lib/_emerge/depgraph.py

# Copyright 1999-2018 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2

from __future__ import division, print_function, unicode_literals

import collections
import errno
import functools
import io
import logging
import stat
import sys
import textwrap
import warnings
from collections import deque
from itertools import chain

import portage
from portage import os, OrderedDict
from portage import _unicode_decode, _unicode_encode, _encodings
from portage.const import PORTAGE_PACKAGE_ATOM, USER_CONFIG_PATH, VCS_DIRS
from portage.dbapi import dbapi
from portage.dbapi.dep_expand import dep_expand
from portage.dbapi.DummyTree import DummyTree
from portage.dbapi.IndexedPortdb import IndexedPortdb
from portage.dbapi._similar_name_search import similar_name_search
from portage.dep import Atom, best_match_to_list, extract_affecting_use, \
	check_required_use, human_readable_required_use, match_from_list, \
	_repo_separator
from portage.dep._slot_operator import (ignore_built_slot_operator_deps,
	strip_slots)
from portage.eapi import eapi_has_strong_blocks, eapi_has_required_use, \
	_get_eapi_attrs
from portage.exception import (InvalidAtom, InvalidData, InvalidDependString,
	PackageNotFound, PortageException)
from portage.localization import _
from portage.output import colorize, create_color_func, \
	darkgreen, green
bad = create_color_func("BAD")
from portage.package.ebuild.config import _get_feature_flags
from portage.package.ebuild.getmaskingstatus import \
	_getmaskingstatus, _MaskReason
from portage._sets import SETPREFIX
from portage._sets.base import InternalPackageSet
from portage.util import ConfigProtect, shlex_split, new_protect_filename
from portage.util import cmp_sort_key, writemsg, writemsg_stdout
from portage.util import ensure_dirs
from portage.util import writemsg_level, write_atomic
from portage.util.digraph import digraph
from portage.util._async.TaskScheduler import TaskScheduler
from portage.util._eventloop.EventLoop import EventLoop
from portage.util._eventloop.global_event_loop import global_event_loop
from portage.versions import _pkg_str, catpkgsplit

from _emerge.AtomArg import AtomArg
from _emerge.Blocker import Blocker
from _emerge.BlockerCache import BlockerCache
from _emerge.BlockerDepPriority import BlockerDepPriority
from .chk_updated_cfg_files import chk_updated_cfg_files
from _emerge.countdown import countdown
from _emerge.create_world_atom import create_world_atom
from _emerge.Dependency import Dependency
from _emerge.DependencyArg import DependencyArg
from _emerge.DepPriority import DepPriority
from _emerge.DepPriorityNormalRange import DepPriorityNormalRange
from _emerge.DepPrioritySatisfiedRange import DepPrioritySatisfiedRange
from _emerge.EbuildMetadataPhase import EbuildMetadataPhase
from _emerge.FakeVartree import FakeVartree
from _emerge._find_deep_system_runtime_deps import _find_deep_system_runtime_deps
from _emerge.is_valid_package_atom import insert_category_into_atom, \
	is_valid_package_atom
from _emerge.Package import Package
from _emerge.PackageArg import PackageArg
from _emerge.PackageVirtualDbapi import PackageVirtualDbapi
from _emerge.RootConfig import RootConfig
from _emerge.search import search
from _emerge.SetArg import SetArg
from _emerge.show_invalid_depstring_notice import show_invalid_depstring_notice
from _emerge.UnmergeDepPriority import UnmergeDepPriority
from _emerge.UseFlagDisplay import pkg_use_display
from _emerge.UserQuery import UserQuery

from _emerge.resolver.backtracking import Backtracker, BacktrackParameter
from _emerge.resolver.DbapiProvidesIndex import DbapiProvidesIndex
from _emerge.resolver.package_tracker import PackageTracker, PackageTrackerDbapiWrapper
from _emerge.resolver.slot_collision import slot_conflict_handler
from _emerge.resolver.circular_dependency import circular_dependency_handler
from _emerge.resolver.output import Display, format_unmatched_atom

if sys.hexversion >= 0x3000000:
	basestring = str
	long = int
	_unicode = str
else:
	_unicode = unicode

class _scheduler_graph_config(object):
	def __init__(self, trees, pkg_cache, graph, mergelist):
		self.trees = trees
		self.pkg_cache = pkg_cache
		self.graph = graph
		self.mergelist = mergelist

def _wildcard_set(atoms):
	pkgs = InternalPackageSet(allow_wildcard=True)
	for x in atoms:
		try:
			x = Atom(x, allow_wildcard=True, allow_repo=False)
		except portage.exception.InvalidAtom:
			x = Atom("*/" + x, allow_wildcard=True, allow_repo=False)
		pkgs.add(x)
	return pkgs

class _frozen_depgraph_config(object):

	def __init__(self, settings, trees, myopts, params, spinner):
		self.settings = settings
		self.target_root = settings["EROOT"]
		self.myopts = myopts
		self.edebug = 0
		if settings.get("PORTAGE_DEBUG", "") == "1":
			self.edebug = 1
		self.spinner = spinner
		self.requested_depth = params.get("deep", 0)
		self._running_root = trees[trees._running_eroot]["root_config"]
		self.pkgsettings = {}
		self.trees = {}
		self._trees_orig = trees
		self.roots = {}
		# All Package instances
		self._pkg_cache = {}
		self._highest_license_masked = {}
		# We can't know that an soname dep is unsatisfied if there are
		# any unbuilt ebuilds in the graph, since unbuilt ebuilds have
		# no soname data. Therefore, only enable soname dependency
		# resolution if --usepkgonly is enabled, or for removal actions.
		self.soname_deps_enabled = (
			("--usepkgonly" in myopts or "remove" in params) and
			params.get("ignore_soname_deps") != "y")
		dynamic_deps = "dynamic_deps" in params
		ignore_built_slot_operator_deps = myopts.get(
			"--ignore-built-slot-operator-deps", "n") == "y"
		for myroot in trees:
			self.trees[myroot] = {}
			# Create a RootConfig instance that references
			# the FakeVartree instead of the real one.
			self.roots[myroot] = RootConfig(
				trees[myroot]["vartree"].settings,
				self.trees[myroot],
				trees[myroot]["root_config"].setconfig)
			for tree in ("porttree", "bintree"):
				self.trees[myroot][tree] = trees[myroot][tree]
			self.trees[myroot]["vartree"] = \
				FakeVartree(trees[myroot]["root_config"],
					pkg_cache=self._pkg_cache,
					pkg_root_config=self.roots[myroot],
					dynamic_deps=dynamic_deps,
					ignore_built_slot_operator_deps=ignore_built_slot_operator_deps,
					soname_deps=self.soname_deps_enabled)
			self.pkgsettings[myroot] = portage.config(
				clone=self.trees[myroot]["vartree"].settings)
			if self.soname_deps_enabled and "remove" not in params:
				self.trees[myroot]["bintree"] = DummyTree(
					DbapiProvidesIndex(trees[myroot]["bintree"].dbapi))

		if params.get("ignore_world", False):
			self._required_set_names = set()
		else:
			self._required_set_names = set(["world"])

		atoms = ' '.join(myopts.get("--exclude", [])).split()
		self.excluded_pkgs = _wildcard_set(atoms)
		atoms = ' '.join(myopts.get("--reinstall-atoms", [])).split()
		self.reinstall_atoms = _wildcard_set(atoms)
		atoms = ' '.join(myopts.get("--usepkg-exclude", [])).split()
		self.usepkg_exclude = _wildcard_set(atoms)
		atoms = ' '.join(myopts.get("--useoldpkg-atoms", [])).split()
		self.useoldpkg_atoms = _wildcard_set(atoms)
		atoms = ' '.join(myopts.get("--rebuild-exclude", [])).split()
		self.rebuild_exclude = _wildcard_set(atoms)
		atoms = ' '.join(myopts.get("--rebuild-ignore", [])).split()
		self.rebuild_ignore = _wildcard_set(atoms)

		self.rebuild_if_new_rev = "--rebuild-if-new-rev" in myopts
		self.rebuild_if_new_ver = "--rebuild-if-new-ver" in myopts
		self.rebuild_if_unbuilt = "--rebuild-if-unbuilt" in myopts

class _depgraph_sets(object):
	def __init__(self):
		# contains all sets added to the graph
		self.sets = {}
		# contains non-set atoms given as arguments
		self.sets['__non_set_args__'] = InternalPackageSet(allow_repo=True)
		# contains all atoms from all sets added to the graph, including
		# atoms given as arguments
		self.atoms = InternalPackageSet(allow_repo=True)
		self.atom_arg_map = {}

class _rebuild_config(object):
	def __init__(self, frozen_config, backtrack_parameters):
		self._graph = digraph()
		self._frozen_config = frozen_config
		self.rebuild_list = backtrack_parameters.rebuild_list.copy()
		self.orig_rebuild_list = self.rebuild_list.copy()
		self.reinstall_list = backtrack_parameters.reinstall_list.copy()
		self.rebuild_if_new_rev = frozen_config.rebuild_if_new_rev
		self.rebuild_if_new_ver = frozen_config.rebuild_if_new_ver
		self.rebuild_if_unbuilt = frozen_config.rebuild_if_unbuilt
		self.rebuild = (self.rebuild_if_new_rev or self.rebuild_if_new_ver or
			self.rebuild_if_unbuilt)

	def add(self, dep_pkg, dep):
		parent = dep.collapsed_parent
		priority = dep.collapsed_priority
		rebuild_exclude = self._frozen_config.rebuild_exclude
		rebuild_ignore = self._frozen_config.rebuild_ignore
		if (self.rebuild and isinstance(parent, Package) and
			parent.built and priority.buildtime and
			isinstance(dep_pkg, Package) and
			not rebuild_exclude.findAtomForPackage(parent) and
			not rebuild_ignore.findAtomForPackage(dep_pkg)):
			self._graph.add(dep_pkg, parent, priority)

	def _needs_rebuild(self, dep_pkg):
		"""Check whether packages that depend on dep_pkg need to be rebuilt."""
		dep_root_slot = (dep_pkg.root, dep_pkg.slot_atom)
		if dep_pkg.built or dep_root_slot in self.orig_rebuild_list:
			return False

		if self.rebuild_if_unbuilt:
			# dep_pkg is being installed from source, so binary
			# packages for parents are invalid. Force rebuild
			return True

		trees = self._frozen_config.trees
		vardb = trees[dep_pkg.root]["vartree"].dbapi
		if self.rebuild_if_new_rev:
			# Parent packages are valid if a package with the same
			# cpv is already installed.
			return dep_pkg.cpv not in vardb.match(dep_pkg.slot_atom)

		# Otherwise, parent packages are valid if a package with the same
		# version (excluding revision) is already installed.
		assert self.rebuild_if_new_ver
		cpv_norev = catpkgsplit(dep_pkg.cpv)[:-1]
		for inst_cpv in vardb.match(dep_pkg.slot_atom):
			inst_cpv_norev = catpkgsplit(inst_cpv)[:-1]
			if inst_cpv_norev == cpv_norev:
				return False

		return True

	def _trigger_rebuild(self, parent, build_deps):
		root_slot = (parent.root, parent.slot_atom)
		if root_slot in self.rebuild_list:
			return False
		trees = self._frozen_config.trees
		reinstall = False
		for slot_atom, dep_pkg in build_deps.items():
			dep_root_slot = (dep_pkg.root, slot_atom)
			if self._needs_rebuild(dep_pkg):
				self.rebuild_list.add(root_slot)
				return True
			elif ("--usepkg" in self._frozen_config.myopts and
				(dep_root_slot in self.reinstall_list or
				dep_root_slot in self.rebuild_list or
				not dep_pkg.installed)):

