[rubygems/rubygems] Vendor tsort into rubygems

So that it loads a consistent version of the library and `rubygems` is
never affected by gem activation conflicts related to `tsort`.

Getting CI green required updating one `bundler` spec, because `tsort`
is no longer loaded by `bundle clean` until after `BUNDLE_PATH` has been
changed, so to ensure it is found, it needs to be installed under
`BUNDLE_PATH` as well (which will be different from the global system
path on Bundler 3, meaning installing `tsort` to the global system path
is not enough there). This spec workaround can be removed once we also
vendor `tsort` inside `bundler`.

https://github.com/rubygems/rubygems/commit/d326880999

lib/rubygems/dependency_list.rb

@@ -5,7 +5,7 @@
 # See LICENSE.txt for permissions.
 #++
 
-require 'tsort'
+require_relative 'tsort'
 require_relative 'deprecate'
 
 ##
@@ -20,7 +20,7 @@ class Gem::DependencyList
   attr_reader :specs
 
   include Enumerable
-  include TSort
+  include Gem::TSort
 
   ##
   # Allows enabling/disabling use of development dependencies

lib/rubygems/request_set.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
-require 'tsort'
+require_relative 'tsort'
 
 ##
 # A RequestSet groups a request to activate a set of dependencies.
@@ -15,7 +15,7 @@ require 'tsort'
 #   #=> ["nokogiri-1.6.0", "mini_portile-0.5.1", "pg-0.17.0"]
 
 class Gem::RequestSet
-  include TSort
+  include Gem::TSort
 
   ##
   # Array of gems to install even if already installed

lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'tsort'
+require_relative '../../../../tsort'
 
 require_relative 'dependency_graph/log'
 require_relative 'dependency_graph/vertex'
@@ -17,7 +17,7 @@ module Gem::Resolver::Molinillo
       vertices.values.each { |v| yield v }
     end
 
-    include TSort
+    include Gem::TSort
 
     # @!visibility private
     alias tsort_each_node each

lib/rubygems/tsort.rb

@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+require_relative 'tsort/lib/tsort'

