From aab7a55cd362540e7d67a2cf12c2f270d0d6bb59 Mon Sep 17 00:00:00 2001
From: lolwut <hsbt@ruby-lang.org>
Date: Thu, 12 Mar 2026 10:24:30 +0900
Subject: [ruby/rubygems] Warn when require_relative is used to load compiled
 extensions during gem build

When a gem has native extensions and uses `require_relative` to load
a path without a corresponding .rb file in the gem, warn that this
will break in RubyGems 4.2, which will stop copying compiled
extensions into the gem's lib directory. Recommend using `require`
instead.

https://github.com/ruby/rubygems/commit/1198c24a08

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 lib/rubygems/specification_policy.rb    | 28 +++++++++++++++++
 test/rubygems/test_gem_specification.rb | 55 +++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/lib/rubygems/specification_policy.rb b/lib/rubygems/specification_policy.rb
index 0fcb635394..8ab82ee4a9 100644
--- a/lib/rubygems/specification_policy.rb
+++ b/lib/rubygems/specification_policy.rb
@@ -476,6 +476,7 @@ or set it to nil if you don't want to specify a license.
 
     validate_rake_extensions(builder)
     validate_rust_extensions(builder)
+    validate_extension_require_relative
   end
 
   def validate_rust_extensions(builder) # :nodoc:
@@ -496,6 +497,33 @@ You have specified rake based extension, but rake is not added as runtime depend
     WARNING
   end
 
+  def validate_extension_require_relative # :nodoc:
+    return unless @specification.extensions.any?
+
+    require_paths = @specification.require_paths
+
+    @specification.files.each do |rb_file|
+      next unless rb_file.end_with?(".rb")
+      next unless require_paths.any? {|rp| rb_file.start_with?("#{rp}/") }
+      next unless File.file?(rb_file)
+
+      File.foreach(rb_file).with_index(1) do |line, lineno|
+        next unless line =~ /^\s*require_relative\s+["']([^"']+)["']/
+
+        required_path = Regexp.last_match(1)
+        resolved = File.join(File.dirname(rb_file), required_path)
+
+        next if @specification.files.any? {|f| f == "#{resolved}.rb" || f == resolved }
+
+        warning <<~WARNING
+          #{rb_file}:#{lineno} uses `require_relative "#{required_path}"` to load a compiled extension.
+          This will break in RubyGems 4.2, which will stop copying compiled extensions into the gem's lib directory.
+          Use `require` instead of `require_relative` to load compiled extensions.
+        WARNING
+      end
+    end
+  end
+
   def validate_unique_links
     links = @specification.metadata.slice(*METADATA_LINK_KEYS)
     grouped = links.group_by {|_key, uri| uri }
diff --git a/test/rubygems/test_gem_specification.rb b/test/rubygems/test_gem_specification.rb
index 7675ade415..cf01a40b8c 100644
--- a/test/rubygems/test_gem_specification.rb
+++ b/test/rubygems/test_gem_specification.rb
@@ -2887,6 +2887,61 @@ duplicate dependency on c (>= 1.2.3, development), (~> 1.2) use:
     end
   end
 
+  def test_validate_extension_require_relative_warning
+    util_setup_validate
+
+    Dir.chdir @tempdir do
+      @a1.extensions = ["ext/a/extconf.rb"]
+      @a1.files = %w[lib/code.rb lib/a.rb ext/a/extconf.rb]
+
+      File.write File.join("lib", "a.rb"), 'require_relative "a/a"'
+
+      use_ui @ui do
+        @a1.validate
+      end
+
+      assert_match(%r{require_relative "a/a"}, @ui.error)
+      assert_match(/will break in RubyGems 4\.2/, @ui.error)
+      assert_match(/Use `require` instead of `require_relative`/, @ui.error)
+    end
+  end
+
+  def test_validate_extension_require_relative_no_warning_when_rb_exists
+    util_setup_validate
+
+    Dir.chdir @tempdir do
+      @a1.extensions = ["ext/a/extconf.rb"]
+      @a1.files = %w[lib/code.rb lib/a.rb lib/a/a.rb ext/a/extconf.rb]
+
+      FileUtils.mkdir_p File.join("lib", "a")
+      File.write File.join("lib", "a.rb"), 'require_relative "a/a"'
+      File.write File.join("lib", "a", "a.rb"), ""
+
+      use_ui @ui do
+        @a1.validate
+      end
+
+      refute_match(/require_relative/, @ui.error)
+    end
+  end
+
+  def test_validate_extension_require_relative_no_warning_without_extensions
+    util_setup_validate
+
+    Dir.chdir @tempdir do
+      @a1.extensions = []
+      @a1.files = %w[lib/code.rb lib/a.rb]
+
+      File.write File.join("lib", "a.rb"), 'require_relative "a/a"'
+
+      use_ui @ui do
+        @a1.validate
+      end
+
+      refute_match(/require_relative/, @ui.error)
+    end
+  end
+
   def test_validate_description
     util_setup_validate
 
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