From f20ad4889d5c7af44581373d25fd326ce796c4b3 Mon Sep 17 00:00:00 2001
From: hsbt <hsbt@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sat, 18 Jun 2016 05:11:55 +0000
Subject: * lib/rubygems.rb, lib/rubygems/*, test/rubygems/*: Update rubygems  
 HEAD(2c6d256). It contains to update vendored Molinillo to 0.5.0.  
 https://github.com/rubygems/rubygems/pull/1638

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55441 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 .../lib/molinillo/delegates/resolution_state.rb    |  50 +++++
 .../molinillo/delegates/specification_provider.rb  |  80 ++++++++
 .../molinillo/lib/molinillo/dependency_graph.rb    | 202 ++++++---------------
 .../lib/molinillo/dependency_graph/action.rb       |  35 ++++
 .../dependency_graph/add_edge_no_circular.rb       |  58 ++++++
 .../lib/molinillo/dependency_graph/add_vertex.rb   |  61 +++++++
 .../dependency_graph/detach_vertex_named.rb        |  53 ++++++
 .../lib/molinillo/dependency_graph/log.rb          | 114 ++++++++++++
 .../lib/molinillo/dependency_graph/set_payload.rb  |  45 +++++
 .../lib/molinillo/dependency_graph/tag.rb          |  35 ++++
 .../lib/molinillo/dependency_graph/vertex.rb       | 123 +++++++++++++
 .../resolver/molinillo/lib/molinillo/errors.rb     |   2 +-
 .../molinillo/lib/molinillo/gem_metadata.rb        |   2 +-
 .../resolver/molinillo/lib/molinillo/resolution.rb | 109 +++++------
 .../resolver/molinillo/lib/molinillo/state.rb      |   6 +-
 15 files changed, 772 insertions(+), 203 deletions(-)
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
 create mode 100644 lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb

(limited to 'lib/rubygems/resolver')

diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
new file mode 100644
index 0000000000..1bbc72c1f6
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+module Gem::Resolver::Molinillo
+  # @!visibility private
+  module Delegates
+    # Delegates all {Gem::Resolver::Molinillo::ResolutionState} methods to a `#state` property.
+    module ResolutionState
+      # (see Gem::Resolver::Molinillo::ResolutionState#name)
+      def name
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.name
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#requirements)
+      def requirements
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.requirements
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#activated)
+      def activated
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.activated
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#requirement)
+      def requirement
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.requirement
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#possibilities)
+      def possibilities
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.possibilities
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#depth)
+      def depth
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.depth
+      end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#conflicts)
+      def conflicts
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.conflicts
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb
new file mode 100644
index 0000000000..71903c7e86
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+module Gem::Resolver::Molinillo
+  module Delegates
+    # Delegates all {Gem::Resolver::Molinillo::SpecificationProvider} methods to a
+    # `#specification_provider` property.
+    module SpecificationProvider
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#search_for)
+      def search_for(dependency)
+        with_no_such_dependency_error_handling do
+          specification_provider.search_for(dependency)
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#dependencies_for)
+      def dependencies_for(specification)
+        with_no_such_dependency_error_handling do
+          specification_provider.dependencies_for(specification)
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#requirement_satisfied_by?)
+      def requirement_satisfied_by?(requirement, activated, spec)
+        with_no_such_dependency_error_handling do
+          specification_provider.requirement_satisfied_by?(requirement, activated, spec)
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#name_for)
+      def name_for(dependency)
+        with_no_such_dependency_error_handling do
+          specification_provider.name_for(dependency)
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#name_for_explicit_dependency_source)
+      def name_for_explicit_dependency_source
+        with_no_such_dependency_error_handling do
+          specification_provider.name_for_explicit_dependency_source
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#name_for_locking_dependency_source)
+      def name_for_locking_dependency_source
+        with_no_such_dependency_error_handling do
+          specification_provider.name_for_locking_dependency_source
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#sort_dependencies)
+      def sort_dependencies(dependencies, activated, conflicts)
+        with_no_such_dependency_error_handling do
+          specification_provider.sort_dependencies(dependencies, activated, conflicts)
+        end
+      end
+
+      # (see Gem::Resolver::Molinillo::SpecificationProvider#allow_missing?)
+      def allow_missing?(dependency)
+        with_no_such_dependency_error_handling do
+          specification_provider.allow_missing?(dependency)
+        end
+      end
+
+      private
+
+      # Ensures any raised {NoSuchDependencyError} has its
+      # {NoSuchDependencyError#required_by} set.
+      # @yield
+      def with_no_such_dependency_error_handling
+        yield
+      rescue NoSuchDependencyError => error
+        if state
+          vertex = activated.vertex_named(name_for(error.dependency))
+          error.required_by += vertex.incoming_edges.map { |e| e.origin.name }
+          error.required_by << name_for_explicit_dependency_source unless vertex.explicit_requirements.empty?
+        end
+        raise
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
index 42563664d6..6189a717cd 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
@@ -2,6 +2,9 @@
 require 'set'
 require 'tsort'
 