				# A direct rebuild dependency is being installed. We
				# should update the parent as well to the latest binary,
				# if that binary is valid.
				#
				# To validate the binary, we check whether all of the
				# rebuild dependencies are present on the same binhost.
				#
				# 1) If parent is present on the binhost, but one of its
				#    rebuild dependencies is not, then the parent should
				#    be rebuilt from source.
				# 2) Otherwise, the parent binary is assumed to be valid,
				#    because all of its rebuild dependencies are
				#    consistent.
				bintree = trees[parent.root]["bintree"]
				uri = bintree.get_pkgindex_uri(parent.cpv)
				dep_uri = bintree.get_pkgindex_uri(dep_pkg.cpv)
				bindb = bintree.dbapi
				if self.rebuild_if_new_ver and uri and uri != dep_uri:
					cpv_norev = catpkgsplit(dep_pkg.cpv)[:-1]
					for cpv in bindb.match(dep_pkg.slot_atom):
						if cpv_norev == catpkgsplit(cpv)[:-1]:
							dep_uri = bintree.get_pkgindex_uri(cpv)
							if uri == dep_uri:
								break
				if uri and uri != dep_uri:
					# 1) Remote binary package is invalid because it was
					#    built without dep_pkg. Force rebuild.
					self.rebuild_list.add(root_slot)
					return True
				elif (parent.installed and
					root_slot not in self.reinstall_list):
					try:
						bin_build_time, = bindb.aux_get(parent.cpv,
							["BUILD_TIME"])
					except KeyError:
						continue
					if bin_build_time != _unicode(parent.build_time):
						# 2) Remote binary package is valid, and local package
						#    is not up to date. Force reinstall.
						reinstall = True
		if reinstall:
			self.reinstall_list.add(root_slot)
		return reinstall

	def trigger_rebuilds(self):
		"""
		Trigger rebuilds where necessary. If pkgA has been updated, and pkgB
		depends on pkgA at both build-time and run-time, pkgB needs to be
		rebuilt.
		"""
		need_restart = False
		graph = self._graph
		build_deps = {}

		leaf_nodes = deque(graph.leaf_nodes())

		# Trigger rebuilds bottom-up (starting with the leaves) so that parents
		# will always know which children are being rebuilt.
		while graph:
			if not leaf_nodes:
				# We'll have to drop an edge. This should be quite rare.
				leaf_nodes.append(graph.order[-1])

			node = leaf_nodes.popleft()
			if node not in graph:
				# This can be triggered by circular dependencies.
				continue
			slot_atom = node.slot_atom

			# Remove our leaf node from the graph, keeping track of deps.
			parents = graph.parent_nodes(node)
			graph.remove(node)
			node_build_deps = build_deps.get(node, {})
			for parent in parents:
				if parent == node:
					# Ignore a direct cycle.
					continue
				parent_bdeps = build_deps.setdefault(parent, {})
				parent_bdeps[slot_atom] = node
				if not graph.child_nodes(parent):
					leaf_nodes.append(parent)

			# Trigger rebuilds for our leaf node. Because all of our children
			# have been processed, the build_deps will be completely filled in,
			# and self.rebuild_list / self.reinstall_list will tell us whether
			# any of our children need to be rebuilt or reinstalled.
			if self._trigger_rebuild(node, node_build_deps):
				need_restart = True

		return need_restart


class _use_changes(tuple):
	def __new__(cls, new_use, new_changes, required_use_satisfied=True):
		obj = tuple.__new__(cls, [new_use, new_changes])
		obj.required_use_satisfied = required_use_satisfied
		return obj


class _dynamic_depgraph_config(object):

	"""
	``dynamic_depgraph_config`` is an object that is used to collect settings and important data structures that are
	used in calculating Portage dependencies. Each depgraph created by the depgraph.py code gets its own
	``dynamic_depgraph_config``, whereas ``frozen_depgraph_config`` is shared among all depgraphs.

	**self.digraph**

	Of particular importance is the instance variable ``self.digraph``, which is an instance of
	``portage.util.digraph``, a directed graph data structure. ``portage.util.digraph`` is used for a variety of
	purposes in the Portage codebase, but in this particular scenario as ``self.digraph``, it is used to create a
	dependency tree of Portage packages. So for ``self.digraph``, each *node* of the directed graph is a ``Package``,
	while *edges* connect nodes and each edge can have a Priority. The Priority setting is used to help resolve
	circular dependencies, and should be interpreted in the direction of parent to child.

	Conceptually, think of ``self.digraph`` as containing user-specified packages or sets at the very top, with
	dependencies hanging down as children, and dependencies of those children as children of children, etc. The depgraph
	is intended to model dependency relationships, not the order that packages should be installed.

	**resolving the digraph**

	To convert a digraph to an ordered list of packages to merge in an order where all dependencies are properly
	satisfied, we would first start by looking at leaf nodes, which are nodes that have no dependencies of their own. We
	could then traverse the digraph upwards from the leaf nodes, towards the parents. Along the way, depending on emerge
	options, we could make decisions what packages should be installed or rebuilt. This is how ``self.digraph`` is used
	in the code.

	**digraph creation**

	The ``depgraph.py`` code creates the digraph by first adding emerge arguments to the digraph as the main parents,
	so if ``@world`` is specified, then the world set is added as the main parents. Then, ``emerge`` will determine
	the dependencies of these packages, and depending on what options are passed to ``emerge``, will look at installed
	packages, binary packages and available ebuilds that could be merged to satisfy dependencies, and these will be
	added as children in the digraph. Children of children will be added as dependencies as needed, depending on the
	depth setting used by ``emerge``.

	As the digraph is created, it is perfectly fine for Packages to be added to the digraph that conflict with one
	another. After the digraph has been fully populated to the necessary depth, code within ``depgraph.py`` will
	identify any conflicts that are modeled within the digraph and determine the best way to handle them.

	"""

	def __init__(self, depgraph, myparams, allow_backtracking, backtrack_parameters):
		self.myparams = myparams.copy()
		self._vdb_loaded = False
		self._allow_backtracking = allow_backtracking
		# Maps nodes to the reasons they were selected for reinstallation.
		self._reinstall_nodes = {}
		# Contains a filtered view of preferred packages that are selected
		# from available repositories.
		self._filtered_trees = {}
		# Contains installed packages and new packages that have been added
		# to the graph.
		self._graph_trees = {}
		# Caches visible packages returned from _select_package, for use in
		# depgraph._iter_atoms_for_pkg() SLOT logic.
		self._visible_pkgs = {}
		#contains the args created by select_files
		self._initial_arg_list = []
		self.digraph = portage.digraph()
		# manages sets added to the graph
		self.sets = {}
		# contains all nodes pulled in by self.sets
		self._set_nodes = set()
		# Contains only Blocker -> Uninstall edges
		self._blocker_uninstalls = digraph()
		# Contains only Package -> Blocker edges
		self._blocker_parents = digraph()
		# Contains only irrelevant Package -> Blocker edges
		self._irrelevant_blockers = digraph()
		# Contains only unsolvable Package -> Blocker edges
		self._unsolvable_blockers = digraph()
		# Contains all Blocker -> Blocked Package edges
		# Do not initialize this until the depgraph _validate_blockers
		# method is called, so that the _in_blocker_conflict method can
		# assert that _validate_blockers has been called first.
		self._blocked_pkgs = None
		# Contains world packages that have been protected from
		# uninstallation but may not have been added to the graph
		# if the graph is not complete yet.
		self._blocked_world_pkgs = {}
		# Contains packages whose dependencies have been traversed.
		# This use used to check if we have accounted for blockers
		# relevant to a package.
		self._traversed_pkg_deps = set()
		self._parent_atoms = {}
		self._slot_conflict_handler = None
		self._circular_dependency_handler = None
		self._serialized_tasks_cache = None
		self._scheduler_graph = None
		self._displayed_list = None
		self._pprovided_args = []
		self._missing_args = []
		self._masked_installed = set()
		self._masked_license_updates = set()
		self._unsatisfied_deps_for_display = []
		self._unsatisfied_blockers_for_display = None
		self._circular_deps_for_display = None
		self._dep_stack = []
		self._dep_disjunctive_stack = []
		self._unsatisfied_deps = []
		self._initially_unsatisfied_deps = []
		self._ignored_deps = []
		self._highest_pkg_cache = {}
		self._highest_pkg_cache_cp_map = {}
		self._flatten_atoms_cache = {}
		self._changed_deps_pkgs = {}

		# Binary packages that have been rejected because their USE
		# didn't match the user's config. It maps packages to a set
		# of flags causing the rejection.
		self.ignored_binaries = {}

		self._needed_unstable_keywords = backtrack_parameters.needed_unstable_keywords
		self._needed_p_mask_changes = backtrack_parameters.needed_p_mask_changes
		self._needed_license_changes = backtrack_parameters.needed_license_changes
		self._needed_use_config_changes = backtrack_parameters.needed_use_config_changes
		self._runtime_pkg_mask = backtrack_parameters.runtime_pkg_mask
		self._slot_operator_replace_installed = backtrack_parameters.slot_operator_replace_installed
		self._prune_rebuilds = backtrack_parameters.prune_rebuilds
		self._need_restart = False
		self._need_config_reload = False
		# For conditions that always require user intervention, such as
		# unsatisfied REQUIRED_USE (currently has no autounmask support).
		self._skip_restart = False
		self._backtrack_infos = {}

		self._buildpkgonly_deps_unsatisfied = False
		self._autounmask = depgraph._frozen_config.myopts.get('--autounmask') != 'n'
		self._displayed_autounmask = False
		self._success_without_autounmask = False
		self._autounmask_backtrack_disabled = False
		self._required_use_unsatisfied = False
		self._traverse_ignored_deps = False
		self._complete_mode = False
		self._slot_operator_deps = {}
		self._installed_sonames = collections.defaultdict(list)
		self._package_tracker = PackageTracker(
			soname_deps=depgraph._frozen_config.soname_deps_enabled)
		# Track missed updates caused by solved conflicts.
		self._conflict_missed_update = collections.defaultdict(dict)

		for myroot in depgraph._frozen_config.trees:
			self.sets[myroot] = _depgraph_sets()
			vardb = depgraph._frozen_config.trees[myroot]["vartree"].dbapi
			# This dbapi instance will model the state that the vdb will
			# have after new packages have been installed.
			fakedb = PackageTrackerDbapiWrapper(myroot, self._package_tracker)

			def graph_tree():
				pass
			graph_tree.dbapi = fakedb
			self._graph_trees[myroot] = {}
			self._filtered_trees[myroot] = {}
			# Substitute the graph tree for the vartree in dep_check() since we
			# want atom selections to be consistent with package selections
			# have already been made.
			self._graph_trees[myroot]["porttree"]   = graph_tree
			self._graph_trees[myroot]["vartree"]    = graph_tree
			self._graph_trees[myroot]["graph_db"]   = graph_tree.dbapi
			self._graph_trees[myroot]["graph"]      = self.digraph
			self._graph_trees[myroot]["want_update_pkg"] = depgraph._want_update_pkg
			self._graph_trees[myroot]["downgrade_probe"] = depgraph._downgrade_probe
			def filtered_tree():
				pass
			filtered_tree.dbapi = _dep_check_composite_db(depgraph, myroot)
			self._filtered_trees[myroot]["porttree"] = filtered_tree
			self._visible_pkgs[myroot] = PackageVirtualDbapi(vardb.settings)

