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stbi/Lib/site-packages/pip/_internal/index/package_finder.py

+"""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: {}'.format(ext))
+            if "binary" not in self._formats and ext == WHEEL_EXTENSION:
+                reason = 'No binaries permitted for {}'.format(
+                    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 {})'.format(
+                        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:
+            reason = 'No sources permitted for {}'.format(self.project_name)
+            return (False, reason)
+
+        if not version:
+            version = _extract_version_from_fragment(
+                egg_info, self._canonical_name,
+            )
+        if not version:
+            reason = 'Missing project version for {}'.format(self.project_name)
+            return (False, reason)
+
+        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(
+                    "{} is not a supported wheel for this platform. It "
+                    "can't be sorted.".format(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 {}'.format(
+                    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