Remove importing from vcs in pip/_internal/__init__.py.

This also renames the current vcs/__init__.py to vcs/versioncontrol.py.

11 files changed, 627 insertions, 617 deletions

diff --git a/src/pip/_internal/__init__.py b/src/pip/_internal/__init__.py
index 9c1637cfc..fbadc28ac 100755
--- a/src/pip/_internal/__init__.py
+++ b/src/pip/_internal/__init__.py
@@ -42,7 +42,6 @@ from pip._internal.cli.main_parser import parse_command
 from pip._internal.commands import commands_dict
 from pip._internal.exceptions import PipError
 from pip._internal.utils import deprecation
-from pip._internal.vcs import git, mercurial, subversion, bazaar  # noqa
 from pip._vendor.urllib3.exceptions import InsecureRequestWarning
 
 logger = logging.getLogger(__name__)
diff --git a/src/pip/_internal/download.py b/src/pip/_internal/download.py
index 38a67c3cc..c98fae5d3 100644
--- a/src/pip/_internal/download.py
+++ b/src/pip/_internal/download.py
@@ -52,7 +52,7 @@ if MYPY_CHECK_RUNNING:
     from optparse import Values
     from pip._internal.models.link import Link
     from pip._internal.utils.hashes import Hashes
-    from pip._internal.vcs import AuthInfo, VersionControl
+    from pip._internal.vcs.versioncontrol import AuthInfo, VersionControl
 
 try:
     import ssl  # noqa
diff --git a/src/pip/_internal/index.py b/src/pip/_internal/index.py
index 5b42a7c72..eaa4e88c5 100644
--- a/src/pip/_internal/index.py
+++ b/src/pip/_internal/index.py
@@ -82,8 +82,8 @@ def _match_vcs_scheme(url):
 
