From 4ace702de4bf0c4f20cc11ac766677085921789d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E3=81=AA=E3=81=A4=E3=81=8D?= <i@ntk.me>
Date: Fri, 24 Oct 2025 17:20:31 -0700
Subject: [PATCH] Add Sass::GemPackageImporter

---
 lib/sass/compiler.rb                   |  1 +
 lib/sass/gem_package_importer.rb       | 18 ++++++++
 spec/sass/gem_package_importer_spec.rb | 61 ++++++++++++++++++++++++++
 3 files changed, 80 insertions(+)
 create mode 100644 lib/sass/gem_package_importer.rb
 create mode 100644 spec/sass/gem_package_importer_spec.rb

diff --git a/lib/sass/compiler.rb b/lib/sass/compiler.rb
index 0d118152..79a5516a 100644
--- a/lib/sass/compiler.rb
+++ b/lib/sass/compiler.rb
@@ -11,6 +11,7 @@
 require_relative 'embedded_protocol'
 require_relative 'exception'
 require_relative 'fork_tracker'
+require_relative 'gem_package_importer'
 require_relative 'logger/silent'
 require_relative 'logger/source_location'
 require_relative 'logger/source_span'
diff --git a/lib/sass/gem_package_importer.rb b/lib/sass/gem_package_importer.rb
new file mode 100644
index 00000000..b0b0eee2
--- /dev/null
+++ b/lib/sass/gem_package_importer.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Sass
+  # The built-in RubyGems package importer. This loads pkg: URLs from gems.
+  class GemPackageImporter
+    # @!visibility private
+    def find_file_url(url, _canonicalize_context)
+      return unless url.start_with?('pkg:')
+
+      library, _, path = url[4..].partition('/')
+      gem_dir = Gem::Dependency.new(library).to_spec.gem_dir
+
+      "file://#{'/' unless gem_dir.start_with?('/')}#{gem_dir}/#{path}"
+    rescue Gem::MissingSpecError
+      nil
+    end
+  end
+end
diff --git a/spec/sass/gem_package_importer_spec.rb b/spec/sass/gem_package_importer_spec.rb
new file mode 100644
index 00000000..cce9ebd6
--- /dev/null
+++ b/spec/sass/gem_package_importer_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Sass::GemPackageImporter do
+  around do |example|
+    require 'bundler/inline'
+
+    sandbox do |dir|
+      dir.write({
+                  '_test.scss' => '/* test */',
+                  '_index.scss' => '@use "test";',
+                  'test.gemspec' => <<~GEMSPEC
+                    Gem::Specification.new do |spec|
+                      spec.name = 'test'
+                      spec.summary = 'test'
+                      spec.authors = ['test']
+                      spec.version = '0.0.1'
+                      spec.files = Dir['**/*']
+                    end
+                  GEMSPEC
+                })
+
+      gemfile do
+        gem 'test', path: dir.path, require: false
+      end
+
+      example.call
+    end
+  end
+
+  describe 'resolves pkg: url' do
+    it 'without subpath' do
+      expect(Sass.compile_string('@use "pkg:test";',
+                                 importers: [described_class.new],
+                                 logger: Sass::Logger.silent).css)
+        .to eq('/* test */')
+    end
+
+    it 'with subpath' do
+      expect(Sass.compile_string('@use "pkg:test/test";',
+                                 importers: [described_class.new],
+                                 logger: Sass::Logger.silent).css)
+        .to eq('/* test */')
+    end
+
+    it 'with uppercase scheme' do
+      expect(Sass.compile_string('@use "PKG:test";',
+                                 importers: [described_class.new],
+                                 logger: Sass::Logger.silent).css)
+        .to eq('/* test */')
+    end
+
+    it 'with precent-encoding' do
+      expect(Sass.compile_string('@use "pkg:%74%65%73%74";',
+                                 importers: [described_class.new],
+                                 logger: Sass::Logger.silent).css)
+        .to eq('/* test */')
+    end
+  end
+end