			# Passing in graph_tree as the vartree here could lead to better
			# atom selections in some cases by causing atoms for packages that
			# have been added to the graph to be preferred over other choices.
			# However, it can trigger atom selections that result in
			# unresolvable direct circular dependencies. For example, this
			# happens with gwydion-dylan which depends on either itself or
			# gwydion-dylan-bin. In case gwydion-dylan is not yet installed,
			# gwydion-dylan-bin needs to be selected in order to avoid a
			# an unresolvable direct circular dependency.
			#
			# To solve the problem described above, pass in "graph_db" so that
			# packages that have been added to the graph are distinguishable
			# from other available packages and installed packages. Also, pass
			# the parent package into self._select_atoms() calls so that
			# unresolvable direct circular dependencies can be detected and
			# avoided when possible.
			self._filtered_trees[myroot]["graph_db"] = graph_tree.dbapi
			self._filtered_trees[myroot]["graph"]    = self.digraph
			self._filtered_trees[myroot]["vartree"] = \
				depgraph._frozen_config.trees[myroot]["vartree"]
			self._filtered_trees[myroot]["want_update_pkg"] = depgraph._want_update_pkg
			self._filtered_trees[myroot]["downgrade_probe"] = depgraph._downgrade_probe

			dbs = []
			#               (db, pkg_type, built, installed, db_keys)
			if "remove" in self.myparams:
				# For removal operations, use _dep_check_composite_db
				# for availability and visibility checks. This provides
				# consistency with install operations, so we don't
				# get install/uninstall cycles like in bug #332719.
				self._graph_trees[myroot]["porttree"] = filtered_tree
			else:
				if "--usepkgonly" not in depgraph._frozen_config.myopts:
					portdb = depgraph._frozen_config.trees[myroot]["porttree"].dbapi
					db_keys = list(portdb._aux_cache_keys)
					dbs.append((portdb, "ebuild", False, False, db_keys))

				if "--usepkg" in depgraph._frozen_config.myopts:
					bindb  = depgraph._frozen_config.trees[myroot]["bintree"].dbapi
					db_keys = list(bindb._aux_cache_keys)
					dbs.append((bindb,  "binary", True, False, db_keys))

			vardb  = depgraph._frozen_config.trees[myroot]["vartree"].dbapi
			db_keys = list(depgraph._frozen_config._trees_orig[myroot
				]["vartree"].dbapi._aux_cache_keys)
			dbs.append((vardb, "installed", True, True, db_keys))
			self._filtered_trees[myroot]["dbs"] = dbs

class depgraph(object):

	# Represents the depth of a node that is unreachable from explicit
	# user arguments (or their deep dependencies). Such nodes are pulled
	# in by the _complete_graph method.
	_UNREACHABLE_DEPTH = object()

	pkg_tree_map = RootConfig.pkg_tree_map

	def __init__(self, settings, trees, myopts, myparams, spinner,
		frozen_config=None, backtrack_parameters=BacktrackParameter(), allow_backtracking=False):
		if frozen_config is None:
			frozen_config = _frozen_depgraph_config(settings, trees,
			myopts, myparams, spinner)
		self._frozen_config = frozen_config
		self._dynamic_config = _dynamic_depgraph_config(self, myparams,
			allow_backtracking, backtrack_parameters)
		self._rebuild = _rebuild_config(frozen_config, backtrack_parameters)

		self._select_atoms = self._select_atoms_highest_available
		self._select_package = self._select_pkg_highest_available

		self._event_loop = (portage._internal_caller and
			global_event_loop() or EventLoop(main=False))

		self._select_atoms_parent = None

		self.query = UserQuery(myopts).query

	def _index_binpkgs(self):
		for root in self._frozen_config.trees:
			bindb = self._frozen_config.trees[root]["bintree"].dbapi
			if bindb._provides_index:
				# don't repeat this when backtracking
				continue
			root_config = self._frozen_config.roots[root]
			for cpv in self._frozen_config._trees_orig[
				root]["bintree"].dbapi.cpv_all():
				bindb._provides_inject(
					self._pkg(cpv, "binary", root_config))

	def _load_vdb(self):
		"""
		Load installed package metadata if appropriate. This used to be called
		from the constructor, but that wasn't very nice since this procedure
		is slow and it generates spinner output. So, now it's called on-demand
		by various methods when necessary.
		"""

		if self._dynamic_config._vdb_loaded:
			return

		for myroot in self._frozen_config.trees:

			dynamic_deps = "dynamic_deps" in self._dynamic_config.myparams
			preload_installed_pkgs = \
				"--nodeps" not in self._frozen_config.myopts

			fake_vartree = self._frozen_config.trees[myroot]["vartree"]
			if not fake_vartree.dbapi:
				# This needs to be called for the first depgraph, but not for
				# backtracking depgraphs that share the same frozen_config.
				fake_vartree.sync()

				# FakeVartree.sync() populates virtuals, and we want
				# self.pkgsettings to have them populated too.
				self._frozen_config.pkgsettings[myroot] = \
					portage.config(clone=fake_vartree.settings)

			if preload_installed_pkgs:
				vardb = fake_vartree.dbapi

				if not dynamic_deps:
					for pkg in vardb:
						self._dynamic_config._package_tracker.add_installed_pkg(pkg)
						self._add_installed_sonames(pkg)
				else:
					max_jobs = self._frozen_config.myopts.get("--jobs")
					max_load = self._frozen_config.myopts.get("--load-average")
					scheduler = TaskScheduler(
						self._dynamic_deps_preload(fake_vartree),
						max_jobs=max_jobs,
						max_load=max_load,
						event_loop=fake_vartree._portdb._event_loop)
					scheduler.start()
					scheduler.wait()

		self._dynamic_config._vdb_loaded = True

	def _dynamic_deps_preload(self, fake_vartree):
		portdb = fake_vartree._portdb
		for pkg in fake_vartree.dbapi:
			self._spinner_update()
			self._dynamic_config._package_tracker.add_installed_pkg(pkg)
			self._add_installed_sonames(pkg)
			ebuild_path, repo_path = \
				portdb.findname2(pkg.cpv, myrepo=pkg.repo)
			if ebuild_path is None:
				fake_vartree.dynamic_deps_preload(pkg, None)
				continue
			metadata, ebuild_hash = portdb._pull_valid_cache(
				pkg.cpv, ebuild_path, repo_path)
			if metadata is not None:
				fake_vartree.dynamic_deps_preload(pkg, metadata)
			else:
				proc =  EbuildMetadataPhase(cpv=pkg.cpv,
					ebuild_hash=ebuild_hash,
					portdb=portdb, repo_path=repo_path,
					settings=portdb.doebuild_settings)
				proc.addExitListener(
					self._dynamic_deps_proc_exit(pkg, fake_vartree))
				yield proc

	class _dynamic_deps_proc_exit(object):

		__slots__ = ('_pkg', '_fake_vartree')

		def __init__(self, pkg, fake_vartree):
			self._pkg = pkg
			self._fake_vartree = fake_vartree

		def __call__(self, proc):
			metadata = None
			if proc.returncode == os.EX_OK:
				metadata = proc.metadata
			self._fake_vartree.dynamic_deps_preload(self._pkg, metadata)

	def _spinner_update(self):
		if self._frozen_config.spinner:
			self._frozen_config.spinner.update()

	def _compute_abi_rebuild_info(self):
		"""
		Fill self._forced_rebuilds with packages that cause rebuilds.
		"""

		debug = "--debug" in self._frozen_config.myopts
		installed_sonames = self._dynamic_config._installed_sonames
		package_tracker = self._dynamic_config._package_tracker

		# Get all atoms that might have caused a forced rebuild.
		atoms = {}
		for s in self._dynamic_config._initial_arg_list:
			if s.force_reinstall:
				root = s.root_config.root
				atoms.setdefault(root, set()).update(s.pset)

		if debug:
			writemsg_level("forced reinstall atoms:\n",
				level=logging.DEBUG, noiselevel=-1)

			for root in atoms:
				writemsg_level("   root: %s\n" % root,
					level=logging.DEBUG, noiselevel=-1)
				for atom in atoms[root]:
					writemsg_level("      atom: %s\n" % atom,
						level=logging.DEBUG, noiselevel=-1)
			writemsg_level("\n\n",
				level=logging.DEBUG, noiselevel=-1)

		# Go through all slot operator deps and check if one of these deps
		# has a parent that is matched by one of the atoms from above.
		forced_rebuilds = {}

		for root, rebuild_atoms in atoms.items():

			for slot_atom in rebuild_atoms:

				inst_pkg, reinst_pkg = \
					self._select_pkg_from_installed(root, slot_atom)

				if inst_pkg is reinst_pkg or reinst_pkg is None:
					continue

				if (inst_pkg is not None and
					inst_pkg.requires is not None):
					for atom in inst_pkg.requires:
						initial_providers = installed_sonames.get(
							(root, atom))
						if initial_providers is None:
							continue
						final_provider = next(
							package_tracker.match(root, atom),
							None)
						if final_provider:
							continue
						for provider in initial_providers:
							# Find the replacement child.
							child = next((pkg for pkg in
								package_tracker.match(
								root, provider.slot_atom)
								if not pkg.installed), None)

							if child is None:
								continue

							forced_rebuilds.setdefault(
								root, {}).setdefault(
								child, set()).add(inst_pkg)

				# Generate pseudo-deps for any slot-operator deps of
				# inst_pkg. Its deps aren't in _slot_operator_deps
				# because it hasn't been added to the graph, but we
				# are interested in any rebuilds that it triggered.
				built_slot_op_atoms = []
				if inst_pkg is not None:
					selected_atoms = self._select_atoms_probe(
						inst_pkg.root, inst_pkg)
					for atom in selected_atoms:
						if atom.slot_operator_built:
							built_slot_op_atoms.append(atom)

					if not built_slot_op_atoms:
						continue

				# Use a cloned list, since we may append to it below.
				deps = self._dynamic_config._slot_operator_deps.get(
					(root, slot_atom), [])[:]

				if built_slot_op_atoms and reinst_pkg is not None:
					for child in self._dynamic_config.digraph.child_nodes(
						reinst_pkg):

						if child.installed:
							continue

						for atom in built_slot_op_atoms:
							# NOTE: Since atom comes from inst_pkg, and
							# reinst_pkg is the replacement parent, there's
							# no guarantee that atom will completely match
							# child. So, simply use atom.cp and atom.slot
							# for matching.
							if atom.cp != child.cp:
								continue
							if atom.slot and atom.slot != child.slot:
								continue
							deps.append(Dependency(atom=atom, child=child,
								root=child.root, parent=reinst_pkg))

				for dep in deps:
					if dep.child.installed:
						# Find the replacement child.
						child = next((pkg for pkg in
							self._dynamic_config._package_tracker.match(
							dep.root, dep.child.slot_atom)
							if not pkg.installed), None)

						if child is None:
							continue

						inst_child = dep.child

					else:
						child = dep.child
						inst_child = self._select_pkg_from_installed(
							child.root, child.slot_atom)[0]