lib/rubygems/tsort/lib/tsort.rb

@@ -0,0 +1,454 @@
+# frozen_string_literal: true
+
+#--
+# tsort.rb - provides a module for topological sorting and strongly connected components.
+#++
+#
+
+#
+# Gem::TSort implements topological sorting using Tarjan's algorithm for
+# strongly connected components.
+#
+# Gem::TSort is designed to be able to be used with any object which can be
+# interpreted as a directed graph.
+#
+# Gem::TSort requires two methods to interpret an object as a graph,
+# tsort_each_node and tsort_each_child.
+#
+# * tsort_each_node is used to iterate for all nodes over a graph.
+# * tsort_each_child is used to iterate for child nodes of a given node.
+#
+# The equality of nodes are defined by eql? and hash since
+# Gem::TSort uses Hash internally.
+#
+# == A Simple Example
+#
+# The following example demonstrates how to mix the Gem::TSort module into an
+# existing class (in this case, Hash). Here, we're treating each key in
+# the hash as a node in the graph, and so we simply alias the required
+# #tsort_each_node method to Hash's #each_key method. For each key in the
+# hash, the associated value is an array of the node's child nodes. This
+# choice in turn leads to our implementation of the required #tsort_each_child
+# method, which fetches the array of child nodes and then iterates over that
+# array using the user-supplied block.
+#
+#   require 'rubygems/tsort/lib/tsort'
+#
+#   class Hash
+#     include Gem::TSort
+#     alias tsort_each_node each_key
+#     def tsort_each_child(node, &block)
+#       fetch(node).each(&block)
+#     end
+#   end
+#
+#   {1=>[2, 3], 2=>[3], 3=>[], 4=>[]}.tsort
+#   #=> [3, 2, 1, 4]
+#
+#   {1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}.strongly_connected_components
+#   #=> [[4], [2, 3], [1]]
+#
+# == A More Realistic Example
+#
+# A very simple `make' like tool can be implemented as follows:
+#
+#   require 'rubygems/tsort/lib/tsort'
+#
+#   class Make
+#     def initialize
+#       @dep = {}
+#       @dep.default = []
+#     end
+#
+#     def rule(outputs, inputs=[], &block)
+#       triple = [outputs, inputs, block]
+#       outputs.each {|f| @dep[f] = [triple]}
+#       @dep[triple] = inputs
+#     end
+#
+#     def build(target)
+#       each_strongly_connected_component_from(target) {|ns|
+#         if ns.length != 1
+#           fs = ns.delete_if {|n| Array === n}
+#           raise Gem::TSort::Cyclic.new("cyclic dependencies: #{fs.join ', '}")
+#         end
+#         n = ns.first
+#         if Array === n
+#           outputs, inputs, block = n
+#           inputs_time = inputs.map {|f| File.mtime f}.max
+#           begin
+#             outputs_time = outputs.map {|f| File.mtime f}.min
+#           rescue Errno::ENOENT
+#             outputs_time = nil
+#           end
+#           if outputs_time == nil ||
+#              inputs_time != nil && outputs_time <= inputs_time
+#             sleep 1 if inputs_time != nil && inputs_time.to_i == Time.now.to_i
+#             block.call
+#           end
+#         end
+#       }
+#     end
+#
+#     def tsort_each_child(node, &block)
+#       @dep[node].each(&block)
+#     end
+#     include Gem::TSort
+#   end
+#
+#   def command(arg)
+#     print arg, "\n"
+#     system arg
+#   end
+#
+#   m = Make.new
+#   m.rule(%w[t1]) { command 'date > t1' }
+#   m.rule(%w[t2]) { command 'date > t2' }
+#   m.rule(%w[t3]) { command 'date > t3' }
+#   m.rule(%w[t4], %w[t1 t3]) { command 'cat t1 t3 > t4' }
+#   m.rule(%w[t5], %w[t4 t2]) { command 'cat t4 t2 > t5' }
+#   m.build('t5')
+#
+# == Bugs
+#
+# * 'tsort.rb' is wrong name because this library uses
+#   Tarjan's algorithm for strongly connected components.
+#   Although 'strongly_connected_components.rb' is correct but too long.
+#
+# == References
+#
+# R. E. Tarjan, "Depth First Search and Linear Graph Algorithms",
+# <em>SIAM Journal on Computing</em>, Vol. 1, No. 2, pp. 146-160, June 1972.
+#
+
+module Gem
+  module TSort
+    class Cyclic < StandardError
+    end
+
+    # Returns a topologically sorted array of nodes.
+    # The array is sorted from children to parents, i.e.
+    # the first element has no child and the last node has no parent.
+    #
+    # If there is a cycle, Gem::TSort::Cyclic is raised.
+    #
+    #   class G
+    #     include Gem::TSort
+    #     def initialize(g)
+    #       @g = g
+    #     end
+    #     def tsort_each_child(n, &b) @g[n].each(&b) end
+    #     def tsort_each_node(&b) @g.each_key(&b) end
+    #   end
+    #
+    #   graph = G.new({1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]})
+    #   p graph.tsort #=> [4, 2, 3, 1]
+    #
+    #   graph = G.new({1=>[2], 2=>[3, 4], 3=>[2], 4=>[]})
+    #   p graph.tsort # raises Gem::TSort::Cyclic
+    #
+    def tsort
+      each_node = method(:tsort_each_node)
+      each_child = method(:tsort_each_child)
+      Gem::TSort.tsort(each_node, each_child)
+    end
+
+    # Returns a topologically sorted array of nodes.
+    # The array is sorted from children to parents, i.e.
+    # the first element has no child and the last node has no parent.
+    #
+    # The graph is represented by _each_node_ and _each_child_.
