--- a/lib/python3.8/site-packages/pip/_internal/index/package_finder.py	Mon Jul 27 03:47:31 2020 -0400
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,1013 +0,0 @@
-"""Routines related to PyPI, indexes"""
-
-# The following comment should be removed at some point in the future.
-# mypy: strict-optional=False
-
-from __future__ import absolute_import
-
-import logging
-import re
-
-from pip._vendor.packaging import specifiers
-from pip._vendor.packaging.utils import canonicalize_name
-from pip._vendor.packaging.version import parse as parse_version
-
-from pip._internal.exceptions import (
-    BestVersionAlreadyInstalled,
-    DistributionNotFound,
-    InvalidWheelFilename,
-    UnsupportedWheel,
-)
-from pip._internal.index.collector import parse_links
-from pip._internal.models.candidate import InstallationCandidate
-from pip._internal.models.format_control import FormatControl
-from pip._internal.models.link import Link
-from pip._internal.models.selection_prefs import SelectionPreferences
-from pip._internal.models.target_python import TargetPython
-from pip._internal.models.wheel import Wheel
-from pip._internal.utils.filetypes import WHEEL_EXTENSION
-from pip._internal.utils.logging import indent_log
-from pip._internal.utils.misc import build_netloc
-from pip._internal.utils.packaging import check_requires_python
-from pip._internal.utils.typing import MYPY_CHECK_RUNNING
-from pip._internal.utils.unpacking import SUPPORTED_EXTENSIONS
-from pip._internal.utils.urls import url_to_path
-
-if MYPY_CHECK_RUNNING:
-    from typing import (
-        FrozenSet, Iterable, List, Optional, Set, Text, Tuple, Union,
-    )
-
-    from pip._vendor.packaging.tags import Tag
-    from pip._vendor.packaging.version import _BaseVersion
-
-    from pip._internal.index.collector import LinkCollector
-    from pip._internal.models.search_scope import SearchScope
-    from pip._internal.req import InstallRequirement
-    from pip._internal.utils.hashes import Hashes
-
-    BuildTag = Union[Tuple[()], Tuple[int, str]]
-    CandidateSortingKey = (
-        Tuple[int, int, int, _BaseVersion, BuildTag, Optional[int]]
-    )
-
-
-__all__ = ['FormatControl', 'BestCandidateResult', 'PackageFinder']
-
-
-logger = logging.getLogger(__name__)
-
-
-def _check_link_requires_python(
-    link,  # type: Link
-    version_info,  # type: Tuple[int, int, int]
-    ignore_requires_python=False,  # type: bool
-):
-    # type: (...) -> bool
-    """
-    Return whether the given Python version is compatible with a link'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.
-    """
-    try:
-        is_compatible = check_requires_python(
-            link.requires_python, version_info=version_info,
-        )
-    except specifiers.InvalidSpecifier:
-        logger.debug(
-            "Ignoring invalid Requires-Python (%r) for link: %s",
-            link.requires_python, link,
-        )
-    else:
-        if not is_compatible:
-            version = '.'.join(map(str, version_info))
-            if not ignore_requires_python:
-                logger.debug(
-                    'Link requires a different Python (%s not in: %r): %s',
-                    version, link.requires_python, link,
-                )
-                return False
-
-            logger.debug(
-                'Ignoring failed Requires-Python check (%s not in: %r) '
-                'for link: %s',
-                version, link.requires_python, link,
-            )
-
-    return True
-
-
-class LinkEvaluator(object):
-
-    """
-    Responsible for evaluating links for a particular project.
-    """
-
-    _py_version_re = re.compile(r'-py([123]\.?[0-9]?)$')
-
-    # Don't include an allow_yanked default value to make sure each call
-    # site considers whether yanked releases are allowed. This also causes
-    # that decision to be made explicit in the calling code, which helps
-    # people when reading the code.
-    def __init__(
-        self,
-        project_name,    # type: str
-        canonical_name,  # type: str
-        formats,         # type: FrozenSet[str]
-        target_python,   # type: TargetPython
-        allow_yanked,    # type: bool
-        ignore_requires_python=None,  # type: Optional[bool]
-    ):
-        # type: (...) -> None
-        """
-        :param project_name: The user supplied package name.
-        :param canonical_name: The canonical package name.
