--- a/lib/python3.8/site-packages/pip/_internal/legacy_resolve.py	Mon Jul 27 03:47:31 2020 -0400
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,430 +0,0 @@
-"""Dependency Resolution
-
-The dependency resolution in pip is performed as follows:
-
-for top-level requirements:
-    a. only one spec allowed per project, regardless of conflicts or not.
-       otherwise a "double requirement" exception is raised
-    b. they override sub-dependency requirements.
-for sub-dependencies
-    a. "first found, wins" (where the order is breadth first)
-"""
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-# mypy: disallow-untyped-defs=False
-
-import logging
-import sys
-from collections import defaultdict
-from itertools import chain
-
-from pip._vendor.packaging import specifiers
-
-from pip._internal.exceptions import (
-    BestVersionAlreadyInstalled,
-    DistributionNotFound,
-    HashError,
-    HashErrors,
-    UnsupportedPythonVersion,
-)
-from pip._internal.utils.logging import indent_log
-from pip._internal.utils.misc import dist_in_usersite, normalize_version_info
-from pip._internal.utils.packaging import (
-    check_requires_python,
-    get_requires_python,
-)
-from pip._internal.utils.typing import MYPY_CHECK_RUNNING
-
-if MYPY_CHECK_RUNNING:
-    from typing import Callable, DefaultDict, List, Optional, Set, Tuple
-    from pip._vendor import pkg_resources
-
-    from pip._internal.distributions import AbstractDistribution
-    from pip._internal.index.package_finder import PackageFinder
-    from pip._internal.operations.prepare import RequirementPreparer
-    from pip._internal.req.req_install import InstallRequirement
-    from pip._internal.req.req_set import RequirementSet
-
-    InstallRequirementProvider = Callable[
-        [str, InstallRequirement], InstallRequirement
-    ]
-    DiscoveredDependencies = DefaultDict[str, List[InstallRequirement]]
-
-logger = logging.getLogger(__name__)
-
-
-def _check_dist_requires_python(
-    dist,  # type: pkg_resources.Distribution
-    version_info,  # type: Tuple[int, int, int]
-    ignore_requires_python=False,  # type: bool
-):
-    # type: (...) -> None
-    """
-    Check whether the given Python version is compatible with a distribution's
-    "Requires-Python" value.
-
-    :param version_info: A 3-tuple of ints representing the Python
-        major-minor-micro version to check.
-    :param ignore_requires_python: Whether to ignore the "Requires-Python"
-        value if the given Python version isn't compatible.
-
-    :raises UnsupportedPythonVersion: When the given Python version isn't
-        compatible.
-    """
-    requires_python = get_requires_python(dist)
-    try:
-        is_compatible = check_requires_python(
-            requires_python, version_info=version_info,
-        )
-    except specifiers.InvalidSpecifier as exc:
-        logger.warning(
-            "Package %r has an invalid Requires-Python: %s",
-            dist.project_name, exc,
-        )
-        return
-
-    if is_compatible:
-        return
-
-    version = '.'.join(map(str, version_info))
-    if ignore_requires_python:
-        logger.debug(
-            'Ignoring failed Requires-Python check for package %r: '
-            '%s not in %r',
-            dist.project_name, version, requires_python,
-        )
-        return
-
-    raise UnsupportedPythonVersion(
-        'Package {!r} requires a different Python: {} not in {!r}'.format(
-            dist.project_name, version, requires_python,
-        ))
-
-
-class Resolver(object):
-    """Resolves which packages need to be installed/uninstalled to perform \
-    the requested operation without breaking the requirements of any package.
-    """
-
-    _allowed_strategies = {"eager", "only-if-needed", "to-satisfy-only"}
-
-    def __init__(
-        self,
-        preparer,  # type: RequirementPreparer
-        finder,  # type: PackageFinder
-        make_install_req,  # type: InstallRequirementProvider
-        use_user_site,  # type: bool
-        ignore_dependencies,  # type: bool
-        ignore_installed,  # type: bool
-        ignore_requires_python,  # type: bool
-        force_reinstall,  # type: bool
-        upgrade_strategy,  # type: str
-        py_version_info=None,  # type: Optional[Tuple[int, ...]]
-    ):
-        # type: (...) -> None
-        super(Resolver, self).__init__()
-        assert upgrade_strategy in self._allowed_strategies
-
-        if py_version_info is None:
-            py_version_info = sys.version_info[:3]
-        else:
-            py_version_info = normalize_version_info(py_version_info)
-
-        self._py_version_info = py_version_info
-
-        self.preparer = preparer
-        self.finder = finder
-
-        self.upgrade_strategy = upgrade_strategy
-        self.force_reinstall = force_reinstall
-        self.ignore_dependencies = ignore_dependencies
-        self.ignore_installed = ignore_installed
-        self.ignore_requires_python = ignore_requires_python
-        self.use_user_site = use_user_site
-        self._make_install_req = make_install_req
-
-        self._discovered_dependencies = \
-            defaultdict(list)  # type: DiscoveredDependencies
-
-    def resolve(self, requirement_set):
-        # type: (RequirementSet) -> None
-        """Resolve what operations need to be done
-
-        As a side-effect of this method, the packages (and their dependencies)
-        are downloaded, unpacked and prepared for installation. This
-        preparation is done by ``pip.operations.prepare``.