+    # _each_node_ should have +call+ method which yields for each node in the graph.
+    # _each_child_ should have +call+ method which takes a node argument and yields for each child node.
+    #
+    # If there is a cycle, Gem::TSort::Cyclic is raised.
+    #
+    #   g = {1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   p Gem::TSort.tsort(each_node, each_child) #=> [4, 2, 3, 1]
+    #
+    #   g = {1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   p Gem::TSort.tsort(each_node, each_child) # raises Gem::TSort::Cyclic
+    #
+    def TSort.tsort(each_node, each_child)
+      Gem::TSort.tsort_each(each_node, each_child).to_a
+    end
+
+    # The iterator version of the #tsort method.
+    # <tt><em>obj</em>.tsort_each</tt> is similar to <tt><em>obj</em>.tsort.each</tt>, but
+    # modification of _obj_ during the iteration may lead to unexpected results.
+    #
+    # #tsort_each returns +nil+.
+    # If there is a cycle, Gem::TSort::Cyclic is raised.
+    #
+    #   class G
+    #     include Gem::TSort
+    #     def initialize(g)
+    #       @g = g
+    #     end
+    #     def tsort_each_child(n, &b) @g[n].each(&b) end
+    #     def tsort_each_node(&b) @g.each_key(&b) end
+    #   end
+    #
+    #   graph = G.new({1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]})
+    #   graph.tsort_each {|n| p n }
+    #   #=> 4
+    #   #   2
+    #   #   3
+    #   #   1
+    #
+    def tsort_each(&block) # :yields: node
+      each_node = method(:tsort_each_node)
+      each_child = method(:tsort_each_child)
+      Gem::TSort.tsort_each(each_node, each_child, &block)
+    end
+
+    # The iterator version of the Gem::TSort.tsort method.
+    #
+    # The graph is represented by _each_node_ and _each_child_.
+    # _each_node_ should have +call+ method which yields for each node in the graph.
+    # _each_child_ should have +call+ method which takes a node argument and yields for each child node.
+    #
+    #   g = {1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   Gem::TSort.tsort_each(each_node, each_child) {|n| p n }
+    #   #=> 4
+    #   #   2
+    #   #   3
+    #   #   1
+    #
+    def TSort.tsort_each(each_node, each_child) # :yields: node
+      return to_enum(__method__, each_node, each_child) unless block_given?
+
+      Gem::TSort.each_strongly_connected_component(each_node, each_child) {|component|
+        if component.size == 1
+          yield component.first
+        else
+          raise Cyclic.new("topological sort failed: #{component.inspect}")
+        end
+      }
+    end
+
+    # Returns strongly connected components as an array of arrays of nodes.
+    # The array is sorted from children to parents.
+    # Each elements of the array represents a strongly connected component.
+    #
+    #   class G
+    #     include Gem::TSort
+    #     def initialize(g)
+    #       @g = g
+    #     end
+    #     def tsort_each_child(n, &b) @g[n].each(&b) end
+    #     def tsort_each_node(&b) @g.each_key(&b) end
+    #   end
+    #
+    #   graph = G.new({1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]})
+    #   p graph.strongly_connected_components #=> [[4], [2], [3], [1]]
+    #
+    #   graph = G.new({1=>[2], 2=>[3, 4], 3=>[2], 4=>[]})
+    #   p graph.strongly_connected_components #=> [[4], [2, 3], [1]]
+    #
+    def strongly_connected_components
+      each_node = method(:tsort_each_node)
+      each_child = method(:tsort_each_child)
+      Gem::TSort.strongly_connected_components(each_node, each_child)
+    end
+
+    # Returns strongly connected components as an array of arrays of nodes.
+    # The array is sorted from children to parents.
+    # Each elements of the array represents a strongly connected component.
+    #
+    # The graph is represented by _each_node_ and _each_child_.
+    # _each_node_ should have +call+ method which yields for each node in the graph.
+    # _each_child_ should have +call+ method which takes a node argument and yields for each child node.
+    #
+    #   g = {1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   p Gem::TSort.strongly_connected_components(each_node, each_child)
+    #   #=> [[4], [2], [3], [1]]
+    #
+    #   g = {1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   p Gem::TSort.strongly_connected_components(each_node, each_child)
+    #   #=> [[4], [2, 3], [1]]
+    #
+    def TSort.strongly_connected_components(each_node, each_child)
+      Gem::TSort.each_strongly_connected_component(each_node, each_child).to_a
+    end
+
+    # The iterator version of the #strongly_connected_components method.
+    # <tt><em>obj</em>.each_strongly_connected_component</tt> is similar to
+    # <tt><em>obj</em>.strongly_connected_components.each</tt>, but
+    # modification of _obj_ during the iteration may lead to unexpected results.
+    #
+    # #each_strongly_connected_component returns +nil+.
+    #
+    #   class G
+    #     include Gem::TSort
+    #     def initialize(g)
+    #       @g = g
+    #     end
+    #     def tsort_each_child(n, &b) @g[n].each(&b) end
+    #     def tsort_each_node(&b) @g.each_key(&b) end
+    #   end
+    #
+    #   graph = G.new({1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]})
