Merge prepare version of RubyGems 3.2.0

83 files changed, 1124 insertions, 511 deletions

diff --git a/lib/rubygems/available_set.rb b/lib/rubygems/available_set.rb
index 80ef29df64..499483d9e9 100644
--- a/lib/rubygems/available_set.rb
+++ b/lib/rubygems/available_set.rb
@@ -73,7 +73,7 @@ class Gem::AvailableSet
   end
 
   def match_platform!
-    @set.reject! {|t| !Gem::Platform.match(t.spec.platform) }
+    @set.reject! {|t| !Gem::Platform.match_spec?(t.spec) }
     @sorted = nil
     self
   end
diff --git a/lib/rubygems/command_manager.rb b/lib/rubygems/command_manager.rb
index 1dcb577f7e..97e52544ca 100644
--- a/lib/rubygems/command_manager.rb
+++ b/lib/rubygems/command_manager.rb
@@ -73,7 +73,7 @@ class Gem::CommandManager
   ].freeze
 
   ALIAS_COMMANDS = {
-    'i' => 'install'
+    'i' => 'install',
   }.freeze
 
   ##
@@ -174,8 +174,8 @@ class Gem::CommandManager
     else
       cmd_name = args.shift.downcase
       cmd = find_command cmd_name
-      cmd.invoke_with_build_args args, build_args
       cmd.deprecation_warning if cmd.deprecated?
+      cmd.invoke_with_build_args args, build_args
     end
   end
 
diff --git a/lib/rubygems/commands/build_command.rb b/lib/rubygems/commands/build_command.rb
index eaf8573d8f..fff5f7c76f 100644
--- a/lib/rubygems/commands/build_command.rb
+++ b/lib/rubygems/commands/build_command.rb
@@ -61,14 +61,18 @@ Gems can be saved to a specified filename with the output option:
   end
 
   def execute
-    gem_name = get_one_optional_argument || find_gemspec
-    build_gem(gem_name)
+    if build_path = options[:build_path]
+      Dir.chdir(build_path) { build_gem }
+      return
+    end
+
+    build_gem
   end
 
   private
 
-  def find_gemspec
-    gemspecs = Dir.glob("*.gemspec").sort
+  def find_gemspec(glob = "*.gemspec")
+    gemspecs = Dir.glob(glob).sort
 
     if gemspecs.size > 1
       alert_error "Multiple gemspecs found: #{gemspecs}, please specify one"
@@ -78,28 +82,19 @@ Gems can be saved to a specified filename with the output option:
     gemspecs.first
   end
 
-  def build_gem(gem_name)
-    gemspec = File.exist?(gem_name) ? gem_name : "#{gem_name}.gemspec"
-
-    if File.exist?(gemspec)
-      spec = Gem::Specification.load(gemspec)
-
-      if options[:build_path]
-        Dir.chdir(File.dirname(gemspec)) do
-          spec = Gem::Specification.load(File.basename(gemspec))
-          build_package(spec)
-        end
-      else
-        build_package(spec)
-      end
+  def build_gem
+    gemspec = resolve_gem_name
 
+    if gemspec
+      build_package(gemspec)
     else
-      alert_error "Gemspec file not found: #{gemspec}"
+      alert_error error_message
       terminate_interaction(1)
     end
   end
 
-  def build_package(spec)
+  def build_package(gemspec)
+    spec = Gem::Specification.load(gemspec)
     if spec
       Gem::Package.build(
         spec,
@@ -112,4 +107,26 @@ Gems can be saved to a specified filename with the output option:
       terminate_interaction 1
     end
   end
+
+  def resolve_gem_name
+    return find_gemspec unless gem_name
+
+    if File.exist?(gem_name)
+      gem_name
+    else
+      find_gemspec("#{gem_name}.gemspec") || find_gemspec(gem_name)
+    end
+  end
+
+  def error_message
+    if gem_name
+      "Couldn't find a gemspec file matching '#{gem_name}' in #{Dir.pwd}"
+    else
+      "Couldn't find a gemspec file in #{Dir.pwd}"
+    end
+  end
+
+  def gem_name
+    get_one_optional_argument
+  end
 end
diff --git a/lib/rubygems/commands/cert_command.rb b/lib/rubygems/commands/cert_command.rb
index e5355d3652..998df0621b 100644
--- a/lib/rubygems/commands/cert_command.rb
+++ b/lib/rubygems/commands/cert_command.rb
@@ -311,4 +311,4 @@ For further reading on signing gems see `ri Gem::Security`.
     # It's simple, but is all we need
     email =~ /\A.+@.+\z/
   end
-end if defined?(OpenSSL::SSL)
+end if Gem::HAVE_OPENSSL
diff --git a/lib/rubygems/commands/help_command.rb b/lib/rubygems/commands/help_command.rb
index 9ba8bf1293..4e8d7600fb 100644
--- a/lib/rubygems/commands/help_command.rb
+++ b/lib/rubygems/commands/help_command.rb
@@ -332,6 +332,8 @@ platform.
     @command_manager.command_names.each do |cmd_name|
       command = @command_manager[cmd_name]
 
+      next if command.deprecated?
+
       summary =
         if command
           command.summary
diff --git a/lib/rubygems/commands/owner_command.rb b/lib/rubygems/commands/owner_command.rb
index 0f01823967..46172854cf 100644
--- a/lib/rubygems/commands/owner_command.rb
+++ b/lib/rubygems/commands/owner_command.rb
@@ -53,7 +53,7 @@ permission to.
   def execute
     @host = options[:host]
 
-    sign_in
+    sign_in(scope: get_owner_scope)
     name = get_one_gem_name
 
     add_owners    name, options[:add]
@@ -102,10 +102,18 @@ permission to.
   private
 
   def send_owner_request(method, name, owner)
-    rubygems_api_request method, "api/v1/gems/#{name}/owners" do |request|
+    rubygems_api_request method, "api/v1/gems/#{name}/owners", scope: get_owner_scope(method: method) do |request|
       request.set_form_data 'email' => owner
       request.add_field "Authorization", api_key
       request.add_field "OTP", options[:otp] if options[:otp]
     end
   end
+
+  def get_owner_scope(method: nil)
+    if method == :post || options.any? && options[:add].any?
+      :add_owner
+    elsif method == :delete || options.any? && options[:remove].any?
+      :remove_owner
+    end
+  end
 end
diff --git a/lib/rubygems/commands/pristine_command.rb b/lib/rubygems/commands/pristine_command.rb
index db8136c9a6..143105981e 100644
--- a/lib/rubygems/commands/pristine_command.rb
+++ b/lib/rubygems/commands/pristine_command.rb
@@ -170,7 +170,7 @@ extensions will be restored.
         :install_dir => spec.base_dir,
         :env_shebang => env_shebang,
         :build_args => spec.build_args,
-        :bin_dir => bin_dir
+        :bin_dir => bin_dir,
       }
 
       if options[:only_executables]
diff --git a/lib/rubygems/commands/push_command.rb b/lib/rubygems/commands/push_command.rb
index 003b2dacc7..8885269ecb 100644
--- a/lib/rubygems/commands/push_command.rb
+++ b/lib/rubygems/commands/push_command.rb
@@ -61,7 +61,7 @@ The push command will use ~/.gem/credentials to authenticate to a server, but yo
               options[:host]
             end
 
-    sign_in @host
+    sign_in @host, scope: get_push_scope
 
     send_gem(gem_name)
   end
@@ -86,7 +86,7 @@ The push command will use ~/.gem/credentials to authenticate to a server, but yo
   private
 
   def send_push_request(name, args)
-    rubygems_api_request(*args) do |request|
+    rubygems_api_request(*args, scope: get_push_scope) do |request|
       request.body = Gem.read_binary name
       request.add_field "Content-Length", request.body.size
       request.add_field "Content-Type",   "application/octet-stream"
@@ -100,7 +100,11 @@ The push command will use ~/.gem/credentials to authenticate to a server, but yo
 
     [
       gem_metadata["default_gem_server"],
-      gem_metadata["allowed_push_host"]
+      gem_metadata["allowed_push_host"],
     ]
   end
+
+  def get_push_scope
+    :push_rubygem
+  end
 end
diff --git a/lib/rubygems/commands/query_command.rb b/lib/rubygems/commands/query_command.rb
index 406a34e549..789afd6509 100644
--- a/lib/rubygems/commands/query_command.rb
+++ b/lib/rubygems/commands/query_command.rb
@@ -9,6 +9,14 @@ class Gem::Commands::QueryCommand < Gem::Command
 
   include Gem::QueryUtils
 
+  alias warning_without_suggested_alternatives deprecation_warning
+  def deprecation_warning
+    warning_without_suggested_alternatives
+
+    message = "It is recommended that you use `gem search` or `gem list` instead.\n"
+    alert_warning message unless Gem::Deprecate.skip
+  end
+
   def initialize(name = 'query',
                  summary = 'Query gem information in local or remote repositories')
     super name, summary,
@@ -23,4 +31,13 @@ class Gem::Commands::QueryCommand < Gem::Command
 
     add_query_options
   end
+
+  def description # :nodoc:
+    <<-EOF
+The query command is the basis for the list and search commands.
+
+You should really use the list and search commands instead.  This command
+is too hard to use.
+    EOF
+  end
 end
diff --git a/lib/rubygems/commands/server_command.rb b/lib/rubygems/commands/server_command.rb
index 91d5e267f8..594cf77f66 100644
--- a/lib/rubygems/commands/server_command.rb
+++ b/lib/rubygems/commands/server_command.rb
@@ -1,8 +1,12 @@
 # frozen_string_literal: true
 require 'rubygems/command'
 require 'rubygems/server'
+require 'rubygems/deprecate'
 
 class Gem::Commands::ServerCommand < Gem::Command
+  extend Gem::Deprecate
+  rubygems_deprecate_command
+
   def initialize
     super 'server', 'Documentation and gem repository HTTP server',
           :port => 8808, :gemdir => [], :daemon => false
diff --git a/lib/rubygems/commands/setup_command.rb b/lib/rubygems/commands/setup_command.rb
index b63920ab8d..22b1371a1f 100644
--- a/lib/rubygems/commands/setup_command.rb
+++ b/lib/rubygems/commands/setup_command.rb
@@ -322,13 +322,10 @@ By default, this RubyGems will install gem as:
     libs.each do |tool, path|
       say "Installing #{tool}" if @verbose
 
-      lib_files = rb_files_in path
-      lib_files.concat(bundler_template_files) if tool == 'Bundler'
-
-      pem_files = pem_files_in path
+      lib_files = files_in path
 
       Dir.chdir path do
-        install_file_list(lib_files + pem_files, lib_dir)
+        install_file_list(lib_files, lib_dir)
       end
     end
   end
@@ -394,10 +391,6 @@ By default, this RubyGems will install gem as:
     specs_dir = File.join(options[:destdir], specs_dir) unless Gem.win_platform?
     mkdir_p specs_dir, :mode => 0755
 
-    # Workaround for non-git environment.
-    gemspec = File.open('bundler/bundler.gemspec', 'rb'){|f| f.read.gsub(/`git ls-files -z`/, "''") }
-    File.open('bundler/bundler.gemspec', 'w'){|f| f.write gemspec }
-
     bundler_spec = Gem::Specification.load("bundler/bundler.gemspec")
     bundler_spec.files = Dir.chdir("bundler") { Dir["{*.md,{lib,exe,man}/**/*}"] }
     bundler_spec.executables -= %w[bundler bundle_ruby]
@@ -518,44 +511,24 @@ By default, this RubyGems will install gem as:
     [lib_dir, bin_dir]
   end
 
-  def pem_files_in(dir)
-    Dir.chdir dir do
-      Dir[File.join('**', '*pem')]
-    end
-  end
-
-  def rb_files_in(dir)
+  def files_in(dir)
     Dir.chdir dir do
-      Dir[File.join('**', '*rb')]
+      Dir.glob(File.join('**', '*'), File::FNM_DOTMATCH).
+        select{|f| !File.directory?(f) }
     end
   end
 
   # for installation of bundler as default gems
   def bundler_man1_files_in(dir)
     Dir.chdir dir do
-      Dir['bundle*.1{,.txt,.ronn}']
+      Dir['bundle*.1']
     end
   end
 
   # for installation of bundler as default gems
   def bundler_man5_files_in(dir)
     Dir.chdir dir do
-      Dir['gemfile.5{,.txt,.ronn}']
-    end
-  end
-
-  def bundler_template_files
-    Dir.chdir "bundler/lib" do
-      Dir.glob(File.join('bundler', 'templates', '**', '*'), File::FNM_DOTMATCH).
-        select{|f| !File.directory?(f) }
-    end
-  end
-
-  # for cleanup old bundler files
-  def template_files_in(dir)
-    Dir.chdir dir do
-      Dir.glob(File.join('templates', '**', '*'), File::FNM_DOTMATCH).
-        select{|f| !File.directory?(f) }
+      Dir['gemfile.5']
     end
   end
 
@@ -595,11 +568,9 @@ abort "#{deprecation_message}"
     lib_dirs = { File.join(lib_dir, 'rubygems') => 'lib/rubygems' }
     lib_dirs[File.join(lib_dir, 'bundler')] = 'bundler/lib/bundler'
     lib_dirs.each do |old_lib_dir, new_lib_dir|
-      lib_files = rb_files_in(new_lib_dir)
-      lib_files.concat(template_files_in(new_lib_dir)) if new_lib_dir =~ /bundler/
+      lib_files = files_in(new_lib_dir)
 
-      old_lib_files = rb_files_in(old_lib_dir)
-      old_lib_files.concat(template_files_in(old_lib_dir)) if old_lib_dir =~ /bundler/
+      old_lib_files = files_in(old_lib_dir)
 
       to_remove = old_lib_files - lib_files
 
@@ -617,16 +588,25 @@ abort "#{deprecation_message}"
   def remove_old_man_files(man_dir)
     man_dirs = { man_dir => "bundler/man" }
     man_dirs.each do |old_man_dir, new_man_dir|
-      ["1", "5"].each do |section|
-        man_files = send(:"bundler_man#{section}_files_in", new_man_dir)
+      man1_files = bundler_man1_files_in(new_man_dir)
 
-        old_man_dir_with_section = "#{old_man_dir}/man#{section}"
-        old_man_files = send(:"bundler_man#{section}_files_in", old_man_dir_with_section)
+      old_man1_dir = "#{old_man_dir}/man1"
+      old_man1_files = bundler_man1_files_in(old_man1_dir)
+      old_man1_files += Dir.chdir(old_man1_dir) { Dir["bundle*.1.{txt,ronn}"] }
 
-        man_to_remove = old_man_files - man_files
+      man1_to_remove = old_man1_files - man1_files
 
-        remove_file_list(man_to_remove, old_man_dir_with_section)
-      end
+      remove_file_list(man1_to_remove, old_man1_dir)
+
+      man5_files = bundler_man5_files_in(new_man_dir)
+
+      old_man5_dir = "#{old_man_dir}/man5"
+      old_man5_files = bundler_man5_files_in(old_man5_dir)
+      old_man5_files += Dir.chdir(old_man5_dir) { Dir["gemfile.5.{txt,ronn}"] }
+
+      man5_to_remove = old_man5_files - man5_files
+
+      remove_file_list(man5_to_remove, old_man5_dir)
     end
   end
 
diff --git a/lib/rubygems/commands/sources_command.rb b/lib/rubygems/commands/sources_command.rb
index 3be3a5dc79..f74fb12e42 100644
--- a/lib/rubygems/commands/sources_command.rb
+++ b/lib/rubygems/commands/sources_command.rb
@@ -34,6 +34,10 @@ class Gem::Commands::SourcesCommand < Gem::Command
       options[:update] = value
     end
 
+    add_option '-f', '--[no-]force', "Do not show any confirmation prompts and behave as if 'yes' was always answered" do |value, options|
+      options[:force] = value
+    end
+
     add_proxy_option
   end
 
@@ -71,7 +75,7 @@ class Gem::Commands::SourcesCommand < Gem::Command
 Do you want to add this source?
       QUESTION
 
-      terminate_interaction 1 unless ask_yes_no question
+      terminate_interaction 1 unless options[:force] || ask_yes_no(question)
     end
   end
 