					# Make sure the child's slot/subslot has changed. If it
					# hasn't, then another child has forced this rebuild.
					if inst_child and inst_child.slot == child.slot and \
						inst_child.sub_slot == child.sub_slot:
						continue

					if dep.parent.installed:
						# Find the replacement parent.
						parent = next((pkg for pkg in
							self._dynamic_config._package_tracker.match(
							dep.parent.root, dep.parent.slot_atom)
							if not pkg.installed), None)

						if parent is None:
							continue

					else:
						parent = dep.parent

					# The child has forced a rebuild of the parent
					forced_rebuilds.setdefault(root, {}
						).setdefault(child, set()).add(parent)

		if debug:
			writemsg_level("slot operator dependencies:\n",
				level=logging.DEBUG, noiselevel=-1)

			for (root, slot_atom), deps in self._dynamic_config._slot_operator_deps.items():
				writemsg_level("   (%s, %s)\n" % \
					(root, slot_atom), level=logging.DEBUG, noiselevel=-1)
				for dep in deps:
					writemsg_level("      parent: %s\n" % dep.parent, level=logging.DEBUG, noiselevel=-1)
					writemsg_level("        child: %s (%s)\n" % (dep.child, dep.priority), level=logging.DEBUG, noiselevel=-1)

			writemsg_level("\n\n",
				level=logging.DEBUG, noiselevel=-1)


			writemsg_level("forced rebuilds:\n",
				level=logging.DEBUG, noiselevel=-1)

			for root in forced_rebuilds:
				writemsg_level("   root: %s\n" % root,
					level=logging.DEBUG, noiselevel=-1)
				for child in forced_rebuilds[root]:
					writemsg_level("      child: %s\n" % child,
						level=logging.DEBUG, noiselevel=-1)
					for parent in forced_rebuilds[root][child]:
						writemsg_level("         parent: %s\n" % parent,
							level=logging.DEBUG, noiselevel=-1)
			writemsg_level("\n\n",
				level=logging.DEBUG, noiselevel=-1)

		self._forced_rebuilds = forced_rebuilds

	def _show_abi_rebuild_info(self):

		if not self._forced_rebuilds:
			return

		writemsg_stdout("\nThe following packages are causing rebuilds:\n\n", noiselevel=-1)

		for root in self._forced_rebuilds:
			for child in self._forced_rebuilds[root]:
				writemsg_stdout("  %s causes rebuilds for:\n" % (child,), noiselevel=-1)
				for parent in self._forced_rebuilds[root][child]:
					writemsg_stdout("    %s\n" % (parent,), noiselevel=-1)

	def _eliminate_ignored_binaries(self):
		"""
		Eliminate any package from self._dynamic_config.ignored_binaries
		for which a more optimal alternative exists.
		"""
		for pkg in list(self._dynamic_config.ignored_binaries):

			for selected_pkg in self._dynamic_config._package_tracker.match(
				pkg.root, pkg.slot_atom):

				if selected_pkg > pkg:
					self._dynamic_config.ignored_binaries.pop(pkg)
					break

				# NOTE: The Package.__ge__ implementation accounts for
				# differences in build_time, so the warning about "ignored"
				# packages will be triggered if both packages are the same
				# version and selected_pkg is not the most recent build.
				if (selected_pkg.type_name == "binary" and
					selected_pkg >= pkg):
					self._dynamic_config.ignored_binaries.pop(pkg)
					break

				if selected_pkg.installed and \
					selected_pkg.cpv == pkg.cpv and \
					selected_pkg.build_time == pkg.build_time:
					# We don't care about ignored binaries when an
					# identical installed instance is selected to
					# fill the slot.
					self._dynamic_config.ignored_binaries.pop(pkg)
					break

	def _ignored_binaries_autounmask_backtrack(self):
		"""
		Check if there are ignored binaries that would have been
		accepted with the current autounmask USE changes.

		@rtype: bool
		@return: True if there are unnecessary rebuilds that
			can be avoided by backtracking
		"""
		if not all([
			self._dynamic_config._allow_backtracking,
			self._dynamic_config._needed_use_config_changes,
			self._dynamic_config.ignored_binaries]):
			return False

		self._eliminate_ignored_binaries()

		# _eliminate_ignored_binaries may have eliminated
		# all of the ignored binaries
		if not self._dynamic_config.ignored_binaries:
			return False

		use_changes = collections.defaultdict(
			functools.partial(collections.defaultdict, dict))
		for pkg, (new_use, changes) in self._dynamic_config._needed_use_config_changes.items():
			if pkg in self._dynamic_config.digraph:
				use_changes[pkg.root][pkg.slot_atom] = (pkg, new_use)

		for pkg in self._dynamic_config.ignored_binaries:
			selected_pkg, new_use = use_changes[pkg.root].get(
				pkg.slot_atom, (None, None))
			if new_use is None:
				continue

			if new_use != pkg.use.enabled:
				continue

			if selected_pkg > pkg:
				continue

			return True

		return False

	def _changed_deps_report(self):
		"""
		Report ebuilds for which the ebuild dependencies have
		changed since the installed instance was built. This is
		completely silent in the following cases:

		  * --changed-deps or --dynamic-deps is enabled
		  * none of the packages with changed deps are in the graph
		"""
		if (self._dynamic_config.myparams.get("changed_deps", "n") == "y" or
			"dynamic_deps" in self._dynamic_config.myparams):
			return

		report_pkgs = []
		for pkg, ebuild in self._dynamic_config._changed_deps_pkgs.items():
			if pkg.repo != ebuild.repo:
				continue
			report_pkgs.append((pkg, ebuild))

		if not report_pkgs:
			return

		# TODO: Detect and report various issues:
		# - packages with unsatisfiable dependencies
		# - packages involved directly in slot or blocker conflicts
		# - direct parents of conflict packages
		# - packages that prevent upgrade of dependencies to latest versions
		graph = self._dynamic_config.digraph
		in_graph = False
		for pkg, ebuild in report_pkgs:
			if pkg in graph:
				in_graph = True
				break

		# Packages with changed deps are harmless if they're not in the
		# graph, so it's safe to silently ignore them. This suppresses
		# noise for the unaffected user, even though some of the changed
		# dependencies might be worthy of revision bumps.
		if not in_graph:
			return

		writemsg("\n%s\n\n" % colorize("WARN",
			"!!! Detected ebuild dependency change(s) without revision bump:"),
			noiselevel=-1)

		for pkg, ebuild in report_pkgs:
			writemsg("    %s::%s" % (pkg.cpv, pkg.repo), noiselevel=-1)
			if pkg.root_config.settings["ROOT"] != "/":
				writemsg(" for %s" % (pkg.root,), noiselevel=-1)
			writemsg("\n", noiselevel=-1)

		msg = []
		if '--quiet' not in self._frozen_config.myopts:
			msg.extend([
			"",
			"NOTE: Refer to the following page for more information about dependency",
			"      change(s) without revision bump:",
			"",
			"          https://wiki.gentoo.org/wiki/Project:Portage/Changed_Deps",
			"",
			"      In order to suppress reports about dependency changes, add",
			"      --changed-deps-report=n to the EMERGE_DEFAULT_OPTS variable in",
			"      '/etc/portage/make.conf'.",
			])

		# Include this message for --quiet mode, since the user may be experiencing
		# problems that are solvable by using --changed-deps.
		msg.extend([
			"",
			"HINT: In order to avoid problems involving changed dependencies, use the",
			"      --changed-deps option to automatically trigger rebuilds when changed",
			"      dependencies are detected. Refer to the emerge man page for more",
			"      information about this option.",
		])

		for line in msg:
			if line:
				line = colorize("INFORM", line)
			writemsg(line + "\n", noiselevel=-1)

	def _show_ignored_binaries(self):
		"""
		Show binaries that have been ignored because their USE didn't
		match the user's config.
		"""
		if not self._dynamic_config.ignored_binaries \
			or '--quiet' in self._frozen_config.myopts:
			return

		self._eliminate_ignored_binaries()

		ignored_binaries = {}

		for pkg in self._dynamic_config.ignored_binaries:
			for reason, info in self._dynamic_config.\
				ignored_binaries[pkg].items():
				ignored_binaries.setdefault(reason, {})[pkg] = info

		if self._dynamic_config.myparams.get(
			"binpkg_respect_use") in ("y", "n"):
			ignored_binaries.pop("respect_use", None)

		if self._dynamic_config.myparams.get(
			"binpkg_changed_deps") in ("y", "n"):
			ignored_binaries.pop("changed_deps", None)

		if not ignored_binaries:
			return

		self._show_merge_list()

		if ignored_binaries.get("respect_use"):
			self._show_ignored_binaries_respect_use(
				ignored_binaries["respect_use"])

		if ignored_binaries.get("changed_deps"):
			self._show_ignored_binaries_changed_deps(
				ignored_binaries["changed_deps"])

	def _show_ignored_binaries_respect_use(self, respect_use):

		writemsg("\n!!! The following binary packages have been ignored " + \
				"due to non matching USE:\n\n", noiselevel=-1)

		for pkg, flags in respect_use.items():
			flag_display = []
			for flag in sorted(flags):
				if flag not in pkg.use.enabled:
					flag = "-" + flag
				flag_display.append(flag)
			flag_display = " ".join(flag_display)
			# The user can paste this line into package.use
			writemsg("    =%s %s" % (pkg.cpv, flag_display), noiselevel=-1)
			if pkg.root_config.settings["ROOT"] != "/":
				writemsg(" # for %s" % (pkg.root,), noiselevel=-1)
			writemsg("\n", noiselevel=-1)

		msg = [
			"",
			"NOTE: The --binpkg-respect-use=n option will prevent emerge",
			"      from ignoring these binary packages if possible.",
			"      Using --binpkg-respect-use=y will silence this warning."
		]

		for line in msg:
			if line:
				line = colorize("INFORM", line)
			writemsg(line + "\n", noiselevel=-1)

	def _show_ignored_binaries_changed_deps(self, changed_deps):

		writemsg("\n!!! The following binary packages have been "
			"ignored due to changed dependencies:\n\n",
			noiselevel=-1)

		for pkg in changed_deps:
			msg = "     %s%s%s" % (pkg.cpv, _repo_separator, pkg.repo)
			if pkg.root_config.settings["ROOT"] != "/":
				msg += " for %s" % pkg.root
			writemsg("%s\n" % msg, noiselevel=-1)

		msg = [
			"",
			"NOTE: The --binpkg-changed-deps=n option will prevent emerge",
			"      from ignoring these binary packages if possible.",
			"      Using --binpkg-changed-deps=y will silence this warning."
		]

		for line in msg:
			if line:
				line = colorize("INFORM", line)
			writemsg(line + "\n", noiselevel=-1)

	def _get_missed_updates(self):

		# In order to minimize noise, show only the highest
		# missed update from each SLOT.
		missed_updates = {}
		for pkg, mask_reasons in \
			chain(self._dynamic_config._runtime_pkg_mask.items(),
				self._dynamic_config._conflict_missed_update.items()):
			if pkg.installed:
				# Exclude installed here since we only
				# want to show available updates.
				continue
			missed_update = True
			any_selected = False
			for chosen_pkg in self._dynamic_config._package_tracker.match(
				pkg.root, pkg.slot_atom):
				any_selected = True
				if chosen_pkg > pkg or (not chosen_pkg.installed and \
					chosen_pkg.version == pkg.version):
					missed_update = False
					break
			if any_selected and missed_update:
				k = (pkg.root, pkg.slot_atom)
				if k in missed_updates:
					other_pkg, mask_type, parent_atoms = missed_updates[k]
					if other_pkg > pkg:
						continue
				for mask_type, parent_atoms in mask_reasons.items():
					if not parent_atoms:
						continue
					missed_updates[k] = (pkg, mask_type, parent_atoms)
					break

		return missed_updates

	def _show_missed_update(self):

		missed_updates = self._get_missed_updates()

		if not missed_updates:
			return

		missed_update_types = {}
		for pkg, mask_type, parent_atoms in missed_updates.values():
			missed_update_types.setdefault(mask_type,
				[]).append((pkg, parent_atoms))

		if '--quiet' in self._frozen_config.myopts and \
			'--debug' not in self._frozen_config.myopts:
			missed_update_types.pop("slot conflict", None)
			missed_update_types.pop("missing dependency", None)

		self._show_missed_update_slot_conflicts(
			missed_update_types.get("slot conflict"))

		self._show_missed_update_unsatisfied_dep(
			missed_update_types.get("missing dependency"))

	def _show_missed_update_unsatisfied_dep(self, missed_updates):

		if not missed_updates:
			return

		self._show_merge_list()
		backtrack_masked = []

		for pkg, parent_atoms in missed_updates:

			try:
				for parent, root, atom in parent_atoms:
					self._show_unsatisfied_dep(root, atom, myparent=parent,
						check_backtrack=True)
			except self._backtrack_mask:
				# This is displayed below in abbreviated form.
				backtrack_masked.append((pkg, parent_atoms))
				continue

			writemsg("\n!!! The following update has been skipped " + \
				"due to unsatisfied dependencies:\n\n", noiselevel=-1)

