[ruby/rubygems] Add global gem cache shared by RubyGems and Bundler

Add opt-in support for a global .gem file cache at ~/.cache/gem/gems
(respects XDG_CACHE_HOME). This allows sharing cached gems across all
Ruby installations and between RubyGems and Bundler.

Enable via:
- Environment: RUBYGEMS_GLOBAL_GEM_CACHE=true
- gemrc: global_gem_cache: true
- Bundler: bundle config set global_gem_cache true

When enabled, RubyGems checks the global cache before downloading and
copies downloaded gems to the cache. Bundler's existing global_gem_cache
setting now uses the same unified cache location.

https://github.com/ruby/rubygems/commit/417e10d6a1

2 files changed, 97 insertions, 0 deletions

diff --git a/test/rubygems/test_gem_config_file.rb b/test/rubygems/test_gem_config_file.rb
index 4230eda4d3..79bf5f582c 100644
--- a/test/rubygems/test_gem_config_file.rb
+++ b/test/rubygems/test_gem_config_file.rb
@@ -83,6 +83,33 @@ class TestGemConfigFile < Gem::TestCase
     util_config_file %W[--config-file #{@temp_conf}]
 
     assert_equal true, @cfg.ipv4_fallback_enabled
+  ensure
+    ENV.delete("IPV4_FALLBACK_ENABLED")
+  end
+
+  def test_initialize_global_gem_cache_default
+    util_config_file %W[--config-file #{@temp_conf}]
+
+    assert_equal false, @cfg.global_gem_cache
+  end
+
+  def test_initialize_global_gem_cache_env
+    ENV["RUBYGEMS_GLOBAL_GEM_CACHE"] = "true"
+    util_config_file %W[--config-file #{@temp_conf}]
+
+    assert_equal true, @cfg.global_gem_cache
+  ensure
+    ENV.delete("RUBYGEMS_GLOBAL_GEM_CACHE")
+  end
+
+  def test_initialize_global_gem_cache_gemrc
+    File.open @temp_conf, "w" do |fp|
+      fp.puts "global_gem_cache: true"
+    end
+
+    util_config_file %W[--config-file #{@temp_conf}]
+
+    assert_equal true, @cfg.global_gem_cache
   end
 
   def test_initialize_handle_arguments_config_file
diff --git a/test/rubygems/test_gem_remote_fetcher.rb b/test/rubygems/test_gem_remote_fetcher.rb
index 9badd75b42..e914e91677 100644
--- a/test/rubygems/test_gem_remote_fetcher.rb
+++ b/test/rubygems/test_gem_remote_fetcher.rb
@@ -575,6 +575,76 @@ class TestGemRemoteFetcher < Gem::TestCase
     end
   end
 
+  def test_download_with_global_gem_cache
+    # Use a temp directory to safely test global cache behavior
+    test_cache_dir = File.join(@tempdir, "global_gem_cache_test")
+
+    Gem.stub :global_gem_cache_path, test_cache_dir do
+      Gem.configuration.global_gem_cache = true
+
+      # Use the real RemoteFetcher with stubbed fetch_path
+      fetcher = Gem::RemoteFetcher.fetcher
+      def fetcher.fetch_path(uri, *rest)
+        File.binread File.join(@test_gem_dir, "a-1.gem")
+      end
+      fetcher.instance_variable_set(:@test_gem_dir, File.dirname(@a1_gem))
+
+      a1_cache_gem = @a1.cache_file
+      assert_equal a1_cache_gem, fetcher.download(@a1, "http://gems.example.com")
+
+      # Verify gem was also copied to global cache
+      global_cache_gem = File.join(test_cache_dir, @a1.file_name)
+      assert File.exist?(global_cache_gem), "Gem should be copied to global cache"
+    end
+  ensure
+    Gem.configuration.global_gem_cache = false
+  end
+
+  def test_download_uses_global_gem_cache
+    # Use a temp directory to safely test global cache behavior
+    test_cache_dir = File.join(@tempdir, "global_gem_cache_test")
+
+    Gem.stub :global_gem_cache_path, test_cache_dir do
+      Gem.configuration.global_gem_cache = true
+
+      # Pre-populate global cache
+      FileUtils.mkdir_p test_cache_dir
+      global_cache_gem = File.join(test_cache_dir, @a1.file_name)
+      FileUtils.cp @a1_gem, global_cache_gem
+
+      fetcher = Gem::RemoteFetcher.fetcher
+
+      # Should return global cache path without downloading
+      result = fetcher.download(@a1, "http://gems.example.com")
+      assert_equal global_cache_gem, result
+    end
+  ensure
+    Gem.configuration.global_gem_cache = false
+  end
+
+  def test_download_without_global_gem_cache
+    # Use a temp directory to safely test global cache behavior
+    test_cache_dir = File.join(@tempdir, "global_gem_cache_test")
+
+    Gem.stub :global_gem_cache_path, test_cache_dir do
+      Gem.configuration.global_gem_cache = false
+
+      # Use the real RemoteFetcher with stubbed fetch_path
+      fetcher = Gem::RemoteFetcher.fetcher
+      def fetcher.fetch_path(uri, *rest)
+        File.binread File.join(@test_gem_dir, "a-1.gem")
+      end
+      fetcher.instance_variable_set(:@test_gem_dir, File.dirname(@a1_gem))
+
+      a1_cache_gem = @a1.cache_file
+      assert_equal a1_cache_gem, fetcher.download(@a1, "http://gems.example.com")
+
+      # Verify gem was NOT copied to global cache
+      global_cache_gem = File.join(test_cache_dir, @a1.file_name)
+      refute File.exist?(global_cache_gem), "Gem should not be copied to global cache when disabled"
+    end
+  end
+
   private
 
   def assert_error(exception_class = Exception)