@@ -86,7 +90,7 @@ https://rubygems.org is recommended for security over #{uri}
 Do you want to add this insecure source?
       QUESTION
 
-      terminate_interaction 1 unless ask_yes_no question
+      terminate_interaction 1 unless options[:force] || ask_yes_no(question)
     end
   end
 
diff --git a/lib/rubygems/commands/specification_command.rb b/lib/rubygems/commands/specification_command.rb
index e4a8afab21..3fddaaaf30 100644
--- a/lib/rubygems/commands/specification_command.rb
+++ b/lib/rubygems/commands/specification_command.rb
@@ -126,6 +126,12 @@ Specific fields in the specification can be extracted in YAML format:
       terminate_interaction 1
     end
 
+    platform = get_platform_from_requirements(options)
+
+    if platform
+      specs = specs.select{|s| s.platform.to_s == platform }
+    end
+
     unless options[:all]
       specs = [specs.max_by {|s| s.version }]
     end
diff --git a/lib/rubygems/commands/yank_command.rb b/lib/rubygems/commands/yank_command.rb
index 6ad74de96b..0e08bbfd5d 100644
--- a/lib/rubygems/commands/yank_command.rb
+++ b/lib/rubygems/commands/yank_command.rb
@@ -47,7 +47,7 @@ data you will need to change them immediately and yank your gem.
   def execute
     @host = options[:host]
 
-    sign_in @host
+    sign_in @host, scope: get_yank_scope
 
     version   = get_version_from_requirements(options[:version])
     platform  = get_platform_from_requirements(options)
@@ -72,7 +72,7 @@ data you will need to change them immediately and yank your gem.
 
   def yank_api_request(method, version, platform, api)
     name = get_one_gem_name
-    response = rubygems_api_request(method, api, host) do |request|
+    response = rubygems_api_request(method, api, host, scope: get_yank_scope) do |request|
       request.add_field("Authorization", api_key)
       request.add_field("OTP", options[:otp]) if options[:otp]
 
@@ -93,7 +93,7 @@ data you will need to change them immediately and yank your gem.
     nil
   end
 
-  def get_platform_from_requirements(requirements)
-    Gem.platforms[1].to_s if requirements.key? :added_platform
+  def get_yank_scope
+    :yank_rubygem
   end
 end
diff --git a/lib/rubygems/core_ext/kernel_require.rb b/lib/rubygems/core_ext/kernel_require.rb
index edf046651e..4b867c55e9 100644
--- a/lib/rubygems/core_ext/kernel_require.rb
+++ b/lib/rubygems/core_ext/kernel_require.rb
@@ -17,6 +17,8 @@ module Kernel
     private :gem_original_require
   end
 
+  file = Gem::KERNEL_WARN_IGNORES_INTERNAL_ENTRIES ? "<internal:#{__FILE__}>" : __FILE__
+  module_eval <<'RUBY', file, __LINE__ + 1
   ##
   # When RubyGems is required, Kernel#require is replaced with our own which
   # is capable of loading gems on demand.
@@ -166,6 +168,7 @@ module Kernel
       end
     end
   end
+RUBY
 
   private :require
 
diff --git a/lib/rubygems/core_ext/kernel_warn.rb b/lib/rubygems/core_ext/kernel_warn.rb
index e030ef815c..3373cfdd3b 100644
--- a/lib/rubygems/core_ext/kernel_warn.rb
+++ b/lib/rubygems/core_ext/kernel_warn.rb
@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
 # `uplevel` keyword argument of Kernel#warn is available since ruby 2.5.
-if RUBY_VERSION >= "2.5"
+if RUBY_VERSION >= "2.5" && !Gem::KERNEL_WARN_IGNORES_INTERNAL_ENTRIES
 
   module Kernel
     rubygems_path = "#{__dir__}/" # Frames to be skipped start with this path.
 
-    original_warn = method(:warn)
+    original_warn = instance_method(:warn)
 
     remove_method :warn
 
@@ -17,9 +17,9 @@ if RUBY_VERSION >= "2.5"
     module_function define_method(:warn) {|*messages, **kw|
       unless uplevel = kw[:uplevel]
         if Gem.java_platform?
-          return original_warn.call(*messages)
+          return original_warn.bind(self).call(*messages)
         else
-          return original_warn.call(*messages, **kw)
+          return original_warn.bind(self).call(*messages, **kw)
         end
       end
 
@@ -45,11 +45,10 @@ if RUBY_VERSION >= "2.5"
             end
           end
         end
-        uplevel = start
+        kw[:uplevel] = start
       end
 
-      kw[:uplevel] = uplevel
-      original_warn.call(*messages, **kw)
+      original_warn.bind(self).call(*messages, **kw)
     }
   end
 end
diff --git a/lib/rubygems/defaults.rb b/lib/rubygems/defaults.rb
index 2d0b077fdc..8aae67cd6b 100644
--- a/lib/rubygems/defaults.rb
+++ b/lib/rubygems/defaults.rb
@@ -38,13 +38,13 @@ module Gem
              [
                File.dirname(RbConfig::CONFIG['sitedir']),
                'Gems',
-               RbConfig::CONFIG['ruby_version']
+               RbConfig::CONFIG['ruby_version'],
              ]
            else
              [
                RbConfig::CONFIG['rubylibprefix'],
                'gems',
-               RbConfig::CONFIG['ruby_version']
+               RbConfig::CONFIG['ruby_version'],
              ]
            end
 
diff --git a/lib/rubygems/dependency.rb b/lib/rubygems/dependency.rb
index 8634d71a72..68f3e3d991 100644
--- a/lib/rubygems/dependency.rb
+++ b/lib/rubygems/dependency.rb
@@ -281,7 +281,7 @@ class Gem::Dependency
 
     if platform_only
       matches.reject! do |spec|
-        spec.nil? || !Gem::Platform.match(spec.platform)
+        spec.nil? || !Gem::Platform.match_spec?(spec)
       end
     end
 
diff --git a/lib/rubygems/dependency_installer.rb b/lib/rubygems/dependency_installer.rb
index 1afdc4b4c2..fb555a46d4 100644
--- a/lib/rubygems/dependency_installer.rb
+++ b/lib/rubygems/dependency_installer.rb
@@ -27,7 +27,7 @@ class Gem::DependencyInstaller
     :wrappers            => true,
     :build_args          => nil,
     :build_docs_in_background => false,
-    :install_as_default => false
+    :install_as_default => false,
   }.freeze
 
   ##
@@ -283,10 +283,9 @@ class Gem::DependencyInstaller
     request_set.development_shallow = @dev_shallow
     request_set.soft_missing = @force
     request_set.prerelease = @prerelease
-    request_set.remote = false unless consider_remote?
 
     installer_set = Gem::Resolver::InstallerSet.new @domain
-    installer_set.ignore_installed = @only_install_dir
+    installer_set.ignore_installed = (@minimal_deps == false) || @only_install_dir
 
     if consider_local?
       if dep_or_name =~ /\.gem$/ and File.file? dep_or_name
@@ -307,6 +306,7 @@ class Gem::DependencyInstaller
 
     dependency =
       if spec = installer_set.local?(dep_or_name)
+        installer_set.remote = nil if spec.dependencies.none?
         Gem::Dependency.new spec.name, version
       elsif String === dep_or_name
         Gem::Dependency.new dep_or_name, version
@@ -321,6 +321,7 @@ class Gem::DependencyInstaller
     installer_set.add_always_install dependency
 
     request_set.always_install = installer_set.always_install
+    request_set.remote = installer_set.consider_remote?
 
     if @ignore_dependencies
       installer_set.ignore_dependencies = true
diff --git a/lib/rubygems/ext/builder.rb b/lib/rubygems/ext/builder.rb
index afc8cb0ee4..f6de6a50d7 100644
--- a/lib/rubygems/ext/builder.rb
+++ b/lib/rubygems/ext/builder.rb
@@ -10,14 +10,6 @@ require_relative '../user_interaction'
 class Gem::Ext::Builder
   include Gem::UserInteraction
 
-  ##
-  # The builder shells-out to run various commands after changing the
-  # directory.  This means multiple installations cannot be allowed to build
-  # extensions in parallel as they may change each other's directories leading
-  # to broken extensions or failed installations.
-
-  CHDIR_MUTEX = Mutex.new # :nodoc:
-
   attr_accessor :build_args # :nodoc:
 
   def self.class_name
@@ -25,8 +17,8 @@ class Gem::Ext::Builder
     $1.downcase
   end
 
-  def self.make(dest_path, results)
-    unless File.exist? 'Makefile'
+  def self.make(dest_path, results, make_dir = Dir.pwd)
+    unless File.exist? File.join(make_dir, 'Makefile')
       raise Gem::InstallError, 'Makefile not found'
     end
 
@@ -44,32 +36,32 @@ class Gem::Ext::Builder
       cmd = [
         make_program,
         destdir,
-        target
+        target,
       ].join(' ').rstrip
       begin
-        run(cmd, results, "make #{target}".rstrip)
+        run(cmd, results, "make #{target}".rstrip, make_dir)
       rescue Gem::InstallError
         raise unless target == 'clean' # ignore clean failure
       end
     end
   end
 
-  def self.run(command, results, command_name = nil)
+  def self.run(command, results, command_name = nil, dir = Dir.pwd)
     verbose = Gem.configuration.really_verbose
 
     begin
       rubygems_gemdeps, ENV['RUBYGEMS_GEMDEPS'] = ENV['RUBYGEMS_GEMDEPS'], nil
       if verbose
-        puts("current directory: #{Dir.pwd}")
+        puts("current directory: #{dir}")
         p(command)
       end
-      results << "current directory: #{Dir.pwd}"
+      results << "current directory: #{dir}"
       results << (command.respond_to?(:shelljoin) ? command.shelljoin : command)
 
       require "open3"
       # Set $SOURCE_DATE_EPOCH for the subprocess.
       env = {'SOURCE_DATE_EPOCH' => Gem.source_date_epoch_string}
-      output, status = Open3.capture2e(env, *command)
+      output, status = Open3.capture2e(env, *command, :chdir => dir)
       if verbose
         puts output
       else
@@ -161,22 +153,10 @@ EOF
     begin
       FileUtils.mkdir_p dest_path
 
-      CHDIR_MUTEX.synchronize do
-        pwd = Dir.getwd
-        Dir.chdir extension_dir
-        begin
-          results = builder.build(extension, dest_path,
-                                  results, @build_args, lib_dir)
-
-          verbose { results.join("\n") }
-        ensure
-          begin
-            Dir.chdir pwd
-          rescue SystemCallError
-            Dir.chdir dest_path
-          end
-        end
-      end
+      results = builder.build(extension, dest_path,
+                              results, @build_args, lib_dir, extension_dir)
+
+      verbose { results.join("\n") }
 
       write_gem_make_out results.join "\n"
     rescue => e
@@ -201,6 +181,7 @@ EOF
 
     dest_path = @spec.extension_dir
 
+    require "fileutils"
     FileUtils.rm_f @spec.gem_build_complete_path
 
     @spec.extensions.each do |extension|
diff --git a/lib/rubygems/ext/cmake_builder.rb b/lib/rubygems/ext/cmake_builder.rb
index 519372e742..2efec91f15 100644
--- a/lib/rubygems/ext/cmake_builder.rb
+++ b/lib/rubygems/ext/cmake_builder.rb
@@ -2,15 +2,15 @@
 require_relative '../command'
 
 class Gem::Ext::CmakeBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
-    unless File.exist?('Makefile')
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, cmake_dir=Dir.pwd)
+    unless File.exist?(File.join(cmake_dir, 'Makefile'))
       cmd = "cmake . -DCMAKE_INSTALL_PREFIX=#{dest_path}"
       cmd << " #{Gem::Command.build_args.join ' '}" unless Gem::Command.build_args.empty?
 
-      run cmd, results
+      run cmd, results, class_name, cmake_dir
     end
 
-    make dest_path, results
+    make dest_path, results, cmake_dir
 
     results
   end
diff --git a/lib/rubygems/ext/configure_builder.rb b/lib/rubygems/ext/configure_builder.rb
index 209e75fe8e..36a758989b 100644
--- a/lib/rubygems/ext/configure_builder.rb
+++ b/lib/rubygems/ext/configure_builder.rb
@@ -6,15 +6,15 @@
 #++
 
 class Gem::Ext::ConfigureBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
-    unless File.exist?('Makefile')
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, configure_dir=Dir.pwd)
+    unless File.exist?(File.join(configure_dir, 'Makefile'))
       cmd = "sh ./configure --prefix=#{dest_path}"
       cmd << " #{args.join ' '}" unless args.empty?
 
-      run cmd, results
+      run cmd, results, class_name, configure_dir
     end
 
-    make dest_path, results
+    make dest_path, results, configure_dir
 
     results
   end
diff --git a/lib/rubygems/ext/ext_conf_builder.rb b/lib/rubygems/ext/ext_conf_builder.rb
index 305e1dcfb1..fede270417 100644
--- a/lib/rubygems/ext/ext_conf_builder.rb
+++ b/lib/rubygems/ext/ext_conf_builder.rb
@@ -8,11 +8,11 @@
 require 'shellwords'
 
 class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd)
     require 'fileutils'
     require 'tempfile'
 
-    tmp_dest = Dir.mktmpdir(".gem.", ".")
+    tmp_dest = Dir.mktmpdir(".gem.", extension_dir)
 
     # Some versions of `mktmpdir` return absolute paths, which will break make
     # if the paths contain spaces. However, on Ruby 1.9.x on Windows, relative
@@ -23,9 +23,9 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
     # spaces do not work.
     #
     # Details: https://github.com/rubygems/rubygems/issues/977#issuecomment-171544940
-    tmp_dest = get_relative_path(tmp_dest)
+    tmp_dest = get_relative_path(tmp_dest, extension_dir)
 
-    Tempfile.open %w[siteconf .rb], "." do |siteconf|
+    Tempfile.open %w[siteconf .rb], extension_dir do |siteconf|
       siteconf.puts "require 'rbconfig'"
       siteconf.puts "dest_path = #{tmp_dest.dump}"
       %w[sitearchdir sitelibdir].each do |dir|
@@ -38,19 +38,22 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
       destdir = ENV["DESTDIR"]
 
       begin
+        # workaround for https://github.com/oracle/truffleruby/issues/2115
+        siteconf_path = RUBY_ENGINE == "truffleruby" ? siteconf.path.dup : siteconf.path
         cmd = Gem.ruby.shellsplit << "-I" << File.expand_path("../../..", __FILE__) <<
-              "-r" << get_relative_path(siteconf.path) << File.basename(extension)
+              "-r" << get_relative_path(siteconf_path, extension_dir) << File.basename(extension)
         cmd.push(*args)
 
         begin
-          run(cmd, results) do |s, r|
-            if File.exist? 'mkmf.log'
+          run(cmd, results, class_name, extension_dir) do |s, r|
+            mkmf_log = File.join(extension_dir, 'mkmf.log')
+            if File.exist? mkmf_log
               unless s.success?
                 r << "To see why this extension failed to compile, please check" \
                   " the mkmf.log which can be found here:\n"
                 r << "  " + File.join(dest_path, 'mkmf.log') + "\n"
               end
-              FileUtils.mv 'mkmf.log', dest_path
+              FileUtils.mv mkmf_log, dest_path
             end
           end
           siteconf.unlink
@@ -58,18 +61,20 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
         ENV["DESTDIR"] = nil
 
-        make dest_path, results
+        make dest_path, results, extension_dir
 
         if tmp_dest
+          full_tmp_dest = File.join(extension_dir, tmp_dest)
+
           # TODO remove in RubyGems 3
           if Gem.install_extension_in_lib and lib_dir
             FileUtils.mkdir_p lib_dir
-            entries = Dir.entries(tmp_dest) - %w[. ..]
-            entries = entries.map {|entry| File.join tmp_dest, entry }
+            entries = Dir.entries(full_tmp_dest) - %w[. ..]
+            entries = entries.map {|entry| File.join full_tmp_dest, entry }
             FileUtils.cp_r entries, lib_dir, :remove_destination => true
           end
 
-          FileUtils::Entry_.new(tmp_dest).traverse do |ent|
+          FileUtils::Entry_.new(full_tmp_dest).traverse do |ent|
             destent = ent.class.new(dest_path, ent.rel)
             destent.exist? or FileUtils.mv(ent.path, destent.path)
           end
@@ -87,8 +92,8 @@ class Gem::Ext::ExtConfBuilder < Gem::Ext::Builder
 
   private
 
-  def self.get_relative_path(path)
-    path[0..Dir.pwd.length - 1] = '.' if path.start_with?(Dir.pwd)
+  def self.get_relative_path(path, base)
+    path[0..base.length - 1] = '.' if path.start_with?(base)
     path
   end
 end
diff --git a/lib/rubygems/ext/rake_builder.rb b/lib/rubygems/ext/rake_builder.rb
index 53507090fe..34c3922f2f 100644
--- a/lib/rubygems/ext/rake_builder.rb
+++ b/lib/rubygems/ext/rake_builder.rb
@@ -8,9 +8,9 @@
 require "shellwords"
 
 class Gem::Ext::RakeBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil)
+  def self.build(extension, dest_path, results, args=[], lib_dir=nil, extension_dir=Dir.pwd)
     if File.basename(extension) =~ /mkrf_conf/i
-      run([Gem.ruby, File.basename(extension), *args], results)
+      run([Gem.ruby, File.basename(extension), *args], results, class_name, extension_dir)
     end
 
     rake = ENV['rake']
@@ -26,7 +26,7 @@ class Gem::Ext::RakeBuilder < Gem::Ext::Builder
     end
 
     rake_args = ["RUBYARCHDIR=#{dest_path}", "RUBYLIBDIR=#{dest_path}", *args]
-    run(rake + rake_args, results)
+    run(rake + rake_args, results, class_name, extension_dir)
 
     results
   end
diff --git a/lib/rubygems/gemcutter_utilities.rb b/lib/rubygems/gemcutter_utilities.rb
index bba9280691..d021f47e24 100644
--- a/lib/rubygems/gemcutter_utilities.rb
+++ b/lib/rubygems/gemcutter_utilities.rb
@@ -8,10 +8,12 @@ require 'rubygems/text'
 module Gem::GemcutterUtilities
 
   ERROR_CODE = 1
+  API_SCOPES = %i[index_rubygems push_rubygem yank_rubygem add_owner remove_owner access_webhooks show_dashboard].freeze
 
   include Gem::Text
 
   attr_writer :host
+  attr_writer :scope
 
   ##
   # Add the --key option
@@ -72,7 +74,7 @@ module Gem::GemcutterUtilities
   #
   # If +allowed_push_host+ metadata is present, then it will only allow that host.
 