			writemsg(str(pkg.slot_atom), noiselevel=-1)
			if pkg.root_config.settings["ROOT"] != "/":
				writemsg(" for %s" % (pkg.root,), noiselevel=-1)
			writemsg("\n\n", noiselevel=-1)

			selected_pkg = next(self._dynamic_config._package_tracker.match(
				pkg.root, pkg.slot_atom), None)

			writemsg("  selected: %s\n" % (selected_pkg,), noiselevel=-1)
			writemsg("  skipped: %s (see unsatisfied dependency below)\n"
				% (pkg,), noiselevel=-1)

			for parent, root, atom in parent_atoms:
				self._show_unsatisfied_dep(root, atom, myparent=parent)
				writemsg("\n", noiselevel=-1)

		if backtrack_masked:
			# These are shown in abbreviated form, in order to avoid terminal
			# flooding from mask messages as reported in bug #285832.
			writemsg("\n!!! The following update(s) have been skipped " + \
				"due to unsatisfied dependencies\n" + \
				"!!! triggered by backtracking:\n\n", noiselevel=-1)
			for pkg, parent_atoms in backtrack_masked:
				writemsg(str(pkg.slot_atom), noiselevel=-1)
				if pkg.root_config.settings["ROOT"] != "/":
					writemsg(" for %s" % (pkg.root,), noiselevel=-1)
				writemsg("\n", noiselevel=-1)

	def _show_missed_update_slot_conflicts(self, missed_updates):

		if not missed_updates:
			return

		self._show_merge_list()
		msg = []
		msg.append("\nWARNING: One or more updates/rebuilds have been " + \
			"skipped due to a dependency conflict:\n\n")

		indent = "  "
		for pkg, parent_atoms in missed_updates:
			msg.append(str(pkg.slot_atom))
			if pkg.root_config.settings["ROOT"] != "/":
				msg.append(" for %s" % (pkg.root,))
			msg.append("\n\n")

			msg.append(indent)
			msg.append(str(pkg))
			msg.append(" conflicts with\n")

			for parent, atom in parent_atoms:
				if isinstance(parent,
					(PackageArg, AtomArg)):
					# For PackageArg and AtomArg types, it's
					# redundant to display the atom attribute.
					msg.append(2*indent)
					msg.append(str(parent))
					msg.append("\n")
				else:
					# Display the specific atom from SetArg or
					# Package types.
					atom, marker = format_unmatched_atom(
						pkg, atom, self._pkg_use_enabled)

					msg.append(2*indent)
					msg.append("%s required by %s\n" % (atom, parent))
					msg.append(2*indent)
					msg.append(marker)
					msg.append("\n")
			msg.append("\n")

		writemsg("".join(msg), noiselevel=-1)

	def _show_slot_collision_notice(self):
		"""Show an informational message advising the user to mask one of the
		the packages. In some cases it may be possible to resolve this
		automatically, but support for backtracking (removal nodes that have
		already been selected) will be required in order to handle all possible
		cases.
		"""

		if not any(self._dynamic_config._package_tracker.slot_conflicts()):
			return

		self._show_merge_list()

		if self._dynamic_config._slot_conflict_handler is None:
			self._dynamic_config._slot_conflict_handler = slot_conflict_handler(self)
		handler = self._dynamic_config._slot_conflict_handler

		conflict = handler.get_conflict()
		writemsg(conflict, noiselevel=-1)

		explanation = handler.get_explanation()
		if explanation:
			writemsg(explanation, noiselevel=-1)
			return

		if "--quiet" in self._frozen_config.myopts:
			return

		msg = []
		msg.append("It may be possible to solve this problem ")
		msg.append("by using package.mask to prevent one of ")
		msg.append("those packages from being selected. ")
		msg.append("However, it is also possible that conflicting ")
		msg.append("dependencies exist such that they are impossible to ")
		msg.append("satisfy simultaneously.  If such a conflict exists in ")
		msg.append("the dependencies of two different packages, then those ")
		msg.append("packages can not be installed simultaneously.")
		backtrack_opt = self._frozen_config.myopts.get('--backtrack')
		if not self._dynamic_config._allow_backtracking and \
			(backtrack_opt is None or \
			(backtrack_opt > 0 and backtrack_opt < 30)):
			msg.append(" You may want to try a larger value of the ")
			msg.append("--backtrack option, such as --backtrack=30, ")
			msg.append("in order to see if that will solve this conflict ")
			msg.append("automatically.")

		for line in textwrap.wrap(''.join(msg), 70):
			writemsg(line + '\n', noiselevel=-1)
		writemsg('\n', noiselevel=-1)

		msg = []
		msg.append("For more information, see MASKED PACKAGES ")
		msg.append("section in the emerge man page or refer ")
		msg.append("to the Gentoo Handbook.")
		for line in textwrap.wrap(''.join(msg), 70):
			writemsg(line + '\n', noiselevel=-1)
		writemsg('\n', noiselevel=-1)

	def _solve_non_slot_operator_slot_conflicts(self):
		"""
		This function solves slot conflicts which can
		be solved by simply choosing one of the conflicting
		and removing all the other ones.
		It is able to solve somewhat more complex cases where
		conflicts can only be solved simultaniously.
		"""
		debug = "--debug" in self._frozen_config.myopts

		# List all conflicts. Ignore those that involve slot operator rebuilds
		# as the logic there needs special slot conflict behavior which isn't
		# provided by this function.
		conflicts = []
		for conflict in self._dynamic_config._package_tracker.slot_conflicts():
			slot_key = conflict.root, conflict.atom
			if slot_key not in self._dynamic_config._slot_operator_replace_installed:
				conflicts.append(conflict)

		if not conflicts:
			return

		if debug:
			writemsg_level(
				"\n!!! Slot conflict handler started.\n",
				level=logging.DEBUG, noiselevel=-1)

		# Get a set of all conflicting packages.
		conflict_pkgs = set()
		for conflict in conflicts:
			conflict_pkgs.update(conflict)

		# Get the list of other packages which are only
		# required by conflict packages.
		indirect_conflict_candidates = set()
		for pkg in conflict_pkgs:
			indirect_conflict_candidates.update(self._dynamic_config.digraph.child_nodes(pkg))
		indirect_conflict_candidates.difference_update(conflict_pkgs)

		indirect_conflict_pkgs = set()
		while indirect_conflict_candidates:
			pkg = indirect_conflict_candidates.pop()

			only_conflict_parents = True
			for parent, atom in self._dynamic_config._parent_atoms.get(pkg, []):
				if parent not in conflict_pkgs and parent not in indirect_conflict_pkgs:
					only_conflict_parents = False
					break
			if not only_conflict_parents:
				continue

			indirect_conflict_pkgs.add(pkg)
			for child in self._dynamic_config.digraph.child_nodes(pkg):
				if child in conflict_pkgs or child in indirect_conflict_pkgs:
					continue
				indirect_conflict_candidates.add(child)

		# Create a graph containing the conflict packages
		# and a special 'non_conflict_node' that represents
		# all non-conflict packages.
		conflict_graph = digraph()

		non_conflict_node = "(non-conflict package)"
		conflict_graph.add(non_conflict_node, None)

		for pkg in chain(conflict_pkgs, indirect_conflict_pkgs):
			conflict_graph.add(pkg, None)

		# Add parent->child edges for each conflict package.
		# Parents, which aren't conflict packages are represented
		# by 'non_conflict_node'.
		# If several conflicting packages are matched, but not all,
		# add a tuple with the matched packages to the graph.
		class or_tuple(tuple):
			"""
			Helper class for debug printing.
			"""
			def __str__(self):
				return "(%s)" % ",".join(str(pkg) for pkg in self)

		non_matching_forced = set()
		for conflict in conflicts:
			if debug:
				writemsg_level("   conflict:\n", level=logging.DEBUG, noiselevel=-1)
				writemsg_level("      root: %s\n" % conflict.root, level=logging.DEBUG, noiselevel=-1)
				writemsg_level("      atom: %s\n" % conflict.atom, level=logging.DEBUG, noiselevel=-1)
				for pkg in conflict:
					writemsg_level("      pkg: %s\n" % pkg, level=logging.DEBUG, noiselevel=-1)

			all_parent_atoms = set()
			highest_pkg = None
			inst_pkg = None
			for pkg in conflict:
				if pkg.installed:
					inst_pkg = pkg
				if highest_pkg is None or highest_pkg < pkg:
					highest_pkg = pkg
				all_parent_atoms.update(
					self._dynamic_config._parent_atoms.get(pkg, []))

			for parent, atom in all_parent_atoms:
				is_arg_parent = (inst_pkg is not None and
					not self._want_installed_pkg(inst_pkg))
				is_non_conflict_parent = parent not in conflict_pkgs and \
					parent not in indirect_conflict_pkgs

				if debug:
					writemsg_level("      parent: %s\n" % parent, level=logging.DEBUG, noiselevel=-1)
					writemsg_level("      arg, non-conflict: %s, %s\n" % (is_arg_parent, is_non_conflict_parent),
						level=logging.DEBUG, noiselevel=-1)
					writemsg_level("         atom: %s\n" % atom, level=logging.DEBUG, noiselevel=-1)

				if is_non_conflict_parent:
					parent = non_conflict_node

				matched = []
				for pkg in conflict:
					if (pkg is highest_pkg and
						not highest_pkg.installed and
						inst_pkg is not None and
						inst_pkg.sub_slot != highest_pkg.sub_slot and
						not self._downgrade_probe(highest_pkg)):
						# If an upgrade is desired, force the highest
						# version into the graph (bug #531656).
						non_matching_forced.add(highest_pkg)

					if atom.match(pkg.with_use(
						self._pkg_use_enabled(pkg))) and \
						not (is_arg_parent and pkg.installed):
						matched.append(pkg)

				if debug:
					for match in matched:
						writemsg_level("         match: %s\n" % match, level=logging.DEBUG, noiselevel=-1)

				if len(matched) > 1:
					# Even if all packages match, this parent must still
					# be added to the conflict_graph. Otherwise, we risk
					# removing all of these packages from the depgraph,
					# which could cause a missed update (bug #522084).
					conflict_graph.add(or_tuple(matched), parent)
				elif len(matched) == 1:
					conflict_graph.add(matched[0], parent)
				else:
					# This typically means that autounmask broke a
					# USE-dep, but it could also be due to the slot
					# not matching due to multislot (bug #220341).
					# Either way, don't try to solve this conflict.
					# Instead, force them all into the graph so that
					# they are protected from removal.
					non_matching_forced.update(conflict)
					if debug:
						for pkg in conflict:
							writemsg_level("         non-match: %s\n" % pkg,
								level=logging.DEBUG, noiselevel=-1)

		for pkg in indirect_conflict_pkgs:
			for parent, atom in self._dynamic_config._parent_atoms.get(pkg, []):
				if parent not in conflict_pkgs and \
					parent not in indirect_conflict_pkgs:
					parent = non_conflict_node
				conflict_graph.add(pkg, parent)

		if debug:
			writemsg_level(
				"\n!!! Slot conflict graph:\n",
				level=logging.DEBUG, noiselevel=-1)
			conflict_graph.debug_print()

		# Now select required packages. Collect them in the
		# 'forced' set.
		forced = set([non_conflict_node])
		forced.update(non_matching_forced)
		unexplored = set([non_conflict_node])
		# or_tuples get special handling. We first explore
		# all packages in the hope of having forced one of
		# the packages in the tuple. This way we don't have
		# to choose one.
		unexplored_tuples = set()
		explored_nodes = set()

		while unexplored:
			while True:
				try:
					node = unexplored.pop()
				except KeyError:
					break
				for child in conflict_graph.child_nodes(node):
					# Don't explore a node more than once, in order
					# to avoid infinite recursion. The forced set
					# cannot be used for this purpose, since it can
					# contain unexplored nodes from non_matching_forced.
					if child in explored_nodes:
						continue
					explored_nodes.add(child)
					forced.add(child)
					if isinstance(child, Package):
						unexplored.add(child)
					else:
						unexplored_tuples.add(child)

