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diff --git a/jni/ruby/lib/rubygems/resolver.rb b/jni/ruby/lib/rubygems/resolver.rb
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+require 'rubygems/dependency'
+require 'rubygems/exceptions'
+require 'rubygems/util/list'
+
+require 'uri'
+require 'net/http'
+
+##
+# Given a set of Gem::Dependency objects as +needed+ and a way to query the
+# set of available specs via +set+, calculates a set of ActivationRequest
+# objects which indicate all the specs that should be activated to meet the
+# all the requirements.
+
+class Gem::Resolver
+
+  ##
+  # If the DEBUG_RESOLVER environment variable is set then debugging mode is
+  # enabled for the resolver.  This will display information about the state
+  # of the resolver while a set of dependencies is being resolved.
+
+  DEBUG_RESOLVER = !ENV['DEBUG_RESOLVER'].nil?
+
+  require 'pp' if DEBUG_RESOLVER
+
+  ##
+  # Contains all the conflicts encountered while doing resolution
+
+  attr_reader :conflicts
+
+  ##
+  # Set to true if all development dependencies should be considered.
+
+  attr_accessor :development
+
+  ##
+  # Set to true if immediate development dependencies should be considered.
+
+  attr_accessor :development_shallow
+
+  ##
+  # When true, no dependencies are looked up for requested gems.
+
+  attr_accessor :ignore_dependencies
+
+  ##
+  # List of dependencies that could not be found in the configured sources.
+
+  attr_reader :missing
+
+  attr_reader :stats
+
+  ##
+  # Hash of gems to skip resolution.  Keyed by gem name, with arrays of
+  # gem specifications as values.
+
+  attr_accessor :skip_gems
+
+  ##
+  # When a missing dependency, don't stop. Just go on and record what was
+  # missing.
+
+  attr_accessor :soft_missing
+
+  ##
+  # Combines +sets+ into a ComposedSet that allows specification lookup in a
+  # uniform manner.  If one of the +sets+ is itself a ComposedSet its sets are
+  # flattened into the result ComposedSet.
+
+  def self.compose_sets *sets
+    sets.compact!
+
+    sets = sets.map do |set|
+      case set
+      when Gem::Resolver::BestSet then
+        set
+      when Gem::Resolver::ComposedSet then
+        set.sets
+      else
+        set
+      end
+    end.flatten
+
+    case sets.length
+    when 0 then
+      raise ArgumentError, 'one set in the composition must be non-nil'
+    when 1 then
+      sets.first
+    else
+      Gem::Resolver::ComposedSet.new(*sets)
+    end
+  end
+
+  ##
+  # Creates a Resolver that queries only against the already installed gems
+  # for the +needed+ dependencies.
+
+  def self.for_current_gems needed
+    new needed, Gem::Resolver::CurrentSet.new
+  end
+
+  ##
+  # Create Resolver object which will resolve the tree starting
+  # with +needed+ Dependency objects.
+  #
+  # +set+ is an object that provides where to look for specifications to
+  # satisfy the Dependencies. This defaults to IndexSet, which will query
+  # rubygems.org.
+
+  def initialize needed, set = nil
+    @set = set || Gem::Resolver::IndexSet.new
+    @needed = needed
+
+    @conflicts           = []
+    @development         = false
+    @development_shallow = false
+    @ignore_dependencies = false
+    @missing             = []
+    @skip_gems           = {}
+    @soft_missing        = false
+    @stats               = Gem::Resolver::Stats.new
+  end
+
+  def explain stage, *data # :nodoc:
+    return unless DEBUG_RESOLVER
+
+    d = data.map { |x| x.pretty_inspect }.join(", ")
+    $stderr.printf "%10s %s\n", stage.to_s.upcase, d
+  end
+
+  def explain_list stage # :nodoc:
+    return unless DEBUG_RESOLVER
+
+    data = yield
+    $stderr.printf "%10s (%d entries)\n", stage.to_s.upcase, data.size
+    PP.pp data, $stderr unless data.empty?
+  end
+
+  ##
+  # Creates an ActivationRequest for the given +dep+ and the last +possible+
+  # specification.
+  #
+  # Returns the Specification and the ActivationRequest
+
+  def activation_request dep, possible # :nodoc:
+    spec = possible.pop
+
+    explain :activate, [spec.full_name, possible.size]
+    explain :possible, possible
+
+    activation_request =
+      Gem::Resolver::ActivationRequest.new spec, dep, possible
+
+    return spec, activation_request
+  end
+
+  def requests s, act, reqs=nil # :nodoc:
+    return reqs if @ignore_dependencies
+
+    s.fetch_development_dependencies if @development
+
+    s.dependencies.reverse_each do |d|
+      next if d.type == :development and not @development
+      next if d.type == :development and @development_shallow and
+              act.development?
+      next if d.type == :development and @development_shallow and
+              act.parent
+
+      reqs.add Gem::Resolver::DependencyRequest.new(d, act)
+      @stats.requirement!