-  def rubygems_api_request(method, path, host = nil, allowed_push_host = nil, &block)
+  def rubygems_api_request(method, path, host = nil, allowed_push_host = nil, scope: nil, &block)
     require 'net/http'
 
     self.host = host if host
@@ -95,11 +97,19 @@ module Gem::GemcutterUtilities
 
     request_method = Net::HTTP.const_get method.to_s.capitalize
     response = Gem::RemoteFetcher.fetcher.request(uri, request_method, &block)
-    return response unless mfa_unauthorized?(response)
 
-    Gem::RemoteFetcher.fetcher.request(uri, request_method) do |req|
-      req.add_field "OTP", get_otp
-      block.call(req)
+    if mfa_unauthorized?(response)
+      response = Gem::RemoteFetcher.fetcher.request(uri, request_method) do |req|
+        req.add_field "OTP", get_otp
+        block.call(req)
+      end
+    end
+
+    if api_key_forbidden?(response)
+      update_scope(scope)
+      Gem::RemoteFetcher.fetcher.request(uri, request_method, &block)
+    else
+      response
     end
   end
 
@@ -112,19 +122,37 @@ module Gem::GemcutterUtilities
     ask 'Code: '
   end
 
+  def update_scope(scope)
+    sign_in_host        = self.host
+    pretty_host         = pretty_host(sign_in_host)
+    update_scope_params = { scope => true }
+
+    say "The existing key doesn't have access of #{scope} on #{pretty_host}. Please sign in to update access."
+
+    email    = ask "   Email: "
+    password = ask_for_password "Password: "
+
+    response = rubygems_api_request(:put, "api/v1/api_key",
+                                    sign_in_host, scope: scope) do |request|
+      request.basic_auth email, password
+      request.add_field "OTP", options[:otp] if options[:otp]
+      request.body = URI.encode_www_form({:api_key => api_key }.merge(update_scope_params))
+    end
+
+    with_response response do |resp|
+      say "Added #{scope} scope to the existing API key"
+    end
+  end
+
   ##
   # Signs in with the RubyGems API at +sign_in_host+ and sets the rubygems API
   # key.
 
-  def sign_in(sign_in_host = nil)
+  def sign_in(sign_in_host = nil, scope: nil)
     sign_in_host ||= self.host
     return if api_key
 
-    pretty_host = if Gem::DEFAULT_HOST == sign_in_host
-                    'RubyGems.org'
-                  else
-                    sign_in_host
-                  end
+    pretty_host = pretty_host(sign_in_host)
 
     say "Enter your #{pretty_host} credentials."
     say "Don't have an account yet? " +
@@ -134,14 +162,18 @@ module Gem::GemcutterUtilities
     password = ask_for_password "Password: "
     say "\n"
 
-    response = rubygems_api_request(:get, "api/v1/api_key",
-                                    sign_in_host) do |request|
+    key_name     = get_key_name(scope)
+    scope_params = get_scope_params(scope)
+
+    response = rubygems_api_request(:post, "api/v1/api_key",
+                                    sign_in_host, scope: scope) do |request|
       request.basic_auth email, password
       request.add_field "OTP", options[:otp] if options[:otp]
+      request.body = URI.encode_www_form({ name: key_name }.merge(scope_params))
     end
 
     with_response response do |resp|
-      say "Signed in."
+      say "Signed in with API key: #{key_name}."
       set_api_key host, resp.body
     end
   end
@@ -195,4 +227,48 @@ module Gem::GemcutterUtilities
     end
   end
 
+  private
+
+  def pretty_host(host)
+    if Gem::DEFAULT_HOST == host
+      'RubyGems.org'
+    else
+      host
+    end
+  end
+
+  def get_scope_params(scope)
+    scope_params = {}
+
+    if scope
+      scope_params = { scope => true }
+    else
+      say "Please select scopes you want to enable for the API key (y/n)"
+      API_SCOPES.each do |scope|
+        selected = ask "#{scope} [y/N]: "
+        scope_params[scope] = true if selected =~ /^[yY](es)?$/
+      end
+      say "\n"
+    end
+
+    scope_params
+  end
+
+  def get_key_name(scope)
+    hostname = Socket.gethostname || "unkown-host"
+    user = ENV["USER"] || ENV["USERNAME"] || "unkown-user"
+    ts = Time.now.strftime("%Y%m%d%H%M%S")
+    default_key_name = "#{hostname}-#{user}-#{ts}"
+
+    key_name = ask "API Key name [#{default_key_name}]: " unless scope
+    if key_name.nil? || key_name.empty?
+      default_key_name
+    else
+      key_name
+    end
+  end
+
+  def api_key_forbidden?(response)
+    response.kind_of?(Net::HTTPForbidden) && response.body.start_with?("The API key doesn't have access")
+  end
 end
diff --git a/lib/rubygems/indexer.rb b/lib/rubygems/indexer.rb
index 9f4bd12c46..31285ca962 100644
--- a/lib/rubygems/indexer.rb
+++ b/lib/rubygems/indexer.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 require 'rubygems'
 require 'rubygems/package'
-require 'time'
 require 'tmpdir'
 
 ##
diff --git a/lib/rubygems/install_update_options.rb b/lib/rubygems/install_update_options.rb
index b46b53e76b..ef1ad1edcb 100644
--- a/lib/rubygems/install_update_options.rb
+++ b/lib/rubygems/install_update_options.rb
@@ -122,10 +122,10 @@ module Gem::InstallUpdateOptions
       options[:minimal_deps] = true
     end
 
-    add_option(:"Install/Update", "--minimal-deps",
+    add_option(:"Install/Update", "--[no-]minimal-deps",
                 "Don't upgrade any dependencies that already",
                 "meet version requirements") do |value, options|
-      options[:minimal_deps] = true
+      options[:minimal_deps] = value
     end
 
     add_option(:"Install/Update", "--[no-]post-install-message",
diff --git a/lib/rubygems/installer.rb b/lib/rubygems/installer.rb
index 33171a8eb9..2c583743b9 100644
--- a/lib/rubygems/installer.rb
+++ b/lib/rubygems/installer.rb
@@ -12,7 +12,6 @@ require 'rubygems/deprecate'
 require 'rubygems/package'
 require 'rubygems/ext'
 require 'rubygems/user_interaction'
-require 'fileutils'
 
 ##
 # The installer installs the files contained in the .gem into the Gem.home.
@@ -433,7 +432,7 @@ class Gem::Installer
   #
 
   def default_spec_file
-    File.join Gem.default_specifications_dir, "#{spec.full_name}.gemspec"
+    File.join gem_home, "specifications", "default", "#{spec.full_name}.gemspec"
   end
 
   ##
@@ -492,7 +491,11 @@ class Gem::Installer
 
       mode = File.stat(bin_path).mode
       dir_mode = options[:prog_mode] || (mode | 0111)
-      FileUtils.chmod dir_mode, bin_path unless dir_mode == mode
+
+      unless dir_mode == mode
+        require 'fileutils'
+        FileUtils.chmod dir_mode, bin_path
+      end
 
       check_executable_overwrite filename
 
@@ -527,6 +530,7 @@ class Gem::Installer
   def generate_bin_script(filename, bindir)
     bin_script_path = File.join bindir, formatted_program_filename(filename)
 
+    require 'fileutils'
     FileUtils.rm_f bin_script_path # prior install may have been --no-wrappers
 
     File.open bin_script_path, 'wb', 0755 do |file|
@@ -670,7 +674,7 @@ class Gem::Installer
       :env_shebang  => false,
       :force        => false,
       :only_install_dir => false,
-      :post_install_message => true
+      :post_install_message => true,
     }.merge options
 
     @env_shebang         = options[:env_shebang]
@@ -693,11 +697,10 @@ class Gem::Installer
     @build_args = options[:build_args] || Gem::Command.build_args
 
     unless @build_root.nil?
-      require 'pathname'
-      @build_root = Pathname.new(@build_root).expand_path
-      @bin_dir = File.join(@build_root, options[:bin_dir] || Gem.bindir(@gem_home))
-      @gem_home = File.join(@build_root, @gem_home)
-      alert_warning "You build with buildroot.\n  Build root: #{@build_root}\n  Bin dir: #{@bin_dir}\n  Gem home: #{@gem_home}"
+      @bin_dir = File.join(@build_root, @bin_dir.gsub(/^[a-zA-Z]:/, ''))
+      @gem_home = File.join(@build_root, @gem_home.gsub(/^[a-zA-Z]:/, ''))
+      @plugins_dir = File.join(@build_root, @plugins_dir.gsub(/^[a-zA-Z]:/, ''))
+      alert_warning "You build with buildroot.\n  Build root: #{@build_root}\n  Bin dir: #{@bin_dir}\n  Gem home: #{@gem_home}\n  Plugins dir: #{@plugins_dir}"
     end
   end
 
diff --git a/lib/rubygems/installer_test_case.rb b/lib/rubygems/installer_test_case.rb
index d78b6a4712..416dac7be6 100644
--- a/lib/rubygems/installer_test_case.rb
+++ b/lib/rubygems/installer_test_case.rb
@@ -108,9 +108,9 @@ class Gem::InstallerTestCase < Gem::TestCase
   #
   # And returns a Gem::Installer for the @spec that installs into @gemhome
 
-  def setup_base_installer
+  def setup_base_installer(force = true)
     @gem = setup_base_gem
-    util_installer @spec, @gemhome
+    util_installer @spec, @gemhome, false, force
   end
 
   ##
@@ -182,7 +182,7 @@ class Gem::InstallerTestCase < Gem::TestCase
   #   lib/code.rb
   #   ext/a/mkrf_conf.rb
 
-  def util_setup_gem(ui = @ui)
+  def util_setup_gem(ui = @ui, force = true)
     @spec.files << File.join('lib', 'code.rb')
     @spec.extensions << File.join('ext', 'a', 'mkrf_conf.rb')
 
@@ -214,17 +214,18 @@ class Gem::InstallerTestCase < Gem::TestCase
       end
     end
 
-    Gem::Installer.at @gem
+    Gem::Installer.at @gem, :force => force
   end
 
   ##
   # Creates an installer for +spec+ that will install into +gem_home+.  If
   # +user+ is true a user-install will be performed.
 
-  def util_installer(spec, gem_home, user=false)
+  def util_installer(spec, gem_home, user=false, force=true)
     Gem::Installer.at(spec.cache_file,
                        :install_dir => gem_home,
-                       :user_install => user)
+                       :user_install => user,
+                       :force => force)
   end
 
   @@symlink_supported = nil
diff --git a/lib/rubygems/name_tuple.rb b/lib/rubygems/name_tuple.rb
index cb5604e8dd..3d0afa3094 100644
--- a/lib/rubygems/name_tuple.rb
+++ b/lib/rubygems/name_tuple.rb
@@ -59,7 +59,7 @@ class Gem::NameTuple
   # Indicate if this NameTuple matches the current platform.
 
   def match_platform?
-    Gem::Platform.match @platform
+    Gem::Platform.match_gem? @platform, @name
   end
 
   ##
diff --git a/lib/rubygems/openssl.rb b/lib/rubygems/openssl.rb
index 39ef91e888..c44f619c4c 100644
--- a/lib/rubygems/openssl.rb
+++ b/lib/rubygems/openssl.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-begin
-  require "openssl"
-rescue LoadError => e
-  raise unless e.path == 'openssl'
+autoload :OpenSSL, "openssl"
+
+module Gem
+  HAVE_OPENSSL = defined? OpenSSL::SSL # :nodoc:
 end
diff --git a/lib/rubygems/package.rb b/lib/rubygems/package.rb
index 9b53cd4a7b..0587cd212b 100644
--- a/lib/rubygems/package.rb
+++ b/lib/rubygems/package.rb
@@ -44,7 +44,6 @@
 require "rubygems"
 require 'rubygems/security'
 require 'rubygems/user_interaction'
-require 'zlib'
 
 class Gem::Package
   include Gem::UserInteraction
@@ -186,6 +185,8 @@ class Gem::Package
   # Creates a new package that will read or write to the file +gem+.
 
   def initialize(gem, security_policy) # :notnew:
+    require 'zlib'
+
     @gem = gem
 
     @build_time      = Gem.source_date_epoch
@@ -297,7 +298,7 @@ class Gem::Package
 
     setup_signer(
       signer_options: {
-        expiration_length_days: Gem.configuration.cert_expiration_length_days
+        expiration_length_days: Gem.configuration.cert_expiration_length_days,
       }
     )
 
diff --git a/lib/rubygems/package/tar_header.rb b/lib/rubygems/package/tar_header.rb
index f19aea549d..ce9b49e3eb 100644
--- a/lib/rubygems/package/tar_header.rb
+++ b/lib/rubygems/package/tar_header.rb
@@ -229,7 +229,7 @@ class Gem::Package::TarHeader
       gname,
       oct(devmajor, 7),
       oct(devminor, 7),
-      prefix
+      prefix,
     ]
 
     header = header.pack PACK_FORMAT
diff --git a/lib/rubygems/package/tar_test_case.rb b/lib/rubygems/package/tar_test_case.rb
index 5fc34d2e8c..1161d0a5a8 100644
--- a/lib/rubygems/package/tar_test_case.rb
+++ b/lib/rubygems/package/tar_test_case.rb
@@ -90,7 +90,7 @@ class Gem::Package::TarTestCase < Gem::TestCase
       ASCIIZ("wheel", 32),   # char gname[32];     ASCIIZ
       Z(to_oct(0, 7)),       # char devmajor[8];   0 padded, octal, null
       Z(to_oct(0, 7)),       # char devminor[8];   0 padded, octal, null
-      ASCIIZ(dname, 155)     # char prefix[155];   ASCII + (Z unless filled)
+      ASCIIZ(dname, 155), # char prefix[155];   ASCII + (Z unless filled)
     ]
 
     h = arr.join
diff --git a/lib/rubygems/platform.rb b/lib/rubygems/platform.rb
index 34306fcf83..a500fd24c8 100644
--- a/lib/rubygems/platform.rb
+++ b/lib/rubygems/platform.rb
@@ -9,11 +9,7 @@ require "rubygems/deprecate"
 class Gem::Platform
   @local = nil
 