-        :param formats: The formats allowed for this package. Should be a set
-            with 'binary' or 'source' or both in it.
-        :param target_python: The target Python interpreter to use when
-            evaluating link compatibility. This is used, for example, to
-            check wheel compatibility, as well as when checking the Python
-            version, e.g. the Python version embedded in a link filename
-            (or egg fragment) and against an HTML link's optional PEP 503
-            "data-requires-python" attribute.
-        :param allow_yanked: Whether files marked as yanked (in the sense
-            of PEP 592) are permitted to be candidates for install.
-        :param ignore_requires_python: Whether to ignore incompatible
-            PEP 503 "data-requires-python" values in HTML links. Defaults
-            to False.
-        """
-        if ignore_requires_python is None:
-            ignore_requires_python = False
-
-        self._allow_yanked = allow_yanked
-        self._canonical_name = canonical_name
-        self._ignore_requires_python = ignore_requires_python
-        self._formats = formats
-        self._target_python = target_python
-
-        self.project_name = project_name
-
-    def evaluate_link(self, link):
-        # type: (Link) -> Tuple[bool, Optional[Text]]
-        """
-        Determine whether a link is a candidate for installation.
-
-        :return: A tuple (is_candidate, result), where `result` is (1) a
-            version string if `is_candidate` is True, and (2) if
-            `is_candidate` is False, an optional string to log the reason
-            the link fails to qualify.
-        """
-        version = None
-        if link.is_yanked and not self._allow_yanked:
-            reason = link.yanked_reason or '<none given>'
-            # Mark this as a unicode string to prevent "UnicodeEncodeError:
-            # 'ascii' codec can't encode character" in Python 2 when
-            # the reason contains non-ascii characters.
-            return (False, u'yanked for reason: {}'.format(reason))
-
-        if link.egg_fragment:
-            egg_info = link.egg_fragment
-            ext = link.ext
-        else:
-            egg_info, ext = link.splitext()
-            if not ext:
-                return (False, 'not a file')
-            if ext not in SUPPORTED_EXTENSIONS:
-                return (False, 'unsupported archive format: %s' % ext)
-            if "binary" not in self._formats and ext == WHEEL_EXTENSION:
-                reason = 'No binaries permitted for %s' % self.project_name
-                return (False, reason)
-            if "macosx10" in link.path and ext == '.zip':
-                return (False, 'macosx10 one')
-            if ext == WHEEL_EXTENSION:
-                try:
-                    wheel = Wheel(link.filename)
-                except InvalidWheelFilename:
-                    return (False, 'invalid wheel filename')
-                if canonicalize_name(wheel.name) != self._canonical_name:
-                    reason = 'wrong project name (not %s)' % self.project_name
-                    return (False, reason)
-
-                supported_tags = self._target_python.get_tags()
-                if not wheel.supported(supported_tags):
-                    # Include the wheel's tags in the reason string to
-                    # simplify troubleshooting compatibility issues.
-                    file_tags = wheel.get_formatted_file_tags()
-                    reason = (
-                        "none of the wheel's tags match: {}".format(
-                            ', '.join(file_tags)
-                        )
-                    )
-                    return (False, reason)
-
-                version = wheel.version
-
-        # This should be up by the self.ok_binary check, but see issue 2700.
-        if "source" not in self._formats and ext != WHEEL_EXTENSION:
-            return (False, 'No sources permitted for %s' % self.project_name)
-
-        if not version:
-            version = _extract_version_from_fragment(
-                egg_info, self._canonical_name,
-            )
-        if not version:
-            return (
-                False, 'Missing project version for %s' % self.project_name,
-            )
-
-        match = self._py_version_re.search(version)
-        if match:
-            version = version[:match.start()]
-            py_version = match.group(1)
-            if py_version != self._target_python.py_version:
-                return (False, 'Python version is incorrect')
-
-        supports_python = _check_link_requires_python(
-            link, version_info=self._target_python.py_version_info,
-            ignore_requires_python=self._ignore_requires_python,
-        )
-        if not supports_python:
-            # Return None for the reason text to suppress calling
-            # _log_skipped_link().