			# Now handle unexplored or_tuples. Move on with packages
			# once we had to choose one.
			while unexplored_tuples:
				nodes = unexplored_tuples.pop()
				if any(node in forced for node in nodes):
					# At least one of the packages in the
					# tuple is already forced, which means the
					# dependency represented by this tuple
					# is satisfied.
					continue

				# We now have to choose one of packages in the tuple.
				# In theory one could solve more conflicts if we'd be
				# able to try different choices here, but that has lots
				# of other problems. For now choose the package that was
				# pulled first, as this should be the most desirable choice
				# (otherwise it wouldn't have been the first one).
				forced.add(nodes[0])
				unexplored.add(nodes[0])
				break

		# Remove 'non_conflict_node' and or_tuples from 'forced'.
		forced = set(pkg for pkg in forced if isinstance(pkg, Package))

		# Add dependendencies of forced packages.
		stack = list(forced)
		traversed = set()
		while stack:
			pkg = stack.pop()
			traversed.add(pkg)
			for child in conflict_graph.child_nodes(pkg):
				if (isinstance(child, Package) and
					child not in traversed):
					forced.add(child)
					stack.append(child)

		non_forced = set(pkg for pkg in conflict_pkgs if pkg not in forced)

		if debug:
			writemsg_level(
				"\n!!! Slot conflict solution:\n",
				level=logging.DEBUG, noiselevel=-1)
			for conflict in conflicts:
				writemsg_level(
					"   Conflict: (%s, %s)\n" % (conflict.root, conflict.atom),
					level=logging.DEBUG, noiselevel=-1)
				for pkg in conflict:
					if pkg in forced:
						writemsg_level(
							"      keep:   %s\n" % pkg,
							level=logging.DEBUG, noiselevel=-1)
					else:
						writemsg_level(
							"      remove: %s\n" % pkg,
							level=logging.DEBUG, noiselevel=-1)

		broken_packages = set()
		for pkg in non_forced:
			for parent, atom in self._dynamic_config._parent_atoms.get(pkg, []):
				if isinstance(parent, Package) and parent not in non_forced:
					# Non-forcing set args are expected to be a parent of all
					# packages in the conflict.
					broken_packages.add(parent)
			self._remove_pkg(pkg)

		# Process the dependencies of choosen conflict packages
		# again to  properly account for blockers.
		broken_packages.update(forced)

		# Filter out broken packages which have been removed during
		# recursive removal in self._remove_pkg.
		broken_packages = list(pkg for pkg in broken_packages if pkg in broken_packages \
			if self._dynamic_config._package_tracker.contains(pkg, installed=False))

		self._dynamic_config._dep_stack.extend(broken_packages)

		if broken_packages:
			# Process dependencies. This cannot fail because we just ensured that
			# the remaining packages satisfy all dependencies.
			self._create_graph()

		# Record missed updates.
		for conflict in conflicts:
			if not any(pkg in non_forced for pkg in conflict):
				continue
			for pkg in conflict:
				if pkg not in non_forced:
					continue

				for other in conflict:
					if other is pkg:
						continue

					for parent, atom in self._dynamic_config._parent_atoms.get(other, []):
						if not atom.match(pkg.with_use(self._pkg_use_enabled(pkg))):
							self._dynamic_config._conflict_missed_update[pkg].setdefault(
								"slot conflict", set())
							self._dynamic_config._conflict_missed_update[pkg]["slot conflict"].add(
								(parent, atom))


	def _process_slot_conflicts(self):
		"""
		If there are any slot conflicts and backtracking is enabled,
		_complete_graph should complete the graph before this method
		is called, so that all relevant reverse dependencies are
		available for use in backtracking decisions.
		"""

		self._solve_non_slot_operator_slot_conflicts()

		if not self._validate_blockers():
			# Blockers don't trigger the _skip_restart flag, since
			# backtracking may solve blockers when it solves slot
			# conflicts (or by blind luck).
			raise self._unknown_internal_error()

		# Both _process_slot_conflict and _slot_operator_trigger_reinstalls
		# can call _slot_operator_update_probe, which requires that
		# self._dynamic_config._blocked_pkgs has been initialized by a
		# call to the _validate_blockers method.
		for conflict in self._dynamic_config._package_tracker.slot_conflicts():
			self._process_slot_conflict(conflict)

		if self._dynamic_config._allow_backtracking:
			self._slot_operator_trigger_reinstalls()

	def _process_slot_conflict(self, conflict):
		"""
		Process slot conflict data to identify specific atoms which
		lead to conflict. These atoms only match a subset of the
		packages that have been pulled into a given slot.
		"""
		root = conflict.root
		slot_atom = conflict.atom
		slot_nodes = conflict.pkgs

		debug = "--debug" in self._frozen_config.myopts

		slot_parent_atoms = set()
		for pkg in slot_nodes:
			parent_atoms = self._dynamic_config._parent_atoms.get(pkg)
			if not parent_atoms:
				continue
			slot_parent_atoms.update(parent_atoms)

		conflict_pkgs = []
		conflict_atoms = {}
		for pkg in slot_nodes:

			if self._dynamic_config._allow_backtracking and \
				pkg in self._dynamic_config._runtime_pkg_mask:
				if debug:
					writemsg_level(
						"!!! backtracking loop detected: %s %s\n" % \
						(pkg,
						self._dynamic_config._runtime_pkg_mask[pkg]),
						level=logging.DEBUG, noiselevel=-1)

			parent_atoms = self._dynamic_config._parent_atoms.get(pkg)
			if parent_atoms is None:
				parent_atoms = set()
				self._dynamic_config._parent_atoms[pkg] = parent_atoms

			all_match = True
			for parent_atom in slot_parent_atoms:
				if parent_atom in parent_atoms:
					continue
				parent, atom = parent_atom
				if atom.match(pkg.with_use(self._pkg_use_enabled(pkg))):
					parent_atoms.add(parent_atom)
				else:
					all_match = False
					conflict_atoms.setdefault(parent_atom, set()).add(pkg)

			if not all_match:
				conflict_pkgs.append(pkg)

		if conflict_pkgs and \
			self._dynamic_config._allow_backtracking and \
			not self._accept_blocker_conflicts():
			remaining = []
			for pkg in conflict_pkgs:
				if self._slot_conflict_backtrack_abi(pkg,
					slot_nodes, conflict_atoms):
					backtrack_infos = self._dynamic_config._backtrack_infos
					config = backtrack_infos.setdefault("config", {})
					config.setdefault("slot_conflict_abi", set()).add(pkg)
				else:
					remaining.append(pkg)
			if remaining:
				self._slot_confict_backtrack(root, slot_atom,
					slot_parent_atoms, remaining)

	def _slot_confict_backtrack(self, root, slot_atom,
		all_parents, conflict_pkgs):

		debug = "--debug" in self._frozen_config.myopts
		existing_node = next(self._dynamic_config._package_tracker.match(
			root, slot_atom, installed=False))
		# In order to avoid a missed update, first mask lower versions
		# that conflict with higher versions (the backtracker visits
		# these in reverse order).
		conflict_pkgs.sort(reverse=True)
		backtrack_data = []
		for to_be_masked in conflict_pkgs:
			# For missed update messages, find out which
			# atoms matched to_be_selected that did not
			# match to_be_masked.
			parent_atoms = \
				self._dynamic_config._parent_atoms.get(to_be_masked, set())
			conflict_atoms = set(parent_atom for parent_atom in all_parents \
				if parent_atom not in parent_atoms)
			backtrack_data.append((to_be_masked, conflict_atoms))

		to_be_masked = backtrack_data[-1][0]

		self._dynamic_config._backtrack_infos.setdefault(
			"slot conflict", []).append(backtrack_data)
		self._dynamic_config._need_restart = True
		if debug:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("backtracking due to slot conflict:")
			msg.append("   first package:  %s" % existing_node)
			msg.append("  package to mask: %s" % to_be_masked)
			msg.append("      slot: %s" % slot_atom)
			msg.append("   parents: %s" % ", ".join( \
				"(%s, '%s')" % (ppkg, atom) for ppkg, atom in all_parents))
			msg.append("")
			writemsg_level("".join("%s\n" % l for l in msg),
				noiselevel=-1, level=logging.DEBUG)

	def _slot_conflict_backtrack_abi(self, pkg, slot_nodes, conflict_atoms):
		"""
		If one or more conflict atoms have a slot/sub-slot dep that can be resolved
		by rebuilding the parent package, then schedule the rebuild via
		backtracking, and return True. Otherwise, return False.
		"""

		found_update = False
		for parent_atom, conflict_pkgs in conflict_atoms.items():
			parent, atom = parent_atom

			if not isinstance(parent, Package):
				continue

			if not parent.built:
				continue

			if not atom.soname and not (
				atom.package and atom.slot_operator_built):
				continue

			for other_pkg in slot_nodes:
				if other_pkg in conflict_pkgs:
					continue

				dep = Dependency(atom=atom, child=other_pkg,
					parent=parent, root=pkg.root)

				new_dep = \
					self._slot_operator_update_probe_slot_conflict(dep)
				if new_dep is not None:
					self._slot_operator_update_backtrack(dep,
						new_dep=new_dep)
					found_update = True

		return found_update

	def _slot_change_probe(self, dep):
		"""
		@rtype: bool
		@return: True if dep.child should be rebuilt due to a change
			in sub-slot (without revbump, as in bug #456208).
		"""
		if not (isinstance(dep.parent, Package) and \
			not dep.parent.built and dep.child.built):
			return None

		root_config = self._frozen_config.roots[dep.root]
		matches = []
		try:
			matches.append(self._pkg(dep.child.cpv, "ebuild",
				root_config, myrepo=dep.child.repo))
		except PackageNotFound:
			pass

		for unbuilt_child in chain(matches,
			self._iter_match_pkgs(root_config, "ebuild",
			Atom("=%s" % (dep.child.cpv,)))):
			if unbuilt_child in self._dynamic_config._runtime_pkg_mask:
				continue
			if self._frozen_config.excluded_pkgs.findAtomForPackage(
				unbuilt_child,
				modified_use=self._pkg_use_enabled(unbuilt_child)):
				continue
			if not self._pkg_visibility_check(unbuilt_child):
				continue
			break
		else:
			return None

		if unbuilt_child.slot == dep.child.slot and \
			unbuilt_child.sub_slot == dep.child.sub_slot:
			return None

		return unbuilt_child

	def _slot_change_backtrack(self, dep, new_child_slot):
		child = dep.child
		if "--debug" in self._frozen_config.myopts:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("backtracking due to slot/sub-slot change:")
			msg.append("   child package:  %s" % child)
			msg.append("      child slot:  %s/%s" %
				(child.slot, child.sub_slot))
			msg.append("       new child:  %s" % new_child_slot)
			msg.append("  new child slot:  %s/%s" %
				(new_child_slot.slot, new_child_slot.sub_slot))
			msg.append("   parent package: %s" % dep.parent)
			msg.append("   atom: %s" % dep.atom)
			msg.append("")
			writemsg_level("\n".join(msg),
				noiselevel=-1, level=logging.DEBUG)
		backtrack_infos = self._dynamic_config._backtrack_infos
		config = backtrack_infos.setdefault("config", {})

		# mask unwanted binary packages if necessary
		masks = {}
		if not child.installed:
			masks.setdefault(dep.child, {})["slot_operator_mask_built"] = None
		if masks:
			config.setdefault("slot_operator_mask_built", {}).update(masks)

