Stop bumping RUBY_PATCHLEVEL in release versions (#15502)

[[Misc #21770]](https://bugs.ruby-lang.org/issues/21770)

2 files changed, 8 insertions, 1 deletions

diff --git a/test/ruby/test_rubyoptions.rb b/test/ruby/test_rubyoptions.rb
index a057e64a4a..2ec6478a7f 100644
--- a/test/ruby/test_rubyoptions.rb
+++ b/test/ruby/test_rubyoptions.rb
@@ -1319,4 +1319,10 @@ class TestRubyOptions < Test::Unit::TestCase
   def test_toplevel_ruby
     assert_instance_of Module, ::Ruby
   end
+
+  def test_ruby_patchlevel
+    # We stopped bumping RUBY_PATCHLEVEL at Ruby 4.0.0.
+    # Released versions have RUBY_PATCHLEVEL 0, and un-released versions have -1.
+    assert_include [-1, 0], RUBY_PATCHLEVEL
+  end
 end
diff --git a/tool/merger.rb b/tool/merger.rb
index 795e97a86e..2eedded66c 100755
--- a/tool/merger.rb
+++ b/tool/merger.rb
@@ -65,7 +65,8 @@ class << Merger = Object.new
     if teeny
       v[2].succ!
     end
-    if pl != '-1' # trunk does not have patchlevel
+    # We stopped bumping RUBY_PATCHLEVEL at Ruby 4.0.0.
+    if Integer(v[0]) <= 3
       pl.succ!
     end