-            return (False, None)
-
-        logger.debug('Found link %s, version: %s', link, version)
-
-        return (True, version)
-
-
-def filter_unallowed_hashes(
-    candidates,    # type: List[InstallationCandidate]
-    hashes,        # type: Hashes
-    project_name,  # type: str
-):
-    # type: (...) -> List[InstallationCandidate]
-    """
-    Filter out candidates whose hashes aren't allowed, and return a new
-    list of candidates.
-
-    If at least one candidate has an allowed hash, then all candidates with
-    either an allowed hash or no hash specified are returned.  Otherwise,
-    the given candidates are returned.
-
-    Including the candidates with no hash specified when there is a match
-    allows a warning to be logged if there is a more preferred candidate
-    with no hash specified.  Returning all candidates in the case of no
-    matches lets pip report the hash of the candidate that would otherwise
-    have been installed (e.g. permitting the user to more easily update
-    their requirements file with the desired hash).
-    """
-    if not hashes:
-        logger.debug(
-            'Given no hashes to check %s links for project %r: '
-            'discarding no candidates',
-            len(candidates),
-            project_name,
-        )
-        # Make sure we're not returning back the given value.
-        return list(candidates)
-
-    matches_or_no_digest = []
-    # Collect the non-matches for logging purposes.
-    non_matches = []
-    match_count = 0
-    for candidate in candidates:
-        link = candidate.link
-        if not link.has_hash:
-            pass
-        elif link.is_hash_allowed(hashes=hashes):
-            match_count += 1
-        else:
-            non_matches.append(candidate)
-            continue
-
-        matches_or_no_digest.append(candidate)
-
-    if match_count:
-        filtered = matches_or_no_digest
-    else:
-        # Make sure we're not returning back the given value.
-        filtered = list(candidates)
-
-    if len(filtered) == len(candidates):
-        discard_message = 'discarding no candidates'
-    else:
-        discard_message = 'discarding {} non-matches:\n  {}'.format(
-            len(non_matches),
-            '\n  '.join(str(candidate.link) for candidate in non_matches)
-        )
-
-    logger.debug(
-        'Checked %s links for project %r against %s hashes '
-        '(%s matches, %s no digest): %s',
-        len(candidates),
-        project_name,
-        hashes.digest_count,
-        match_count,
-        len(matches_or_no_digest) - match_count,
-        discard_message
-    )
-
-    return filtered
-
-
-class CandidatePreferences(object):
-
-    """
-    Encapsulates some of the preferences for filtering and sorting
-    InstallationCandidate objects.
-    """
-
-    def __init__(
-        self,
-        prefer_binary=False,  # type: bool
-        allow_all_prereleases=False,  # type: bool
-    ):
-        # type: (...) -> None
-        """
-        :param allow_all_prereleases: Whether to allow all pre-releases.
-        """
-        self.allow_all_prereleases = allow_all_prereleases
-        self.prefer_binary = prefer_binary
-
-
-class BestCandidateResult(object):
-    """A collection of candidates, returned by `PackageFinder.find_best_candidate`.
-
-    This class is only intended to be instantiated by CandidateEvaluator's
-    `compute_best_candidate()` method.
-    """
-
-    def __init__(
-        self,
-        candidates,             # type: List[InstallationCandidate]
-        applicable_candidates,  # type: List[InstallationCandidate]
-        best_candidate,         # type: Optional[InstallationCandidate]
-    ):
-        # type: (...) -> None
-        """
-        :param candidates: A sequence of all available candidates found.
-        :param applicable_candidates: The applicable candidates.
-        :param best_candidate: The most preferred candidate found, or None
-            if no applicable candidates were found.
-        """
-        assert set(applicable_candidates) <= set(candidates)
-
-        if best_candidate is None:
-            assert not applicable_candidates
-        else:
-            assert best_candidate in applicable_candidates
-
-        self._applicable_candidates = applicable_candidates
-        self._candidates = candidates
-
-        self.best_candidate = best_candidate
-
-    def iter_all(self):
-        # type: () -> Iterable[InstallationCandidate]
-        """Iterate through all candidates.
-        """
-        return iter(self._candidates)
-
-    def iter_applicable(self):
-        # type: () -> Iterable[InstallationCandidate]
-        """Iterate through the applicable candidates.