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log'
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex'
+
 module Gem::Resolver::Molinillo
   # A directed acyclic graph that is tuned to hold named dependencies
   class DependencyGraph
@@ -10,15 +13,16 @@ module Gem::Resolver::Molinillo
     # Enumerates through the vertices of the graph.
     # @return [Array<Vertex>] The graph's vertices.
     def each
+      return vertices.values.each unless block_given?
       vertices.values.each { |v| yield v }
     end
 
     include TSort
 
-    # @visibility private
-    alias_method :tsort_each_node, :each
+    # @!visibility private
+    alias tsort_each_node each
 
-    # @visibility private
+    # @!visibility private
     def tsort_each_child(vertex, &block)
       vertex.successors.each(&block)
     end
@@ -44,9 +48,27 @@ module Gem::Resolver::Molinillo
     #   by {Vertex#name}
     attr_reader :vertices
 
+    # @return [Log] the op log for this graph
+    attr_reader :log
+
     # Initializes an empty dependency graph
     def initialize
       @vertices = {}
+      @log = Log.new
+    end
+
+    # Tags the current state of the dependency as the given tag
+    # @param  [Object] tag an opaque tag for the current state of the graph
+    # @return [Void]
+    def tag(tag)
+      log.tag(self, tag)
+    end
+
+    # Rewinds the graph to the state tagged as `tag`
+    # @param  [Object] tag the tag to rewind to
+    # @return [Void]
+    def rewind_to(tag)
+      log.rewind_to(self, tag)
     end
 
     # Initializes a copy of a {DependencyGraph}, ensuring that all {#vertices}
@@ -55,6 +77,7 @@ module Gem::Resolver::Molinillo
     def initialize_copy(other)
       super
       @vertices = {}
+      @log = other.log.dup
       traverse = lambda do |new_v, old_v|
         return if new_v.outgoing_edges.size == old_v.outgoing_edges.size
         old_v.outgoing_edges.each do |edge|
@@ -75,6 +98,22 @@ module Gem::Resolver::Molinillo
       "#{self.class}:#{vertices.values.inspect}"
     end
 
+    # @return [String] Returns a dot format representation of the graph
+    def to_dot
+      dot_vertices = []
+      dot_edges = []
+      vertices.each do |n, v|
+        dot_vertices << "  #{n} [label=\"{#{n}|#{v.payload}}\"]"
+        v.outgoing_edges.each do |e|
+          dot_edges << "  #{e.origin.name} -> #{e.destination.name} [label=\"#{e.requirement}\"]"
+        end
+      end
+      dot_vertices.sort!
+      dot_edges.sort!
+      dot = dot_vertices.unshift('digraph G {').push('') + dot_edges.push('}')
+      dot.join("\n")
+    end
+
     # @return [Boolean] whether the two dependency graphs are equal, determined
     #   by a recursive traversal of each {#root_vertices} and its
     #   {Vertex#successors}
@@ -93,12 +132,9 @@ module Gem::Resolver::Molinillo
     # @param [Object] requirement the requirement that is requiring the child
     # @return [void]
     def add_child_vertex(name, payload, parent_names, requirement)
-      vertex = add_vertex(name, payload)
+      root = !parent_names.delete(nil) { true }
+      vertex = add_vertex(name, payload, root)
       parent_names.each do |parent_name|
-        unless parent_name
-          vertex.root = true
-          next
-        end
         parent_node = vertex_named(parent_name)
         add_edge(parent_node, vertex, requirement)
       end
@@ -110,10 +146,7 @@ module Gem::Resolver::Molinillo
     # @param [Object] payload
     # @return [Vertex] the vertex that was added to `self`
     def add_vertex(name, payload, root = false)
-      vertex = vertices[name] ||= Vertex.new(name, payload)
-      vertex.payload ||= payload
-      vertex.root ||= root
-      vertex
+      log.add_vertex(self, name, payload, root)
     end
 
     # Detaches the {#vertex_named} `name` {Vertex} from the graph, recursively
@@ -121,16 +154,7 @@ module Gem::Resolver::Molinillo
     # @param [String] name
     # @return [void]
     def detach_vertex_named(name)
-      return unless vertex = vertices.delete(name)
-      vertex.outgoing_edges.each do |e|
-        v = e.destination
-        v.incoming_edges.delete(e)
-        detach_vertex_named(v.name) unless v.root? || v.predecessors.any?
-      end
-      vertex.incoming_edges.each do |e|
-        v = e.origin
-        v.outgoing_edges.delete(e)
-      end
+      log.detach_vertex_named(self, name)
     end
 