-
-        Once PyPI has static dependency metadata available, it would be
-        possible to move the preparation to become a step separated from
-        dependency resolution.
-        """
-        # If any top-level requirement has a hash specified, enter
-        # hash-checking mode, which requires hashes from all.
-        root_reqs = (
-            requirement_set.unnamed_requirements +
-            list(requirement_set.requirements.values())
-        )
-
-        # Actually prepare the files, and collect any exceptions. Most hash
-        # exceptions cannot be checked ahead of time, because
-        # req.populate_link() needs to be called before we can make decisions
-        # based on link type.
-        discovered_reqs = []  # type: List[InstallRequirement]
-        hash_errors = HashErrors()
-        for req in chain(root_reqs, discovered_reqs):
-            try:
-                discovered_reqs.extend(self._resolve_one(requirement_set, req))
-            except HashError as exc:
-                exc.req = req
-                hash_errors.append(exc)
-
-        if hash_errors:
-            raise hash_errors
-
-    def _is_upgrade_allowed(self, req):
-        # type: (InstallRequirement) -> bool
-        if self.upgrade_strategy == "to-satisfy-only":
-            return False
-        elif self.upgrade_strategy == "eager":
-            return True
-        else:
-            assert self.upgrade_strategy == "only-if-needed"
-            return req.is_direct
-
-    def _set_req_to_reinstall(self, req):
-        # type: (InstallRequirement) -> None
-        """
-        Set a requirement to be installed.
-        """
-        # Don't uninstall the conflict if doing a user install and the
-        # conflict is not a user install.
-        if not self.use_user_site or dist_in_usersite(req.satisfied_by):
-            req.should_reinstall = True
-        req.satisfied_by = None
-
-    def _check_skip_installed(self, req_to_install):
-        # type: (InstallRequirement) -> Optional[str]
-        """Check if req_to_install should be skipped.
-
-        This will check if the req is installed, and whether we should upgrade
-        or reinstall it, taking into account all the relevant user options.
-
-        After calling this req_to_install will only have satisfied_by set to
-        None if the req_to_install is to be upgraded/reinstalled etc. Any
-        other value will be a dist recording the current thing installed that
-        satisfies the requirement.
-
-        Note that for vcs urls and the like we can't assess skipping in this
-        routine - we simply identify that we need to pull the thing down,
-        then later on it is pulled down and introspected to assess upgrade/
-        reinstalls etc.
-
-        :return: A text reason for why it was skipped, or None.
-        """
-        if self.ignore_installed:
-            return None
-
-        req_to_install.check_if_exists(self.use_user_site)
-        if not req_to_install.satisfied_by:
-            return None
-
-        if self.force_reinstall:
-            self._set_req_to_reinstall(req_to_install)
-            return None
-
-        if not self._is_upgrade_allowed(req_to_install):
-            if self.upgrade_strategy == "only-if-needed":
-                return 'already satisfied, skipping upgrade'
-            return 'already satisfied'
-
-        # Check for the possibility of an upgrade.  For link-based
-        # requirements we have to pull the tree down and inspect to assess
-        # the version #, so it's handled way down.
-        if not req_to_install.link:
-            try:
-                self.finder.find_requirement(req_to_install, upgrade=True)
-            except BestVersionAlreadyInstalled:
-                # Then the best version is installed.
-                return 'already up-to-date'
-            except DistributionNotFound:
-                # No distribution found, so we squash the error.  It will
-                # be raised later when we re-try later to do the install.
-                # Why don't we just raise here?
-                pass
-
-        self._set_req_to_reinstall(req_to_install)
-        return None
-
-    def _get_abstract_dist_for(self, req):
-        # type: (InstallRequirement) -> AbstractDistribution
-        """Takes a InstallRequirement and returns a single AbstractDist \
-        representing a prepared variant of the same.
-        """
-        if req.editable:
-            return self.preparer.prepare_editable_requirement(req)
-
-        # satisfied_by is only evaluated by calling _check_skip_installed,
-        # so it must be None here.
-        assert req.satisfied_by is None
-        skip_reason = self._check_skip_installed(req)
-
-        if req.satisfied_by:
-            return self.preparer.prepare_installed_requirement(
-                req, skip_reason
-            )
-
-        upgrade_allowed = self._is_upgrade_allowed(req)
-
-        # We eagerly populate the link, since that's our "legacy" behavior.
-        require_hashes = self.preparer.require_hashes
-        req.populate_link(self.finder, upgrade_allowed, require_hashes)
-        abstract_dist = self.preparer.prepare_linked_requirement(req)
-
-        # NOTE
-        # The following portion is for determining if a certain package is
-        # going to be re-installed/upgraded or not and reporting to the user.
