Remove SortedSet autoload and set/sorted_set

Implements [Feature #21287]

NEWS.md

@@ -105,6 +105,11 @@ The following bundled gems are updated.
 
     [[Feature #21258]]
 
+* With the move of `Set` from stdlib to core class, `set/sorted_set.rb` has
+  been removed, and `SortedSet` is no longer an autoloaded constant. Please
+  install the `sorted_set` gem and `require 'sorted_set'` to use `SortedSet`.
+  [[Feature #21287]]
+
 ## C API updates
 
 * IO
@@ -130,3 +135,4 @@ The following bundled gems are updated.
 [Bug #21049]:     https://bugs.ruby-lang.org/issues/21049
 [Feature #21216]: https://bugs.ruby-lang.org/issues/21216
 [Feature #21258]: https://bugs.ruby-lang.org/issues/21258
+[Feature #21287]: https://bugs.ruby-lang.org/issues/21287

lib/set/sorted_set.rb

@@ -1,6 +0,0 @@
-begin
-  require 'sorted_set'
-rescue ::LoadError
-  raise "The `SortedSet` class has been extracted from the `set` library. " \
-        "You must use the `sorted_set` gem or other alternatives."
-end

prelude.rb

@@ -26,8 +26,6 @@ module Kernel
   private :pp
 end
 
-autoload :SortedSet, 'set/sorted_set'
-
 module Enumerable
   # Makes a set from the enumerable object with given arguments.
   def to_set(klass = Set, *args, &block)

spec/ruby/core/set/sortedset/sortedset_spec.rb

@@ -1,6 +1,7 @@
 require_relative '../../../spec_helper'
 
 describe "SortedSet" do
+  ruby_version_is ""..."3.5" do
     it "raises error including message that it has been extracted from the set stdlib" do
       -> {
         SortedSet
@@ -8,4 +9,5 @@ describe "SortedSet" do
         e.message.should.include?("The `SortedSet` class has been extracted from the `set` library")
       }
     end
+  end
 end

test/set/fixtures/fake_sorted_set_gem/sorted_set.rb

@@ -1,9 +0,0 @@
-Object.instance_exec do
-  # Remove the constant to cancel autoload that would be fired by
-  # `class SortedSet` and cause circular require.
-  remove_const :SortedSet if const_defined?(:SortedSet)
-end
-
-class SortedSet < Set
-  # ...
-end

test/set/test_sorted_set.rb

@@ -1,45 +0,0 @@
-# frozen_string_literal: false
-require 'test/unit'
-require 'set'
-
-class TC_SortedSet < Test::Unit::TestCase
-  def base_dir
-    "#{__dir__}/../lib"
-  end
-
-  def assert_runs(ruby, options: nil)
-    options = ['-I', base_dir, *options]
-    r = system(RbConfig.ruby, *options, '-e', ruby)
-    assert(r)
-  end
-
-  def test_error
-    assert_runs <<~RUBY
-      require "set"
-
-      r = begin
-        puts SortedSet.new
-      rescue Exception => e
-        e.message
-      end
-      raise r unless r.match?(/has been extracted/)
-    RUBY
-  end
-
-  def test_ok_with_gem
-    assert_runs <<~RUBY, options: ['-I', "#{__dir__}/fixtures/fake_sorted_set_gem"]
-      require "set"
-
-      var = SortedSet.new.to_s
-    RUBY
-  end
-
-  def test_ok_require
-    assert_runs <<~RUBY, options: ['-I', "#{__dir__}/fixtures/fake_sorted_set_gem"]
-      require "set"
-      require "sorted_set"
-
-      var = SortedSet.new.to_s
-    RUBY
-  end
-end