-        """
-        return iter(self._applicable_candidates)
-
-
-class CandidateEvaluator(object):
-
-    """
-    Responsible for filtering and sorting candidates for installation based
-    on what tags are valid.
-    """
-
-    @classmethod
-    def create(
-        cls,
-        project_name,         # type: str
-        target_python=None,   # type: Optional[TargetPython]
-        prefer_binary=False,  # type: bool
-        allow_all_prereleases=False,  # type: bool
-        specifier=None,       # type: Optional[specifiers.BaseSpecifier]
-        hashes=None,          # type: Optional[Hashes]
-    ):
-        # type: (...) -> CandidateEvaluator
-        """Create a CandidateEvaluator object.
-
-        :param target_python: The target Python interpreter to use when
-            checking compatibility. If None (the default), a TargetPython
-            object will be constructed from the running Python.
-        :param specifier: An optional object implementing `filter`
-            (e.g. `packaging.specifiers.SpecifierSet`) to filter applicable
-            versions.
-        :param hashes: An optional collection of allowed hashes.
-        """
-        if target_python is None:
-            target_python = TargetPython()
-        if specifier is None:
-            specifier = specifiers.SpecifierSet()
-
-        supported_tags = target_python.get_tags()
-
-        return cls(
-            project_name=project_name,
-            supported_tags=supported_tags,
-            specifier=specifier,
-            prefer_binary=prefer_binary,
-            allow_all_prereleases=allow_all_prereleases,
-            hashes=hashes,
-        )
-
-    def __init__(
-        self,
-        project_name,         # type: str
-        supported_tags,       # type: List[Tag]
-        specifier,            # type: specifiers.BaseSpecifier
-        prefer_binary=False,  # type: bool
-        allow_all_prereleases=False,  # type: bool
-        hashes=None,                  # type: Optional[Hashes]
-    ):
-        # type: (...) -> None
-        """
-        :param supported_tags: The PEP 425 tags supported by the target
-            Python in order of preference (most preferred first).
-        """
-        self._allow_all_prereleases = allow_all_prereleases
-        self._hashes = hashes
-        self._prefer_binary = prefer_binary
-        self._project_name = project_name
-        self._specifier = specifier
-        self._supported_tags = supported_tags
-
-    def get_applicable_candidates(
-        self,
-        candidates,  # type: List[InstallationCandidate]
-    ):
-        # type: (...) -> List[InstallationCandidate]
-        """
-        Return the applicable candidates from a list of candidates.
-        """
-        # Using None infers from the specifier instead.
-        allow_prereleases = self._allow_all_prereleases or None
-        specifier = self._specifier
-        versions = {
-            str(v) for v in specifier.filter(
-                # We turn the version object into a str here because otherwise
-                # when we're debundled but setuptools isn't, Python will see
-                # packaging.version.Version and
-                # pkg_resources._vendor.packaging.version.Version as different
-                # types. This way we'll use a str as a common data interchange
-                # format. If we stop using the pkg_resources provided specifier
-                # and start using our own, we can drop the cast to str().
-                (str(c.version) for c in candidates),
-                prereleases=allow_prereleases,
-            )
-        }
-
-        # Again, converting version to str to deal with debundling.
-        applicable_candidates = [
-            c for c in candidates if str(c.version) in versions
-        ]
-
-        filtered_applicable_candidates = filter_unallowed_hashes(
-            candidates=applicable_candidates,
-            hashes=self._hashes,
-            project_name=self._project_name,
-        )
-
-        return sorted(filtered_applicable_candidates, key=self._sort_key)
-
-    def _sort_key(self, candidate):
-        # type: (InstallationCandidate) -> CandidateSortingKey
-        """
-        Function to pass as the `key` argument to a call to sorted() to sort
-        InstallationCandidates by preference.
-
-        Returns a tuple such that tuples sorting as greater using Python's
-        default comparison operator are more preferred.
-
-        The preference is as follows:
-
-        First and foremost, candidates with allowed (matching) hashes are
-        always preferred over candidates without matching hashes. This is
-        because e.g. if the only candidate with an allowed hash is yanked,
-        we still want to use that candidate.
-
-        Second, excepting hash considerations, candidates that have been
-        yanked (in the sense of PEP 592) are always less preferred than
-        candidates that haven't been yanked. Then:
-
-        If not finding wheels, they are sorted by version only.
