Assume UTF-8 when detecting Rails

lib/ruby_lsp/setup_bundler.rb

@@ -286,7 +286,7 @@ def correct_relative_remote_paths
     sig { returns(T::Boolean) }
     def rails_app?
       config = Pathname.new("config/application.rb").expand_path
-      application_contents = config.read if config.exist?
+      application_contents = config.read(external_encoding: Encoding::UTF_8) if config.exist?
       return false unless application_contents
 
       /class .* < (::)?Rails::Application/.match?(application_contents)

sorbet/rbi/shims/encoding.rbi

@@ -0,0 +1,7 @@
+# typed: true
+
+class Encoding < Object
+  sig {returns(Encoding)}
+  sig {returns(String)}
+  def self.default_external; end
+end

sorbet/rbi/shims/pathname.rbi

@@ -0,0 +1,16 @@
+# typed: false
+
+class Pathname
+  sig do
+    params(
+      external_encoding: T.any(String, Encoding),
+      internal_encoding: T.any(String, Encoding),
+      encoding: T.any(String, Encoding),
+      textmode: BasicObject,
+      binmode: BasicObject,
+      autoclose: BasicObject,
+      mode: String,
+    ).returns(String)
+  end
+  def read(external_encoding: T.unsafe(nil), internal_encoding: T.unsafe(nil), encoding: T.unsafe(nil), textmode: T.unsafe(nil), binmode: T.unsafe(nil), autoclose: T.unsafe(nil), mode: T.unsafe(nil)); end
+end

test/fixtures/rails_application.rb

@@ -1,4 +1,5 @@
 module MyApp
   class Application < Rails::Application
+    # あ
   end
 end

test/setup_bundler_test.rb

@@ -506,6 +506,39 @@ def test_ruby_lsp_rails_is_automatically_included_in_rails_apps
     end
   end
 
+  def test_ruby_lsp_rails_detection_handles_lang_from_environment
+    with_default_external_encoding("us-ascii") do
+      Dir.mktmpdir do |dir|
+        FileUtils.mkdir("#{dir}/config")
+        FileUtils.cp("test/fixtures/rails_application.rb", "#{dir}/config/application.rb")
+        Dir.chdir(dir) do
+          File.write(File.join(dir, "Gemfile"), <<~GEMFILE)
+            source "https://rubygems.org"
+            gem "rails"
+          GEMFILE
+
+          capture_subprocess_io do
+            Bundler.with_unbundled_env do
+              # Run bundle install to generate the lockfile
+              system("bundle install")
+            end
+          end
+
+          Object.any_instance.expects(:system).with(
+            bundle_env(dir, ".ruby-lsp/Gemfile"),
+            "(bundle check || bundle install) 1>&2",
+          ).returns(true)
+          Bundler.with_unbundled_env do
+            run_script(dir)
+          end
+
+          assert_path_exists(".ruby-lsp/Gemfile")
+          assert_match('gem "ruby-lsp-rails"', File.read(".ruby-lsp/Gemfile"))
+        end
+      end
+    end
+  end
+
   def test_recovers_from_stale_lockfiles
     Dir.mktmpdir do |dir|
       custom_dir = File.join(dir, ".ruby-lsp")
@@ -575,6 +608,30 @@ def test_recovers_from_stale_lockfiles
 
   private
 
+  def with_default_external_encoding(encoding, &block)
+    ignore_warnings do
+      original_encoding = Encoding.default_external
+      begin
+        Encoding.default_external = encoding
+        block.call
+      ensure
+        Encoding.default_external = original_encoding
+      end
+    end
+  end
+
+  def ignore_warnings(&block)
+    # Since overwriting the encoding emits a warning
+    previous = $VERBOSE
+    $VERBOSE = nil
+
+    begin
+      block.call
+    ensure
+      $VERBOSE = previous
+    end
+  end
+
   # This method runs the script and then immediately unloads it. This allows us to make assertions against the effects
   # of running the script multiple times
   def run_script(path = Dir.pwd, expected_path: nil, **options)