     Returns the matched VCS scheme, or None if there's no match.
     """
-    from pip._internal.vcs import VcsSupport
-    for scheme in VcsSupport.schemes:
+    from pip._internal.vcs import vcs
+    for scheme in vcs.schemes:
         if url.lower().startswith(scheme) and url[len(scheme)] in '+:':
             return scheme
     return None
diff --git a/src/pip/_internal/vcs/__init__.py b/src/pip/_internal/vcs/__init__.py
index 317a15c33..cb573ab6d 100644
--- a/src/pip/_internal/vcs/__init__.py
+++ b/src/pip/_internal/vcs/__init__.py
@@ -1,600 +1,12 @@
-"""Handles all VCS (version control) support"""
-from __future__ import absolute_import
-
-import errno
-import logging
-import os
-import shutil
-import sys
-
-from pip._vendor import pkg_resources
-from pip._vendor.six.moves.urllib import parse as urllib_parse
-
-from pip._internal.exceptions import BadCommand
-from pip._internal.utils.misc import (
-    ask_path_exists, backup_dir, call_subprocess, display_path, rmtree,
+# Expose a limited set of classes and functions so callers outside of
+# the vcs package don't need to import deeper than `pip._internal.vcs`.
+# (The test directory and imports protected by MYPY_CHECK_RUNNING may
+# still need to import from a vcs sub-package.)
+from pip._internal.vcs.versioncontrol import (  # noqa: F401
+    RemoteNotFoundError, make_vcs_requirement_url, vcs,
 )
-from pip._internal.utils.typing import MYPY_CHECK_RUNNING
-
-if MYPY_CHECK_RUNNING:
-    from typing import (
-        Any, Dict, Iterable, List, Mapping, Optional, Text, Tuple, Type
-    )
-    from pip._internal.utils.ui import SpinnerInterface
-
-    AuthInfo = Tuple[Optional[str], Optional[str]]
-
-__all__ = ['vcs']
-
-
-logger = logging.getLogger(__name__)
-
-
-def make_vcs_requirement_url(repo_url, rev, project_name, subdir=None):
-    """
-    Return the URL for a VCS requirement.
-
-    Args:
-      repo_url: the remote VCS url, with any needed VCS prefix (e.g. "git+").
-      project_name: the (unescaped) project name.
-    """
-    egg_project_name = pkg_resources.to_filename(project_name)
-    req = '{}@{}#egg={}'.format(repo_url, rev, egg_project_name)
-    if subdir:
-        req += '&subdirectory={}'.format(subdir)
-
-    return req
-
-
-class RemoteNotFoundError(Exception):
-    pass
-
-
-class RevOptions(object):
-
-    """
-    Encapsulates a VCS-specific revision to install, along with any VCS
-    install options.
-
-    Instances of this class should be treated as if immutable.
-    """
-
-    def __init__(
-        self,
-        vc_class,  # type: Type[VersionControl]
-        rev=None,  # type: Optional[str]
-        extra_args=None,  # type: Optional[List[str]]
-    ):
-        # type: (...) -> None
-        """
-        Args:
-          vc_class: a VersionControl subclass.
-          rev: the name of the revision to install.
-          extra_args: a list of extra options.
-        """
-        if extra_args is None:
-            extra_args = []
-
-        self.extra_args = extra_args
-        self.rev = rev
-        self.vc_class = vc_class
-
-    def __repr__(self):
-        return '<RevOptions {}: rev={!r}>'.format(self.vc_class.name, self.rev)
-
-    @property
-    def arg_rev(self):
-        # type: () -> Optional[str]
-        if self.rev is None:
-            return self.vc_class.default_arg_rev
-
-        return self.rev
-
-    def to_args(self):
-        # type: () -> List[str]
-        """
-        Return the VCS-specific command arguments.
-        """
-        args = []  # type: List[str]
-        rev = self.arg_rev
-        if rev is not None:
-            args += self.vc_class.get_base_rev_args(rev)
-        args += self.extra_args
-
-        return args
-
-    def to_display(self):
-        # type: () -> str
-        if not self.rev:
-            return ''
-
-        return ' (to revision {})'.format(self.rev)
-
-    def make_new(self, rev):
-        # type: (str) -> RevOptions
-        """
-        Make a copy of the current instance, but with a new rev.
-
-        Args:
-          rev: the name of the revision for the new object.
-        """
-        return self.vc_class.make_rev_options(rev, extra_args=self.extra_args)
-
-
-class VcsSupport(object):
-    _registry = {}  # type: Dict[str, VersionControl]
-    schemes = ['ssh', 'git', 'hg', 'bzr', 'sftp', 'svn']
-
-    def __init__(self):
-        # type: () -> None
-        # Register more schemes with urlparse for various version control
-        # systems
-        urllib_parse.uses_netloc.extend(self.schemes)
-        # Python >= 2.7.4, 3.3 doesn't have uses_fragment
-        if getattr(urllib_parse, 'uses_fragment', None):
-            urllib_parse.uses_fragment.extend(self.schemes)
-        super(VcsSupport, self).__init__()
-
-    def __iter__(self):
-        return self._registry.__iter__()
-
-    @property
-    def backends(self):
-        # type: () -> List[VersionControl]
-        return list(self._registry.values())
-
-    @property
-    def dirnames(self):
-        # type: () -> List[str]
-        return [backend.dirname for backend in self.backends]
-
-    @property
-    def all_schemes(self):
-        # type: () -> List[str]
-        schemes = []  # type: List[str]
-        for backend in self.backends:
-            schemes.extend(backend.schemes)
-        return schemes
-
-    def register(self, cls):
-        # type: (Type[VersionControl]) -> None
-        if not hasattr(cls, 'name'):
-            logger.warning('Cannot register VCS %s', cls.__name__)
-            return
-        if cls.name not in self._registry:
-            self._registry[cls.name] = cls()
-            logger.debug('Registered VCS backend: %s', cls.name)
-
-    def unregister(self, name):
-        # type: (str) -> None
-        if name in self._registry:
-            del self._registry[name]
-
-    def get_backend_for_dir(self, location):
-        # type: (str) -> Optional[VersionControl]
-        """
-        Return a VersionControl object if a repository of that type is found
-        at the given directory.
-        """
-        for vcs_backend in self._registry.values():
-            if vcs_backend.controls_location(location):
-                logger.debug('Determine that %s uses VCS: %s',
-                             location, vcs_backend.name)
-                return vcs_backend
-        return None
-
-    def get_backend(self, name):
-        # type: (str) -> Optional[VersionControl]
-        """
-        Return a VersionControl object or None.
-        """
-        name = name.lower()
-        return self._registry.get(name)
-
-
-vcs = VcsSupport()
-
-
-class VersionControl(object):
-    name = ''
-    dirname = ''
-    repo_name = ''
-    # List of supported schemes for this Version Control
-    schemes = ()  # type: Tuple[str, ...]
-    # Iterable of environment variable names to pass to call_subprocess().
-    unset_environ = ()  # type: Tuple[str, ...]
-    default_arg_rev = None  # type: Optional[str]
-
-    @classmethod