-  attr_accessor :cpu
-
-  attr_accessor :os
-
-  attr_accessor :version
+  attr_accessor :cpu, :os, :version
 
   def self.local
     arch = RbConfig::CONFIG['arch']
@@ -22,18 +18,33 @@ class Gem::Platform
   end
 
   def self.match(platform)
-    Gem.platforms.any? do |local_platform|
+    match_platforms?(platform, Gem.platforms)
+  end
+
+  def self.match_platforms?(platform, platforms)
+    platforms.any? do |local_platform|
       platform.nil? or
         local_platform == platform or
         (local_platform != Gem::Platform::RUBY and local_platform =~ platform)
     end
   end
+  private_class_method :match_platforms?
+
+  def self.match_spec?(spec)
+    match_gem?(spec.platform, spec.name)
+  end
+
+  def self.match_gem?(platform, gem_name)
+    # Note: this method might be redefined by Ruby implementations to
+    # customize behavior per RUBY_ENGINE, gem_name or other criteria.
+    match_platforms?(platform, Gem.platforms)
+  end
 
   def self.installable?(spec)
     if spec.respond_to? :installable_platform?
       spec.installable_platform?
     else
-      match spec.platform
+      match_spec? spec
     end
   end
 
diff --git a/lib/rubygems/query_utils.rb b/lib/rubygems/query_utils.rb
index 4e9b6efee6..ea0f260ab4 100644
--- a/lib/rubygems/query_utils.rb
+++ b/lib/rubygems/query_utils.rb
@@ -57,15 +57,6 @@ module Gem::QueryUtils
     "--local --name-matches // --no-details --versions --no-installed"
   end
 
-  def description # :nodoc:
-    <<-EOF
-The query command is the basis for the list and search commands.
-
-You should really use the list and search commands instead.  This command
-is too hard to use.
-    EOF
-  end
-
   def execute
     gem_names = Array(options[:name])
 
diff --git a/lib/rubygems/remote_fetcher.rb b/lib/rubygems/remote_fetcher.rb
index 40ac0e95c0..8ebe6acc70 100644
--- a/lib/rubygems/remote_fetcher.rb
+++ b/lib/rubygems/remote_fetcher.rb
@@ -78,7 +78,6 @@ class Gem::RemoteFetcher
   def initialize(proxy=nil, dns=nil, headers={})
     require 'net/http'
     require 'stringio'
-    require 'time'
     require 'uri'
 
     Socket.do_not_reverse_lookup = true
@@ -263,7 +262,7 @@ class Gem::RemoteFetcher
   rescue Timeout::Error
     raise UnknownHostError.new('timed out', uri)
   rescue IOError, SocketError, SystemCallError,
-         *(OpenSSL::SSL::SSLError if defined?(OpenSSL)) => e
+         *(OpenSSL::SSL::SSLError if Gem::HAVE_OPENSSL) => e
     if e.message =~ /getaddrinfo/
       raise UnknownHostError.new('no such name', uri)
     else
diff --git a/lib/rubygems/request.rb b/lib/rubygems/request.rb
index 75f9e9979a..1ed0fbcb99 100644
--- a/lib/rubygems/request.rb
+++ b/lib/rubygems/request.rb
@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 require 'net/http'
-require 'time'
 require 'rubygems/user_interaction'
 
 class Gem::Request
@@ -45,7 +44,8 @@ class Gem::Request
   end
 
   def self.configure_connection_for_https(connection, cert_files)
-    require 'openssl'
+    raise Gem::Exception.new('OpenSSl is not available. Install OpenSSL and rebuild Ruby (preferred) or use non-HTTPS sources') unless Gem::HAVE_OPENSSL
+
     connection.use_ssl = true
     connection.verify_mode =
       Gem.configuration.ssl_verify_mode || OpenSSL::SSL::VERIFY_PEER
@@ -125,7 +125,7 @@ class Gem::Request
 
   def connection_for(uri)
     @connection_pool.checkout
-  rescue defined?(OpenSSL::SSL) ? OpenSSL::SSL::SSLError : Errno::EHOSTDOWN,
+  rescue Gem::HAVE_OPENSSL ? OpenSSL::SSL::SSLError : Errno::EHOSTDOWN,
          Errno::EHOSTDOWN => e
     raise Gem::RemoteFetcher::FetchError.new(e.message, uri)
   end
@@ -143,6 +143,7 @@ class Gem::Request
     request.add_field 'Keep-Alive', '30'
 
     if @last_modified
+      require 'time'
       request.add_field 'If-Modified-Since', @last_modified.httpdate
     end
 
diff --git a/lib/rubygems/request_set/gem_dependency_api.rb b/lib/rubygems/request_set/gem_dependency_api.rb
index 9fbe3a1e44..7188b07346 100644
--- a/lib/rubygems/request_set/gem_dependency_api.rb
+++ b/lib/rubygems/request_set/gem_dependency_api.rb
@@ -88,7 +88,7 @@ class Gem::RequestSet::GemDependencyAPI
     :truffleruby  => Gem::Platform::RUBY,
     :x64_mingw    => x64_mingw,
     :x64_mingw_20 => x64_mingw,
-    :x64_mingw_21 => x64_mingw
+    :x64_mingw_21 => x64_mingw,
   }.freeze
 
   gt_eq_0        = Gem::Requirement.new '>= 0'
@@ -379,7 +379,7 @@ class Gem::RequestSet::GemDependencyAPI
         Gem::Requirement.create requirements
       end
 
-    return unless gem_platforms options
+    return unless gem_platforms name, options
 
     groups = gem_group name, options
 
@@ -532,7 +532,7 @@ Gem dependencies file #{@path} includes git reference for both ref/branch and ta
   # Handles the platforms: option from +options+.  Returns true if the
   # platform matches the current platform.
 
-  def gem_platforms(options) # :nodoc:
+  def gem_platforms(name, options) # :nodoc:
     platform_names = Array(options.delete :platform)
     platform_names.concat Array(options.delete :platforms)
     platform_names.concat @current_platforms if @current_platforms
@@ -543,7 +543,7 @@ Gem dependencies file #{@path} includes git reference for both ref/branch and ta
       raise ArgumentError, "unknown platform #{platform_name.inspect}" unless
         platform = PLATFORM_MAP[platform_name]
 
-      next false unless Gem::Platform.match platform
+      next false unless Gem::Platform.match_gem? platform, name
 
       if engines = ENGINE_MAP[platform_name]
         next false unless engines.include? Gem.ruby_engine
diff --git a/lib/rubygems/requirement.rb b/lib/rubygems/requirement.rb
index a2a5c7bca1..430060e2ff 100644
--- a/lib/rubygems/requirement.rb
+++ b/lib/rubygems/requirement.rb
@@ -16,7 +16,7 @@ class Gem::Requirement
     "<"  =>  lambda {|v, r| v <  r },
     ">=" =>  lambda {|v, r| v >= r },
     "<=" =>  lambda {|v, r| v <= r },
-    "~>" =>  lambda {|v, r| v >= r && v.release < r.bump }
+    "~>" =>  lambda {|v, r| v >= r && v.release < r.bump },
   }.freeze
 
   SOURCE_SET_REQUIREMENT = Struct.new(:for_lockfile).new "!" # :nodoc:
diff --git a/lib/rubygems/resolver.rb b/lib/rubygems/resolver.rb
index fa5f5e6bb2..e1c0d2dd0a 100644
--- a/lib/rubygems/resolver.rb
+++ b/lib/rubygems/resolver.rb
@@ -281,7 +281,7 @@ class Gem::Resolver
         amount_constrained(dependency),
         conflicts[name] ? 0 : 1,
         activated.vertex_named(name).payload ? 0 : search_for(dependency).count,
-        i # for stable sort
+        i, # for stable sort
       ]
     end
   end
diff --git a/lib/rubygems/resolver/activation_request.rb b/lib/rubygems/resolver/activation_request.rb
index 293df1efe9..ae35681db9 100644
--- a/lib/rubygems/resolver/activation_request.rb
+++ b/lib/rubygems/resolver/activation_request.rb
@@ -28,12 +28,20 @@ class Gem::Resolver::ActivationRequest
     when Gem::Specification
       @spec == other
     when Gem::Resolver::ActivationRequest
-      @spec == other.spec && @request == other.request
+      @spec == other.spec
     else
       false
     end
   end
 
+  def eql?(other)
+    self == other
+  end
+
+  def hash
+    @spec.hash
+  end
+
   ##
   # Is this activation request for a development dependency?
 
diff --git a/lib/rubygems/resolver/api_specification.rb b/lib/rubygems/resolver/api_specification.rb
index 232c2b041b..589ea1ba61 100644
--- a/lib/rubygems/resolver/api_specification.rb
+++ b/lib/rubygems/resolver/api_specification.rb
@@ -46,6 +46,10 @@ class Gem::Resolver::APISpecification < Gem::Resolver::Specification
       @dependencies == other.dependencies
   end
 
+  def hash
+    @set.hash ^ @name.hash ^ @version.hash ^ @platform.hash ^ @dependencies.hash
+  end
+
   def fetch_development_dependencies # :nodoc:
     spec = source.fetch_spec Gem::NameTuple.new @name, @version, @platform
 
@@ -53,7 +57,7 @@ class Gem::Resolver::APISpecification < Gem::Resolver::Specification
   end
 
   def installable_platform? # :nodoc:
-    Gem::Platform.match @platform
+    Gem::Platform.match_gem? @platform, @name
   end
 
   def pretty_print(q) # :nodoc:
diff --git a/lib/rubygems/resolver/conflict.rb b/lib/rubygems/resolver/conflict.rb
index 2ce63feef2..4c4588d7e8 100644
--- a/lib/rubygems/resolver/conflict.rb
+++ b/lib/rubygems/resolver/conflict.rb
@@ -85,7 +85,7 @@ class Gem::Resolver::Conflict
       activated, requirement,
       request_path(@activated).reverse.join(", depends on\n    "),
       request_path(@failed_dep).reverse.join(", depends on\n    "),
-      matching,
+      matching
     ]
   end
 
diff --git a/lib/rubygems/resolver/dependency_request.rb b/lib/rubygems/resolver/dependency_request.rb
index 77539c340f..356aadb3b2 100644
--- a/lib/rubygems/resolver/dependency_request.rb
+++ b/lib/rubygems/resolver/dependency_request.rb
@@ -28,7 +28,7 @@ class Gem::Resolver::DependencyRequest
     when Gem::Dependency
       @dependency == other
     when Gem::Resolver::DependencyRequest
-      @dependency == other.dependency && @requester == other.requester
+      @dependency == other.dependency
     else
       false
     end
diff --git a/lib/rubygems/resolver/index_specification.rb b/lib/rubygems/resolver/index_specification.rb
index d80f121189..3b75b719b0 100644
--- a/lib/rubygems/resolver/index_specification.rb
+++ b/lib/rubygems/resolver/index_specification.rb
@@ -33,6 +33,17 @@ class Gem::Resolver::IndexSpecification < Gem::Resolver::Specification
     spec.dependencies
   end
 
+  def ==(other)
+    self.class === other &&
+      @name == other.name &&
+      @version == other.version &&
+      @platform == other.platform
+  end
+
+  def hash
+    @name.hash ^ @version.hash ^ @platform.hash
+  end
+
   def inspect # :nodoc:
     '#<%s %s source %s>' % [self.class, full_name, @source]
   end
diff --git a/lib/rubygems/resolver/installer_set.rb b/lib/rubygems/resolver/installer_set.rb
index eaa7e207b2..b0e4ce5a37 100644
--- a/lib/rubygems/resolver/installer_set.rb
+++ b/lib/rubygems/resolver/installer_set.rb
@@ -32,7 +32,6 @@ class Gem::Resolver::InstallerSet < Gem::Resolver::Set
     super()
 
     @domain = domain
-    @remote = consider_remote?
 
     @f = Gem::SpecFetcher.fetcher
 
@@ -170,7 +169,7 @@ class Gem::Resolver::InstallerSet < Gem::Resolver::Set
     always_install = @always_install.map {|s| s.full_name }
 
     '#<%s domain: %s specs: %p always install: %p>' % [
-      self.class, @domain, @specs.keys, always_install,
+      self.class, @domain, @specs.keys, always_install
     ]
   end
 
diff --git a/lib/rubygems/resolver/lock_set.rb b/lib/rubygems/resolver/lock_set.rb
index 1ab03e753b..eabf217aba 100644
--- a/lib/rubygems/resolver/lock_set.rb
+++ b/lib/rubygems/resolver/lock_set.rb
@@ -28,7 +28,7 @@ class Gem::Resolver::LockSet < Gem::Resolver::Set
   def add(name, version, platform) # :nodoc:
     version = Gem::Version.new version
     specs = [
-      Gem::Resolver::LockSpecification.new(self, name, version, @sources, platform)
+      Gem::Resolver::LockSpecification.new(self, name, version, @sources, platform),
     ]
 
     @specs.concat specs
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo.rb b/lib/rubygems/resolver/molinillo/lib/molinillo.rb
index 0ae4b6a912..f67badbde7 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo.rb
@@ -1,9 +1,10 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/gem_metadata'
-require 'rubygems/resolver/molinillo/lib/molinillo/errors'
-require 'rubygems/resolver/molinillo/lib/molinillo/resolver'
-require 'rubygems/resolver/molinillo/lib/molinillo/modules/ui'
-require 'rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider'
+
+require_relative 'molinillo/gem_metadata'
+require_relative 'molinillo/errors'
+require_relative 'molinillo/resolver'
+require_relative 'molinillo/modules/ui'
+require_relative 'molinillo/modules/specification_provider'
 
 # Gem::Resolver::Molinillo is a generic dependency resolution algorithm.
 module Gem::Resolver::Molinillo
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
index 1bbc72c1f6..d540d3baff 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # @!visibility private
   module Delegates
@@ -45,6 +46,12 @@ module Gem::Resolver::Molinillo
         current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
         current_state.conflicts
       end
+
+      # (see Gem::Resolver::Molinillo::ResolutionState#unused_unwind_options)
+      def unused_unwind_options
+        current_state = state || Gem::Resolver::Molinillo::ResolutionState.empty
+        current_state.unused_unwind_options
+      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
index 71903c7e86..2ddb0ac426 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   module Delegates
     # Delegates all {Gem::Resolver::Molinillo::SpecificationProvider} methods to a
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
index b413e3ab6a..773bb3417f 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb
@@ -1,9 +1,10 @@
 # frozen_string_literal: true
+
 require 'set'
 require 'tsort'
 
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log'
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex'
+require_relative 'dependency_graph/log'
+require_relative 'dependency_graph/vertex'
 
 module Gem::Resolver::Molinillo
   # A directed acyclic graph that is tuned to hold named dependencies
@@ -123,6 +124,7 @@ module Gem::Resolver::Molinillo
       dot.join("\n")
     end
 