     # @param [String] name
@@ -158,134 +182,22 @@ module Gem::Resolver::Molinillo
       add_edge_no_circular(origin, destination, requirement)
     end
 
+    # Sets the payload of the vertex with the given name
+    # @param [String] name the name of the vertex
+    # @param [Object] payload the payload
+    # @return [Void]
+    def set_payload(name, payload)
+      log.set_payload(self, name, payload)
+    end
+
     private
 
     # Adds a new {Edge} to the dependency graph without checking for
     # circularity.
+    # @param (see #add_edge)
+    # @return (see #add_edge)
     def add_edge_no_circular(origin, destination, requirement)
-      edge = Edge.new(origin, destination, requirement)
-      origin.outgoing_edges << edge
-      destination.incoming_edges << edge
-      edge
-    end
-
-    # A vertex in a {DependencyGraph} that encapsulates a {#name} and a
-    # {#payload}
-    class Vertex
-      # @return [String] the name of the vertex
-      attr_accessor :name
-
-      # @return [Object] the payload the vertex holds
-      attr_accessor :payload
-
-      # @return [Arrary<Object>] the explicit requirements that required
-      #   this vertex
-      attr_reader :explicit_requirements
-
-      # @return [Boolean] whether the vertex is considered a root vertex
-      attr_accessor :root
-      alias_method :root?, :root
-
-      # Initializes a vertex with the given name and payload.
-      # @param [String] name see {#name}
-      # @param [Object] payload see {#payload}
-      def initialize(name, payload)
-        @name = name
-        @payload = payload
-        @explicit_requirements = []
-        @outgoing_edges = []
-        @incoming_edges = []
-      end
-
-      # @return [Array<Object>] all of the requirements that required
-      #   this vertex
-      def requirements
-        incoming_edges.map(&:requirement) + explicit_requirements
-      end
-
-      # @return [Array<Edge>] the edges of {#graph} that have `self` as their
-      #   {Edge#origin}
-      attr_accessor :outgoing_edges
-
-      # @return [Array<Edge>] the edges of {#graph} that have `self` as their
-      #   {Edge#destination}
-      attr_accessor :incoming_edges
-
-      # @return [Array<Vertex>] the vertices of {#graph} that have an edge with
-      #   `self` as their {Edge#destination}
-      def predecessors
-        incoming_edges.map(&:origin)
-      end
-
-      # @return [Array<Vertex>] the vertices of {#graph} where `self` is a
-      #   {#descendent?}
-      def recursive_predecessors
-        vertices = predecessors
-        vertices += vertices.map(&:recursive_predecessors).flatten(1)
-        vertices.uniq!
-        vertices
-      end
-
-      # @return [Array<Vertex>] the vertices of {#graph} that have an edge with
-      #   `self` as their {Edge#origin}
-      def successors
-        outgoing_edges.map(&:destination)
-      end
-
-      # @return [Array<Vertex>] the vertices of {#graph} where `self` is an
-      #   {#ancestor?}
-      def recursive_successors
-        vertices = successors
-        vertices += vertices.map(&:recursive_successors).flatten(1)
-        vertices.uniq!
-        vertices
-      end
-
-      # @return [String] a string suitable for debugging
-      def inspect
-        "#{self.class}:#{name}(#{payload.inspect})"
-      end
-
-      # @return [Boolean] whether the two vertices are equal, determined
-      #   by a recursive traversal of each {Vertex#successors}
-      def ==(other)
-        shallow_eql?(other) &&
-          successors.to_set == other.successors.to_set
-      end
-
-      # @param  [Vertex] other the other vertex to compare to
-      # @return [Boolean] whether the two vertices are equal, determined
-      #   solely by {#name} and {#payload} equality
-      def shallow_eql?(other)
-        other &&
-          name == other.name &&
-          payload == other.payload
-      end
-
-      alias_method :eql?, :==
-
-      # @return [Fixnum] a hash for the vertex based upon its {#name}
-      def hash
-        name.hash
-      end
-
-      # Is there a path from `self` to `other` following edges in the
-      # dependency graph?
-      # @return true iff there is a path following edges within this {#graph}
-      def path_to?(other)
-        equal?(other) || successors.any? { |v| v.path_to?(other) }
-      end
-
-      alias_method :descendent?, :path_to?
-
-      # Is there a path from `other` to `self` following edges in the
-      # dependency graph?
-      # @return true iff there is a path following edges within this {#graph}
-      def ancestor?(other)
-        other.path_to?(self)
-      end
-
-      alias_method :is_reachable_from?, :ancestor?
+      log.add_edge_no_circular(self, origin.name, destination.name, requirement)
     end
   end
 end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb
new file mode 100644
index 0000000000..dbf4b0b803
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # An action that modifies a {DependencyGraph} that is reversible.
+    # @abstract
+    class Action
+      # rubocop:disable Lint/UnusedMethodArgument
+
+      # @return [Symbol] The name of the action.
+      def self.name
+        raise 'Abstract'
+      end
+
+      # Performs the action on the given graph.
+      # @param  [DependencyGraph] graph the graph to perform the action on.