-    def should_add_vcs_url_prefix(cls, remote_url):
-        """
-        Return whether the vcs prefix (e.g. "git+") should be added to a
-        repository's remote url when used in a requirement.
-        """
-        return not remote_url.lower().startswith('{}:'.format(cls.name))
-
-    @classmethod
-    def get_subdirectory(cls, repo_dir):
-        """
-        Return the path to setup.py, relative to the repo root.
-        """
-        return None
-
-    @classmethod
-    def get_requirement_revision(cls, repo_dir):
-        """
-        Return the revision string that should be used in a requirement.
-        """
-        return cls.get_revision(repo_dir)
-
-    @classmethod
-    def get_src_requirement(cls, repo_dir, project_name):
-        """
-        Return the requirement string to use to redownload the files
-        currently at the given repository directory.
-
-        Args:
-          project_name: the (unescaped) project name.
-
-        The return value has a form similar to the following:
-
-            {repository_url}@{revision}#egg={project_name}
-        """
-        repo_url = cls.get_remote_url(repo_dir)
-        if repo_url is None:
-            return None
-
-        if cls.should_add_vcs_url_prefix(repo_url):
-            repo_url = '{}+{}'.format(cls.name, repo_url)
-
-        revision = cls.get_requirement_revision(repo_dir)
-        subdir = cls.get_subdirectory(repo_dir)
-        req = make_vcs_requirement_url(repo_url, revision, project_name,
-                                       subdir=subdir)
-
-        return req
-
-    @staticmethod
-    def get_base_rev_args(rev):
-        """
-        Return the base revision arguments for a vcs command.
-
-        Args:
-          rev: the name of a revision to install.  Cannot be None.
-        """
-        raise NotImplementedError
-
-    @classmethod
-    def make_rev_options(cls, rev=None, extra_args=None):
-        # type: (Optional[str], Optional[List[str]]) -> RevOptions
-        """
-        Return a RevOptions object.
-
-        Args:
-          rev: the name of a revision to install.
-          extra_args: a list of extra options.
-        """
-        return RevOptions(cls, rev, extra_args=extra_args)
-
-    @classmethod
-    def _is_local_repository(cls, repo):
-        # type: (str) -> bool
-        """
-           posix absolute paths start with os.path.sep,
-           win32 ones start with drive (like c:\\folder)
-        """
-        drive, tail = os.path.splitdrive(repo)
-        return repo.startswith(os.path.sep) or bool(drive)
-
-    def export(self, location, url):
-        """
-        Export the repository at the url to the destination location
-        i.e. only download the files, without vcs informations
-
-        :param url: the repository URL starting with a vcs prefix.
-        """
-        raise NotImplementedError
-
-    @classmethod
-    def get_netloc_and_auth(cls, netloc, scheme):
-        """
-        Parse the repository URL's netloc, and return the new netloc to use
-        along with auth information.
-
-        Args:
-          netloc: the original repository URL netloc.
-          scheme: the repository URL's scheme without the vcs prefix.
-
-        This is mainly for the Subversion class to override, so that auth
-        information can be provided via the --username and --password options
-        instead of through the URL.  For other subclasses like Git without
-        such an option, auth information must stay in the URL.
-
-        Returns: (netloc, (username, password)).
-        """
-        return netloc, (None, None)
-
-    @classmethod
-    def get_url_rev_and_auth(cls, url):
-        # type: (str) -> Tuple[str, Optional[str], AuthInfo]
-        """
-        Parse the repository URL to use, and return the URL, revision,
-        and auth info to use.
-
-        Returns: (url, rev, (username, password)).
-        """
-        scheme, netloc, path, query, frag = urllib_parse.urlsplit(url)
-        if '+' not in scheme:
-            raise ValueError(
-                "Sorry, {!r} is a malformed VCS url. "
-                "The format is <vcs>+<protocol>://<url>, "
-                "e.g. svn+http://myrepo/svn/MyApp#egg=MyApp".format(url)
-            )
-        # Remove the vcs prefix.
-        scheme = scheme.split('+', 1)[1]
-        netloc, user_pass = cls.get_netloc_and_auth(netloc, scheme)
-        rev = None
-        if '@' in path:
-            path, rev = path.rsplit('@', 1)
-        url = urllib_parse.urlunsplit((scheme, netloc, path, query, ''))
-        return url, rev, user_pass
-
-    @staticmethod
-    def make_rev_args(username, password):
-        """
-        Return the RevOptions "extra arguments" to use in obtain().
-        """
-        return []
-
-    def get_url_rev_options(self, url):
-        # type: (str) -> Tuple[str, RevOptions]
-        """
-        Return the URL and RevOptions object to use in obtain() and in
-        some cases export(), as a tuple (url, rev_options).
-        """
-        url, rev, user_pass = self.get_url_rev_and_auth(url)
-        username, password = user_pass
-        extra_args = self.make_rev_args(username, password)
-        rev_options = self.make_rev_options(rev, extra_args=extra_args)
-
-        return url, rev_options
-
-    @staticmethod
-    def normalize_url(url):
-        # type: (str) -> str
-        """
-        Normalize a URL for comparison by unquoting it and removing any
-        trailing slash.
-        """
-        return urllib_parse.unquote(url).rstrip('/')
-
-    @classmethod
-    def compare_urls(cls, url1, url2):
-        # type: (str, str) -> bool
-        """
-        Compare two repo URLs for identity, ignoring incidental differences.
-        """
-        return (cls.normalize_url(url1) == cls.normalize_url(url2))
-
-    def fetch_new(self, dest, url, rev_options):
-        """
-        Fetch a revision from a repository, in the case that this is the
-        first fetch from the repository.
-
-        Args:
-          dest: the directory to fetch the repository to.
-          rev_options: a RevOptions object.
-        """
-        raise NotImplementedError
-
-    def switch(self, dest, url, rev_options):
-        """
-        Switch the repo at ``dest`` to point to ``URL``.
-
-        Args:
-          rev_options: a RevOptions object.
-        """
-        raise NotImplementedError
-
-    def update(self, dest, url, rev_options):
-        """
-        Update an already-existing repo to the given ``rev_options``.
-
-        Args:
-          rev_options: a RevOptions object.
-        """
-        raise NotImplementedError
-
-    @classmethod
-    def is_commit_id_equal(cls, dest, name):
-        """
-        Return whether the id of the current commit equals the given name.
-
-        Args:
-          dest: the repository directory.
-          name: a string name.
-        """
-        raise NotImplementedError
-
-    def obtain(self, dest, url):
-        # type: (str, str) -> None