-        If finding wheels, then the sort order is by version, then:
-          1. existing installs
-          2. wheels ordered via Wheel.support_index_min(self._supported_tags)
-          3. source archives
-        If prefer_binary was set, then all wheels are sorted above sources.
-
-        Note: it was considered to embed this logic into the Link
-              comparison operators, but then different sdist links
-              with the same version, would have to be considered equal
-        """
-        valid_tags = self._supported_tags
-        support_num = len(valid_tags)
-        build_tag = ()  # type: BuildTag
-        binary_preference = 0
-        link = candidate.link
-        if link.is_wheel:
-            # can raise InvalidWheelFilename
-            wheel = Wheel(link.filename)
-            if not wheel.supported(valid_tags):
-                raise UnsupportedWheel(
-                    "%s is not a supported wheel for this platform. It "
-                    "can't be sorted." % wheel.filename
-                )
-            if self._prefer_binary:
-                binary_preference = 1
-            pri = -(wheel.support_index_min(valid_tags))
-            if wheel.build_tag is not None:
-                match = re.match(r'^(\d+)(.*)$', wheel.build_tag)
-                build_tag_groups = match.groups()
-                build_tag = (int(build_tag_groups[0]), build_tag_groups[1])
-        else:  # sdist
-            pri = -(support_num)
-        has_allowed_hash = int(link.is_hash_allowed(self._hashes))
-        yank_value = -1 * int(link.is_yanked)  # -1 for yanked.
-        return (
-            has_allowed_hash, yank_value, binary_preference, candidate.version,
-            build_tag, pri,
-        )
-
-    def sort_best_candidate(
-        self,
-        candidates,    # type: List[InstallationCandidate]
-    ):
-        # type: (...) -> Optional[InstallationCandidate]
-        """
-        Return the best candidate per the instance's sort order, or None if
-        no candidate is acceptable.
-        """
-        if not candidates:
-            return None
-
-        best_candidate = max(candidates, key=self._sort_key)
-
-        # Log a warning per PEP 592 if necessary before returning.
-        link = best_candidate.link
-        if link.is_yanked:
-            reason = link.yanked_reason or '<none given>'
-            msg = (
-                # Mark this as a unicode string to prevent
-                # "UnicodeEncodeError: 'ascii' codec can't encode character"
-                # in Python 2 when the reason contains non-ascii characters.
-                u'The candidate selected for download or install is a '
-                'yanked version: {candidate}\n'
-                'Reason for being yanked: {reason}'
-            ).format(candidate=best_candidate, reason=reason)
-            logger.warning(msg)
-
-        return best_candidate
-
-    def compute_best_candidate(
-        self,
-        candidates,      # type: List[InstallationCandidate]
-    ):
-        # type: (...) -> BestCandidateResult
-        """
-        Compute and return a `BestCandidateResult` instance.
-        """
-        applicable_candidates = self.get_applicable_candidates(candidates)
-
-        best_candidate = self.sort_best_candidate(applicable_candidates)
-
-        return BestCandidateResult(
-            candidates,
-            applicable_candidates=applicable_candidates,
-            best_candidate=best_candidate,
-        )
-
-
-class PackageFinder(object):
-    """This finds packages.
-
-    This is meant to match easy_install's technique for looking for
-    packages, by reading pages and looking for appropriate links.
-    """
-
-    def __init__(
-        self,
-        link_collector,       # type: LinkCollector
-        target_python,        # type: TargetPython
-        allow_yanked,         # type: bool
-        format_control=None,  # type: Optional[FormatControl]
-        candidate_prefs=None,         # type: CandidatePreferences
-        ignore_requires_python=None,  # type: Optional[bool]
-    ):
-        # type: (...) -> None
-        """
-        This constructor is primarily meant to be used by the create() class
-        method and from tests.
-
-        :param format_control: A FormatControl object, used to control
-            the selection of source packages / binary packages when consulting
-            the index and links.
-        :param candidate_prefs: Options to use when creating a
-            CandidateEvaluator object.
-        """
-        if candidate_prefs is None:
-            candidate_prefs = CandidatePreferences()
-
-        format_control = format_control or FormatControl(set(), set())
-
-        self._allow_yanked = allow_yanked
-        self._candidate_prefs = candidate_prefs
-        self._ignore_requires_python = ignore_requires_python
-        self._link_collector = link_collector
-        self._target_python = target_python
-
-        self.format_control = format_control
-
-        # These are boring links that have already been logged somehow.
