures()

@check('repofncache', 'repository has an fncache')
def has_repofncache():
    return 'fncache' in getrepofeatures()

@check('vcr', 'vcr http mocking library')
def has_vcr():
    try:
        import vcr
        vcr.VCR
        return True
    except (ImportError, AttributeError):
        pass
    return False