+    # @param [DependencyGraph] other
     # @return [Boolean] whether the two dependency graphs are equal, determined
     #   by a recursive traversal of each {#root_vertices} and its
     #   {Vertex#successors}
@@ -147,8 +149,8 @@ module Gem::Resolver::Molinillo
       vertex = add_vertex(name, payload, root)
       vertex.explicit_requirements << requirement if root
       parent_names.each do |parent_name|
-        parent_node = vertex_named(parent_name)
-        add_edge(parent_node, vertex, requirement)
+        parent_vertex = vertex_named(parent_name)
+        add_edge(parent_vertex, vertex, requirement)
       end
       vertex
     end
@@ -189,7 +191,7 @@ module Gem::Resolver::Molinillo
     # @return [Edge] the added edge
     def add_edge(origin, destination, requirement)
       if destination.path_to?(origin)
-        raise CircularDependencyError.new([origin, destination])
+        raise CircularDependencyError.new(path(destination, origin))
       end
       add_edge_no_circular(origin, destination, requirement)
     end
@@ -218,5 +220,37 @@ module Gem::Resolver::Molinillo
     def add_edge_no_circular(origin, destination, requirement)
       log.add_edge_no_circular(self, origin.name, destination.name, requirement)
     end
+
+    # Returns the path between two vertices
+    # @raise [ArgumentError] if there is no path between the vertices
+    # @param [Vertex] from
+    # @param [Vertex] to
+    # @return [Array<Vertex>] the shortest path from `from` to `to`
+    def path(from, to)
+      distances = Hash.new(vertices.size + 1)
+      distances[from.name] = 0
+      predecessors = {}
+      each do |vertex|
+        vertex.successors.each do |successor|
+          if distances[successor.name] > distances[vertex.name] + 1
+            distances[successor.name] = distances[vertex.name] + 1
+            predecessors[successor] = vertex
+          end
+        end
+      end
+
+      path = [to]
+      while before = predecessors[to]
+        path << before
+        to = before
+        break if to == from
+      end
+
+      unless path.last.equal?(from)
+        raise ArgumentError, "There is no path from #{from.name} to #{to.name}"
+      end
+
+      path.reverse
+    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
index eeedabb069..cc140031b3 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # An action that modifies a {DependencyGraph} that is reversible.
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
index e994e59d05..5570483253 100644
--- 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
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
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
index 6cde933080..f1411d5efa 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/delete_edge.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
index d44aaf1f06..3b48d77a50 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
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
index fa03e2d365..92f60d5be8 100644
--- 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
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
index 5cdd84b5c1..7aeb8847ec 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/log.rb
@@ -1,10 +1,11 @@
 # 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/delete_edge'
-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'
+
+require_relative 'add_edge_no_circular'
+require_relative 'add_vertex'
+require_relative 'delete_edge'
+require_relative 'detach_vertex_named'
+require_relative 'set_payload'
+require_relative 'tag'
 
 module Gem::Resolver::Molinillo
   class DependencyGraph
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
index 02cfba64a7..726292a2c3 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/set_payload.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
index 0cb08075ca..bfe6fd31f8 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/tag.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph/action'
+
+require_relative 'action'
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # @!visibility private
@@ -13,11 +14,11 @@ module Gem::Resolver::Molinillo
       end
 
       # (see Action#up)
-      def up(_graph)
+      def up(graph)
       end
 
       # (see Action#down)
-      def down(_graph)
+      def down(graph)
       end
 
       # @!group Tag
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb
index cebd9cafdd..88b6580a52 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph/vertex.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   class DependencyGraph
     # A vertex in a {DependencyGraph} that encapsulates a {#name} and a
@@ -32,7 +33,7 @@ module Gem::Resolver::Molinillo
       # @return [Array<Object>] all of the requirements that required
       #   this vertex
       def requirements
-        incoming_edges.map(&:requirement) + explicit_requirements
+        (incoming_edges.map(&:requirement) + explicit_requirements).uniq
       end
 
       # @return [Array<Edge>] the edges of {#graph} that have `self` as their
@@ -49,14 +50,25 @@ module Gem::Resolver::Molinillo
         incoming_edges.map(&:origin)
       end
 
-      # @return [Array<Vertex>] the vertices of {#graph} where `self` is a
+      # @return [Set<Vertex>] the vertices of {#graph} where `self` is a
       #   {#descendent?}
       def recursive_predecessors
-        vertices = predecessors
-        vertices += vertices.map(&:recursive_predecessors).flatten(1)
-        vertices.uniq!
+        _recursive_predecessors
+      end
+
+      # @param [Set<Vertex>] vertices the set to add the predecessors to
+      # @return [Set<Vertex>] the vertices of {#graph} where `self` is a
+      #   {#descendent?}
+      def _recursive_predecessors(vertices = Set.new)
+        incoming_edges.each do |edge|
+          vertex = edge.origin
+          next unless vertices.add?(vertex)
+          vertex._recursive_predecessors(vertices)
+        end
+
         vertices
       end
+      protected :_recursive_predecessors
 
       # @return [Array<Vertex>] the vertices of {#graph} that have an edge with
       #   `self` as their {Edge#origin}
@@ -64,14 +76,25 @@ module Gem::Resolver::Molinillo
         outgoing_edges.map(&:destination)
       end
 
-      # @return [Array<Vertex>] the vertices of {#graph} where `self` is an
+      # @return [Set<Vertex>] the vertices of {#graph} where `self` is an
       #   {#ancestor?}
       def recursive_successors
-        vertices = successors
-        vertices += vertices.map(&:recursive_successors).flatten(1)
-        vertices.uniq!
+        _recursive_successors
+      end
+
+      # @param [Set<Vertex>] vertices the set to add the successors to
+      # @return [Set<Vertex>] the vertices of {#graph} where `self` is an
+      #   {#ancestor?}
+      def _recursive_successors(vertices = Set.new)
+        outgoing_edges.each do |edge|
+          vertex = edge.destination
+          next unless vertices.add?(vertex)
+          vertex._recursive_successors(vertices)
+        end
+
         vertices
       end
+      protected :_recursive_successors
 
       # @return [String] a string suitable for debugging
       def inspect
@@ -107,11 +130,21 @@ module Gem::Resolver::Molinillo
       # 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) }
+        _path_to?(other)
       end
 
       alias descendent? path_to?
 
+      # @param [Vertex] other the vertex to check if there's a path to
+      # @param [Set<Vertex>] visited the vertices of {#graph} that have been visited
+      # @return [Boolean] whether there is a path to `other` from `self`
+      def _path_to?(other, visited = Set.new)
+        return false unless visited.add?(self)
+        return true if equal?(other)
+        successors.any? { |v| v._path_to?(other, visited) }
+      end
+      protected :_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}
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
index 129246bf4a..2ec6b068ac 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/errors.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # An error that occurred during the resolution process
   class ResolverError < StandardError; end
@@ -17,7 +18,7 @@ module Gem::Resolver::Molinillo
     # @param [Array<Object>] required_by @see {#required_by}
     def initialize(dependency, required_by = [])
       @dependency = dependency
-      @required_by = required_by
+      @required_by = required_by.uniq
       super()
     end
 
@@ -41,11 +42,11 @@ module Gem::Resolver::Molinillo
     attr_reader :dependencies
 
     # Initializes a new error with the given circular vertices.
-    # @param [Array<DependencyGraph::Vertex>] nodes the nodes in the dependency
+    # @param [Array<DependencyGraph::Vertex>] vertices the vertices in the dependency
     #   that caused the error
-    def initialize(nodes)
-      super "There is a circular dependency between #{nodes.map(&:name).join(' and ')}"
-      @dependencies = nodes.map(&:payload).to_set
+    def initialize(vertices)
+      super "There is a circular dependency between #{vertices.map(&:name).join(' and ')}"
+      @dependencies = vertices.map { |vertex| vertex.payload.possibilities.last }.to_set
     end
   end
 
@@ -55,11 +56,16 @@ module Gem::Resolver::Molinillo
     #   resolution to fail
     attr_reader :conflicts
 
+    # @return [SpecificationProvider] the specification provider used during
+    #   resolution
+    attr_reader :specification_provider
+
     # Initializes a new error with the given version conflicts.
     # @param [{String => Resolution::Conflict}] conflicts see {#conflicts}
-    def initialize(conflicts)
+    # @param [SpecificationProvider] specification_provider see {#specification_provider}
+    def initialize(conflicts, specification_provider)
       pairs = []
-      conflicts.values.flatten.map(&:requirements).flatten.each do |conflicting|
+      conflicts.values.flat_map(&:requirements).each do |conflicting|
         conflicting.each do |source, conflict_requirements|
           conflict_requirements.each do |c|
             pairs << [c, source]
@@ -69,7 +75,69 @@ module Gem::Resolver::Molinillo
 
       super "Unable to satisfy the following requirements:\n\n" \
         "#{pairs.map { |r, d| "- `#{r}` required by `#{d}`" }.join("\n")}"
+
       @conflicts = conflicts
+      @specification_provider = specification_provider
+    end
+
+    require_relative 'delegates/specification_provider'
+    include Delegates::SpecificationProvider
+
+    # @return [String] An error message that includes requirement trees,
+    #   which is much more detailed & customizable than the default message
+    # @param [Hash] opts the options to create a message with.
+    # @option opts [String] :solver_name The user-facing name of the solver
+    # @option opts [String] :possibility_type The generic name of a possibility
+    # @option opts [Proc] :reduce_trees A proc that reduced the list of requirement trees
+    # @option opts [Proc] :printable_requirement A proc that pretty-prints requirements
+    # @option opts [Proc] :additional_message_for_conflict A proc that appends additional
+    #   messages for each conflict
+    # @option opts [Proc] :version_for_spec A proc that returns the version number for a
+    #   possibility
+    def message_with_trees(opts = {})
+      solver_name = opts.delete(:solver_name) { self.class.name.split('::').first }
+      possibility_type = opts.delete(:possibility_type) { 'possibility named' }
+      reduce_trees = opts.delete(:reduce_trees) { proc { |trees| trees.uniq.sort_by(&:to_s) } }
+      printable_requirement = opts.delete(:printable_requirement) { proc { |req| req.to_s } }
+      additional_message_for_conflict = opts.delete(:additional_message_for_conflict) { proc {} }
+      version_for_spec = opts.delete(:version_for_spec) { proc(&:to_s) }
+      incompatible_version_message_for_conflict = opts.delete(:incompatible_version_message_for_conflict) do
+        proc do |name, _conflict|
+          %(#{solver_name} could not find compatible versions for #{possibility_type} "#{name}":)
+        end
+      end
+
+      conflicts.sort.reduce(''.dup) do |o, (name, conflict)|
+        o << "\n" << incompatible_version_message_for_conflict.call(name, conflict) << "\n"
+        if conflict.locked_requirement
+          o << %(  In snapshot (#{name_for_locking_dependency_source}):\n)
+          o << %(    #{printable_requirement.call(conflict.locked_requirement)}\n)
+          o << %(\n)
+        end
+        o << %(  In #{name_for_explicit_dependency_source}:\n)
+        trees = reduce_trees.call(conflict.requirement_trees)
+
+        o << trees.map do |tree|
+          t = ''.dup
+          depth = 2
+          tree.each do |req|
+            t << '  ' * depth << req.to_s
+            unless tree.last == req
+              if spec = conflict.activated_by_name[name_for(req)]
+                t << %( was resolved to #{version_for_spec.call(spec)}, which)
+              end
+              t << %( depends on)
+            end
+            t << %(\n)
+            depth += 1
+          end
+          t
+        end.join("\n")
+
+        additional_message_for_conflict.call(o, name, conflict)
+
+        o
+      end.strip
     end
   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 c5b5bd729f..6b5ada7ade 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/gem_metadata.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # The version of Gem::Resolver::Molinillo.
-  VERSION = '0.5.7'.freeze
+  VERSION = '0.7.0'.freeze
 end
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider.rb
index 916345b12a..a44b9c0d5d 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # Provides information about specifcations and dependencies to the resolver,
   # allowing the {Resolver} class to remain generic while still providing power
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/modules/ui.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/modules/ui.rb
index dbc4e000e4..a810fd519c 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/modules/ui.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/modules/ui.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # Conveys information about the resolution process to a user.
   module UI
@@ -48,7 +49,8 @@ module Gem::Resolver::Molinillo
       if debug?
         debug_info = yield
         debug_info = debug_info.inspect unless debug_info.is_a?(String)
-        output.puts debug_info.split("\n").map { |s| ' ' * depth + s }
+        debug_info = debug_info.split("\n").map { |s| ":#{depth.to_s.rjust 4}: #{s}" }
+        output.puts debug_info
       end
     end
 
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
index 73a4242157..f1c60ec544 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/resolution.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   class Resolver
     # A specific resolution from a given {Resolver}
@@ -8,22 +9,125 @@ module Gem::Resolver::Molinillo
       # @attr [{String,Nil=>[Object]}] requirements the requirements that caused the conflict
       # @attr [Object, nil] existing the existing spec that was in conflict with
       #   the {#possibility}
-      # @attr [Object] possibility the spec that was unable to be activated due
-      #   to a conflict
+      # @attr [Object] possibility_set the set of specs that was unable to be
+      #   activated due to a conflict.
       # @attr [Object] locked_requirement the relevant locking requirement.
       # @attr [Array<Array<Object>>] requirement_trees the different requirement
       #   trees that led to every requirement for the conflicting name.
       # @attr [{String=>Object}] activated_by_name the already-activated specs.
+      # @attr [Object] underlying_error an error that has occurred during resolution, and
+      #    will be raised at the end of it if no resolution is found.
       Conflict = Struct.new(
         :requirement,
         :requirements,
         :existing,
-        :possibility,
+        :possibility_set,
         :locked_requirement,
         :requirement_trees,
-        :activated_by_name
+        :activated_by_name,
+        :underlying_error
       )
 
+      class Conflict
+        # @return [Object] a spec that was unable to be activated due to a conflict
+        def possibility
+          possibility_set && possibility_set.latest_version
+        end
+      end
+
+      # A collection of possibility states that share the same dependencies
+      # @attr [Array] dependencies the dependencies for this set of possibilities
+      # @attr [Array] possibilities the possibilities
+      PossibilitySet = Struct.new(:dependencies, :possibilities)
+
+      class PossibilitySet
+        # String representation of the possibility set, for debugging
+        def to_s
+          "[#{possibilities.join(', ')}]"
+        end
+
+        # @return [Object] most up-to-date dependency in the possibility set
+        def latest_version
+          possibilities.last
+        end
+      end
+
+      # Details of the state to unwind to when a conflict occurs, and the cause of the unwind
+      # @attr [Integer] state_index the index of the state to unwind to
+      # @attr [Object] state_requirement the requirement of the state we're unwinding to
+      # @attr [Array] requirement_tree for the requirement we're relaxing
+      # @attr [Array] conflicting_requirements the requirements that combined to cause the conflict
+      # @attr [Array] requirement_trees for the conflict
+      # @attr [Array] requirements_unwound_to_instead array of unwind requirements that were chosen over this unwind
+      UnwindDetails = Struct.new(
+        :state_index,
+        :state_requirement,
+        :requirement_tree,
+        :conflicting_requirements,
+        :requirement_trees,
+        :requirements_unwound_to_instead
+      )
+
+      class UnwindDetails
+        include Comparable
+
+        # We compare UnwindDetails when choosing which state to unwind to. If
+        # two options have the same state_index we prefer the one most
+        # removed from a requirement that caused the conflict. Both options
+        # would unwind to the same state, but a `grandparent` option will
+        # filter out fewer of its possibilities after doing so - where a state
+        # is both a `parent` and a `grandparent` to requirements that have
+        # caused a conflict this is the correct behaviour.
+        # @param [UnwindDetail] other UnwindDetail to be compared
+        # @return [Integer] integer specifying ordering
+        def <=>(other)
+          if state_index > other.state_index
+            1
+          elsif state_index == other.state_index
+            reversed_requirement_tree_index <=> other.reversed_requirement_tree_index
+          else
+            -1
+          end
+        end
+
+        # @return [Integer] index of state requirement in reversed requirement tree
+        #    (the conflicting requirement itself will be at position 0)
+        def reversed_requirement_tree_index
+          @reversed_requirement_tree_index ||=
+            if state_requirement
+              requirement_tree.reverse.index(state_requirement)
+            else
+              999_999
+            end
+        end
+
+        # @return [Boolean] where the requirement of the state we're unwinding
+        #    to directly caused the conflict. Note: in this case, it is
+        #    impossible for the state we're unwinding to to be a parent of
+        #    any of the other conflicting requirements (or we would have
+        #    circularity)
+        def unwinding_to_primary_requirement?
+          requirement_tree.last == state_requirement
+        end
+
+        # @return [Array] array of sub-dependencies to avoid when choosing a
+        #    new possibility for the state we've unwound to. Only relevant for
+        #    non-primary unwinds
+        def sub_dependencies_to_avoid
+          @requirements_to_avoid ||=
+            requirement_trees.map do |tree|
+              index = tree.index(state_requirement)
+              tree[index + 1] if index
+            end.compact
+        end
+
+        # @return [Array] array of all the requirements that led to the need for
+        #    this unwind
+        def all_requirements
+          @all_requirements ||= requirement_trees.flatten(1)
+        end
+      end
+
       # @return [SpecificationProvider] the provider that knows about
       #   dependencies, requirements, specifications, versions, etc.
       attr_reader :specification_provider
@@ -64,7 +168,7 @@ module Gem::Resolver::Molinillo
         start_resolution
 
         while state
-          break unless state.requirements.any? || state.requirement
+          break if !state.requirement && state.requirements.empty?
           indicate_progress
           if state.respond_to?(:pop_possibility_state) # DependencyState
             debug(depth) { "Creating possibility state for #{requirement} (#{possibilities.count} remaining)" }
@@ -78,7 +182,7 @@ module Gem::Resolver::Molinillo
           process_topmost_state
         end
 