-        self._logged_links = set()  # type: Set[Link]
-
-    # Don't include an allow_yanked default value to make sure each call
-    # site considers whether yanked releases are allowed. This also causes
-    # that decision to be made explicit in the calling code, which helps
-    # people when reading the code.
-    @classmethod
-    def create(
-        cls,
-        link_collector,      # type: LinkCollector
-        selection_prefs,     # type: SelectionPreferences
-        target_python=None,  # type: Optional[TargetPython]
-    ):
-        # type: (...) -> PackageFinder
-        """Create a PackageFinder.
-
-        :param selection_prefs: The candidate selection preferences, as a
-            SelectionPreferences object.
-        :param target_python: The target Python interpreter to use when
-            checking compatibility. If None (the default), a TargetPython
-            object will be constructed from the running Python.
-        """
-        if target_python is None:
-            target_python = TargetPython()
-
-        candidate_prefs = CandidatePreferences(
-            prefer_binary=selection_prefs.prefer_binary,
-            allow_all_prereleases=selection_prefs.allow_all_prereleases,
-        )
-
-        return cls(
-            candidate_prefs=candidate_prefs,
-            link_collector=link_collector,
-            target_python=target_python,
-            allow_yanked=selection_prefs.allow_yanked,
-            format_control=selection_prefs.format_control,
-            ignore_requires_python=selection_prefs.ignore_requires_python,
-        )
-
-    @property
-    def search_scope(self):
-        # type: () -> SearchScope
-        return self._link_collector.search_scope
-
-    @search_scope.setter
-    def search_scope(self, search_scope):
-        # type: (SearchScope) -> None
-        self._link_collector.search_scope = search_scope
-
-    @property
-    def find_links(self):
-        # type: () -> List[str]
-        return self._link_collector.find_links
-
-    @property
-    def index_urls(self):
-        # type: () -> List[str]
-        return self.search_scope.index_urls
-
-    @property
-    def trusted_hosts(self):
-        # type: () -> Iterable[str]
-        for host_port in self._link_collector.session.pip_trusted_origins:
-            yield build_netloc(*host_port)
-
-    @property
-    def allow_all_prereleases(self):
-        # type: () -> bool
-        return self._candidate_prefs.allow_all_prereleases
-
-    def set_allow_all_prereleases(self):
-        # type: () -> None
-        self._candidate_prefs.allow_all_prereleases = True
-
-    def make_link_evaluator(self, project_name):
-        # type: (str) -> LinkEvaluator
-        canonical_name = canonicalize_name(project_name)
-        formats = self.format_control.get_allowed_formats(canonical_name)
-
-        return LinkEvaluator(
-            project_name=project_name,
-            canonical_name=canonical_name,
-            formats=formats,
-            target_python=self._target_python,
-            allow_yanked=self._allow_yanked,
-            ignore_requires_python=self._ignore_requires_python,
-        )
-
-    def _sort_links(self, links):
-        # type: (Iterable[Link]) -> List[Link]
-        """
-        Returns elements of links in order, non-egg links first, egg links
-        second, while eliminating duplicates
-        """
-        eggs, no_eggs = [], []
-        seen = set()  # type: Set[Link]
-        for link in links:
-            if link not in seen:
-                seen.add(link)
-                if link.egg_fragment:
-                    eggs.append(link)
-                else:
-                    no_eggs.append(link)
-        return no_eggs + eggs
-
-    def _log_skipped_link(self, link, reason):
-        # type: (Link, Text) -> None
-        if link not in self._logged_links:
-            # Mark this as a unicode string to prevent "UnicodeEncodeError:
-            # 'ascii' codec can't encode character" in Python 2 when
-            # the reason contains non-ascii characters.
-            #   Also, put the link at the end so the reason is more visible
-            # and because the link string is usually very long.
-            logger.debug(u'Skipping link: %s: %s', reason, link)
-            self._logged_links.add(link)
-
-    def get_install_candidate(self, link_evaluator, link):
-        # type: (LinkEvaluator, Link) -> Optional[InstallationCandidate]
-        """
-        If the link is a candidate for install, convert it to an
-        InstallationCandidate and return it. Otherwise, return None.
