Add Ractor#default_port

Author: soutaro

core/ractor.rbs

@@ -424,6 +424,14 @@ class Ractor
   %a{deprecated: Use Ractor.[]= instead}
   def []=: [T] (interned sym, T val) -> T
 
+  # <!--
+  #   rdoc-file=ractor.rb
+  #   - ractor.default_port -> port object
+  # -->
+  # return default port of the Ractor.
+  #
+  def default_port: () -> Port[untyped]
+
   # <!--
   #   rdoc-file=ractor.rb
   #   - inspect()

test/stdlib/Ractor_test.rb

@@ -105,6 +105,13 @@ class RactorInstanceTest < Test::Unit::TestCase
 
   testing "::Ractor"
 
+  def test_default_port
+    assert_send_type(
+      "() -> ::Ractor::Port[untyped]",
+      Ractor.current, :default_port
+    )
+  end
+
   def test_inspect
     assert_send_type "() -> String",
                      Ractor.current, :inspect