+    end
+
+    @set.prefetch reqs
+
+    @stats.record_requirements reqs
+
+    reqs
+  end
+
+  ##
+  # Proceed with resolution! Returns an array of ActivationRequest objects.
+
+  def resolve
+    @conflicts = []
+
+    needed = Gem::Resolver::RequirementList.new
+
+    @needed.reverse_each do |n|
+      request = Gem::Resolver::DependencyRequest.new n, nil
+
+      needed.add request
+      @stats.requirement!
+    end
+
+    @stats.record_requirements needed
+
+    res = resolve_for needed, nil
+
+    raise Gem::DependencyResolutionError, res if
+      res.kind_of? Gem::Resolver::Conflict
+
+    res.to_a
+  end
+
+  ##
+  # Extracts the specifications that may be able to fulfill +dependency+ and
+  # returns those that match the local platform and all those that match.
+
+  def find_possible dependency # :nodoc:
+    all = @set.find_all dependency
+
+    if (skip_dep_gems = skip_gems[dependency.name]) && !skip_dep_gems.empty?
+      matching = all.select do |api_spec|
+        skip_dep_gems.any? { |s| api_spec.version == s.version }
+      end
+
+      all = matching unless matching.empty?
+    end
+
+    matching_platform = select_local_platforms all
+
+    return matching_platform, all
+  end
+
+  def handle_conflict(dep, existing) # :nodoc:
+    # There is a conflict! We return the conflict object which will be seen by
+    # the caller and be handled at the right level.
+
+    # If the existing activation indicates that there are other possibles for
+    # it, then issue the conflict on the dependency for the activation itself.
+    # Otherwise, if there was a requester, issue it on the requester's
+    # request itself.
+    # Finally, if the existing request has no requester (toplevel) unwind to
+    # it anyway.
+
+    if existing.others_possible?
+      conflict =
+        Gem::Resolver::Conflict.new dep, existing
+    elsif dep.requester
+      depreq = dep.requester.request
+      conflict =
+        Gem::Resolver::Conflict.new depreq, existing, dep
+    elsif existing.request.requester.nil?
+      conflict =
+        Gem::Resolver::Conflict.new dep, existing
+    else
+      raise Gem::DependencyError, "Unable to figure out how to unwind conflict"
+    end
+
+    @conflicts << conflict unless @conflicts.include? conflict
+
+    return conflict
+  end
+
+  # Contains the state for attempting activation of a set of possible specs.
+  # +needed+ is a Gem::List of DependencyRequest objects that, well, need
+  # to be satisfied.
+  # +specs+ is the List of ActivationRequest that are being tested.
+  # +dep+ is the DependencyRequest that was used to generate this state.
+  # +spec+ is the Specification for this state.
+  # +possible+ is List of DependencyRequest objects that can be tried to
+  # find a  complete set.
+  # +conflicts+ is a [DependencyRequest, Conflict] hit tried to
+  # activate the state.
+  #
+  State = Struct.new(:needed, :specs, :dep, :spec, :possibles, :conflicts) do
+    def summary # :nodoc:
+      nd = needed.map { |s| s.to_s }.sort if nd
+
+      if specs then
+        ss = specs.map { |s| s.full_name }.sort
+        ss.unshift ss.length
+      end
+
+      d = dep.to_s
+      d << " from #{dep.requester.full_name}" if dep.requester
+
+      ps = possibles.map { |p| p.full_name }.sort
+      ps.unshift ps.length
+
+      cs = conflicts.map do |(s, c)|
+        [s.full_name, c.conflicting_dependencies.map { |cd| cd.to_s }]
+      end
+
+      { :needed => nd, :specs => ss, :dep => d, :spec => spec.full_name,
+        :possibles => ps, :conflicts => cs }
+    end
+  end
+
+  ##
+  # The meat of the algorithm. Given +needed+ DependencyRequest objects and
+  # +specs+ being a list to ActivationRequest, calculate a new list of
+  # ActivationRequest objects.
+
+  def resolve_for needed, specs # :nodoc:
+    # The State objects that are used to attempt the activation tree.
+    states = []
+
+    while !needed.empty?
+      @stats.iteration!
+
+      dep = needed.remove
+      explain :try, [dep, dep.requester ? dep.requester.request : :toplevel]
+      explain_list(:next5) { needed.next5 }
+      explain_list(:specs) { Array(specs).map { |x| x.full_name }.sort }
+
+      # If there is already a spec activated for the requested name...
+      if specs && existing = specs.find { |s| dep.name == s.name }
+        # then we're done since this new dep matches the existing spec.
+        next if dep.matches_spec? existing
+
+        conflict = handle_conflict dep, existing
+
+        return conflict unless dep.requester
+
+        explain :conflict, dep, :existing, existing.full_name
+
+        depreq = dep.requester.request
+
+        state = nil
+        until states.empty?