-        # This should probably get cleaned up in a future refactor.
-
-        # req.req is only avail after unpack for URL
-        # pkgs repeat check_if_exists to uninstall-on-upgrade
-        # (#14)
-        if not self.ignore_installed:
-            req.check_if_exists(self.use_user_site)
-
-        if req.satisfied_by:
-            should_modify = (
-                self.upgrade_strategy != "to-satisfy-only" or
-                self.force_reinstall or
-                self.ignore_installed or
-                req.link.scheme == 'file'
-            )
-            if should_modify:
-                self._set_req_to_reinstall(req)
-            else:
-                logger.info(
-                    'Requirement already satisfied (use --upgrade to upgrade):'
-                    ' %s', req,
-                )
-
-        return abstract_dist
-
-    def _resolve_one(
-        self,
-        requirement_set,  # type: RequirementSet
-        req_to_install,  # type: InstallRequirement
-    ):
-        # type: (...) -> List[InstallRequirement]
-        """Prepare a single requirements file.
-
-        :return: A list of additional InstallRequirements to also install.
-        """
-        # Tell user what we are doing for this requirement:
-        # obtain (editable), skipping, processing (local url), collecting
-        # (remote url or package name)
-        if req_to_install.constraint or req_to_install.prepared:
-            return []
-
-        req_to_install.prepared = True
-
-        # register tmp src for cleanup in case something goes wrong
-        requirement_set.reqs_to_cleanup.append(req_to_install)
-
-        abstract_dist = self._get_abstract_dist_for(req_to_install)
-
-        # Parse and return dependencies
-        dist = abstract_dist.get_pkg_resources_distribution()
-        # This will raise UnsupportedPythonVersion if the given Python
-        # version isn't compatible with the distribution's Requires-Python.
-        _check_dist_requires_python(
-            dist, version_info=self._py_version_info,
-            ignore_requires_python=self.ignore_requires_python,
-        )
-
-        more_reqs = []  # type: List[InstallRequirement]
-
-        def add_req(subreq, extras_requested):
-            sub_install_req = self._make_install_req(
-                str(subreq),
-                req_to_install,
-            )
-            parent_req_name = req_to_install.name
-            to_scan_again, add_to_parent = requirement_set.add_requirement(
-                sub_install_req,
-                parent_req_name=parent_req_name,
-                extras_requested=extras_requested,
-            )
-            if parent_req_name and add_to_parent:
-                self._discovered_dependencies[parent_req_name].append(
-                    add_to_parent
-                )
-            more_reqs.extend(to_scan_again)
-
-        with indent_log():
-            # We add req_to_install before its dependencies, so that we
-            # can refer to it when adding dependencies.
-            if not requirement_set.has_requirement(req_to_install.name):
-                # 'unnamed' requirements will get added here
-                # 'unnamed' requirements can only come from being directly
-                # provided by the user.
-                assert req_to_install.is_direct
-                requirement_set.add_requirement(
-                    req_to_install, parent_req_name=None,
-                )
-
-            if not self.ignore_dependencies:
-                if req_to_install.extras:
-                    logger.debug(
-                        "Installing extra requirements: %r",
-                        ','.join(req_to_install.extras),
-                    )
-                missing_requested = sorted(
-                    set(req_to_install.extras) - set(dist.extras)
-                )
-                for missing in missing_requested:
-                    logger.warning(
-                        '%s does not provide the extra \'%s\'',
-                        dist, missing
-                    )
-
-                available_requested = sorted(
-                    set(dist.extras) & set(req_to_install.extras)
-                )
-                for subreq in dist.requires(available_requested):
-                    add_req(subreq, extras_requested=available_requested)
-
-            if not req_to_install.editable and not req_to_install.satisfied_by:
-                # XXX: --no-install leads this to report 'Successfully
-                # downloaded' for only non-editable reqs, even though we took
-                # action on them.
-                requirement_set.successfully_downloaded.append(req_to_install)
-
-        return more_reqs
-
-    def get_installation_order(self, req_set):
-        # type: (RequirementSet) -> List[InstallRequirement]
-        """Create the installation order.
-
-        The installation order is topological - requirements are installed
-        before the requiring thing. We break cycles at an arbitrary point,
-        and make no other guarantees.
-        """
-        # The current implementation, which we may change at any point
-        # installs the user specified things in the order given, except when
-        # dependencies must come earlier to achieve topological order.
-        order = []
-        ordered_reqs = set()  # type: Set[InstallRequirement]
-
-        def schedule(req):
-            if req.satisfied_by or req in ordered_reqs:
-                return
-            if req.constraint:
-                return
-            ordered_reqs.add(req)
-            for dep in self._discovered_dependencies[req.name]:
-                schedule(dep)
-            order.append(req)
-
-        for install_req in req_set.requirements.values():
-            schedule(install_req)
-        return order