-        """
-        Install or update in editable mode the package represented by this
-        VersionControl object.
-
-        :param dest: the repository directory in which to install or update.
-        :param url: the repository URL starting with a vcs prefix.
-        """
-        url, rev_options = self.get_url_rev_options(url)
-
-        if not os.path.exists(dest):
-            self.fetch_new(dest, url, rev_options)
-            return
-
-        rev_display = rev_options.to_display()
-        if self.is_repository_directory(dest):
-            existing_url = self.get_remote_url(dest)
-            if self.compare_urls(existing_url, url):
-                logger.debug(
-                    '%s in %s exists, and has correct URL (%s)',
-                    self.repo_name.title(),
-                    display_path(dest),
-                    url,
-                )
-                if not self.is_commit_id_equal(dest, rev_options.rev):
-                    logger.info(
-                        'Updating %s %s%s',
-                        display_path(dest),
-                        self.repo_name,
-                        rev_display,
-                    )
-                    self.update(dest, url, rev_options)
-                else:
-                    logger.info('Skipping because already up-to-date.')
-                return
-
-            logger.warning(
-                '%s %s in %s exists with URL %s',
-                self.name,
-                self.repo_name,
-                display_path(dest),
-                existing_url,
-            )
-            prompt = ('(s)witch, (i)gnore, (w)ipe, (b)ackup ',
-                      ('s', 'i', 'w', 'b'))
-        else:
-            logger.warning(
-                'Directory %s already exists, and is not a %s %s.',
-                dest,
-                self.name,
-                self.repo_name,
-            )
-            # https://github.com/python/mypy/issues/1174
-            prompt = ('(i)gnore, (w)ipe, (b)ackup ',  # type: ignore
-                      ('i', 'w', 'b'))
-
-        logger.warning(
-            'The plan is to install the %s repository %s',
-            self.name,
-            url,
-        )
-        response = ask_path_exists('What to do?  %s' % prompt[0], prompt[1])
-
-        if response == 'a':
-            sys.exit(-1)
-
-        if response == 'w':
-            logger.warning('Deleting %s', display_path(dest))
-            rmtree(dest)
-            self.fetch_new(dest, url, rev_options)
-            return
-
-        if response == 'b':
-            dest_dir = backup_dir(dest)
-            logger.warning(
-                'Backing up %s to %s', display_path(dest), dest_dir,
-            )
-            shutil.move(dest, dest_dir)
-            self.fetch_new(dest, url, rev_options)
-            return
-
-        # Do nothing if the response is "i".
-        if response == 's':
-            logger.info(
-                'Switching %s %s to %s%s',
-                self.repo_name,
-                display_path(dest),
-                url,
-                rev_display,
-            )
-            self.switch(dest, url, rev_options)
-
-    def unpack(self, location, url):
-        # type: (str, str) -> None
-        """
-        Clean up current location and download the url repository
-        (and vcs infos) into location
-
-        :param url: the repository URL starting with a vcs prefix.
-        """
-        if os.path.exists(location):
-            rmtree(location)
-        self.obtain(location, url=url)
-
-    @classmethod
-    def get_remote_url(cls, location):
-        """
-        Return the url used at location
-
-        Raises RemoteNotFoundError if the repository does not have a remote
-        url configured.
-        """
-        raise NotImplementedError
-
-    @classmethod
-    def get_revision(cls, location):
-        """
-        Return the current commit id of the files at the given location.
-        """
-        raise NotImplementedError
-
-    @classmethod
-    def run_command(
-        cls,
-        cmd,  # type: List[str]
-        show_stdout=True,  # type: bool
-        cwd=None,  # type: Optional[str]
-        on_returncode='raise',  # type: str
-        extra_ok_returncodes=None,  # type: Optional[Iterable[int]]
-        command_desc=None,  # type: Optional[str]
-        extra_environ=None,  # type: Optional[Mapping[str, Any]]
-        spinner=None  # type: Optional[SpinnerInterface]
-    ):
-        # type: (...) -> Optional[Text]
-        """
-        Run a VCS subcommand
-        This is simply a wrapper around call_subprocess that adds the VCS
-        command name, and checks that the VCS is available
-        """
-        cmd = [cls.name] + cmd
-        try:
-            return call_subprocess(cmd, show_stdout, cwd,
-                                   on_returncode=on_returncode,
-                                   extra_ok_returncodes=extra_ok_returncodes,
-                                   command_desc=command_desc,
-                                   extra_environ=extra_environ,
-                                   unset_environ=cls.unset_environ,
-                                   spinner=spinner)
-        except OSError as e:
-            # errno.ENOENT = no such file or directory
-            # In other words, the VCS executable isn't available
-            if e.errno == errno.ENOENT:
-                raise BadCommand(
-                    'Cannot find command %r - do you have '
-                    '%r installed and in your '
-                    'PATH?' % (cls.name, cls.name))
-            else:
-                raise  # re-raise exception if a different error occurred
-
-    @classmethod
-    def is_repository_directory(cls, path):
-        # type: (str) -> bool
-        """
-        Return whether a directory path is a repository directory.
-        """
-        logger.debug('Checking in %s for %s (%s)...',
-                     path, cls.dirname, cls.name)
-        return os.path.exists(os.path.join(path, cls.dirname))
-
-    @classmethod
-    def controls_location(cls, location):
-        # type: (str) -> bool
-        """
-        Check if a location is controlled by the vcs.
-        It is meant to be overridden to implement smarter detection
-        mechanisms for specific vcs.
-
-        This can do more than is_repository_directory() alone.  For example,
-        the Git override checks that Git is actually available.
-        """
-        return cls.is_repository_directory(location)
+# Import all vcs modules to register each VCS in the VcsSupport object.
+import pip._internal.vcs.bazaar
+import pip._internal.vcs.git
+import pip._internal.vcs.mercurial
+import pip._internal.vcs.subversion  # noqa: F401
diff --git a/src/pip/_internal/vcs/bazaar.py b/src/pip/_internal/vcs/bazaar.py
index f7ea24c09..4f1e114ba 100644
--- a/src/pip/_internal/vcs/bazaar.py
+++ b/src/pip/_internal/vcs/bazaar.py
@@ -5,9 +5,8 @@ import os
 