+      # @return [Void]
+      def up(graph)
+        raise 'Abstract'
+      end
+
+      # Reverses the action on the given graph.
+      # @param  [DependencyGraph] graph the graph to reverse the action on.
+      # @return [Void]
+      def down(graph)
+        raise 'Abstract'
+      end
+
+      # @return [Action,Nil] The previous action
+      attr_accessor :previous
+
+      # @return [Action,Nil] The next action
+      attr_accessor :next
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
new file mode 100644
index 0000000000..b2d569ddc9
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # @!visibility private
+    # (see DependencyGraph#add_edge_no_circular)
+    class AddEdgeNoCircular < Action
+      # @!group Action
+
+      # (see Action.name)
+      def self.name
+        :add_vertex
+      end
+
+      # (see Action#up)
+      def up(graph)
+        edge = make_edge(graph)
+        edge.origin.outgoing_edges << edge
+        edge.destination.incoming_edges << edge
+        edge
+      end
+
+      # (see Action#down)
+      def down(graph)
+        edge = make_edge(graph)
+        edge.origin.outgoing_edges.delete(edge)
+        edge.destination.incoming_edges.delete(edge)
+      end
+
+      # @!group AddEdgeNoCircular
+
+      # @return [String] the name of the origin of the edge
+      attr_reader :origin
+
+      # @return [String] the name of the destination of the edge
+      attr_reader :destination
+
+      # @return [Object] the requirement that the edge represents
+      attr_reader :requirement
+
+      # @param  [DependencyGraph] graph the graph to find vertices from
+      # @return [Edge] The edge this action adds
+      def make_edge(graph)
+        Edge.new(graph.vertex_named(origin), graph.vertex_named(destination), requirement)
+      end
+
+      # Initialize an action to add an edge to a dependency graph
+      # @param [String] origin the name of the origin of the edge
+      # @param [String] destination the name of the destination of the edge
+      # @param [Object] requirement the requirement that the edge represents
+      def initialize(origin, destination, requirement)
+        @origin = origin
+        @destination = destination
+        @requirement = requirement
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
new file mode 100644
index 0000000000..e8b4278ba4
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # @!visibility private
+    # (see DependencyGraph#add_vertex)
+    class AddVertex < Action # :nodoc:
+      # @!group Action
+
+      # (see Action.name)
+      def self.name
+        :add_vertex
+      end
+
+      # (see Action#up)
+      def up(graph)
+        if existing = graph.vertices[name]
+          @existing_payload = existing.payload
+          @existing_root = existing.root
+        end
+        vertex = existing || Vertex.new(name, payload)
+        graph.vertices[vertex.name] = vertex
+        vertex.payload ||= payload
+        vertex.root ||= root
+        vertex
+      end
+
+      # (see Action#down)
+      def down(graph)
+        if defined?(@existing_payload)
+          vertex = graph.vertices[name]
+          vertex.payload = @existing_payload
+          vertex.root = @existing_root
+        else
+          graph.vertices.delete(name)
+        end
+      end
+
+      # @!group AddVertex
+
+      # @return [String] the name of the vertex
+      attr_reader :name
+
+      # @return [Object] the payload for the vertex
+      attr_reader :payload
+
+      # @return [Boolean] whether the vertex is root or not
+      attr_reader :root
+
+      # Initialize an action to add a vertex to a dependency graph
+      # @param [String] name the name of the vertex
+      # @param [Object] payload the payload for the vertex
+      # @param [Boolean] root whether the vertex is root or not
+      def initialize(name, payload, root)
+        @name = name
+        @payload = payload
+        @root = root
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
new file mode 100644
index 0000000000..59ef7d8c09
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # @!visibility private
+    # @see DependencyGraph#detach_vertex_named
+    class DetachVertexNamed < Action
+      # @!group Action
+
+      # (see Action#name)
+      def self.name
+        :add_vertex
+      end
+
+      # (see Action#up)
+      def up(graph)
+        return unless @vertex = graph.vertices.delete(name)
+        @vertex.outgoing_edges.each do |e|
+          v = e.destination
+          v.incoming_edges.delete(e)
+          graph.detach_vertex_named(v.name) unless v.root? || v.predecessors.any?
+        end
+        @vertex.incoming_edges.each do |e|
+          v = e.origin
+          v.outgoing_edges.delete(e)
+        end
+      end
+
+      # (see Action#down)
+      def down(graph)
+        return unless @vertex
+        graph.vertices[@vertex.name] = @vertex
+        @vertex.outgoing_edges.each do |e|
+          e.destination.incoming_edges << e
+        end
+        @vertex.incoming_edges.each do |e|
+          e.origin.outgoing_edges << e
+        end
+      end
+
+      # @!group DetachVertexNamed
+
+      # @return [String] the name of the vertex to detach
+      attr_reader :name
+
+      # Initialize an action to detach a vertex from a dependency graph
+      # @param [String] name the name of the vertex to detach
