[rubygems/rubygems] Extract generate_index command to rubygems-genera…

…te_index gem

So generate_index can be implemented with dependencies, such as the compact index

Took this approach from feedback in rubygems/rubygems#6853

Running `gem generate_index` by default will use an installed rubygems-generate_index, or install and then use the command from the gem

Apply suggestions from code review

rubygems/rubygems@fc1cb9bc9e

Co-authored-by: Hiroshi SHIBATA <hsbt@ruby-lang.org>

lib/rubygems/command_manager.rb

@@ -249,6 +249,7 @@ def load_and_instantiate(command_name)
   def invoke_command(args, build_args)
     cmd_name = args.shift.downcase
     cmd = find_command cmd_name
+    terminate_interaction 1 unless cmd
     cmd.deprecation_warning if cmd.deprecated?
     cmd.invoke_with_build_args args, build_args
   end

lib/rubygems/commands/generate_index_command.rb

@@ -1,86 +1,51 @@
 # frozen_string_literal: true
 
 require_relative "../command"
-require_relative "../indexer"
 
-##
-# Generates a index files for use as a gem server.
-#
-# See `gem help generate_index`
-
-class Gem::Commands::GenerateIndexCommand < Gem::Command
-  def initialize
-    super "generate_index",
-          "Generates the index files for a gem server directory",
-          directory: ".", build_modern: true
+unless defined? Gem::Commands::GenerateIndexCommand
+  class Gem::Commands::GenerateIndexCommand < Gem::Command
+    module RubygemsTrampoline
+      def description # :nodoc:
+        <<~EOF
+          The generate_index command has been moved to the rubygems-generate_index gem.
+        EOF
+      end
 
-    add_option "-d", "--directory=DIRNAME",
-               "repository base dir containing gems subdir" do |dir, options|
-      options[:directory] = File.expand_path dir
-    end
+      def execute
+        alert_error "Install the rubygems-generate_index gem for the generate_index command"
+      end
 
-    add_option "--[no-]modern",
-               "Generate indexes for RubyGems",
-               "(always true)" do |value, options|
-      options[:build_modern] = value
+      def invoke_with_build_args(args, build_args)
+        name = "rubygems-generate_index"
+        spec = begin
+          Gem::Specification.find_by_name(name)
+        rescue Gem::LoadError
+          require "rubygems/dependency_installer"
+          Gem.install(name, Gem::Requirement.default, Gem::DependencyInstaller::DEFAULT_OPTIONS).find {|s| s.name == name }
+        end
+
+        # remove the methods defined in this file so that the methods defined in the gem are used instead,
+        # and without a method redefinition warning
+        %w[description execute invoke_with_build_args].each do |method|
+          RubygemsTrampoline.remove_method(method)
+        end
+        self.class.singleton_class.remove_method(:new)
+
+        spec.activate
+        Gem.load_plugin_files spec.matches_for_glob("rubygems_plugin#{Gem.suffix_pattern}")
+
+        self.class.new.invoke_with_build_args(args, build_args)
+      end
     end
+    private_constant :RubygemsTrampoline
 
-    deprecate_option("--modern", version: "4.0", extra_msg: "Modern indexes (specs, latest_specs, and prerelease_specs) are always generated, so this option is not needed.")
-    deprecate_option("--no-modern", version: "4.0", extra_msg: "The `--no-modern` option is currently ignored. Modern indexes (specs, latest_specs, and prerelease_specs) are always generated.")
-
-    add_option "--update",
-               "Update modern indexes with gems added",
-               "since the last update" do |value, options|
-      options[:update] = value
+    # remove_method(:initialize) warns, but removing new does not warn
+    def self.new
+      command = allocate
+      command.send(:initialize, "generate_index", "Generates the index files for a gem server directory (requires rubygems-generate_index)")
+      command
     end
-  end
-
-  def defaults_str # :nodoc:
-    "--directory . --modern"
-  end
-
-  def description # :nodoc:
-    <<-EOF
-The generate_index command creates a set of indexes for serving gems
-statically.  The command expects a 'gems' directory under the path given to
-the --directory option.  The given directory will be the directory you serve
-as the gem repository.
 
-For `gem generate_index --directory /path/to/repo`, expose /path/to/repo via
-your HTTP server configuration (not /path/to/repo/gems).
-
-When done, it will generate a set of files like this:
-
-  gems/*.gem                                   # .gem files you want to
-                                               # index
-
-  specs.<version>.gz                           # specs index
-  latest_specs.<version>.gz                    # latest specs index
-  prerelease_specs.<version>.gz                # prerelease specs index
-  quick/Marshal.<version>/<gemname>.gemspec.rz # Marshal quick index file
-
-The .rz extension files are compressed with the inflate algorithm.
-The Marshal version number comes from ruby's Marshal::MAJOR_VERSION and
-Marshal::MINOR_VERSION constants.  It is used to ensure compatibility.
-    EOF
-  end
-
-  def execute
-    # This is always true because it's the only way now.
-    options[:build_modern] = true
-
-    if !File.exist?(options[:directory]) ||
-       !File.directory?(options[:directory])
-      alert_error "unknown directory name #{options[:directory]}."
-      terminate_interaction 1
-    else
-      indexer = Gem::Indexer.new options.delete(:directory), options
-
-      if options[:update]
-        indexer.update_index
-      else
-        indexer.generate_index
-      end
-    end
+    prepend(RubygemsTrampoline)
   end
 end

lib/rubygems/commands/help_command.rb

@@ -333,7 +333,7 @@ def show_commands # :nodoc:
     @command_manager.command_names.each do |cmd_name|
       command = @command_manager[cmd_name]
 
-      next if command.deprecated?
+      next if command&.deprecated?
 
       summary =
         if command