 from pip._vendor.six.moves.urllib import parse as urllib_parse
 
-from pip._internal.download import path_to_url
-from pip._internal.utils.misc import display_path, rmtree
-from pip._internal.vcs import VersionControl, vcs
+from pip._internal.utils.misc import display_path, path_to_url, rmtree
+from pip._internal.vcs.versioncontrol import VersionControl, vcs
 
 logger = logging.getLogger(__name__)
 
diff --git a/src/pip/_internal/vcs/git.py b/src/pip/_internal/vcs/git.py
index e27ed4700..f7469ab5d 100644
--- a/src/pip/_internal/vcs/git.py
+++ b/src/pip/_internal/vcs/git.py
@@ -12,7 +12,9 @@ from pip._internal.exceptions import BadCommand
 from pip._internal.utils.compat import samefile
 from pip._internal.utils.misc import display_path, redact_password_from_url
 from pip._internal.utils.temp_dir import TempDirectory
-from pip._internal.vcs import RemoteNotFoundError, VersionControl, vcs
+from pip._internal.vcs.versioncontrol import (
+    RemoteNotFoundError, VersionControl, vcs,
+)
 
 urlsplit = urllib_parse.urlsplit
 urlunsplit = urllib_parse.urlunsplit
diff --git a/src/pip/_internal/vcs/mercurial.py b/src/pip/_internal/vcs/mercurial.py
index 5f87ce834..db42783dc 100644
--- a/src/pip/_internal/vcs/mercurial.py
+++ b/src/pip/_internal/vcs/mercurial.py
@@ -5,10 +5,9 @@ import os
 
 from pip._vendor.six.moves import configparser
 
-from pip._internal.download import path_to_url
-from pip._internal.utils.misc import display_path
+from pip._internal.utils.misc import display_path, path_to_url
 from pip._internal.utils.temp_dir import TempDirectory
-from pip._internal.vcs import VersionControl, vcs
+from pip._internal.vcs.versioncontrol import VersionControl, vcs
 
 logger = logging.getLogger(__name__)
 
diff --git a/src/pip/_internal/vcs/subversion.py b/src/pip/_internal/vcs/subversion.py
index 0d787009f..4c9b598cd 100644
--- a/src/pip/_internal/vcs/subversion.py
+++ b/src/pip/_internal/vcs/subversion.py
@@ -10,7 +10,7 @@ from pip._internal.utils.misc import (
     display_path, rmtree, split_auth_from_netloc,
 )
 from pip._internal.utils.typing import MYPY_CHECK_RUNNING
-from pip._internal.vcs import VersionControl, vcs
+from pip._internal.vcs.versioncontrol import VersionControl, vcs
 
 _svn_xml_url_re = re.compile('url="([^"]+)"')
 _svn_rev_re = re.compile(r'committed-rev="(\d+)"')
@@ -20,7 +20,7 @@ _svn_info_xml_url_re = re.compile(r'<url>(.*)</url>')
 
 if MYPY_CHECK_RUNNING:
     from typing import List, Optional, Tuple
-    from pip._internal.vcs import RevOptions
+    from pip._internal.vcs.versioncontrol import RevOptions
 
 logger = logging.getLogger(__name__)
 