-        activated.freeze
+        resolve_activated_specs
       ensure
         end_resolution
       end
@@ -103,12 +207,25 @@ module Gem::Resolver::Molinillo
       def start_resolution
         @started_at = Time.now
 
-        handle_missing_or_push_dependency_state(initial_state)
+        push_initial_state
 
         debug { "Starting resolution (#{@started_at})\nUser-requested dependencies: #{original_requested}" }
         resolver_ui.before_resolution
       end
 
+      def resolve_activated_specs
+        activated.vertices.each do |_, vertex|
+          next unless vertex.payload
+
+          latest_version = vertex.payload.possibilities.reverse_each.find do |possibility|
+            vertex.requirements.all? { |req| requirement_satisfied_by?(req, activated, possibility) }
+          end
+
+          activated.set_payload(vertex.name, latest_version)
+        end
+        activated.freeze
+      end
+
       # Ends the resolution process
       # @return [void]
       def end_resolution
@@ -121,11 +238,11 @@ module Gem::Resolver::Molinillo
         debug { 'Activated: ' + Hash[activated.vertices.select { |_n, v| v.payload }].keys.join(', ') } if state
       end
 
-      require 'rubygems/resolver/molinillo/lib/molinillo/state'
-      require 'rubygems/resolver/molinillo/lib/molinillo/modules/specification_provider'
+      require_relative 'state'
+      require_relative 'modules/specification_provider'
 
-      require 'rubygems/resolver/molinillo/lib/molinillo/delegates/resolution_state'
-      require 'rubygems/resolver/molinillo/lib/molinillo/delegates/specification_provider'
+      require_relative 'delegates/resolution_state'
+      require_relative 'delegates/specification_provider'
 
       include Gem::Resolver::Molinillo::Delegates::ResolutionState
       include Gem::Resolver::Molinillo::Delegates::SpecificationProvider
@@ -136,9 +253,12 @@ module Gem::Resolver::Molinillo
         if possibility
           attempt_to_activate
         else
-          create_conflict if state.is_a? PossibilityState
-          unwind_for_conflict until possibility && state.is_a?(DependencyState)
+          create_conflict
+          unwind_for_conflict
         end
+      rescue CircularDependencyError => underlying_error
+        create_conflict(underlying_error)
+        unwind_for_conflict
       end
 
       # @return [Object] the current possibility that the resolution is trying
@@ -153,63 +273,292 @@ module Gem::Resolver::Molinillo
         states.last
       end
 
-      # Creates the initial state for the resolution, based upon the
+      # Creates and pushes the initial state for the resolution, based upon the
       # {#requested} dependencies
-      # @return [DependencyState] the initial state for the resolution
-      def initial_state
+      # @return [void]
+      def push_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 } }
+          original_requested.each do |requested|
+            vertex = dg.add_vertex(name_for(requested), nil, true)
+            vertex.explicit_requirements << requested
+          end
           dg.tag(:initial_state)
         end
 
-        requirements = sort_dependencies(original_requested, graph, {})
-        initial_requirement = requirements.shift
-        DependencyState.new(
-          initial_requirement && name_for(initial_requirement),
-          requirements,
-          graph,
-          initial_requirement,
-          initial_requirement && search_for(initial_requirement),
-          0,
-          {}
-        )
+        push_state_for_requirements(original_requested, true, graph)
       end
 
       # Unwinds the states stack because a conflict has been encountered
       # @return [void]
       def unwind_for_conflict
-        debug(depth) { "Unwinding for conflict: #{requirement} to #{state_index_for_unwind / 2}" }
+        details_for_unwind = build_details_for_unwind
+        unwind_options = unused_unwind_options
+        debug(depth) { "Unwinding for conflict: #{requirement} to #{details_for_unwind.state_index / 2}" }
         conflicts.tap do |c|
-          sliced_states = states.slice!((state_index_for_unwind + 1)..-1)
-          raise VersionConflict.new(c) unless state
+          sliced_states = states.slice!((details_for_unwind.state_index + 1)..-1)
+          raise_error_unless_state(c)
           activated.rewind_to(sliced_states.first || :initial_state) if sliced_states
           state.conflicts = c
+          state.unused_unwind_options = unwind_options
+          filter_possibilities_after_unwind(details_for_unwind)
           index = states.size - 1
           @parents_of.each { |_, a| a.reject! { |i| i >= index } }
+          state.unused_unwind_options.reject! { |uw| uw.state_index >= index }
+        end
+      end
+
+      # Raises a VersionConflict error, or any underlying error, if there is no
+      # current state
+      # @return [void]
+      def raise_error_unless_state(conflicts)
+        return if state
+
+        error = conflicts.values.map(&:underlying_error).compact.first
+        raise error || VersionConflict.new(conflicts, specification_provider)
+      end
+
+      # @return [UnwindDetails] Details of the nearest index to which we could unwind
+      def build_details_for_unwind
+        # Get the possible unwinds for the current conflict
+        current_conflict = conflicts[name]
+        binding_requirements = binding_requirements_for_conflict(current_conflict)
+        unwind_details = unwind_options_for_requirements(binding_requirements)
+
+        last_detail_for_current_unwind = unwind_details.sort.last
+        current_detail = last_detail_for_current_unwind
+
+        # Look for past conflicts that could be unwound to affect the
+        # requirement tree for the current conflict
+        relevant_unused_unwinds = unused_unwind_options.select do |alternative|
+          intersecting_requirements =
+            last_detail_for_current_unwind.all_requirements &
+            alternative.requirements_unwound_to_instead
+          next if intersecting_requirements.empty?
+          # Find the highest index unwind whilst looping through
+          current_detail = alternative if alternative > current_detail
+          alternative
+        end
+
+        # Add the current unwind options to the `unused_unwind_options` array.
+        # The "used" option will be filtered out during `unwind_for_conflict`.
+        state.unused_unwind_options += unwind_details.reject { |detail| detail.state_index == -1 }
+
+        # Update the requirements_unwound_to_instead on any relevant unused unwinds
+        relevant_unused_unwinds.each { |d| d.requirements_unwound_to_instead << current_detail.state_requirement }
+        unwind_details.each { |d| d.requirements_unwound_to_instead << current_detail.state_requirement }
+
+        current_detail
+      end
+
+      # @param [Array<Object>] binding_requirements array of requirements that combine to create a conflict
+      # @return [Array<UnwindDetails>] array of UnwindDetails that have a chance
+      #    of resolving the passed requirements
+      def unwind_options_for_requirements(binding_requirements)
+        unwind_details = []
+
+        trees = []
+        binding_requirements.reverse_each do |r|
+          partial_tree = [r]
+          trees << partial_tree
+          unwind_details << UnwindDetails.new(-1, nil, partial_tree, binding_requirements, trees, [])
+
+          # If this requirement has alternative possibilities, check if any would
+          # satisfy the other requirements that created this conflict
+          requirement_state = find_state_for(r)
+          if conflict_fixing_possibilities?(requirement_state, binding_requirements)
+            unwind_details << UnwindDetails.new(
+              states.index(requirement_state),
+              r,
+              partial_tree,
+              binding_requirements,
+              trees,
+              []
+            )
+          end
+
+          # Next, look at the parent of this requirement, and check if the requirement
+          # could have been avoided if an alternative PossibilitySet had been chosen
+          parent_r = parent_of(r)
+          next if parent_r.nil?
+          partial_tree.unshift(parent_r)
+          requirement_state = find_state_for(parent_r)
+          if requirement_state.possibilities.any? { |set| !set.dependencies.include?(r) }
+            unwind_details << UnwindDetails.new(
+              states.index(requirement_state),
+              parent_r,
+              partial_tree,
+              binding_requirements,
+              trees,
+              []
+            )
+          end
+
+          # Finally, look at the grandparent and up of this requirement, looking
+          # for any possibilities that wouldn't create their parent requirement
+          grandparent_r = parent_of(parent_r)
+          until grandparent_r.nil?
+            partial_tree.unshift(grandparent_r)
+            requirement_state = find_state_for(grandparent_r)
+            if requirement_state.possibilities.any? { |set| !set.dependencies.include?(parent_r) }
+              unwind_details << UnwindDetails.new(
+                states.index(requirement_state),
+                grandparent_r,
+                partial_tree,
+                binding_requirements,
+                trees,
+                []
+              )
+            end
+            parent_r = grandparent_r
+            grandparent_r = parent_of(parent_r)
+          end
+        end
+
+        unwind_details
+      end
+
+      # @param [DependencyState] state
+      # @param [Array] binding_requirements array of requirements
+      # @return [Boolean] whether or not the given state has any possibilities
+      #    that could satisfy the given requirements
+      def conflict_fixing_possibilities?(state, binding_requirements)
+        return false unless state
+
+        state.possibilities.any? do |possibility_set|
+          possibility_set.possibilities.any? do |poss|
+            possibility_satisfies_requirements?(poss, binding_requirements)
+          end
+        end
+      end
+
+      # Filter's a state's possibilities to remove any that would not fix the
+      # conflict we've just rewound from
+      # @param [UnwindDetails] unwind_details details of the conflict just
+      #   unwound from
+      # @return [void]
+      def filter_possibilities_after_unwind(unwind_details)
+        return unless state && !state.possibilities.empty?
+
+        if unwind_details.unwinding_to_primary_requirement?
+          filter_possibilities_for_primary_unwind(unwind_details)
+        else
+          filter_possibilities_for_parent_unwind(unwind_details)
+        end
+      end
+
+      # Filter's a state's possibilities to remove any that would not satisfy
+      # the requirements in the conflict we've just rewound from
+      # @param [UnwindDetails] unwind_details details of the conflict just unwound from
+      # @return [void]
+      def filter_possibilities_for_primary_unwind(unwind_details)
+        unwinds_to_state = unused_unwind_options.select { |uw| uw.state_index == unwind_details.state_index }
+        unwinds_to_state << unwind_details
+        unwind_requirement_sets = unwinds_to_state.map(&:conflicting_requirements)
+
+        state.possibilities.reject! do |possibility_set|
+          possibility_set.possibilities.none? do |poss|
+            unwind_requirement_sets.any? do |requirements|
+              possibility_satisfies_requirements?(poss, requirements)
+            end
+          end
         end
       end
 
-      # @return [Integer] The index to which the resolution should unwind in the
-      #   case of conflict.
-      def state_index_for_unwind
-        current_requirement = requirement
-        existing_requirement = requirement_for_existing_name(name)
-        index = -1
-        [current_requirement, existing_requirement].each do |r|
-          until r.nil?
-            current_state = find_state_for(r)
-            if state_any?(current_state)
-              current_index = states.index(current_state)
-              index = current_index if current_index > index
-              break
+      # @param [Object] possibility a single possibility
+      # @param [Array] requirements an array of requirements
+      # @return [Boolean] whether the possibility satisfies all of the
+      #    given requirements
+      def possibility_satisfies_requirements?(possibility, requirements)
+        name = name_for(possibility)
+
+        activated.tag(:swap)
+        activated.set_payload(name, possibility) if activated.vertex_named(name)
+        satisfied = requirements.all? { |r| requirement_satisfied_by?(r, activated, possibility) }
+        activated.rewind_to(:swap)
+
+        satisfied
+      end
+
+      # Filter's a state's possibilities to remove any that would (eventually)
+      # create a requirement in the conflict we've just rewound from
+      # @param [UnwindDetails] unwind_details details of the conflict just unwound from
+      # @return [void]
+      def filter_possibilities_for_parent_unwind(unwind_details)
+        unwinds_to_state = unused_unwind_options.select { |uw| uw.state_index == unwind_details.state_index }
+        unwinds_to_state << unwind_details
+
+        primary_unwinds = unwinds_to_state.select(&:unwinding_to_primary_requirement?).uniq
+        parent_unwinds = unwinds_to_state.uniq - primary_unwinds
+
+        allowed_possibility_sets = primary_unwinds.flat_map do |unwind|
+          states[unwind.state_index].possibilities.select do |possibility_set|
+            possibility_set.possibilities.any? do |poss|
+              possibility_satisfies_requirements?(poss, unwind.conflicting_requirements)
             end
-            r = parent_of(r)
           end
         end
 
-        index
+        requirements_to_avoid = parent_unwinds.flat_map(&:sub_dependencies_to_avoid)
+
+        state.possibilities.reject! do |possibility_set|
+          !allowed_possibility_sets.include?(possibility_set) &&
+            (requirements_to_avoid - possibility_set.dependencies).empty?
+        end
       end
 
+      # @param [Conflict] conflict
+      # @return [Array] minimal array of requirements that would cause the passed
+      #    conflict to occur.
+      def binding_requirements_for_conflict(conflict)
+        return [conflict.requirement] if conflict.possibility.nil?
+
+        possible_binding_requirements = conflict.requirements.values.flatten(1).uniq
+
+        # When there's a `CircularDependency` error the conflicting requirement
+        # (the one causing the circular) won't be `conflict.requirement`
+        # (which won't be for the right state, because we won't have created it,
+        # because it's circular).
+        # We need to make sure we have that requirement in the conflict's list,
+        # otherwise we won't be able to unwind properly, so we just return all
+        # the requirements for the conflict.
+        return possible_binding_requirements if conflict.underlying_error
+
+        possibilities = search_for(conflict.requirement)
+
+        # If all the requirements together don't filter out all possibilities,
+        # then the only two requirements we need to consider are the initial one
+        # (where the dependency's version was first chosen) and the last
+        if binding_requirement_in_set?(nil, possible_binding_requirements, possibilities)
+          return [conflict.requirement, requirement_for_existing_name(name_for(conflict.requirement))].compact
+        end
+
+        # Loop through the possible binding requirements, removing each one
+        # that doesn't bind. Use a `reverse_each` as we want the earliest set of
+        # binding requirements, and don't use `reject!` as we wish to refine the
+        # array *on each iteration*.
+        binding_requirements = possible_binding_requirements.dup
+        possible_binding_requirements.reverse_each do |req|
+          next if req == conflict.requirement
+          unless binding_requirement_in_set?(req, binding_requirements, possibilities)
+            binding_requirements -= [req]
+          end
+        end
+
+        binding_requirements
+      end
+
+      # @param [Object] requirement we wish to check
+      # @param [Array] possible_binding_requirements array of requirements
+      # @param [Array] possibilities array of possibilities the requirements will be used to filter
+      # @return [Boolean] whether or not the given requirement is required to filter
+      #    out all elements of the array of possibilities.
+      def binding_requirement_in_set?(requirement, possible_binding_requirements, possibilities)
+        possibilities.any? do |poss|
+          possibility_satisfies_requirements?(poss, possible_binding_requirements - [requirement])
+        end
+      end
+
+      # @param [Object] requirement
       # @return [Object] the requirement that led to `requirement` being added
       #   to the list of requirements.
       def parent_of(requirement)
@@ -219,29 +568,27 @@ module Gem::Resolver::Molinillo
         parent_state.requirement
       end
 
+      # @param [String] name
       # @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
+        return nil unless vertex = activated.vertex_named(name)
+        return nil unless vertex.payload
         states.find { |s| s.name == name }.requirement
       end
 
+      # @param [Object] requirement
       # @return [ResolutionState] the state whose `requirement` is the given
       #   `requirement`.
       def find_state_for(requirement)
         return nil unless requirement
-        states.reverse_each.find { |i| requirement == i.requirement && i.is_a?(DependencyState) }
-      end
-
-      # @return [Boolean] whether or not the given state has any possibilities
-      #   left.
-      def state_any?(state)
-        state && state.possibilities.any?
+        states.find { |i| requirement == i.requirement }
       end
 