+      def initialize(name)
+        @name = name
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
new file mode 100644
index 0000000000..874c4480e3
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
@@ -0,0 +1,114 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular'
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex'
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/detach_vertex_named'
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload'
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag'
+
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # A log for dependency graph actions
+    class Log
+      # Initializes an empty log
+      def initialize
+        @current_action = @first_action = nil
+      end
+
+      # @!macro [new] action
+      #   {include:DependencyGraph#$0}
+      #   @param [Graph] graph the graph to perform the action on
+      #   @param (see DependencyGraph#$0)
+      #   @return (see DependencyGraph#$0)
+
+      # @macro action
+      def tag(graph, tag)
+        push_action(graph, Tag.new(tag))
+      end
+
+      # @macro action
+      def add_vertex(graph, name, payload, root)
+        push_action(graph, AddVertex.new(name, payload, root))
+      end
+
+      # @macro action
+      def detach_vertex_named(graph, name)
+        push_action(graph, DetachVertexNamed.new(name))
+      end
+
+      # @macro action
+      def add_edge_no_circular(graph, origin, destination, requirement)
+        push_action(graph, AddEdgeNoCircular.new(origin, destination, requirement))
+      end
+
+      # @macro action
+      def set_payload(graph, name, payload)
+        push_action(graph, SetPayload.new(name, payload))
+      end
+
+      # Pops the most recent action from the log and undoes the action
+      # @param [DependencyGraph] graph
+      # @return [Action] the action that was popped off the log
+      def pop!(graph)
+        return unless action = @current_action
+        unless @current_action = action.previous
+          @first_action = nil
+        end
+        action.down(graph)
+        action
+      end
+
+      extend Enumerable
+
+      # @!visibility private
+      # Enumerates each action in the log
+      # @yield [Action]
+      def each
+        return enum_for unless block_given?
+        action = @first_action
+        loop do
+          break unless action
+          yield action
+          action = action.next
+        end
+        self
+      end
+
+      # @!visibility private
+      # Enumerates each action in the log in reverse order
+      # @yield [Action]
+      def reverse_each
+        return enum_for(:reverse_each) unless block_given?
+        action = @current_action
+        loop do
+          break unless action
+          yield action
+          action = action.previous
+        end
+        self
+      end
+
+      # @macro action
+      def rewind_to(graph, tag)
+        loop do
+          action = pop!(graph)
+          raise "No tag #{tag.inspect} found" unless action
+          break if action.class.name == :tag && action.tag == tag
+        end
+      end
+
+      private
+
+      # Adds the given action to the log, running the action
+      # @param [DependencyGraph] graph
+      # @param [Action] action
+      # @return The value returned by `action.up`
+      def push_action(graph, action)
+        action.previous = @current_action
+        @current_action.next = action if @current_action
+        @current_action = action
+        @first_action ||= action
+        action.up(graph)
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb
new file mode 100644
index 0000000000..633bc64601
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # @!visibility private
+    # @see DependencyGraph#set_payload
+    class SetPayload < Action # :nodoc:
+      # @!group Action
+
+      # (see Action.name)
+      def self.name
+        :set_payload
+      end
+
+      # (see Action#up)
+      def up(graph)
+        vertex = graph.vertex_named(name)
+        @old_payload = vertex.payload
+        vertex.payload = payload
+      end
+
+      # (see Action#down)
+      def down(graph)
+        graph.vertex_named(name).payload = @old_payload
+      end
+
+      # @!group SetPayload
+
+      # @return [String] the name of the vertex
+      attr_reader :name
+
+      # @return [Object] the payload for the vertex
+      attr_reader :payload
+
+      # Initialize an action to add set the payload for a vertex in a dependency
+      # graph
+      # @param [String] name the name of the vertex
+      # @param [Object] payload the payload for the vertex
+      def initialize(name, payload)
+        @name = name
+        @payload = payload
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
new file mode 100644
index 0000000000..808cd6a3d8
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # @!visibility private
+    # @see DependencyGraph#tag
+    class Tag < Action
+      # @!group Action
+
+      # (see Action.name)
+      def self.name
+        :tag
+      end
+
+      # (see Action#up)
+      def up(_graph)
+      end
+
+      # (see Action#down)
+      def down(_graph)
+      end
+
+      # @!group Tag
+
+      # @return [Object] An opaque tag
+      attr_reader :tag
+
+      # Initialize an action to tag a state of a dependency graph
+      # @param [Object] tag an opaque tag
