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Filename : resolver.py
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import contextlib
import functools
import logging
import os
from typing import TYPE_CHECKING, Dict, List, Optional, Set, Tuple, cast

from pip._vendor.packaging.utils import canonicalize_name
from pip._vendor.resolvelib import BaseReporter, ResolutionImpossible
from pip._vendor.resolvelib import Resolver as RLResolver
from pip._vendor.resolvelib.structs import DirectedGraph

from pip._internal.cache import WheelCache
from pip._internal.index.package_finder import PackageFinder
from pip._internal.operations.prepare import RequirementPreparer
from pip._internal.req.constructors import install_req_extend_extras
from pip._internal.req.req_install import InstallRequirement
from pip._internal.req.req_set import RequirementSet
from pip._internal.resolution.base import BaseResolver, InstallRequirementProvider
from pip._internal.resolution.resolvelib.provider import PipProvider
from pip._internal.resolution.resolvelib.reporter import (
    PipDebuggingReporter,
    PipReporter,
)
from pip._internal.utils.packaging import get_requirement

from .base import Candidate, Requirement
from .factory import Factory

if TYPE_CHECKING:
    from pip._vendor.resolvelib.resolvers import Result as RLResult

    Result = RLResult[Requirement, Candidate, str]


logger = logging.getLogger(__name__)


class Resolver(BaseResolver):
    _allowed_strategies = {"eager", "only-if-needed", "to-satisfy-only"}

    def __init__(
        self,
        preparer: RequirementPreparer,
        finder: PackageFinder,
        wheel_cache: Optional[WheelCache],
        make_install_req: InstallRequirementProvider,
        use_user_site: bool,
        ignore_dependencies: bool,
        ignore_installed: bool,
        ignore_requires_python: bool,
        force_reinstall: bool,
        upgrade_strategy: str,
        py_version_info: Optional[Tuple[int, ...]] = None,
    ):
        super().__init__()
        assert upgrade_strategy in self._allowed_strategies

        self.factory = Factory(
            finder=finder,
            preparer=preparer,
            make_install_req=make_install_req,
            wheel_cache=wheel_cache,
            use_user_site=use_user_site,
            force_reinstall=force_reinstall,
            ignore_installed=ignore_installed,
            ignore_requires_python=ignore_requires_python,
            py_version_info=py_version_info,
        )
        self.ignore_dependencies = ignore_dependencies
        self.upgrade_strategy = upgrade_strategy
        self._result: Optional[Result] = None

    def resolve(
        self, root_reqs: List[InstallRequirement], check_supported_wheels: bool
    ) -> RequirementSet:
        collected = self.factory.collect_root_requirements(root_reqs)
        provider = PipProvider(
            factory=self.factory,
            constraints=collected.constraints,
            ignore_dependencies=self.ignore_dependencies,
            upgrade_strategy=self.upgrade_strategy,
            user_requested=collected.user_requested,
        )
        if "PIP_RESOLVER_DEBUG" in os.environ:
            reporter: BaseReporter = PipDebuggingReporter()
        else:
            reporter = PipReporter()
        resolver: RLResolver[Requirement, Candidate, str] = RLResolver(
            provider,
            reporter,
        )

        try:
            limit_how_complex_resolution_can_be = 200000
            result = self._result = resolver.resolve(
                collected.requirements, max_rounds=limit_how_complex_resolution_can_be
            )

        except ResolutionImpossible as e:
            error = self.factory.get_installation_error(
                cast("ResolutionImpossible[Requirement, Candidate]", e),
                collected.constraints,
            )
            raise error from e

        req_set = RequirementSet(check_supported_wheels=check_supported_wheels)
        # process candidates with extras last to ensure their base equivalent is
        # already in the req_set if appropriate.
        # Python's sort is stable so using a binary key function keeps relative order
        # within both subsets.
        for candidate in sorted(
            result.mapping.values(), key=lambda c: c.name != c.project_name
        ):
            ireq = candidate.get_install_requirement()
            if ireq is None:
                if candidate.name != candidate.project_name:
                    # extend existing req's extras
                    with contextlib.suppress(KeyError):
                        req = req_set.get_requirement(candidate.project_name)
                        req_set.add_named_requirement(
                            install_req_extend_extras(
                                req, get_requirement(candidate.name).extras
                            )
                        )
                continue

            # Check if there is already an installation under the same name,
            # and set a flag for later stages to uninstall it, if needed.
            installed_dist = self.factory.get_dist_to_uninstall(candidate)
            if installed_dist is None:
                # There is no existing installation -- nothing to uninstall.
                ireq.should_reinstall = False
            elif self.factory.force_reinstall:
                # The --force-reinstall flag is set -- reinstall.
                ireq.should_reinstall = True
            elif installed_dist.version != candidate.version:
                # The installation is different in version -- reinstall.
                ireq.should_reinstall = True
            elif candidate.is_editable or installed_dist.editable:
                # The incoming distribution is editable, or different in
                # editable-ness to installation -- reinstall.
                ireq.should_reinstall = True
            elif candidate.source_link and candidate.source_link.is_file:
                # The incoming distribution is under file://
                if candidate.source_link.is_wheel:
                    # is a local wheel -- do nothing.
                    logger.info(
                        "%s is already installed with the same version as the "
                        "provided wheel. Use --force-reinstall to force an "
                        "installation of the wheel.",
                        ireq.name,
                    )
                    continue

