Make Gem::CompactIndexClient loadable from a Bundler-shipped copy

The client's subfiles reached sibling RubyGems files with cross-tree
require_relative, which breaks when the copy shipped inside the Bundler
gem is loaded on an older RubyGems: the relative targets are not part of
that copy. Require them by feature name instead so they resolve against
the host RubyGems. vendored_net_http is newer than the oldest supported
host, so require it defensively; in the Bundler context Gem::Net is
always defined by Bundler's own shim before this file loads. Also guard
the entry point against double loading when the host copy and the
shipped copy are required from different paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hsbt

lib/rubygems/compact_index_client.rb

@@ -1,5 +1,9 @@
 # frozen_string_literal: true
 
+# Skip reloading when an identical copy (e.g. the one shipped inside the Bundler
+# gem) was already required from a different path, to avoid redefinition warnings.
+return if defined?(Gem::CompactIndexClient::INFO_REQS)
+
 ##
 # The CompactIndexClient fetches and parses the compact index files
 # (names, versions and info/[gem]) served by a gem server, keeping a

lib/rubygems/compact_index_client/cache_file.rb

@@ -2,7 +2,7 @@
 
 require "digest"
 require "fileutils"
-require_relative "../package"
+require "rubygems/package"
 
 class Gem::CompactIndexClient
   # write cache files in a way that is robust to concurrent modifications

lib/rubygems/compact_index_client/http_fetcher.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "../remote_fetcher"
+require "rubygems/remote_fetcher"
 
 class Gem::CompactIndexClient
   # Fetches compact index files relative to +base_uri+ using

lib/rubygems/compact_index_client/parser.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require_relative "../resolver/api_set/gem_parser"
+require "rubygems/resolver/api_set/gem_parser"
 
 class Gem::CompactIndexClient
   class Parser

lib/rubygems/compact_index_client/updater.rb

@@ -1,7 +1,15 @@
 # frozen_string_literal: true
 
 require "zlib"
-require_relative "../vendored_net_http"
+
+# On RubyGems versions too old to vendor Gem::Net (when this file is loaded
+# from the copy shipped inside the Bundler gem), Bundler's own
+# vendored_net_http shim has already defined it before this file is loaded.
+begin
+  require "rubygems/vendored_net_http" unless defined?(Gem::Net::HTTP)
+rescue LoadError
+  require "net/http"
+end
 
 class Gem::CompactIndexClient
   # Updates the cached files on disk, keeping them in sync with the server