+      def initialize(tag)
+        @tag = tag
+      end
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb
new file mode 100644
index 0000000000..88d109c94f
--- /dev/null
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb
@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+module Gem::Resolver::Molinillo
+  class DependencyGraph
+    # A vertex in a {DependencyGraph} that encapsulates a {#name} and a
+    # {#payload}
+    class Vertex
+      # @return [String] the name of the vertex
+      attr_accessor :name
+
+      # @return [Object] the payload the vertex holds
+      attr_accessor :payload
+
+      # @return [Arrary<Object>] the explicit requirements that required
+      #   this vertex
+      attr_reader :explicit_requirements
+
+      # @return [Boolean] whether the vertex is considered a root vertex
+      attr_accessor :root
+      alias root? root
+
+      # Initializes a vertex with the given name and payload.
+      # @param [String] name see {#name}
+      # @param [Object] payload see {#payload}
+      def initialize(name, payload)
+        @name = name.frozen? ? name : name.dup.freeze
+        @payload = payload
+        @explicit_requirements = []
+        @outgoing_edges = []
+        @incoming_edges = []
+      end
+
+      # @return [Array<Object>] all of the requirements that required
+      #   this vertex
+      def requirements
+        incoming_edges.map(&:requirement) + explicit_requirements
+      end
+
+      # @return [Array<Edge>] the edges of {#graph} that have `self` as their
+      #   {Edge#origin}
+      attr_accessor :outgoing_edges
+
+      # @return [Array<Edge>] the edges of {#graph} that have `self` as their
+      #   {Edge#destination}
+      attr_accessor :incoming_edges
+
+      # @return [Array<Vertex>] the vertices of {#graph} that have an edge with
+      #   `self` as their {Edge#destination}
+      def predecessors
+        incoming_edges.map(&:origin)
+      end
+
+      # @return [Array<Vertex>] the vertices of {#graph} where `self` is a
+      #   {#descendent?}
+      def recursive_predecessors
+        vertices = predecessors
+        vertices += vertices.map(&:recursive_predecessors).flatten(1)
+        vertices.uniq!
+        vertices
+      end
+
+      # @return [Array<Vertex>] the vertices of {#graph} that have an edge with
+      #   `self` as their {Edge#origin}
+      def successors
+        outgoing_edges.map(&:destination)
+      end
+
+      # @return [Array<Vertex>] the vertices of {#graph} where `self` is an
+      #   {#ancestor?}
+      def recursive_successors
+        vertices = successors
+        vertices += vertices.map(&:recursive_successors).flatten(1)
+        vertices.uniq!
+        vertices
+      end
+
+      # @return [String] a string suitable for debugging
+      def inspect
+        "#{self.class}:#{name}(#{payload.inspect})"
+      end
+
+      # @return [Boolean] whether the two vertices are equal, determined
+      #   by a recursive traversal of each {Vertex#successors}
+      def ==(other)
+        shallow_eql?(other) &&
+          successors.to_set == other.successors.to_set
+      end
+
+      # @param  [Vertex] other the other vertex to compare to
+      # @return [Boolean] whether the two vertices are equal, determined
+      #   solely by {#name} and {#payload} equality
+      def shallow_eql?(other)
+        other &&
+          name == other.name &&
+          payload == other.payload
+      end
+
+      alias eql? ==
+
+      # @return [Fixnum] a hash for the vertex based upon its {#name}
+      def hash
+        name.hash
+      end
+
+      # Is there a path from `self` to `other` following edges in the
+      # dependency graph?
+      # @return true iff there is a path following edges within this {#graph}
+      def path_to?(other)
+        equal?(other) || successors.any? { |v| v.path_to?(other) }
+      end
+
+      alias descendent? path_to?
+
+      # Is there a path from `other` to `self` following edges in the
+      # dependency graph?
+      # @return true iff there is a path following edges within this {#graph}
+      def ancestor?(other)
+        other.path_to?(self)
+      end
+
+      alias is_reachable_from? ancestor?
+    end
+  end
+end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
index 3fad948392..129246bf4a 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
@@ -26,7 +26,7 @@ module Gem::Resolver::Molinillo
     def message
       sources = required_by.map { |r| "`#{r}`" }.join(' and ')
       message = "Unable to find a specification for `#{dependency}`"
-      message << " depended upon by #{sources}" unless sources.empty?
+      message += " depended upon by #{sources}" unless sources.empty?
       message
     end
   end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb
index 1b66500f0f..1a82da0e7a 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 module Gem::Resolver::Molinillo
   # The version of Gem::Resolver::Molinillo.
-  VERSION = '0.4.3'.freeze
+  VERSION = '0.5.0'.freeze
 end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
index 2fc18843fe..1fb7a1e921 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
@@ -52,6 +52,7 @@ module Gem::Resolver::Molinillo
         @base = base
         @states = []
         @iteration_counter = 0
+        @parent_of = {}
       end
 