		# trigger replacement of installed packages if necessary
		reinstalls = set()
		if child.installed:
			replacement_atom = self._replace_installed_atom(child)
			if replacement_atom is not None:
				reinstalls.add((child.root, replacement_atom))
		if reinstalls:
			config.setdefault("slot_operator_replace_installed",
				set()).update(reinstalls)

		self._dynamic_config._need_restart = True

	def _slot_operator_update_backtrack(self, dep, new_child_slot=None,
		new_dep=None):
		if new_child_slot is None:
			child = dep.child
		else:
			child = new_child_slot
		if "--debug" in self._frozen_config.myopts:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("backtracking due to missed slot abi update:")
			msg.append("   child package:  %s" % child)
			if new_child_slot is not None:
				msg.append("   new child slot package:  %s" % new_child_slot)
			msg.append("   parent package: %s" % dep.parent)
			if new_dep is not None:
				msg.append("   new parent pkg: %s" % new_dep.parent)
			msg.append("   atom: %s" % dep.atom)
			msg.append("")
			writemsg_level("\n".join(msg),
				noiselevel=-1, level=logging.DEBUG)
		backtrack_infos = self._dynamic_config._backtrack_infos
		config = backtrack_infos.setdefault("config", {})

		# mask unwanted binary packages if necessary
		abi_masks = {}
		if new_child_slot is None:
			if not child.installed:
				abi_masks.setdefault(child, {})["slot_operator_mask_built"] = None
		if not dep.parent.installed:
			abi_masks.setdefault(dep.parent, {})["slot_operator_mask_built"] = None
		if abi_masks:
			config.setdefault("slot_operator_mask_built", {}).update(abi_masks)

		# trigger replacement of installed packages if necessary
		abi_reinstalls = set()
		if dep.parent.installed:
			if new_dep is not None:
				replacement_atom = new_dep.parent.slot_atom
			else:
				replacement_atom = self._replace_installed_atom(dep.parent)
			if replacement_atom is not None:
				abi_reinstalls.add((dep.parent.root, replacement_atom))
		if new_child_slot is None and child.installed:
			replacement_atom = self._replace_installed_atom(child)
			if replacement_atom is not None:
				abi_reinstalls.add((child.root, replacement_atom))
		if abi_reinstalls:
			config.setdefault("slot_operator_replace_installed",
				set()).update(abi_reinstalls)

		self._dynamic_config._need_restart = True

	def _slot_operator_update_probe_slot_conflict(self, dep):
		new_dep = self._slot_operator_update_probe(dep, slot_conflict=True)

		if new_dep is not None:
			return new_dep

		if self._dynamic_config._autounmask is True:

			for autounmask_level in self._autounmask_levels():

				new_dep = self._slot_operator_update_probe(dep,
					slot_conflict=True, autounmask_level=autounmask_level)

				if new_dep is not None:
					return new_dep

		return None

	def _slot_operator_update_probe(self, dep, new_child_slot=False,
		slot_conflict=False, autounmask_level=None):
		"""
		slot/sub-slot := operators tend to prevent updates from getting pulled in,
		since installed packages pull in packages with the slot/sub-slot that they
		were built against. Detect this case so that we can schedule rebuilds
		and reinstalls when appropriate.
		NOTE: This function only searches for updates that involve upgrades
			to higher versions, since the logic required to detect when a
			downgrade would be desirable is not implemented.
		"""

		if dep.child.installed and \
			self._frozen_config.excluded_pkgs.findAtomForPackage(dep.child,
			modified_use=self._pkg_use_enabled(dep.child)):
			return None

		if dep.parent.installed and \
			self._frozen_config.excluded_pkgs.findAtomForPackage(dep.parent,
			modified_use=self._pkg_use_enabled(dep.parent)):
			return None

		debug = "--debug" in self._frozen_config.myopts
		selective = "selective" in self._dynamic_config.myparams
		want_downgrade = None
		want_downgrade_parent = None

		def check_reverse_dependencies(existing_pkg, candidate_pkg,
			replacement_parent=None):
			"""
			Check if candidate_pkg satisfies all of existing_pkg's non-
			slot operator parents.
			"""
			built_slot_operator_parents = set()
			for parent, atom in self._dynamic_config._parent_atoms.get(existing_pkg, []):
				if atom.soname or atom.slot_operator_built:
					built_slot_operator_parents.add(parent)

			for parent, atom in self._dynamic_config._parent_atoms.get(existing_pkg, []):
				if isinstance(parent, Package):
					if parent in built_slot_operator_parents:
						# This parent may need to be rebuilt, so its
						# dependencies aren't necessarily relevant.
						continue

					if replacement_parent is not None and \
						(replacement_parent.slot_atom == parent.slot_atom
						or replacement_parent.cpv == parent.cpv):
						# This parent is irrelevant because we intend to
						# replace it with replacement_parent.
						continue

					if any(pkg is not parent and
						(pkg.slot_atom == parent.slot_atom or
						pkg.cpv == parent.cpv) for pkg in
						self._dynamic_config._package_tracker.match(
						parent.root, Atom(parent.cp))):
						# This parent may need to be eliminated due to a
						# slot conflict,  so its dependencies aren't
						# necessarily relevant.
						continue

					if (not self._too_deep(parent.depth) and
						not self._frozen_config.excluded_pkgs.
						findAtomForPackage(parent,
						modified_use=self._pkg_use_enabled(parent))):
						# Check for common reasons that the parent's
						# dependency might be irrelevant.
						if self._upgrade_available(parent):
							# This parent could be replaced by
							# an upgrade (bug 584626).
							continue
						if parent.installed and self._in_blocker_conflict(parent):
							# This parent could be uninstalled in order
							# to solve a blocker conflict (bug 612772).
							continue
						if self._dynamic_config.digraph.has_edge(parent,
							existing_pkg):
							# There is a direct circular dependency between
							# parent and existing_pkg. This type of
							# relationship tends to prevent updates
							# of packages (bug 612874). Since candidate_pkg
							# is available, we risk a missed update if we
							# don't try to eliminate this parent from the
							# graph. Therefore, we give candidate_pkg a
							# chance, and assume that it will be masked
							# by backtracking if necessary.
							continue

				atom_set = InternalPackageSet(initial_atoms=(atom,),
					allow_repo=True)
				if not atom_set.findAtomForPackage(candidate_pkg,
					modified_use=self._pkg_use_enabled(candidate_pkg)):
					return False
			return True


		for replacement_parent in self._iter_similar_available(dep.parent,
			dep.parent.slot_atom, autounmask_level=autounmask_level):

			if replacement_parent is dep.parent:
				continue

			if replacement_parent < dep.parent:
				if want_downgrade_parent is None:
					want_downgrade_parent = self._downgrade_probe(
						dep.parent)
				if not want_downgrade_parent:
					continue

			if not check_reverse_dependencies(dep.parent, replacement_parent):
				continue

			selected_atoms = None

			try:
				atoms = self._flatten_atoms(replacement_parent,
					self._pkg_use_enabled(replacement_parent))
			except InvalidDependString:
				continue

			if replacement_parent.requires is not None:
				atoms = list(atoms)
				atoms.extend(replacement_parent.requires)

			# List of list of child,atom pairs for each atom.
			replacement_candidates = []
			# Set of all packages all atoms can agree on.
			all_candidate_pkgs = None

			for atom in atoms:
				# The _select_atoms_probe method is expensive, so initialization
				# of this variable is only performed on demand.
				atom_not_selected = None

				if not atom.package:
					unevaluated_atom = None
					if atom.match(dep.child):
						# We are searching for a replacement_parent
						# atom that will pull in a different child,
						# so continue checking the rest of the atoms.
						continue
				else:

					if atom.blocker or \
						atom.cp != dep.child.cp:
						continue

					# Discard USE deps, we're only searching for an
					# approximate pattern, and dealing with USE states
					# is too complex for this purpose.
					unevaluated_atom = atom.unevaluated_atom
					atom = atom.without_use

					if replacement_parent.built and \
						portage.dep._match_slot(atom, dep.child):
						# We are searching for a replacement_parent
						# atom that will pull in a different child,
						# so continue checking the rest of the atoms.
						continue

				candidate_pkg_atoms = []
				candidate_pkgs = []
				for pkg in self._iter_similar_available(
					dep.child, atom):
					if (dep.atom.package and
						pkg.slot == dep.child.slot and
						pkg.sub_slot == dep.child.sub_slot):
						# If slot/sub-slot is identical, then there's
						# no point in updating.
						continue
					if new_child_slot:
						if pkg.slot == dep.child.slot:
							continue
						if pkg < dep.child:
							# the new slot only matters if the
							# package version is higher
							continue
					else:
						if pkg.slot != dep.child.slot:
							continue
						if pkg < dep.child:
							if want_downgrade is None:
								want_downgrade = self._downgrade_probe(dep.child)
							# be careful not to trigger a rebuild when
							# the only version available with a
							# different slot_operator is an older version
							if not want_downgrade:
								continue
						if pkg.version == dep.child.version and not dep.child.built:
							continue

					insignificant = False
					if not slot_conflict and \
						selective and \
						dep.parent.installed and \
						dep.child.installed and \
						dep.parent >= replacement_parent and \
						dep.child.cpv == pkg.cpv:
						# Then can happen if the child's sub-slot changed
						# without a revision bump. The sub-slot change is
						# considered insignificant until one of its parent
						# packages needs to be rebuilt (which may trigger a
						# slot conflict).
						insignificant = True

					if (not insignificant and
						unevaluated_atom is not None):
						# Evaluate USE conditionals and || deps, in order
						# to see if this atom is really desirable, since
						# otherwise we may trigger an undesirable rebuild
						# as in bug #460304.
						if selected_atoms is None:
							selected_atoms = self._select_atoms_probe(
								dep.child.root, replacement_parent)
						atom_not_selected = unevaluated_atom not in selected_atoms
						if atom_not_selected:
							break

					if not insignificant and \
						check_reverse_dependencies(dep.child, pkg,
							replacement_parent=replacement_parent):

						candidate_pkg_atoms.append(
							(pkg, unevaluated_atom or atom))
						candidate_pkgs.append(pkg)

				# When unevaluated_atom is None, it means that atom is
				# an soname atom which is unconditionally selected, and
				# _select_atoms_probe is not applicable.
				if atom_not_selected is None and unevaluated_atom is not None:
					if selected_atoms is None:
						selected_atoms = self._select_atoms_probe(
							dep.child.root, replacement_parent)
					atom_not_selected = unevaluated_atom not in selected_atoms

				if atom_not_selected:
					continue
				replacement_candidates.append(candidate_pkg_atoms)
				if all_candidate_pkgs is None:
					all_candidate_pkgs = set(candidate_pkgs)
				else:
					all_candidate_pkgs.intersection_update(candidate_pkgs)

			if not all_candidate_pkgs:
				# If the atoms that connect parent and child can't agree on
				# any replacement child, we can't do anything.
				continue

			# Now select one of the pkgs as replacement. This is as easy as
			# selecting the highest version.
			# The more complicated part is to choose an atom for the
			# new Dependency object. Choose the one which ranked the selected
			# parent highest.
			selected = None
			for candidate_pkg_atoms in replacement_candidates:
				for i, (pkg, atom) in enumerate(candidate_pkg_atoms):
					if pkg not in all_candidate_pkgs:
						continue
					if selected is None or \
						selected[0] < pkg or \
						(selected[0] is pkg and i < selected[2]):
						selected = (pkg, atom, i)

			if debug:
				msg = []
				msg.append("")
				msg.append("")
				msg.append("slot_operator_update_probe:")
				msg.append("   existing child package:  %s" % dep.child)
				msg.append("   existing parent package: %s" % dep.parent)
				msg.append("   new child package:  %s" % selected[0])
				msg.append("   new parent package: %s" % replacement_parent)
				msg.append("")
				writemsg_level("\n".join(msg),
					noiselevel=-1, level=logging.DEBUG)

			return Dependency(parent=replacement_parent,
				child=selected[0], atom=selected[1])

		if debug:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("slot_operator_update_probe:")
			msg.append("   existing child package:  %s" % dep.child)
			msg.append("   existing parent package: %s" % dep.parent)
			msg.append("   new child package:  %s" % None)
			msg.append("   new parent package: %s" % None)
			msg.append("")
			writemsg_level("\n".join(msg),
				noiselevel=-1, level=logging.DEBUG)

		return None

	def _slot_operator_unsatisfied_probe(self, dep):

		if dep.parent.installed and \
			self._frozen_config.excluded_pkgs.findAtomForPackage(dep.parent,
			modified_use=self._pkg_use_enabled(dep.parent)):
			return False

		debug = "--debug" in self._frozen_config.myopts

		for replacement_parent in self._iter_similar_available(dep.parent,
			dep.parent.slot_atom):

			for atom in replacement_parent.validated_atoms:
				if not atom.slot_operator == "=" or \
					atom.blocker or \
					atom.cp != dep.atom.cp:
					continue