+      # @param [Object] underlying_error
       # @return [Conflict] a {Conflict} that reflects the failure to activate
       #   the {#possibility} in conjunction with the current {#state}
-      def create_conflict
+      def create_conflict(underlying_error = nil)
         vertex = activated.vertex_named(name)
         locked_requirement = locked_requirement_named(name)
 
@@ -250,18 +597,21 @@ module Gem::Resolver::Molinillo
           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) }
+        vertex.incoming_edges.each do |edge|
+          (requirements[edge.origin.payload.latest_version] ||= []).unshift(edge.requirement)
+        end
 
         activated_by_name = {}
-        activated.each { |v| activated_by_name[v.name] = v.payload if v.payload }
+        activated.each { |v| activated_by_name[v.name] = v.payload.latest_version if v.payload }
         conflicts[name] = Conflict.new(
           requirement,
           requirements,
-          vertex.payload,
+          vertex.payload && vertex.payload.latest_version,
           possibility,
           locked_requirement,
           requirement_trees,
-          activated_by_name
+          activated_by_name,
+          underlying_error
         )
       end
 
@@ -272,6 +622,7 @@ module Gem::Resolver::Molinillo
         vertex.requirements.map { |r| requirement_tree_for(r) }
       end
 
+      # @param [Object] requirement
       # @return [Array<Object>] the list of requirements that led to
       #   `requirement` being required.
       def requirement_tree_for(requirement)
@@ -311,116 +662,47 @@ module Gem::Resolver::Molinillo
       # @return [void]
       def attempt_to_activate
         debug(depth) { 'Attempting to activate ' + possibility.to_s }
-        existing_node = activated.vertex_named(name)
-        if existing_node.payload
-          debug(depth) { "Found existing spec (#{existing_node.payload})" }
-          attempt_to_activate_existing_spec(existing_node)
+        existing_vertex = activated.vertex_named(name)
+        if existing_vertex.payload
+          debug(depth) { "Found existing spec (#{existing_vertex.payload})" }
+          attempt_to_filter_existing_spec(existing_vertex)
         else
-          attempt_to_activate_new_spec
-        end
-      end
-
-      # Attempts to activate the current {#possibility} (given that it has
-      # already been activated)
-      # @return [void]
-      def attempt_to_activate_existing_spec(existing_node)
-        existing_spec = existing_node.payload
-        if requirement_satisfied_by?(requirement, activated, existing_spec)
-          new_requirements = requirements.dup
-          push_state_for_requirements(new_requirements, false)
-        else
-          return if attempt_to_swap_possibility
-          create_conflict
-          debug(depth) { "Unsatisfied by existing spec (#{existing_node.payload})" }
-          unwind_for_conflict
-        end
-      end
-
-      # Attempts to swp the current {#possibility} with the already-activated
-      # spec with the given name
-      # @return [Boolean] Whether the possibility was swapped into {#activated}
-      def attempt_to_swap_possibility
-        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
-
-      # Ensures there are no orphaned successors to the given {vertex}.
-      # @param [DependencyGraph::Vertex] vertex the vertex to fix up.
-      # @return [void]
-      def fixup_swapped_children(vertex) # rubocop:disable Metrics/CyclomaticComplexity
-        payload = vertex.payload
-        deps = dependencies_for(payload).group_by(&method(:name_for))
-        vertex.outgoing_edges.each do |outgoing_edge|
-          requirement = outgoing_edge.requirement
-          parent_index = @parents_of[requirement].last
-          succ = outgoing_edge.destination
-          matching_deps = Array(deps[succ.name])
-          dep_matched = matching_deps.include?(requirement)
-
-          # only push the current index when it was originally required by the
-          # same named spec
-          if parent_index && states[parent_index].name == name
-            @parents_of[requirement].push(states.size - 1)
+          latest = possibility.latest_version
+          possibility.possibilities.select! do |possibility|
+            requirement_satisfied_by?(requirement, activated, possibility)
           end
-
-          if matching_deps.empty? && !succ.root? && succ.predecessors.to_a == [vertex]
-            debug(depth) { "Removing orphaned spec #{succ.name} after swapping #{name}" }
-            succ.requirements.each { |r| @parents_of.delete(r) }
-
-            removed_names = activated.detach_vertex_named(succ.name).map(&:name)
-            requirements.delete_if do |r|
-              # the only removed vertices are those with no other requirements,
-              # so it's safe to delete only based upon name here
-              removed_names.include?(name_for(r))
-            end
-          elsif !dep_matched
-            debug(depth) { "Removing orphaned dependency #{requirement} after swapping #{name}" }
-            # also reset if we're removing the edge, but only if its parent has
-            # already been fixed up
-            @parents_of[requirement].push(states.size - 1) if @parents_of[requirement].empty?
-
-            activated.delete_edge(outgoing_edge)
-            requirements.delete(requirement)
+          if possibility.latest_version.nil?
+            # ensure there's a possibility for better error messages
+            possibility.possibilities << latest if latest
+            create_conflict
+            unwind_for_conflict
+          else
+            activate_new_spec
           end
         end
       end
 
-      # Attempts to activate the current {#possibility} (given that it hasn't
-      # already been activated)
+      # Attempts to update the existing vertex's `PossibilitySet` with a filtered version
       # @return [void]
-      def attempt_to_activate_new_spec
-        if new_spec_satisfied?
-          activate_spec
+      def attempt_to_filter_existing_spec(vertex)
+        filtered_set = filtered_possibility_set(vertex)
+        if !filtered_set.possibilities.empty?
+          activated.set_payload(name, filtered_set)
+          new_requirements = requirements.dup
+          push_state_for_requirements(new_requirements, false)
         else
           create_conflict
+          debug(depth) { "Unsatisfied by existing spec (#{vertex.payload})" }
           unwind_for_conflict
         end
       end
 
-      # @return [Boolean] whether the current spec is satisfied as a new
-      # possibility.
-      def new_spec_satisfied?
-        unless requirement_satisfied_by?(requirement, activated, possibility)
-          debug(depth) { 'Unsatisfied by requested spec' }
-          return false
-        end
-
-        locked_requirement = locked_requirement_named(name)
-
-        locked_spec_satisfied = !locked_requirement ||
-          requirement_satisfied_by?(locked_requirement, activated, possibility)
-        debug(depth) { 'Unsatisfied by locked spec' } unless locked_spec_satisfied
-
-        locked_spec_satisfied
+      # Generates a filtered version of the existing vertex's `PossibilitySet` using the
+      # current state's `requirement`
+      # @param [Object] vertex existing vertex
+      # @return [PossibilitySet] filtered possibility set
+      def filtered_possibility_set(vertex)
+        PossibilitySet.new(vertex.payload.dependencies, vertex.payload.possibilities & possibility.possibilities)
       end
 
       # @param [String] requirement_name the spec name to search for
@@ -434,7 +716,7 @@ module Gem::Resolver::Molinillo
       # Add the current {#possibility} to the dependency graph of the current
       # {#state}
       # @return [void]
-      def activate_spec
+      def activate_new_spec
         conflicts.delete(name)
         debug(depth) { "Activated #{name} at #{possibility}" }
         activated.set_payload(name, possibility)
@@ -442,14 +724,14 @@ module Gem::Resolver::Molinillo
       end
 
       # Requires the dependencies that the recently activated spec has
-      # @param [Object] activated_spec the specification that has just been
+      # @param [Object] possibility_set the PossibilitySet that has just been
       #   activated
       # @return [void]
-      def require_nested_dependencies_for(activated_spec)
-        nested_dependencies = dependencies_for(activated_spec)
+      def require_nested_dependencies_for(possibility_set)
+        nested_dependencies = dependencies_for(possibility_set.latest_version)
         debug(depth) { "Requiring nested dependencies (#{nested_dependencies.join(', ')})" }
         nested_dependencies.each do |d|
-          activated.add_child_vertex(name_for(d), nil, [name_for(activated_spec)], d)
+          activated.add_child_vertex(name_for(d), nil, [name_for(possibility_set.latest_version)], d)
           parent_index = states.size - 1
           parents = @parents_of[d]
           parents << parent_index if parents.empty?
@@ -461,23 +743,82 @@ module Gem::Resolver::Molinillo
       # Pushes a new {DependencyState} that encapsulates both existing and new
       # requirements
       # @param [Array] new_requirements
+      # @param [Boolean] requires_sort
+      # @param [Object] new_activated
       # @return [void]
       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_requirement = nil
+        loop do
+          new_requirement = new_requirements.shift
+          break if new_requirement.nil? || states.none? { |s| s.requirement == new_requirement }
+        end
         new_name = new_requirement ? name_for(new_requirement) : ''.freeze
-        possibilities = new_requirement ? search_for(new_requirement) : []
+        possibilities = possibilities_for_requirement(new_requirement)
         handle_missing_or_push_dependency_state DependencyState.new(
           new_name, new_requirements, new_activated,
-          new_requirement, possibilities, depth, conflicts.dup
+          new_requirement, possibilities, depth, conflicts.dup, unused_unwind_options.dup
         )
       end
 
+      # Checks a proposed requirement with any existing locked requirement
+      # before generating an array of possibilities for it.
+      # @param [Object] requirement the proposed requirement
+      # @param [Object] activated
+      # @return [Array] possibilities
+      def possibilities_for_requirement(requirement, activated = self.activated)
+        return [] unless requirement
+        if locked_requirement_named(name_for(requirement))
+          return locked_requirement_possibility_set(requirement, activated)
+        end
+
+        group_possibilities(search_for(requirement))
+      end
+
+      # @param [Object] requirement the proposed requirement
+      # @param [Object] activated
+      # @return [Array] possibility set containing only the locked requirement, if any
+      def locked_requirement_possibility_set(requirement, activated = self.activated)
+        all_possibilities = search_for(requirement)
+        locked_requirement = locked_requirement_named(name_for(requirement))
+
+        # Longwinded way to build a possibilities array with either the locked
+        # requirement or nothing in it. Required, since the API for
+        # locked_requirement isn't guaranteed.
+        locked_possibilities = all_possibilities.select do |possibility|
+          requirement_satisfied_by?(locked_requirement, activated, possibility)
+        end
+
+        group_possibilities(locked_possibilities)
+      end
+
+      # Build an array of PossibilitySets, with each element representing a group of
+      # dependency versions that all have the same sub-dependency version constraints
+      # and are contiguous.
+      # @param [Array] possibilities an array of possibilities
+      # @return [Array<PossibilitySet>] an array of possibility sets
+      def group_possibilities(possibilities)
+        possibility_sets = []
+        current_possibility_set = nil
+
+        possibilities.reverse_each do |possibility|
+          dependencies = dependencies_for(possibility)
+          if current_possibility_set && current_possibility_set.dependencies == dependencies
+            current_possibility_set.possibilities.unshift(possibility)
+          else
+            possibility_sets.unshift(PossibilitySet.new(dependencies, [possibility]))
+            current_possibility_set = possibility_sets.first
+          end
+        end
+
+        possibility_sets
+      end
+
       # Pushes a new {DependencyState}.
       # If the {#specification_provider} says to
       # {SpecificationProvider#allow_missing?} that particular requirement, and
       # there are no possibilities for that requirement, then `state` is not
-      # pushed, and the node in {#activated} is removed, and we continue
+      # pushed, and the vertex in {#activated} is removed, and we continue
       # resolving the remaining requirements.
       # @param [DependencyState] state
       # @return [void]
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/resolver.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/resolver.rb
index 5c59a45c3d..d43121f8ca 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/resolver.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/resolver.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
-require 'rubygems/resolver/molinillo/lib/molinillo/dependency_graph'
+
+require_relative 'dependency_graph'
 
 module Gem::Resolver::Molinillo
   # This class encapsulates a dependency resolver.
@@ -8,7 +9,7 @@ module Gem::Resolver::Molinillo
   #
   #
   class Resolver
-    require 'rubygems/resolver/molinillo/lib/molinillo/resolution'
+    require_relative 'resolution'
 
     # @return [SpecificationProvider] the specification provider used
     #   in the resolution process
diff --git a/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb b/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
index c20de98854..6e7c715fce 100644
--- a/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
+++ b/lib/rubygems/resolver/molinillo/lib/molinillo/state.rb
@@ -1,4 +1,5 @@
 # frozen_string_literal: true
+
 module Gem::Resolver::Molinillo
   # A state that a {Resolution} can be in
   # @attr [String] name the name of the current requirement
@@ -7,7 +8,8 @@ module Gem::Resolver::Molinillo
   # @attr [Object] requirement the current requirement
   # @attr [Object] possibilities the possibilities to satisfy the current requirement
   # @attr [Integer] depth the depth of the resolution
-  # @attr [Set<Object>] conflicts unresolved conflicts
+  # @attr [Hash] conflicts unresolved conflicts, indexed by dependency name
+  # @attr [Array<UnwindDetails>] unused_unwind_options unwinds for previous conflicts that weren't explored
   ResolutionState = Struct.new(
     :name,
     :requirements,
@@ -15,14 +17,15 @@ module Gem::Resolver::Molinillo
     :requirement,
     :possibilities,
     :depth,
-    :conflicts
+    :conflicts,
+    :unused_unwind_options
   )
 
   class ResolutionState
     # Returns an empty resolution state
     # @return [ResolutionState] an empty state
     def self.empty
-      new(nil, [], DependencyGraph.new, nil, nil, 0, Set.new)
+      new(nil, [], DependencyGraph.new, nil, nil, 0, {}, [])
     end
   end
 
@@ -40,7 +43,8 @@ module Gem::Resolver::Molinillo
         requirement,
         [possibilities.pop],
         depth + 1,
-        conflicts.dup
+        conflicts.dup,
+        unused_unwind_options.dup
       ).tap do |state|
         state.activated.tag(state)
       end
diff --git a/lib/rubygems/resolver/specification.rb b/lib/rubygems/resolver/specification.rb
index 7fe2afd3bd..5ae5f15813 100644
--- a/lib/rubygems/resolver/specification.rb
+++ b/lib/rubygems/resolver/specification.rb
@@ -104,7 +104,7 @@ class Gem::Resolver::Specification
   # Returns true if this specification is installable on this platform.
 
   def installable_platform?
-    Gem::Platform.match spec.platform
+    Gem::Platform.match_spec? spec
   end
 
   def local? # :nodoc:
diff --git a/lib/rubygems/s3_uri_signer.rb b/lib/rubygems/s3_uri_signer.rb
index c0b88842a0..f1f9229ca5 100644
--- a/lib/rubygems/s3_uri_signer.rb
+++ b/lib/rubygems/s3_uri_signer.rb
@@ -88,7 +88,7 @@ class Gem::S3URISigner
       "AWS4-HMAC-SHA256",
       date_time,
       credential_info,
-      Digest::SHA256.hexdigest(canonical_request)
+      Digest::SHA256.hexdigest(canonical_request),
     ].join("\n")
   end
 
diff --git a/lib/rubygems/security.rb b/lib/rubygems/security.rb
index bd6d6ff8b9..c80639af6d 100644
--- a/lib/rubygems/security.rb
+++ b/lib/rubygems/security.rb
@@ -6,7 +6,6 @@
 #++
 
 require 'rubygems/exceptions'
-require 'fileutils'
 require_relative 'openssl'
 
 ##
@@ -592,7 +591,7 @@ module Gem::Security
 
 end
 
-if defined?(OpenSSL::SSL)
+if Gem::HAVE_OPENSSL
   require 'rubygems/security/policy'
   require 'rubygems/security/policies'
   require 'rubygems/security/trust_dir'
diff --git a/lib/rubygems/security/policy.rb b/lib/rubygems/security/policy.rb
index 43abdb6d91..7629d64796 100644
--- a/lib/rubygems/security/policy.rb
+++ b/lib/rubygems/security/policy.rb
@@ -194,7 +194,7 @@ class Gem::Security::Policy
     ("[Policy: %s - data: %p signer: %p chain: %p root: %p " +
      "signed-only: %p trusted-only: %p]") % [
        @name, @verify_chain, @verify_data, @verify_root, @verify_signer,
-       @only_signed, @only_trusted,
+       @only_signed, @only_trusted
      ]
   end
 
diff --git a/lib/rubygems/security/signer.rb b/lib/rubygems/security/signer.rb
index 89200f9e38..6c85ab08d2 100644
--- a/lib/rubygems/security/signer.rb
+++ b/lib/rubygems/security/signer.rb
@@ -34,7 +34,7 @@ class Gem::Security::Signer
   attr_reader :options
 