diff --git a/src/pip/_internal/vcs/versioncontrol.py b/src/pip/_internal/vcs/versioncontrol.py
new file mode 100644
index 000000000..317a15c33
--- /dev/null
+++ b/src/pip/_internal/vcs/versioncontrol.py
@@ -0,0 +1,600 @@
+"""Handles all VCS (version control) support"""
+from __future__ import absolute_import
+
+import errno
+import logging
+import os
+import shutil
+import sys
+
+from pip._vendor import pkg_resources
+from pip._vendor.six.moves.urllib import parse as urllib_parse
+
+from pip._internal.exceptions import BadCommand
+from pip._internal.utils.misc import (
+    ask_path_exists, backup_dir, call_subprocess, display_path, rmtree,
+)
+from pip._internal.utils.typing import MYPY_CHECK_RUNNING
+
+if MYPY_CHECK_RUNNING:
+    from typing import (
+        Any, Dict, Iterable, List, Mapping, Optional, Text, Tuple, Type
+    )
+    from pip._internal.utils.ui import SpinnerInterface
+
+    AuthInfo = Tuple[Optional[str], Optional[str]]
+
+__all__ = ['vcs']
+
+
+logger = logging.getLogger(__name__)
+
+
+def make_vcs_requirement_url(repo_url, rev, project_name, subdir=None):
+    """
+    Return the URL for a VCS requirement.
+
+    Args:
+      repo_url: the remote VCS url, with any needed VCS prefix (e.g. "git+").
+      project_name: the (unescaped) project name.
+    """
+    egg_project_name = pkg_resources.to_filename(project_name)
+    req = '{}@{}#egg={}'.format(repo_url, rev, egg_project_name)
+    if subdir:
+        req += '&subdirectory={}'.format(subdir)
+
+    return req
+
+
+class RemoteNotFoundError(Exception):
+    pass
+
+
+class RevOptions(object):
+
+    """
+    Encapsulates a VCS-specific revision to install, along with any VCS
+    install options.
+
+    Instances of this class should be treated as if immutable.
+    """
+
+    def __init__(
+        self,
+        vc_class,  # type: Type[VersionControl]
+        rev=None,  # type: Optional[str]
+        extra_args=None,  # type: Optional[List[str]]
+    ):
+        # type: (...) -> None
+        """
+        Args:
+          vc_class: a VersionControl subclass.
+          rev: the name of the revision to install.
+          extra_args: a list of extra options.
+        """
+        if extra_args is None:
+            extra_args = []
+
+        self.extra_args = extra_args
+        self.rev = rev
+        self.vc_class = vc_class
+
+    def __repr__(self):
+        return '<RevOptions {}: rev={!r}>'.format(self.vc_class.name, self.rev)
+
+    @property
+    def arg_rev(self):
+        # type: () -> Optional[str]
+        if self.rev is None:
+            return self.vc_class.default_arg_rev
+
+        return self.rev
+
+    def to_args(self):
+        # type: () -> List[str]
+        """
+        Return the VCS-specific command arguments.
+        """
+        args = []  # type: List[str]
+        rev = self.arg_rev
+        if rev is not None:
+            args += self.vc_class.get_base_rev_args(rev)
+        args += self.extra_args
+
+        return args
+
+    def to_display(self):
+        # type: () -> str
+        if not self.rev:
+            return ''
+
+        return ' (to revision {})'.format(self.rev)
+
+    def make_new(self, rev):
+        # type: (str) -> RevOptions
+        """
+        Make a copy of the current instance, but with a new rev.
+
+        Args:
+          rev: the name of the revision for the new object.
+        """
+        return self.vc_class.make_rev_options(rev, extra_args=self.extra_args)
+
+
+class VcsSupport(object):
+    _registry = {}  # type: Dict[str, VersionControl]
+    schemes = ['ssh', 'git', 'hg', 'bzr', 'sftp', 'svn']
+
+    def __init__(self):
+        # type: () -> None
+        # Register more schemes with urlparse for various version control
+        # systems
+        urllib_parse.uses_netloc.extend(self.schemes)
+        # Python >= 2.7.4, 3.3 doesn't have uses_fragment
+        if getattr(urllib_parse, 'uses_fragment', None):
+            urllib_parse.uses_fragment.extend(self.schemes)
+        super(VcsSupport, self).__init__()
+
+    def __iter__(self):
+        return self._registry.__iter__()
+
+    @property
+    def backends(self):
+        # type: () -> List[VersionControl]
+        return list(self._registry.values())
+
+    @property
+    def dirnames(self):
+        # type: () -> List[str]
+        return [backend.dirname for backend in self.backends]
+
+    @property
+    def all_schemes(self):
+        # type: () -> List[str]
+        schemes = []  # type: List[str]
+        for backend in self.backends:
+            schemes.extend(backend.schemes)
+        return schemes
+
+    def register(self, cls):
+        # type: (Type[VersionControl]) -> None
+        if not hasattr(cls, 'name'):
+            logger.warning('Cannot register VCS %s', cls.__name__)
+            return
+        if cls.name not in self._registry:
+            self._registry[cls.name] = cls()
+            logger.debug('Registered VCS backend: %s', cls.name)
+
+    def unregister(self, name):
+        # type: (str) -> None
+        if name in self._registry:
+            del self._registry[name]
+
+    def get_backend_for_dir(self, location):
+        # type: (str) -> Optional[VersionControl]
+        """
+        Return a VersionControl object if a repository of that type is found
+        at the given directory.
+        """
+        for vcs_backend in self._registry.values():
+            if vcs_backend.controls_location(location):
+                logger.debug('Determine that %s uses VCS: %s',
+                             location, vcs_backend.name)
+                return vcs_backend
+        return None
+
+    def get_backend(self, name):
+        # type: (str) -> Optional[VersionControl]
+        """
+        Return a VersionControl object or None.
+        """
+        name = name.lower()
+        return self._registry.get(name)
+
+
+vcs = VcsSupport()
+
+
+class VersionControl(object):
+    name = ''
+    dirname = ''
+    repo_name = ''
+    # List of supported schemes for this Version Control
+    schemes = ()  # type: Tuple[str, ...]
+    # Iterable of environment variable names to pass to call_subprocess().
+    unset_environ = ()  # type: Tuple[str, ...]
+    default_arg_rev = None  # type: Optional[str]
+
+    @classmethod
+    def should_add_vcs_url_prefix(cls, remote_url):
+        """
+        Return whether the vcs prefix (e.g. "git+") should be added to a
+        repository's remote url when used in a requirement.
+        """
+        return not remote_url.lower().startswith('{}:'.format(cls.name))
+
+    @classmethod
+    def get_subdirectory(cls, repo_dir):
+        """
+        Return the path to setup.py, relative to the repo root.
+        """
+        return None
+
+    @classmethod
+    def get_requirement_revision(cls, repo_dir):
+        """
+        Return the revision string that should be used in a requirement.
+        """
+        return cls.get_revision(repo_dir)
+
+    @classmethod
+    def get_src_requirement(cls, repo_dir, project_name):
+        """
+        Return the requirement string to use to redownload the files
+        currently at the given repository directory.
+
+        Args:
+          project_name: the (unescaped) project name.
+
+        The return value has a form similar to the following:
+
+            {repository_url}@{revision}#egg={project_name}
+        """
+        repo_url = cls.get_remote_url(repo_dir)
+        if repo_url is None:
+            return None
+
+        if cls.should_add_vcs_url_prefix(repo_url):
+            repo_url = '{}+{}'.format(cls.name, repo_url)
+
+        revision = cls.get_requirement_revision(repo_dir)
+        subdir = cls.get_subdirectory(repo_dir)
+        req = make_vcs_requirement_url(repo_url, revision, project_name,
+                                       subdir=subdir)
+
+        return req
+
+    @staticmethod
+    def get_base_rev_args(rev):
+        """
+        Return the base revision arguments for a vcs command.
+
+        Args:
+          rev: the name of a revision to install.  Cannot be None.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def make_rev_options(cls, rev=None, extra_args=None):
+        # type: (Optional[str], Optional[List[str]]) -> RevOptions
+        """
+        Return a RevOptions object.
+
+        Args:
+          rev: the name of a revision to install.
+          extra_args: a list of extra options.
+        """
+        return RevOptions(cls, rev, extra_args=extra_args)
+
+    @classmethod
+    def _is_local_repository(cls, repo):
+        # type: (str) -> bool
+        """
+           posix absolute paths start with os.path.sep,
+           win32 ones start with drive (like c:\\folder)
+        """
+        drive, tail = os.path.splitdrive(repo)
+        return repo.startswith(os.path.sep) or bool(drive)
+
+    def export(self, location, url):
+        """
+        Export the repository at the url to the destination location
+        i.e. only download the files, without vcs informations
+
+        :param url: the repository URL starting with a vcs prefix.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def get_netloc_and_auth(cls, netloc, scheme):
+        """
+        Parse the repository URL's netloc, and return the new netloc to use
+        along with auth information.
+
+        Args:
+          netloc: the original repository URL netloc.
+          scheme: the repository URL's scheme without the vcs prefix.
+
+        This is mainly for the Subversion class to override, so that auth
+        information can be provided via the --username and --password options
+        instead of through the URL.  For other subclasses like Git without
+        such an option, auth information must stay in the URL.
+
+        Returns: (netloc, (username, password)).
+        """
+        return netloc, (None, None)
+
+    @classmethod
+    def get_url_rev_and_auth(cls, url):
+        # type: (str) -> Tuple[str, Optional[str], AuthInfo]
+        """