+          x = states.pop
+
+          i = existing.request.requester
+          explain :consider, x.spec.full_name, [depreq.name, dep.name, i ? i.name : :top]
+
+          if x.spec.name == depreq.name or
+              x.spec.name == dep.name or
+              (i && (i.name == x.spec.name))
+            explain :found, x.spec.full_name
+            state = x
+            break
+          end
+        end
+
+        return conflict unless state
+
+        @stats.backtracking!
+
+        needed, specs = resolve_for_conflict needed, specs, state
+
+        states << state unless state.possibles.empty?
+
+        next
+      end
+
+      matching, all = find_possible dep
+
+      case matching.size
+      when 0
+        resolve_for_zero dep, all
+      when 1
+        needed, specs =
+          resolve_for_single needed, specs, dep, matching
+      else
+        needed, specs =
+          resolve_for_multiple needed, specs, states, dep, matching
+      end
+    end
+
+    specs
+  end
+
+  ##
+  # Rewinds +needed+ and +specs+ to a previous state in +state+ for a conflict
+  # between +dep+ and +existing+.
+
+  def resolve_for_conflict needed, specs, state # :nodoc:
+    # We exhausted the possibles so it's definitely not going to work out,
+    # bail out.
+    raise Gem::ImpossibleDependenciesError.new state.dep, state.conflicts if
+      state.possibles.empty?
+
+    # Retry resolution with this spec and add it's dependencies
+    spec, act = activation_request state.dep, state.possibles
+
+    needed = requests spec, act, state.needed.dup
+    specs = Gem::List.prepend state.specs, act
+
+    return needed, specs
+  end
+
+  ##
+  # There are multiple +possible+ specifications for this +dep+.  Updates
+  # +needed+, +specs+ and +states+ for further resolution of the +possible+
+  # choices.
+
+  def resolve_for_multiple needed, specs, states, dep, possible # :nodoc:
+    # Sort them so that we try the highest versions first.
+    possible = possible.sort_by do |s|
+      [s.source, s.version, s.platform == Gem::Platform::RUBY ? -1 : 1]
+    end
+
+    spec, act = activation_request dep, possible
+
+    # We may need to try all of +possible+, so we setup state to unwind back
+    # to current +needed+ and +specs+ so we can try another. This is code is
+    # what makes conflict resolution possible.
+    states << State.new(needed.dup, specs, dep, spec, possible, [])
+
+    @stats.record_depth states
+
+    explain :states, states.map { |s| s.dep }
+
+    needed = requests spec, act, needed
+    specs = Gem::List.prepend specs, act
+
+    return needed, specs
+  end
+
+  ##
+  # Add the spec from the +possible+ list to +specs+ and process the spec's
+  # dependencies by adding them to +needed+.
+
+  def resolve_for_single needed, specs, dep, possible # :nodoc:
+    spec, act = activation_request dep, possible
+
+    specs = Gem::List.prepend specs, act
+
+    # Put the deps for at the beginning of needed
+    # rather than the end to match the depth first
+    # searching done by the multiple case code below.
+    #
+    # This keeps the error messages consistent.
+    needed = requests spec, act, needed
+
+    return needed, specs
+  end
+
+  ##
+  # When there are no possible specifications for +dep+ our work is done.
+
+  def resolve_for_zero dep, platform_mismatch # :nodoc:
+    @missing << dep
+
+    unless @soft_missing
+      exc = Gem::UnsatisfiableDependencyError.new dep, platform_mismatch
+      exc.errors = @set.errors
+
+      raise exc
+    end
+  end
+
+  ##
+  # Returns the gems in +specs+ that match the local platform.
+
+  def select_local_platforms specs # :nodoc:
+    specs.select do |spec|
+      Gem::Platform.installable? spec
+    end
+  end
+
+end
+
+##
+# TODO remove in RubyGems 3
+
+Gem::DependencyResolver = Gem::Resolver # :nodoc:
+
+require 'rubygems/resolver/activation_request'
+require 'rubygems/resolver/conflict'
+require 'rubygems/resolver/dependency_request'
+require 'rubygems/resolver/requirement_list'
+require 'rubygems/resolver/stats'
+
+require 'rubygems/resolver/set'
+require 'rubygems/resolver/api_set'
+require 'rubygems/resolver/composed_set'
+require 'rubygems/resolver/best_set'
+require 'rubygems/resolver/current_set'
+require 'rubygems/resolver/git_set'
+require 'rubygems/resolver/index_set'
+require 'rubygems/resolver/installer_set'
+require 'rubygems/resolver/lock_set'
+require 'rubygems/resolver/vendor_set'
+
+require 'rubygems/resolver/specification'
+require 'rubygems/resolver/spec_specification'
+require 'rubygems/resolver/api_specification'
+require 'rubygems/resolver/git_specification'
+require 'rubygems/resolver/index_specification'
+require 'rubygems/resolver/installed_specification'
+require 'rubygems/resolver/local_specification'
+require 'rubygems/resolver/lock_specification'
+require 'rubygems/resolver/vendor_specification'
+