   DEFAULT_OPTIONS = {
-    expiration_length_days: 365
+    expiration_length_days: 365,
   }.freeze
 
   ##
diff --git a/lib/rubygems/server.rb b/lib/rubygems/server.rb
index 70ae44609a..a9529f7923 100644
--- a/lib/rubygems/server.rb
+++ b/lib/rubygems/server.rb
@@ -771,7 +771,7 @@ div.method-source-code pre { color: #ffdead; overflow: hidden; }
         doc_items << {
           :name    => base_name,
           :url     => doc_root(new_path),
-          :summary => ''
+          :summary => '',
         }
       end
 
diff --git a/lib/rubygems/source.rb b/lib/rubygems/source.rb
index ef232ff35d..891cc3e644 100644
--- a/lib/rubygems/source.rb
+++ b/lib/rubygems/source.rb
@@ -79,7 +79,7 @@ class Gem::Source
   def dependency_resolver_set # :nodoc:
     return Gem::Resolver::IndexSet.new self if 'file' == uri.scheme
 
-    bundler_api_uri = uri + './api/v1/dependencies'
+    bundler_api_uri = enforce_trailing_slash(uri) + './api/v1/dependencies'
 
     begin
       fetcher = Gem::RemoteFetcher.fetcher
@@ -130,7 +130,7 @@ class Gem::Source
 
     spec_file_name = name_tuple.spec_name
 
-    source_uri = uri + "#{Gem::MARSHAL_SPEC_DIR}#{spec_file_name}"
+    source_uri = enforce_trailing_slash(uri) + "#{Gem::MARSHAL_SPEC_DIR}#{spec_file_name}"
 
     cache_dir = cache_dir source_uri
 
@@ -174,7 +174,7 @@ class Gem::Source
     file       = FILES[type]
     fetcher    = Gem::RemoteFetcher.fetcher
     file_name  = "#{file}.#{Gem.marshal_version}"
-    spec_path  = uri + "#{file_name}.gz"
+    spec_path  = enforce_trailing_slash(uri) + "#{file_name}.gz"
     cache_dir  = cache_dir spec_path
     local_file = File.join(cache_dir, file_name)
     retried    = false
@@ -223,7 +223,13 @@ class Gem::Source
 
   def typo_squatting?(host, distance_threshold=4)
     return if @uri.host.nil?
-    levenshtein_distance(@uri.host, host) <= distance_threshold
+    levenshtein_distance(@uri.host, host).between? 1, distance_threshold
+  end
+
+  private
+
+  def enforce_trailing_slash(uri)
+    uri.merge(uri.path.gsub(/\/+$/, '') + '/')
   end
 end
 
diff --git a/lib/rubygems/spec_fetcher.rb b/lib/rubygems/spec_fetcher.rb
index f748b090cc..b2bcadc49c 100644
--- a/lib/rubygems/spec_fetcher.rb
+++ b/lib/rubygems/spec_fetcher.rb
@@ -98,7 +98,7 @@ class Gem::SpecFetcher
 
       found[source] = specs.select do |tup|
         if dependency.match?(tup)
-          if matching_platform and !Gem::Platform.match(tup.platform)
+          if matching_platform and !Gem::Platform.match_gem?(tup.platform, tup.name)
             pm = (
               rejected_specs[dependency] ||= \
                 Gem::PlatformMismatch.new(tup.name, tup.version))
diff --git a/lib/rubygems/specification.rb b/lib/rubygems/specification.rb
index cb7ec2b76d..d59f57c49f 100644
--- a/lib/rubygems/specification.rb
+++ b/lib/rubygems/specification.rb
@@ -77,18 +77,18 @@ class Gem::Specification < Gem::BasicSpecification
     -1 => ['(RubyGems versions up to and including 0.7 did not have versioned specifications)'],
     1  => [
       'Deprecated "test_suite_file" in favor of the new, but equivalent, "test_files"',
-      '"test_file=x" is a shortcut for "test_files=[x]"'
+      '"test_file=x" is a shortcut for "test_files=[x]"',
     ],
     2 => [
       'Added "required_rubygems_version"',
       'Now forward-compatible with future versions',
     ],
     3 => [
-      'Added Fixnum validation to the specification_version'
+      'Added Fixnum validation to the specification_version',
     ],
     4 => [
-      'Added sandboxed freeform metadata to the specification version.'
-    ]
+      'Added sandboxed freeform metadata to the specification version.',
+    ],
   }.freeze
 
   MARSHAL_FIELDS = { # :nodoc:
@@ -804,7 +804,7 @@ class Gem::Specification < Gem::BasicSpecification
       stubs = stubs.uniq {|stub| stub.full_name }
 
       _resort!(stubs)
-      @@stubs_by_name = stubs.select {|s| Gem::Platform.match s.platform }.group_by(&:name)
+      @@stubs_by_name = stubs.select {|s| Gem::Platform.match_spec? s }.group_by(&:name)
       stubs
     end
   end
@@ -831,7 +831,7 @@ class Gem::Specification < Gem::BasicSpecification
       @@stubs_by_name[name]
     else
       pattern = "#{name}-*.gemspec"
-      stubs = installed_stubs(dirs, pattern).select {|s| Gem::Platform.match s.platform } + default_stubs(pattern)
+      stubs = installed_stubs(dirs, pattern).select {|s| Gem::Platform.match_spec? s } + default_stubs(pattern)
       stubs = stubs.uniq {|stub| stub.full_name }.group_by(&:name)
       stubs.each_value {|v| _resort!(v) }
 
@@ -1344,7 +1344,7 @@ class Gem::Specification < Gem::BasicSpecification
       true, # has_rdoc
       @new_platform,
       @licenses,
-      @metadata
+      @metadata,
     ]
   end
 
@@ -2450,7 +2450,7 @@ class Gem::Specification < Gem::BasicSpecification
       :version,
       :has_rdoc,
       :default_executable,
-      :metadata
+      :metadata,
     ]
 
     @@attributes.each do |attr_name|
diff --git a/lib/rubygems/ssl_certs/rubygems.global.ssl.fastly.net/DigiCertHighAssuranceEVRootCA.pem b/lib/rubygems/ssl_certs/rubygems.global.ssl.fastly.net/DigiCertHighAssuranceEVRootCA.pem
deleted file mode 100644
index 9e6810ab70..0000000000
--- a/lib/rubygems/ssl_certs/rubygems.global.ssl.fastly.net/DigiCertHighAssuranceEVRootCA.pem
+++ /dev/null
@@ -1,23 +0,0 @@
------BEGIN CERTIFICATE-----
-MIIDxTCCAq2gAwIBAgIQAqxcJmoLQJuPC3nyrkYldzANBgkqhkiG9w0BAQUFADBs
-MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
-d3cuZGlnaWNlcnQuY29tMSswKQYDVQQDEyJEaWdpQ2VydCBIaWdoIEFzc3VyYW5j
-ZSBFViBSb290IENBMB4XDTA2MTExMDAwMDAwMFoXDTMxMTExMDAwMDAwMFowbDEL
-MAkGA1UEBhMCVVMxFTATBgNVBAoTDERpZ2lDZXJ0IEluYzEZMBcGA1UECxMQd3d3
-LmRpZ2ljZXJ0LmNvbTErMCkGA1UEAxMiRGlnaUNlcnQgSGlnaCBBc3N1cmFuY2Ug
-RVYgUm9vdCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMbM5XPm
-+9S75S0tMqbf5YE/yc0lSbZxKsPVlDRnogocsF9ppkCxxLeyj9CYpKlBWTrT3JTW
-PNt0OKRKzE0lgvdKpVMSOO7zSW1xkX5jtqumX8OkhPhPYlG++MXs2ziS4wblCJEM
-xChBVfvLWokVfnHoNb9Ncgk9vjo4UFt3MRuNs8ckRZqnrG0AFFoEt7oT61EKmEFB
-Ik5lYYeBQVCmeVyJ3hlKV9Uu5l0cUyx+mM0aBhakaHPQNAQTXKFx01p8VdteZOE3
-hzBWBOURtCmAEvF5OYiiAhF8J2a3iLd48soKqDirCmTCv2ZdlYTBoSUeh10aUAsg
-EsxBu24LUTi4S8sCAwEAAaNjMGEwDgYDVR0PAQH/BAQDAgGGMA8GA1UdEwEB/wQF
-MAMBAf8wHQYDVR0OBBYEFLE+w2kD+L9HAdSYJhoIAu9jZCvDMB8GA1UdIwQYMBaA
-FLE+w2kD+L9HAdSYJhoIAu9jZCvDMA0GCSqGSIb3DQEBBQUAA4IBAQAcGgaX3Nec
-nzyIZgYIVyHbIUf4KmeqvxgydkAQV8GK83rZEWWONfqe/EW1ntlMMUu4kehDLI6z
-eM7b41N5cdblIZQB2lWHmiRk9opmzN6cN82oNLFpmyPInngiK3BD41VHMWEZ71jF
-hS9OMPagMRYjyOfiZRYzy78aG6A9+MpeizGLYAiJLQwGXFK3xPkKmNEVX58Svnw2
-Yzi9RKR/5CYrCsSXaQ3pjOLAEFe4yHYSkVXySGnYvCoCWw9E1CAx2/S6cCZdkGCe
-vEsXCS+0yx5DaMkHJ8HSXPfqIbloEpw8nL+e/IBcm2PN7EeqJSdnoDfzAIJ9VNep
-+OkuE6N36B9K
------END CERTIFICATE-----
diff --git a/lib/rubygems/ssl_certs/index.rubygems.org/GlobalSignRootCA.pem b/lib/rubygems/ssl_certs/rubygems.org/GlobalSignRootCA.pem
index f4ce4ca43d..f4ce4ca43d 100644
--- a/lib/rubygems/ssl_certs/index.rubygems.org/GlobalSignRootCA.pem
+++ b/lib/rubygems/ssl_certs/rubygems.org/GlobalSignRootCA.pem
diff --git a/lib/rubygems/stub_specification.rb b/lib/rubygems/stub_specification.rb
index 5d4d761953..4246f9de86 100644
--- a/lib/rubygems/stub_specification.rb
+++ b/lib/rubygems/stub_specification.rb
@@ -29,7 +29,7 @@ class Gem::StubSpecification < Gem::BasicSpecification
     # in their require paths, so lets take advantage of that by pre-allocating
     # a require path list for that case.
     REQUIRE_PATH_LIST = { # :nodoc:
-      'lib' => ['lib'].freeze
+      'lib' => ['lib'].freeze,
     }.freeze
 
     def initialize(data, extensions)
diff --git a/lib/rubygems/test_case.rb b/lib/rubygems/test_case.rb
index 09b91b6ac6..a8261ef5c2 100644
--- a/lib/rubygems/test_case.rb
+++ b/lib/rubygems/test_case.rb
@@ -252,14 +252,14 @@ class Gem::TestCase < Minitest::Test
       msg = message(msg) do
         'Expected output containing make command "%s": %s' % [
           ('%s %s' % [make_command, target]).rstrip,
-          output.inspect
+          output.inspect,
         ]
       end
     else
       msg = message(msg) do
         'Expected make command "%s": %s' % [
           ('%s %s' % [make_command, target]).rstrip,
-          output.inspect
+          output.inspect,
         ]
       end
     end
@@ -335,6 +335,7 @@ class Gem::TestCase < Minitest::Test
     @git = ENV['GIT'] || (win_platform? ? 'git.exe' : 'git')
 
     Gem.ensure_gem_subdirectories @gemhome
+    Gem.ensure_default_gem_subdirectories @gemhome
 
     @orig_LOAD_PATH = $LOAD_PATH.dup
     $LOAD_PATH.map! do |s|
@@ -360,26 +361,23 @@ class Gem::TestCase < Minitest::Test
     Gem.send :remove_instance_variable, :@ruby_version if
       Gem.instance_variables.include? :@ruby_version
 
-    FileUtils.mkdir_p @gemhome
     FileUtils.mkdir_p @userhome
 
     ENV['GEM_PRIVATE_KEY_PASSPHRASE'] = PRIVATE_KEY_PASSPHRASE
 
-    @default_dir = File.join @tempdir, 'default'
-    @default_spec_dir = File.join @default_dir, "specifications", "default"
     if Gem.java_platform?
       @orig_default_gem_home = RbConfig::CONFIG['default_gem_home']
-      RbConfig::CONFIG['default_gem_home'] = @default_dir
+      RbConfig::CONFIG['default_gem_home'] = @gemhome
     else
-      Gem.instance_variable_set(:@default_dir, @default_dir)
+      Gem.instance_variable_set(:@default_dir, @gemhome)
     end
-    FileUtils.mkdir_p @default_spec_dir
+
+    @orig_bindir = RbConfig::CONFIG["bindir"]
+    RbConfig::CONFIG["bindir"] = File.join @gemhome, "bin"
 
     Gem::Specification.unresolved_deps.clear
     Gem.use_paths(@gemhome)
 
-    Gem::Security.reset
-
     Gem.loaded_specs.clear
     Gem.instance_variable_set(:@activated_gem_paths, 0)
     Gem.clear_default_specs
@@ -448,6 +446,8 @@ class Gem::TestCase < Minitest::Test
 
     Gem.ruby = @orig_ruby if @orig_ruby
 
+    RbConfig::CONFIG['bindir'] = @orig_bindir
+
     if Gem.java_platform?
       RbConfig::CONFIG['default_gem_home'] = @orig_default_gem_home
     else
@@ -741,7 +741,7 @@ class Gem::TestCase < Minitest::Test
 
   def install_specs(*specs)
     specs.each do |spec|
-      Gem::Installer.for_spec(spec).install
+      Gem::Installer.for_spec(spec, :force => true).install
     end
 
     Gem.searcher = nil
@@ -751,19 +751,6 @@ class Gem::TestCase < Minitest::Test
   # Installs the provided default specs including writing the spec file
 
   def install_default_gems(*specs)
-    install_default_specs(*specs)
-
-    specs.each do |spec|
-      File.open spec.loaded_from, 'w' do |io|
-        io.write spec.to_ruby_for_cache
-      end
-    end
-  end
-
-  ##
-  # Install the provided default specs
-
-  def install_default_specs(*specs)
     specs.each do |spec|
       installer = Gem::Installer.for_spec(spec, :install_as_default => true)
       installer.install
@@ -792,7 +779,7 @@ class Gem::TestCase < Minitest::Test
   def new_default_spec(name, version, deps = nil, *files)
     spec = util_spec name, version, deps
 
-    spec.loaded_from = File.join(@default_spec_dir, spec.spec_name)
+    spec.loaded_from = File.join(@gemhome, "specifications", "default", spec.spec_name)
     spec.files = files
 
     lib_dir = File.join(@tempdir, "default_gems", "lib")
@@ -1517,7 +1504,7 @@ Also, a list:
     PRIVATE_KEY = nil
     PUBLIC_KEY  = nil
     PUBLIC_CERT = nil
-  end if defined?(OpenSSL::SSL)
+  end if Gem::HAVE_OPENSSL
 end
 
 require 'rubygems/test_utilities'
diff --git a/lib/rubygems/uri_formatter.rb b/lib/rubygems/uri_formatter.rb
index ab5cc78e67..3bda896875 100644
--- a/lib/rubygems/uri_formatter.rb
+++ b/lib/rubygems/uri_formatter.rb
@@ -1,5 +1,4 @@
 # frozen_string_literal: true
-require 'cgi'
 
 ##
 # The UriFormatter handles URIs from user-input and escaping.
@@ -18,6 +17,8 @@ class Gem::UriFormatter
   # Creates a new URI formatter for +uri+.
 
   def initialize(uri)
+    require 'cgi'
+
     @uri = uri
   end
 
diff --git a/lib/rubygems/version_option.rb b/lib/rubygems/version_option.rb
index 458a7a6601..be71ef409b 100644
--- a/lib/rubygems/version_option.rb
+++ b/lib/rubygems/version_option.rb
@@ -73,4 +73,10 @@ module Gem::VersionOption
     end
   end
 
+  ##
+  # Extract platform given on the command line
+
+  def get_platform_from_requirements(requirements)
+    Gem.platforms[1].to_s if requirements.key? :added_platform
+  end
 end