+        Parse the repository URL to use, and return the URL, revision,
+        and auth info to use.
+
+        Returns: (url, rev, (username, password)).
+        """
+        scheme, netloc, path, query, frag = urllib_parse.urlsplit(url)
+        if '+' not in scheme:
+            raise ValueError(
+                "Sorry, {!r} is a malformed VCS url. "
+                "The format is <vcs>+<protocol>://<url>, "
+                "e.g. svn+http://myrepo/svn/MyApp#egg=MyApp".format(url)
+            )
+        # Remove the vcs prefix.
+        scheme = scheme.split('+', 1)[1]
+        netloc, user_pass = cls.get_netloc_and_auth(netloc, scheme)
+        rev = None
+        if '@' in path:
+            path, rev = path.rsplit('@', 1)
+        url = urllib_parse.urlunsplit((scheme, netloc, path, query, ''))
+        return url, rev, user_pass
+
+    @staticmethod
+    def make_rev_args(username, password):
+        """
+        Return the RevOptions "extra arguments" to use in obtain().
+        """
+        return []
+
+    def get_url_rev_options(self, url):
+        # type: (str) -> Tuple[str, RevOptions]
+        """
+        Return the URL and RevOptions object to use in obtain() and in
+        some cases export(), as a tuple (url, rev_options).
+        """
+        url, rev, user_pass = self.get_url_rev_and_auth(url)
+        username, password = user_pass
+        extra_args = self.make_rev_args(username, password)
+        rev_options = self.make_rev_options(rev, extra_args=extra_args)
+
+        return url, rev_options
+
+    @staticmethod
+    def normalize_url(url):
+        # type: (str) -> str
+        """
+        Normalize a URL for comparison by unquoting it and removing any
+        trailing slash.
+        """
+        return urllib_parse.unquote(url).rstrip('/')
+
+    @classmethod
+    def compare_urls(cls, url1, url2):
+        # type: (str, str) -> bool
+        """
+        Compare two repo URLs for identity, ignoring incidental differences.
+        """
+        return (cls.normalize_url(url1) == cls.normalize_url(url2))
+
+    def fetch_new(self, dest, url, rev_options):
+        """
+        Fetch a revision from a repository, in the case that this is the
+        first fetch from the repository.
+
+        Args:
+          dest: the directory to fetch the repository to.
+          rev_options: a RevOptions object.
+        """
+        raise NotImplementedError
+
+    def switch(self, dest, url, rev_options):
+        """
+        Switch the repo at ``dest`` to point to ``URL``.
+
+        Args:
+          rev_options: a RevOptions object.
+        """
+        raise NotImplementedError
+
+    def update(self, dest, url, rev_options):
+        """
+        Update an already-existing repo to the given ``rev_options``.
+
+        Args:
+          rev_options: a RevOptions object.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def is_commit_id_equal(cls, dest, name):
+        """
+        Return whether the id of the current commit equals the given name.
+
+        Args:
+          dest: the repository directory.
+          name: a string name.
+        """
+        raise NotImplementedError
+
+    def obtain(self, dest, url):
+        # type: (str, str) -> None
+        """
+        Install or update in editable mode the package represented by this
+        VersionControl object.
+
+        :param dest: the repository directory in which to install or update.
+        :param url: the repository URL starting with a vcs prefix.
+        """
+        url, rev_options = self.get_url_rev_options(url)
+
+        if not os.path.exists(dest):
+            self.fetch_new(dest, url, rev_options)
+            return
+
+        rev_display = rev_options.to_display()
+        if self.is_repository_directory(dest):
+            existing_url = self.get_remote_url(dest)
+            if self.compare_urls(existing_url, url):
+                logger.debug(
+                    '%s in %s exists, and has correct URL (%s)',
+                    self.repo_name.title(),
+                    display_path(dest),
+                    url,
+                )
+                if not self.is_commit_id_equal(dest, rev_options.rev):
+                    logger.info(
+                        'Updating %s %s%s',
+                        display_path(dest),
+                        self.repo_name,
+                        rev_display,
+                    )
+                    self.update(dest, url, rev_options)
+                else:
+                    logger.info('Skipping because already up-to-date.')
+                return
+
+            logger.warning(
+                '%s %s in %s exists with URL %s',
+                self.name,
+                self.repo_name,
+                display_path(dest),
+                existing_url,
+            )
+            prompt = ('(s)witch, (i)gnore, (w)ipe, (b)ackup ',
+                      ('s', 'i', 'w', 'b'))
+        else:
+            logger.warning(
+                'Directory %s already exists, and is not a %s %s.',
+                dest,
+                self.name,
+                self.repo_name,
+            )
+            # https://github.com/python/mypy/issues/1174
+            prompt = ('(i)gnore, (w)ipe, (b)ackup ',  # type: ignore
+                      ('i', 'w', 'b'))
+
+        logger.warning(
+            'The plan is to install the %s repository %s',
+            self.name,
+            url,
+        )
+        response = ask_path_exists('What to do?  %s' % prompt[0], prompt[1])
+
+        if response == 'a':
+            sys.exit(-1)
+
+        if response == 'w':
+            logger.warning('Deleting %s', display_path(dest))
+            rmtree(dest)
+            self.fetch_new(dest, url, rev_options)
+            return
+
+        if response == 'b':
+            dest_dir = backup_dir(dest)
+            logger.warning(
+                'Backing up %s to %s', display_path(dest), dest_dir,
+            )
+            shutil.move(dest, dest_dir)
+            self.fetch_new(dest, url, rev_options)
+            return
+
+        # Do nothing if the response is "i".
+        if response == 's':
+            logger.info(
+                'Switching %s %s to %s%s',
+                self.repo_name,
+                display_path(dest),
+                url,
+                rev_display,
+            )
+            self.switch(dest, url, rev_options)
+
+    def unpack(self, location, url):
+        # type: (str, str) -> None
+        """
+        Clean up current location and download the url repository
+        (and vcs infos) into location
+
+        :param url: the repository URL starting with a vcs prefix.
+        """
+        if os.path.exists(location):
+            rmtree(location)
+        self.obtain(location, url=url)
+
+    @classmethod
+    def get_remote_url(cls, location):
+        """
+        Return the url used at location
+
+        Raises RemoteNotFoundError if the repository does not have a remote
+        url configured.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def get_revision(cls, location):
+        """
+        Return the current commit id of the files at the given location.
+        """
+        raise NotImplementedError
+
+    @classmethod
+    def run_command(
+        cls,
+        cmd,  # type: List[str]
+        show_stdout=True,  # type: bool
+        cwd=None,  # type: Optional[str]
+        on_returncode='raise',  # type: str
+        extra_ok_returncodes=None,  # type: Optional[Iterable[int]]
+        command_desc=None,  # type: Optional[str]
+        extra_environ=None,  # type: Optional[Mapping[str, Any]]
+        spinner=None  # type: Optional[SpinnerInterface]
+    ):
+        # type: (...) -> Optional[Text]
+        """
+        Run a VCS subcommand
+        This is simply a wrapper around call_subprocess that adds the VCS
+        command name, and checks that the VCS is available
+        """
+        cmd = [cls.name] + cmd
+        try:
+            return call_subprocess(cmd, show_stdout, cwd,
+                                   on_returncode=on_returncode,
+                                   extra_ok_returncodes=extra_ok_returncodes,
+                                   command_desc=command_desc,
+                                   extra_environ=extra_environ,
+                                   unset_environ=cls.unset_environ,
+                                   spinner=spinner)
+        except OSError as e:
+            # errno.ENOENT = no such file or directory
+            # In other words, the VCS executable isn't available
+            if e.errno == errno.ENOENT:
+                raise BadCommand(
+                    'Cannot find command %r - do you have '
+                    '%r installed and in your '
+                    'PATH?' % (cls.name, cls.name))
+            else:
+                raise  # re-raise exception if a different error occurred
+
+    @classmethod
+    def is_repository_directory(cls, path):
+        # type: (str) -> bool
+        """
+        Return whether a directory path is a repository directory.
+        """
+        logger.debug('Checking in %s for %s (%s)...',
+                     path, cls.dirname, cls.name)
+        return os.path.exists(os.path.join(path, cls.dirname))
+
+    @classmethod
+    def controls_location(cls, location):
+        # type: (str) -> bool
+        """
+        Check if a location is controlled by the vcs.
+        It is meant to be overridden to implement smarter detection
+        mechanisms for specific vcs.
+
+        This can do more than is_repository_directory() alone.  For example,
+        the Git override checks that Git is actually available.
+        """
+        return cls.is_repository_directory(location)
diff --git a/tests/functional/test_install_vcs_svn.py b/tests/functional/test_install_vcs_svn.py
index 8db3e8f50..3034b0625 100644
--- a/tests/functional/test_install_vcs_svn.py
+++ b/tests/functional/test_install_vcs_svn.py
@@ -2,13 +2,13 @@ from unittest import TestCase
 