				# Discard USE deps, we're only searching for an approximate
				# pattern, and dealing with USE states is too complex for
				# this purpose.
				atom = atom.without_use

				pkg, existing_node = self._select_package(dep.root, atom,
					onlydeps=dep.onlydeps)

				if pkg is not None:

					if debug:
						msg = []
						msg.append("")
						msg.append("")
						msg.append("slot_operator_unsatisfied_probe:")
						msg.append("   existing parent package: %s" % dep.parent)
						msg.append("   existing parent atom: %s" % dep.atom)
						msg.append("   new parent package: %s" % replacement_parent)
						msg.append("   new child package:  %s" % pkg)
						msg.append("")
						writemsg_level("\n".join(msg),
							noiselevel=-1, level=logging.DEBUG)

					return True

		if debug:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("slot_operator_unsatisfied_probe:")
			msg.append("   existing parent package: %s" % dep.parent)
			msg.append("   existing parent atom: %s" % dep.atom)
			msg.append("   new parent package: %s" % None)
			msg.append("   new child package:  %s" % None)
			msg.append("")
			writemsg_level("\n".join(msg),
				noiselevel=-1, level=logging.DEBUG)

		return False

	def _slot_operator_unsatisfied_backtrack(self, dep):

		parent = dep.parent

		if "--debug" in self._frozen_config.myopts:
			msg = []
			msg.append("")
			msg.append("")
			msg.append("backtracking due to unsatisfied "
				"built slot-operator dep:")
			msg.append("   parent package: %s" % parent)
			msg.append("   atom: %s" % dep.atom)
			msg.append("")
			writemsg_level("\n".join(msg),
				noiselevel=-1, level=logging.DEBUG)

		backtrack_infos = self._dynamic_config._backtrack_infos
		config = backtrack_infos.setdefault("config", {})

		# mask unwanted binary packages if necessary
		masks = {}
		if not parent.installed:
			masks.setdefault(parent, {})["slot_operator_mask_built"] = None
		if masks:
			config.setdefault("slot_operator_mask_built", {}).update(masks)

		# trigger replacement of installed packages if necessary
		reinstalls = set()
		if parent.installed:
			replacement_atom = self._replace_installed_atom(parent)
			if replacement_atom is not None:
				reinstalls.add((parent.root, replacement_atom))
		if reinstalls:
			config.setdefault("slot_operator_replace_installed",
				set()).update(reinstalls)

		self._dynamic_config._need_restart = True

	def _in_blocker_conflict(self, pkg):
		"""
		Check if pkg is involved in a blocker conflict. This method
		only works after the _validate_blockers method has been called.
		"""

		if (self._dynamic_config._blocked_pkgs is None
			and not self._validate_blockers()):
			raise self._unknown_internal_error()

		if pkg in self._dynamic_config._blocked_pkgs:
			return True

		if pkg in self._dynamic_config._blocker_parents:
			return True

		return False

	def _upgrade_available(self, pkg):
		"""
		Detect cases where an upgrade of the given package is available
		within the same slot.
		"""
		for available_pkg in self._iter_similar_available(pkg,
			pkg.slot_atom):
			if available_pkg > pkg:
				return True

		return False

	def _downgrade_probe(self, pkg):
		"""
		Detect cases where a downgrade of the given package is considered
		desirable due to the current version being masked or unavailable.
		"""
		available_pkg = None
		for available_pkg in self._iter_similar_available(pkg,
			pkg.slot_atom):
			if available_pkg >= pkg:
				# There's an available package of the same or higher
				# version, so downgrade seems undesirable.
				return False

		return available_pkg is not None

	def _select_atoms_probe(self, root, pkg):
		selected_atoms = []
		use = self._pkg_use_enabled(pkg)
		for k in pkg._dep_keys:
			v = pkg._metadata.get(k)
			if not v:
				continue
			selected_atoms.extend(self._select_atoms(
				root, v, myuse=use, parent=pkg)[pkg])
		return frozenset(x.unevaluated_atom for
			x in selected_atoms)

	def _flatten_atoms(self, pkg, use):
		"""
		Evaluate all dependency atoms of the given package, and return
		them as a frozenset. For performance, results are cached.

		@param pkg: a Package instance
		@type pkg: Package
		@param pkg: set of enabled USE flags
		@type pkg: frozenset
		@rtype: frozenset
		@return: set of evaluated atoms
		"""

		cache_key = (pkg, use)

		try:
			return self._dynamic_config._flatten_atoms_cache[cache_key]
		except KeyError:
			pass

		atoms = []

		for dep_key in pkg._dep_keys:
			dep_string = pkg._metadata[dep_key]
			if not dep_string:
				continue

			dep_string = portage.dep.use_reduce(
				dep_string, uselist=use,
				is_valid_flag=pkg.iuse.is_valid_flag,
				flat=True, token_class=Atom, eapi=pkg.eapi)

			atoms.extend(token for token in dep_string
				if isinstance(token, Atom))

		atoms = frozenset(atoms)

		self._dynamic_config._flatten_atoms_cache[cache_key] = atoms
		return atoms

	def _iter_similar_available(self, graph_pkg, atom, autounmask_level=None):
		"""
		Given a package that's in the graph, do a rough check to
		see if a similar package is available to install. The given
		graph_pkg itself may be yielded only if it's not installed.
		"""

		usepkgonly = "--usepkgonly" in self._frozen_config.myopts
		useoldpkg_atoms = self._frozen_config.useoldpkg_atoms
		use_ebuild_visibility = self._frozen_config.myopts.get(
			'--use-ebuild-visibility', 'n') != 'n'

		for pkg in self._iter_match_pkgs_any(
			graph_pkg.root_config, atom):
			if pkg.cp != graph_pkg.cp:
				# discard old-style virtual match
				continue
			if pkg.installed:
				continue
			if pkg in self._dynamic_config._runtime_pkg_mask:
				continue
			if self._frozen_config.excluded_pkgs.findAtomForPackage(pkg,
				modified_use=self._pkg_use_enabled(pkg)):
				continue
			if pkg.built:
				if self._equiv_binary_installed(pkg):
					continue
				if not (not use_ebuild_visibility and
					(usepkgonly or useoldpkg_atoms.findAtomForPackage(
					pkg, modified_use=self._pkg_use_enabled(pkg)))) and \
					not self._equiv_ebuild_visible(pkg,
					autounmask_level=autounmask_level):
					continue
			if not self._pkg_visibility_check(pkg,
				autounmask_level=autounmask_level):
				continue
			yield pkg

	def _replace_installed_atom(self, inst_pkg):
		"""
		Given an installed package, generate an atom suitable for
		slot_operator_replace_installed backtracking info. The replacement
		SLOT may differ from the installed SLOT, so first search by cpv.
		"""
		built_pkgs = []
		for pkg in self._iter_similar_available(inst_pkg,
			Atom("=%s" % inst_pkg.cpv)):
			if not pkg.built:
				return pkg.slot_atom
			elif not pkg.installed:
				# avoid using SLOT from a built instance
				built_pkgs.append(pkg)

		for pkg in self._iter_similar_available(inst_pkg, inst_pkg.slot_atom):
			if not pkg.built:
				return pkg.slot_atom
			elif not pkg.installed:
				# avoid using SLOT from a built instance
				built_pkgs.append(pkg)

		if built_pkgs:
			best_version = None
			for pkg in built_pkgs:
				if best_version is None or pkg > best_version:
					best_version = pkg
			return best_version.slot_atom

		return None

	def _slot_operator_trigger_reinstalls(self):
		"""
		Search for packages with slot-operator deps on older slots, and schedule
		rebuilds if they can link to a newer slot that's in the graph.
		"""

		rebuild_if_new_slot = self._dynamic_config.myparams.get(
			"rebuild_if_new_slot", "y") == "y"

		for slot_key, slot_info in self._dynamic_config._slot_operator_deps.items():

			for dep in slot_info:

				atom = dep.atom

				if not (atom.soname or atom.slot_operator_built):
					new_child_slot = self._slot_change_probe(dep)
					if new_child_slot is not None:
						self._slot_change_backtrack(dep, new_child_slot)
					continue

				if not (dep.parent and
					isinstance(dep.parent, Package) and dep.parent.built):
					continue

				# If the parent is not installed, check if it needs to be
				# rebuilt against an installed instance, since otherwise
				# it could trigger downgrade of an installed instance as
				# in bug #652938.
				want_update_probe = dep.want_update or not dep.parent.installed

				# Check for slot update first, since we don't want to
				# trigger reinstall of the child package when a newer
				# slot will be used instead.
				if rebuild_if_new_slot and want_update_probe:
					new_dep = self._slot_operator_update_probe(dep,
						new_child_slot=True)
					if new_dep is not None:
						self._slot_operator_update_backtrack(dep,
							new_child_slot=new_dep.child)

				if want_update_probe:
					if self._slot_operator_update_probe(dep):
						self._slot_operator_update_backtrack(dep)

	def _reinstall_for_flags(self, pkg, forced_flags,
		orig_use, orig_iuse, cur_use, cur_iuse):
		"""Return a set of flags that trigger reinstallation, or None if there
		are no such flags."""

		# binpkg_respect_use: Behave like newuse by default. If newuse is
		# False and changed_use is True, then behave like changed_use.
		binpkg_respect_use = (pkg.built and
			self._dynamic_config.myparams.get("binpkg_respect_use")
			in ("y", "auto"))
		newuse = "--newuse" in self._frozen_config.myopts
		changed_use = "changed-use" == self._frozen_config.myopts.get("--reinstall")
		feature_flags = _get_feature_flags(
			_get_eapi_attrs(pkg.eapi))

		if newuse or (binpkg_respect_use and not changed_use):
			flags = set(orig_iuse.symmetric_difference(
				cur_iuse).difference(forced_flags))
			flags.update(orig_iuse.intersection(orig_use).symmetric_difference(
				cur_iuse.intersection(cur_use)))
			flags.difference_update(feature_flags)
			if flags:
				return flags

		elif changed_use or binpkg_respect_use:
			flags = set(orig_iuse.intersection(orig_use).symmetric_difference(
				cur_iuse.intersection(cur_use)))
			flags.difference_update(feature_flags)
			if flags:
				return flags
		return None

	def _changed_deps(self, pkg):

		ebuild = None
		try:
			ebuild = self._pkg(pkg.cpv, "ebuild",
				pkg.root_config, myrepo=pkg.repo)
		except PackageNotFound:
			# Use first available instance of the same version.
			for ebuild in self._iter_match_pkgs(
				pkg.root_config, "ebuild", Atom("=" + pkg.cpv)):
				break

		if ebuild is None:
			changed = False
		else:
			if self._dynamic_config.myparams.get("bdeps") in ("y", "auto"):
				depvars = Package._dep_keys
			else:
				depvars = Package._runtime_keys

			# Use _raw_metadata, in order to avoid interaction
			# with --dynamic-deps.
			try:
				built_deps = []
				for k in depvars:
					dep_struct = portage.dep.use_reduce(
						pkg._raw_metadata[k], uselist=pkg.</