       # Resolves the {#original_requested} dependencies into a full dependency
@@ -67,7 +68,12 @@ module Gem::Resolver::Molinillo
           indicate_progress
           if state.respond_to?(:pop_possibility_state) # DependencyState
             debug(depth) { "Creating possibility state for #{requirement} (#{possibilities.count} remaining)" }
-            state.pop_possibility_state.tap { |s| states.push(s) if s }
+            state.pop_possibility_state.tap do |s|
+              if s
+                states.push(s)
+                activated.tag(s)
+              end
+            end
           end
           process_topmost_state
         end
@@ -118,27 +124,11 @@ module Gem::Resolver::Molinillo
       require 'rubygems/resolver/molinillo/lib/molinillo/state'
       require 'rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider'
 
-      ResolutionState.new.members.each do |member|
-        define_method member do |*args, &block|
-          current_state = state || ResolutionState.empty
-          current_state.send(member, *args, &block)
-        end
-      end
+      require 'rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state'
+      require 'rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider'
 
-      SpecificationProvider.instance_methods(false).each do |instance_method|
-        define_method instance_method do |*args, &block|
-          begin
-            specification_provider.send(instance_method, *args, &block)
-          rescue NoSuchDependencyError => error
-            if state
-              vertex = activated.vertex_named(name_for error.dependency)
-              error.required_by += vertex.incoming_edges.map { |e| e.origin.name }
-              error.required_by << name_for_explicit_dependency_source unless vertex.explicit_requirements.empty?
-            end
-            raise
-          end
-        end
-      end
+      include Gem::Resolver::Molinillo::Delegates::ResolutionState
+      include Gem::Resolver::Molinillo::Delegates::SpecificationProvider
 
       # Processes the topmost available {RequirementState} on the stack
       # @return [void]
@@ -169,6 +159,7 @@ module Gem::Resolver::Molinillo
       def initial_state
         graph = DependencyGraph.new.tap do |dg|
           original_requested.each { |r| dg.add_vertex(name_for(r), nil, true).tap { |v| v.explicit_requirements << r } }
+          dg.tag(:initial_state)
         end
 
         requirements = sort_dependencies(original_requested, graph, {})
@@ -189,8 +180,9 @@ module Gem::Resolver::Molinillo
       def unwind_for_conflict
         debug(depth) { "Unwinding for conflict: #{requirement}" }
         conflicts.tap do |c|
-          states.slice!((state_index_for_unwind + 1)..-1)
+          sliced_states = states.slice!((state_index_for_unwind + 1)..-1)
           raise VersionConflict.new(c) unless state
+          activated.rewind_to(sliced_states.first || :initial_state) if sliced_states
           state.conflicts = c
         end
       end
@@ -217,20 +209,14 @@ module Gem::Resolver::Molinillo
       # @return [Object] the requirement that led to `requirement` being added
       #   to the list of requirements.
       def parent_of(requirement)
-        return nil unless requirement
-        seen = false
-        state = states.reverse_each.find do |s|
-          seen ||= s.requirement == requirement || s.requirements.include?(requirement)
-          seen && s.requirement != requirement && !s.requirements.include?(requirement)
-        end
-        state && state.requirement
+        @parent_of[requirement]
       end
 
       # @return [Object] the requirement that led to a version of a possibility
       #   with the given name being activated.
       def requirement_for_existing_name(name)
         return nil unless activated.vertex_named(name).payload
-        states.reverse_each.find { |s| !s.activated.vertex_named(name).payload }.requirement
+        states.find { |s| s.name == name }.requirement
       end
 
       # @return [ResolutionState] the state whose `requirement` is the given
@@ -250,19 +236,25 @@ module Gem::Resolver::Molinillo
       #   the {#possibility} in conjunction with the current {#state}
       def create_conflict
         vertex = activated.vertex_named(name)
-        requirements = {
-          name_for_explicit_dependency_source => vertex.explicit_requirements,
-          name_for_locking_dependency_source => Array(locked_requirement_named(name)),
-        }
+        locked_requirement = locked_requirement_named(name)
+
+        requirements = {}
+        unless vertex.explicit_requirements.empty?
+          requirements[name_for_explicit_dependency_source] = vertex.explicit_requirements
+        end
+        requirements[name_for_locking_dependency_source] = [locked_requirement] if locked_requirement
         vertex.incoming_edges.each { |edge| (requirements[edge.origin.payload] ||= []).unshift(edge.requirement) }
+
+        activated_by_name = {}
+        activated.each { |v| activated_by_name[v.name] = v.payload if v.payload }
         conflicts[name] = Conflict.new(
           requirement,
-          Hash[requirements.select { |_, r| !r.empty? }],
+          requirements,
           vertex.payload,
           possibility,
-          locked_requirement_named(name),
+          locked_requirement,
           requirement_trees,
-          Hash[activated.map { |v| [v.name, v.payload] }.select(&:last)]
+          activated_by_name
         )
       end
 