+    #   graph.each_strongly_connected_component {|scc| p scc }
+    #   #=> [4]
+    #   #   [2]
+    #   #   [3]
+    #   #   [1]
+    #
+    #   graph = G.new({1=>[2], 2=>[3, 4], 3=>[2], 4=>[]})
+    #   graph.each_strongly_connected_component {|scc| p scc }
+    #   #=> [4]
+    #   #   [2, 3]
+    #   #   [1]
+    #
+    def each_strongly_connected_component(&block) # :yields: nodes
+      each_node = method(:tsort_each_node)
+      each_child = method(:tsort_each_child)
+      Gem::TSort.each_strongly_connected_component(each_node, each_child, &block)
+    end
+
+    # The iterator version of the Gem::TSort.strongly_connected_components method.
+    #
+    # The graph is represented by _each_node_ and _each_child_.
+    # _each_node_ should have +call+ method which yields for each node in the graph.
+    # _each_child_ should have +call+ method which takes a node argument and yields for each child node.
+    #
+    #   g = {1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   Gem::TSort.each_strongly_connected_component(each_node, each_child) {|scc| p scc }
+    #   #=> [4]
+    #   #   [2]
+    #   #   [3]
+    #   #   [1]
+    #
+    #   g = {1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}
+    #   each_node = lambda {|&b| g.each_key(&b) }
+    #   each_child = lambda {|n, &b| g[n].each(&b) }
+    #   Gem::TSort.each_strongly_connected_component(each_node, each_child) {|scc| p scc }
+    #   #=> [4]
+    #   #   [2, 3]
+    #   #   [1]
+    #
+    def TSort.each_strongly_connected_component(each_node, each_child) # :yields: nodes
+      return to_enum(__method__, each_node, each_child) unless block_given?
+
+      id_map = {}
+      stack = []
+      each_node.call {|node|
+        unless id_map.include? node
+          Gem::TSort.each_strongly_connected_component_from(node, each_child, id_map, stack) {|c|
+            yield c
+          }
+        end
+      }
+      nil
+    end
+
+    # Iterates over strongly connected component in the subgraph reachable from
+    # _node_.
+    #
+    # Return value is unspecified.
+    #
+    # #each_strongly_connected_component_from doesn't call #tsort_each_node.
+    #
+    #   class G
+    #     include Gem::TSort
+    #     def initialize(g)
+    #       @g = g
+    #     end
+    #     def tsort_each_child(n, &b) @g[n].each(&b) end
+    #     def tsort_each_node(&b) @g.each_key(&b) end
+    #   end
+    #
+    #   graph = G.new({1=>[2, 3], 2=>[4], 3=>[2, 4], 4=>[]})
+    #   graph.each_strongly_connected_component_from(2) {|scc| p scc }
+    #   #=> [4]
+    #   #   [2]
+    #
+    #   graph = G.new({1=>[2], 2=>[3, 4], 3=>[2], 4=>[]})
+    #   graph.each_strongly_connected_component_from(2) {|scc| p scc }
+    #   #=> [4]
+    #   #   [2, 3]
+    #
+    def each_strongly_connected_component_from(node, id_map={}, stack=[], &block) # :yields: nodes
+      Gem::TSort.each_strongly_connected_component_from(node, method(:tsort_each_child), id_map, stack, &block)
+    end
+
+    # Iterates over strongly connected components in a graph.
+    # The graph is represented by _node_ and _each_child_.
+    #
+    # _node_ is the first node.
+    # _each_child_ should have +call+ method which takes a node argument
+    # and yields for each child node.
+    #
+    # Return value is unspecified.
+    #
+    # #Gem::TSort.each_strongly_connected_component_from is a class method and
+    # it doesn't need a class to represent a graph which includes Gem::TSort.
+    #
+    #   graph = {1=>[2], 2=>[3, 4], 3=>[2], 4=>[]}
+    #   each_child = lambda {|n, &b| graph[n].each(&b) }
+    #   Gem::TSort.each_strongly_connected_component_from(1, each_child) {|scc|
+    #     p scc
+    #   }
+    #   #=> [4]
+    #   #   [2, 3]
+    #   #   [1]
+    #
+    def TSort.each_strongly_connected_component_from(node, each_child, id_map={}, stack=[]) # :yields: nodes
+      return to_enum(__method__, node, each_child, id_map, stack) unless block_given?
+
+      minimum_id = node_id = id_map[node] = id_map.size
+      stack_length = stack.length
+      stack << node
+
+      each_child.call(node) {|child|
+        if id_map.include? child
+          child_id = id_map[child]
+          minimum_id = child_id if child_id && child_id < minimum_id
+        else
+          sub_minimum_id =
+            Gem::TSort.each_strongly_connected_component_from(child, each_child, id_map, stack) {|c|
+              yield c
+            }
+          minimum_id = sub_minimum_id if sub_minimum_id < minimum_id
+        end
+      }
+
+      if node_id == minimum_id
+        component = stack.slice!(stack_length .. -1)
+        component.each {|n| id_map[n] = nil}
+        yield component
+      end
+
+      minimum_id
+    end
+
+    # Should be implemented by a extended class.
+    #
+    # #tsort_each_node is used to iterate for all nodes over a graph.
+    #
+    def tsort_each_node # :yields: node
+      raise NotImplementedError.new
+    end
+
+    # Should be implemented by a extended class.
+    #
+    # #tsort_each_child is used to iterate for child nodes of _node_.
+    #
+    def tsort_each_child(node) # :yields: child
+      raise NotImplementedError.new
+    end
+  end
+end