Deprecate Random::DEFAULT

* Closes [Feature #17351].

NEWS.md

@@ -269,6 +269,17 @@ Outstanding ones only.
     * New class added to enable parallel execution. See doc/ractor.md for
       more details.
 
+* Random
+
+    * `Random::DEFAULT` now refers to the `Random` class instead of being a `Random` instance,
+      so it can work with `Ractor`.
+      [[Feature #17322]]
+
+    * `Random::DEFAULT` is deprecated since its value is now confusing and it is no longer global,
+      use `Kernel.rand`/`Random.rand` directly, or create a `Random` instance with `Random.new` instead.
+      [[Feature #17351]]
+
+
 * String
 
     * The following methods now return or yield String instances
@@ -652,5 +663,7 @@ end
 [Feature #17187]: https://bugs.ruby-lang.org/issues/17187
 [Bug #17221]:     https://bugs.ruby-lang.org/issues/17221
 [Feature #17260]: https://bugs.ruby-lang.org/issues/17260
+[Feature #17322]: https://bugs.ruby-lang.org/issues/17322
+[Feature #17351]: https://bugs.ruby-lang.org/issues/17351
 [Feature #17371]: https://bugs.ruby-lang.org/issues/17371
 [GH-2991]:        https://github.com/ruby/ruby/pull/2991

random.c

@@ -61,6 +61,7 @@
 #include "internal/numeric.h"
 #include "internal/random.h"
 #include "internal/sanitizers.h"
+#include "internal/variable.h"
 #include "ruby_atomic.h"
 #include "ruby/random.h"
 #include "ruby/ractor.h"
@@ -1716,6 +1717,7 @@ InitVM_Random(void)
     rb_define_method(rb_cRandom, "==", rand_mt_equal, 1);
 
     rb_define_const(rb_cRandom, "DEFAULT", rb_cRandom);
+    rb_deprecate_constant(rb_cRandom, "DEFAULT");
 
     rb_define_singleton_method(rb_cRandom, "srand", rb_f_srand, -1);
     rb_define_singleton_method(rb_cRandom, "rand", random_s_rand, -1);

spec/ruby/core/random/default_spec.rb

@@ -3,21 +3,33 @@ require_relative '../../spec_helper'
 describe "Random::DEFAULT" do
 
   it "returns a random number generator" do
+    suppress_warning do
       Random::DEFAULT.should respond_to(:rand)
     end
+  end
 
   ruby_version_is ''...'3.0' do
     it "returns a Random instance" do
+      suppress_warning do
         Random::DEFAULT.should be_an_instance_of(Random)
       end
     end
+  end
 
   ruby_version_is '3.0' do
     it "refers to the Random class" do
+      suppress_warning do
         Random::DEFAULT.should.equal?(Random)
       end
     end
 
+    it "is deprecated" do
+      -> {
+        Random::DEFAULT.should.equal?(Random)
+      }.should complain(/constant Random::DEFAULT is deprecated/)
+    end
+  end
+
   it "changes seed on reboot" do
     seed1 = ruby_exe('p Random::DEFAULT.seed', options: '--disable-gems')
     seed2 = ruby_exe('p Random::DEFAULT.seed', options: '--disable-gems')

test/ruby/test_rand.rb

@@ -394,8 +394,10 @@ class TestRand < Test::Unit::TestCase
   def test_default_seed
     assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
     begin;
+      verbose, $VERBOSE = $VERBOSE, nil
       seed = Random::DEFAULT::seed
       rand1 = Random::DEFAULT::rand
+      $VERBOSE = verbose
       rand2 = Random.new(seed).rand
       assert_equal(rand1, rand2)