@@ -341,15 +333,16 @@ module Gem::Resolver::Molinillo
       # spec with the given name
       # @return [Boolean] Whether the possibility was swapped into {#activated}
       def attempt_to_swap_possibility
-        swapped = activated.dup
-        vertex = swapped.vertex_named(name)
-        vertex.payload = possibility
-        return unless vertex.requirements.
-            all? { |r| requirement_satisfied_by?(r, swapped, possibility) }
-        return unless new_spec_satisfied?
-        actual_vertex = activated.vertex_named(name)
-        actual_vertex.payload = possibility
-        fixup_swapped_children(actual_vertex)
+        activated.tag(:swap)
+        vertex = activated.vertex_named(name)
+        activated.set_payload(name, possibility)
+        if !vertex.requirements.
+           all? { |r| requirement_satisfied_by?(r, activated, possibility) } ||
+            !new_spec_satisfied?
+          activated.rewind_to(:swap)
+          return
+        end
+        fixup_swapped_children(vertex)
         activate_spec
       end
 
@@ -363,7 +356,13 @@ module Gem::Resolver::Molinillo
           if !dep_names.include?(succ.name) && !succ.root? && succ.predecessors.to_a == [vertex]
             debug(depth) { "Removing orphaned spec #{succ.name} after swapping #{name}" }
             activated.detach_vertex_named(succ.name)
-            requirements.delete_if { |r| name_for(r) == succ.name }
+
+            all_successor_names = succ.recursive_successors.map(&:name)
+
+            requirements.delete_if do |requirement|
+              requirement_name = name_for(requirement)
+              (requirement_name == succ.name) || all_successor_names.include?(requirement_name)
+            end
           end
         end
       end
@@ -406,8 +405,7 @@ module Gem::Resolver::Molinillo
       def activate_spec
         conflicts.delete(name)
         debug(depth) { 'Activated ' + name + ' at ' + possibility.to_s }
-        vertex = activated.vertex_named(name)
-        vertex.payload = possibility
+        activated.set_payload(name, possibility)
         require_nested_dependencies_for(possibility)
       end
 
@@ -418,19 +416,22 @@ module Gem::Resolver::Molinillo
       def require_nested_dependencies_for(activated_spec)
         nested_dependencies = dependencies_for(activated_spec)
         debug(depth) { "Requiring nested dependencies (#{nested_dependencies.join(', ')})" }
-        nested_dependencies.each { |d| activated.add_child_vertex(name_for(d), nil, [name_for(activated_spec)], d) }
+        nested_dependencies.each do |d|
+          activated.add_child_vertex(name_for(d), nil, [name_for(activated_spec)], d)
+          @parent_of[d] = requirement
+        end
 
-        push_state_for_requirements(requirements + nested_dependencies, nested_dependencies.size > 0)
+        push_state_for_requirements(requirements + nested_dependencies, !nested_dependencies.empty?)
       end
 
       # Pushes a new {DependencyState} that encapsulates both existing and new
       # requirements
       # @param [Array] new_requirements
       # @return [void]
-      def push_state_for_requirements(new_requirements, requires_sort = true, new_activated = activated.dup)
+      def push_state_for_requirements(new_requirements, requires_sort = true, new_activated = activated)
         new_requirements = sort_dependencies(new_requirements.uniq, new_activated, conflicts) if requires_sort
         new_requirement = new_requirements.shift
-        new_name = new_requirement ? name_for(new_requirement) : ''
+        new_name = new_requirement ? name_for(new_requirement) : ''.freeze
         possibilities = new_requirement ? search_for(new_requirement) : []
         handle_missing_or_push_dependency_state DependencyState.new(
           new_name, new_requirements, new_activated,
@@ -451,7 +452,7 @@ module Gem::Resolver::Molinillo
           state.activated.detach_vertex_named(state.name)
           push_state_for_requirements(state.requirements.dup, false, state.activated)
         else
-          states.push state
+          states.push(state).tap { activated.tag(state) }
         end
       end
     end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
index ac25538a5a..c20de98854 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
@@ -36,12 +36,14 @@ module Gem::Resolver::Molinillo
       PossibilityState.new(
         name,
         requirements.dup,
-        activated.dup,
+        activated,
         requirement,
         [possibilities.pop],
         depth + 1,
         conflicts.dup
-      )
+      ).tap do |state|
+        state.activated.tag(state)
+      end
     end
   end
 
-- 
cgit v1.2.3