 from mock import patch
 
-from pip._internal.vcs import RevOptions
 from pip._internal.vcs.subversion import Subversion
+from pip._internal.vcs.versioncontrol import RevOptions
 
 
 class TestSubversionArgs(TestCase):
     def setUp(self):
-        patcher = patch('pip._internal.vcs.call_subprocess')
+        patcher = patch('pip._internal.vcs.versioncontrol.call_subprocess')
         self.addCleanup(patcher.stop)
         self.call_subprocess_mock = patcher.start()
 
diff --git a/tests/unit/test_vcs.py b/tests/unit/test_vcs.py
index 2ad89ba29..95bce95ec 100644
--- a/tests/unit/test_vcs.py
+++ b/tests/unit/test_vcs.py
@@ -5,13 +5,12 @@ from mock import patch
 from pip._vendor.packaging.version import parse as parse_version
 
 from pip._internal.exceptions import BadCommand
-from pip._internal.vcs import (
-    RevOptions, VersionControl, make_vcs_requirement_url,
-)
+from pip._internal.vcs import make_vcs_requirement_url
 from pip._internal.vcs.bazaar import Bazaar
 from pip._internal.vcs.git import Git, looks_like_hash
 from pip._internal.vcs.mercurial import Mercurial
 from pip._internal.vcs.subversion import Subversion
+from pip._internal.vcs.versioncontrol import RevOptions, VersionControl
 from tests.lib import is_svn_installed, pyversion
 
 if pyversion >= '3':