-        """
-        is_candidate, result = link_evaluator.evaluate_link(link)
-        if not is_candidate:
-            if result:
-                self._log_skipped_link(link, reason=result)
-            return None
-
-        return InstallationCandidate(
-            name=link_evaluator.project_name,
-            link=link,
-            # Convert the Text result to str since InstallationCandidate
-            # accepts str.
-            version=str(result),
-        )
-
-    def evaluate_links(self, link_evaluator, links):
-        # type: (LinkEvaluator, Iterable[Link]) -> List[InstallationCandidate]
-        """
-        Convert links that are candidates to InstallationCandidate objects.
-        """
-        candidates = []
-        for link in self._sort_links(links):
-            candidate = self.get_install_candidate(link_evaluator, link)
-            if candidate is not None:
-                candidates.append(candidate)
-
-        return candidates
-
-    def process_project_url(self, project_url, link_evaluator):
-        # type: (Link, LinkEvaluator) -> List[InstallationCandidate]
-        logger.debug(
-            'Fetching project page and analyzing links: %s', project_url,
-        )
-        html_page = self._link_collector.fetch_page(project_url)
-        if html_page is None:
-            return []
-
-        page_links = list(parse_links(html_page))
-
-        with indent_log():
-            package_links = self.evaluate_links(
-                link_evaluator,
-                links=page_links,
-            )
-
-        return package_links
-
-    def find_all_candidates(self, project_name):
-        # type: (str) -> List[InstallationCandidate]
-        """Find all available InstallationCandidate for project_name
-
-        This checks index_urls and find_links.
-        All versions found are returned as an InstallationCandidate list.
-
-        See LinkEvaluator.evaluate_link() for details on which files
-        are accepted.
-        """
-        collected_links = self._link_collector.collect_links(project_name)
-
-        link_evaluator = self.make_link_evaluator(project_name)
-
-        find_links_versions = self.evaluate_links(
-            link_evaluator,
-            links=collected_links.find_links,
-        )
-
-        page_versions = []
-        for project_url in collected_links.project_urls:
-            package_links = self.process_project_url(
-                project_url, link_evaluator=link_evaluator,
-            )
-            page_versions.extend(package_links)
-
-        file_versions = self.evaluate_links(
-            link_evaluator,
-            links=collected_links.files,
-        )
-        if file_versions:
-            file_versions.sort(reverse=True)
-            logger.debug(
-                'Local files found: %s',
-                ', '.join([
-                    url_to_path(candidate.link.url)
-                    for candidate in file_versions
-                ])
-            )
-
-        # This is an intentional priority ordering
-        return file_versions + find_links_versions + page_versions
-
-    def make_candidate_evaluator(
-        self,
-        project_name,    # type: str
-        specifier=None,  # type: Optional[specifiers.BaseSpecifier]
-        hashes=None,     # type: Optional[Hashes]
-    ):
-        # type: (...) -> CandidateEvaluator
-        """Create a CandidateEvaluator object to use.
-        """
-        candidate_prefs = self._candidate_prefs
-        return CandidateEvaluator.create(
-            project_name=project_name,
-            target_python=self._target_python,
-            prefer_binary=candidate_prefs.prefer_binary,
-            allow_all_prereleases=candidate_prefs.allow_all_prereleases,
-            specifier=specifier,
-            hashes=hashes,
-        )
-
-    def find_best_candidate(
-        self,
-        project_name,       # type: str
-        specifier=None,     # type: Optional[specifiers.BaseSpecifier]
-        hashes=None,        # type: Optional[Hashes]
-    ):
-        # type: (...) -> BestCandidateResult
-        """Find matches for the given project and specifier.
-
-        :param specifier: An optional object implementing `filter`
-            (e.g. `packaging.specifiers.SpecifierSet`) to filter applicable
-            versions.
-
-        :return: A `BestCandidateResult` instance.