                # is a local sdist or path -- reinstall
                ireq.should_reinstall = True
            else:
                continue

            link = candidate.source_link
            if link and link.is_yanked:
                # The reason can contain non-ASCII characters, Unicode
                # is required for Python 2.
                msg = (
                    "The candidate selected for download or install is a "
                    "yanked version: {name!r} candidate (version {version} "
                    "at {link})\nReason for being yanked: {reason}"
                ).format(
                    name=candidate.name,
                    version=candidate.version,
                    link=link,
                    reason=link.yanked_reason or "<none given>",
                )
                logger.warning(msg)

            req_set.add_named_requirement(ireq)

        reqs = req_set.all_requirements
        self.factory.preparer.prepare_linked_requirements_more(reqs)
        for req in reqs:
            req.prepared = True
            req.needs_more_preparation = False
        return req_set

    def get_installation_order(
        self, req_set: RequirementSet
    ) -> List[InstallRequirement]:
        """Get order for installation of requirements in RequirementSet.

        The returned list contains a requirement before another that depends on
        it. This helps ensure that the environment is kept consistent as they
        get installed one-by-one.

        The current implementation creates a topological ordering of the
        dependency graph, giving more weight to packages with less
        or no dependencies, while breaking any cycles in the graph at
        arbitrary points. We make no guarantees about where the cycle
        would be broken, other than it *would* be broken.
        """
        assert self._result is not None, "must call resolve() first"

        if not req_set.requirements:
            # Nothing is left to install, so we do not need an order.
            return []

        graph = self._result.graph
        weights = get_topological_weights(graph, set(req_set.requirements.keys()))

        sorted_items = sorted(
            req_set.requirements.items(),
            key=functools.partial(_req_set_item_sorter, weights=weights),
            reverse=True,
        )
        return [ireq for _, ireq in sorted_items]


def get_topological_weights(
    graph: "DirectedGraph[Optional[str]]", requirement_keys: Set[str]
) -> Dict[Optional[str], int]:
    """Assign weights to each node based on how "deep" they are.

    This implementation may change at any point in the future without prior
    notice.

    We first simplify the dependency graph by pruning any leaves and giving them
    the highest weight: a package without any dependencies should be installed
    first. This is done again and again in the same way, giving ever less weight
    to the newly found leaves. The loop stops when no leaves are left: all
    remaining packages have at least one dependency left in the graph.

    Then we continue with the remaining graph, by taking the length for the
    longest path to any node from root, ignoring any paths that contain a single
    node twice (i.e. cycles). This is done through a depth-first search through
    the graph, while keeping track of the path to the node.

    Cycles in the graph result would result in node being revisited while also
    being on its own path. In this case, take no action. This helps ensure we
    don't get stuck in a cycle.

    When assigning weight, the longer path (i.e. larger length) is preferred.

    We are only interested in the weights of packages that are in the
    requirement_keys.
    """
    path: Set[Optional[str]] = set()
    weights: Dict[Optional[str], int] = {}

    def visit(node: Optional[str]) -> None:
        if node in path:
            # We hit a cycle, so we'll break it here.
            return

        # Time to visit the children!
        path.add(node)
        for child in graph.iter_children(node):
            visit(child)
        path.remove(node)

        if node not in requirement_keys:
            return

        last_known_parent_count = weights.get(node, 0)
        weights[node] = max(last_known_parent_count, len(path))

    # Simplify the graph, pruning leaves that have no dependencies.
    # This is needed for large graphs (say over 200 packages) because the
    # `visit` function is exponentially slower then, taking minutes.
    # See https://github.com/pypa/pip/issues/10557
    # We will loop until we explicitly break the loop.
    while True:
        leaves = set()
        for key in graph:
            if key is None:
                continue
            for _child in graph.iter_children(key):
                # This means we have at least one child
                break
            else:
                # No child.
                leaves.add(key)
        if not leaves:
            # We are done simplifying.
            break
        # Calculate the weight for the leaves.
        weight = len(graph) - 1
        for leaf in leaves:
            if leaf not in requirement_keys:
                continue
            weights[leaf] = weight
        # Remove the leaves from the graph, making it simpler.
        for leaf in leaves:
            graph.remove(leaf)

    # Visit the remaining graph.
    # `None` is guaranteed to be the root node by resolvelib.
    visit(None)

    # Sanity check: all requirement keys should be in the weights,
    # and no other keys should be in the weights.
    difference = set(weights.keys()).difference(requirement_keys)
    assert not difference, difference

    return weights


def _req_set_item_sorter(
    item: Tuple[str, InstallRequirement],
    weights: Dict[Optional[str], int],
) -> Tuple[int, str]:
    """Key function used to sort install requirements for installation.

    Based on the "weight" mapping calculated in ``get_installation_order()``.
    The canonical package name is returned as the second member as a tie-
    breaker to ensure the result is predictable, which is useful in tests.
    """
    name = canonicalize_name(item[0])
    return weights[name], name