capybara/virtualenv/lib/python2.7/site-packages/pip/req/req_install.py
def parse_editable(editable_req, default_vcs=None):
    """Parses an editable requirement into:
        - a requirement name
        - an URL
        - extras
        - editable options
    Accepted requirements:
        svn+http://blahblah@rev#egg=Foobar[baz]&subdirectory=version_subdir
        .[some_extra]
    """

    url = editable_req
    extras = None

    # If a file path is specified with extras, strip off the extras.
    m = re.match(r'^(.+)(\[[^\]]+\])$', url)
    if m:
        url_no_extras = m.group(1)
        extras = m.group(2)
    else:
        url_no_extras = url

    if os.path.isdir(url_no_extras):
        if not os.path.exists(os.path.join(url_no_extras, 'setup.py')):
            raise InstallationError(
                "Directory %r is not installable. File 'setup.py' not found." %
                url_no_extras
            )
        # Treating it as code that has already been checked out
        url_no_extras = path_to_url(url_no_extras)

    if url_no_extras.lower().startswith('file:'):
        if extras:
            return (
                None,
                url_no_extras,
                pkg_resources.Requirement.parse(
                    '__placeholder__' + extras
                ).extras,
                {},
            )
        else:
            return None, url_no_extras, None, {}

    for version_control in vcs:
        if url.lower().startswith('%s:' % version_control):
            url = '%s+%s' % (version_control, url)
            break

    if '+' not in url:
        if default_vcs:
            url = default_vcs + '+' + url
        else:
            raise InstallationError(
                '%s should either be a path to a local project or a VCS url '
                'beginning with svn+, git+, hg+, or bzr+' %
                editable_req
            )

    vc_type = url.split('+', 1)[0].lower()

    if not vcs.get_backend(vc_type):
        error_message = 'For --editable=%s only ' % editable_req + \
            ', '.join([backend.name + '+URL' for backend in vcs.backends]) + \
            ' is currently supported'
        raise InstallationError(error_message)

    try:
        options = _build_editable_options(editable_req)
    except Exception as exc:
        raise InstallationError(
            '--editable=%s error in editable options:%s' % (editable_req, exc)
        )
    if not options or 'egg' not in options:
        req = _build_req_from_url(editable_req)
        if not req:
            raise InstallationError(
                '--editable=%s is not the right format; it must have '
                '#egg=Package' % editable_req
            )
    else:
        req = options['egg']

    package = _strip_postfix(req)
    return package, url, None, options
def parse_editable(editable_req, default_vcs=None):
    """Parses an editable requirement into:
        - a requirement name
        - an URL
        - extras
        - editable options
    Accepted requirements:
        svn+http://blahblah@rev#egg=Foobar[baz]&subdirectory=version_subdir
        .[some_extra]
    """

    url = editable_req
    extras = None

    # If a file path is specified with extras, strip off the extras.
    m = re.match(r'^(.+)(\[[^\]]+\])$', url)
    if m:
        url_no_extras = m.group(1)
        extras = m.group(2)
    else:
        url_no_extras = url

    if os.path.isdir(url_no_extras):
        if not os.path.exists(os.path.join(url_no_extras, 'setup.py')):
            raise InstallationError(
                "Directory %r is not installable. File 'setup.py' not found." %
                url_no_extras
            )
        # Treating it as code that has already been checked out
        url_no_extras = path_to_url(url_no_extras)

    if url_no_extras.lower().startswith('file:'):
        if extras:
            return (
                None,
                url_no_extras,
                pkg_resources.Requirement.parse(
                    '__placeholder__' + extras
                ).extras,
                {},
            )
        else:
            return None, url_no_extras, None, {}

    for version_control in vcs:
        if url.lower().startswith('%s:' % version_control):
            url = '%s+%s' % (version_control, url)
            break

    if '+' not in url:
        if default_vcs:
            url = default_vcs + '+' + url
        else:
            raise InstallationError(
                '%s should either be a path to a local project or a VCS url '
                'beginning with svn+, git+, hg+, or bzr+' %
                editable_req
            )

    vc_type = url.split('+', 1)[0].lower()

    if not vcs.get_backend(vc_type):
        error_message = 'For --editable=%s only ' % editable_req + \
            ', '.join([backend.name + '+URL' for backend in vcs.backends]) + \
            ' is currently supported'
        raise InstallationError(error_message)

    try:
        options = _build_editable_options(editable_req)
    except Exception as exc:
        raise InstallationError(
            '--editable=%s error in editable options:%s' % (editable_req, exc)
        )
    if not options or 'egg' not in options:
        req = _build_req_from_url(editable_req)
        if not req:
            raise InstallationError(
                '--editable=%s is not the right format; it must have '
                '#egg=Package' % editable_req
            )
    else:
        req = options['egg']

    package = _strip_postfix(req)
    return package, url, None, options
Parses an editable requirement into:
        - a requirement name
        - an URL
        - extras
        - editable options
    Accepted requirements:
        svn+http://blahblah@rev#egg=Foobar[baz]&subdirectory=version_subdir
        .[some_extra]