-        """
-        candidates = self.find_all_candidates(project_name)
-        candidate_evaluator = self.make_candidate_evaluator(
-            project_name=project_name,
-            specifier=specifier,
-            hashes=hashes,
-        )
-        return candidate_evaluator.compute_best_candidate(candidates)
-
-    def find_requirement(self, req, upgrade):
-        # type: (InstallRequirement, bool) -> Optional[Link]
-        """Try to find a Link matching req
-
-        Expects req, an InstallRequirement and upgrade, a boolean
-        Returns a Link if found,
-        Raises DistributionNotFound or BestVersionAlreadyInstalled otherwise
-        """
-        hashes = req.hashes(trust_internet=False)
-        best_candidate_result = self.find_best_candidate(
-            req.name, specifier=req.specifier, hashes=hashes,
-        )
-        best_candidate = best_candidate_result.best_candidate
-
-        installed_version = None    # type: Optional[_BaseVersion]
-        if req.satisfied_by is not None:
-            installed_version = parse_version(req.satisfied_by.version)
-
-        def _format_versions(cand_iter):
-            # type: (Iterable[InstallationCandidate]) -> str
-            # This repeated parse_version and str() conversion is needed to
-            # handle different vendoring sources from pip and pkg_resources.
-            # If we stop using the pkg_resources provided specifier and start
-            # using our own, we can drop the cast to str().
-            return ", ".join(sorted(
-                {str(c.version) for c in cand_iter},
-                key=parse_version,
-            )) or "none"
-
-        if installed_version is None and best_candidate is None:
-            logger.critical(
-                'Could not find a version that satisfies the requirement %s '
-                '(from versions: %s)',
-                req,
-                _format_versions(best_candidate_result.iter_all()),
-            )
-
-            raise DistributionNotFound(
-                'No matching distribution found for %s' % req
-            )
-
-        best_installed = False
-        if installed_version and (
-                best_candidate is None or
-                best_candidate.version <= installed_version):
-            best_installed = True
-
-        if not upgrade and installed_version is not None:
-            if best_installed:
-                logger.debug(
-                    'Existing installed version (%s) is most up-to-date and '
-                    'satisfies requirement',
-                    installed_version,
-                )
-            else:
-                logger.debug(
-                    'Existing installed version (%s) satisfies requirement '
-                    '(most up-to-date version is %s)',
-                    installed_version,
-                    best_candidate.version,
-                )
-            return None
-
-        if best_installed:
-            # We have an existing version, and its the best version
-            logger.debug(
-                'Installed version (%s) is most up-to-date (past versions: '
-                '%s)',
-                installed_version,
-                _format_versions(best_candidate_result.iter_applicable()),
-            )
-            raise BestVersionAlreadyInstalled
-
-        logger.debug(
-            'Using version %s (newest of versions: %s)',
-            best_candidate.version,
-            _format_versions(best_candidate_result.iter_applicable()),
-        )
-        return best_candidate.link
-
-
-def _find_name_version_sep(fragment, canonical_name):
-    # type: (str, str) -> int
-    """Find the separator's index based on the package's canonical name.
-
-    :param fragment: A <package>+<version> filename "fragment" (stem) or
-        egg fragment.
-    :param canonical_name: The package's canonical name.
-
-    This function is needed since the canonicalized name does not necessarily
-    have the same length as the egg info's name part. An example::
-
-    >>> fragment = 'foo__bar-1.0'
-    >>> canonical_name = 'foo-bar'
-    >>> _find_name_version_sep(fragment, canonical_name)
-    8
-    """
-    # Project name and version must be separated by one single dash. Find all
-    # occurrences of dashes; if the string in front of it matches the canonical
-    # name, this is the one separating the name and version parts.
-    for i, c in enumerate(fragment):
-        if c != "-":
-            continue
-        if canonicalize_name(fragment[:i]) == canonical_name:
-            return i
-    raise ValueError("{} does not match {}".format(fragment, canonical_name))
-
-
-def _extract_version_from_fragment(fragment, canonical_name):
-    # type: (str, str) -> Optional[str]
-    """Parse the version string from a <package>+<version> filename
-    "fragment" (stem) or egg fragment.
-
-    :param fragment: The string to parse. E.g. foo-2.1
-    :param canonical_name: The canonicalized name of the package this
-        belongs to.
-    """
-    try:
-        version_start = _find_name_version_sep(fragment, canonical_name) + 1
-    except ValueError:
-        return None
-    version = fragment[version_start:]
-    if not version:
-        return None
-    return version