merge revision(s) 7ff1bf317887c0d7b21e91ad548d07b9f05c540c,e89d80702bd98a8276243a7fcaa2a158b3bfb659: [Backport #18516]

    An alias can suppress method redefinition warning

    ---
     test/ruby/test_alias.rb | 11 +++++++++++
     1 file changed, 11 insertions(+)

    Fix memory leak at the same named alias [Bug #18516]

    When aliasing a method to the same name method, set a separate bit
    flag on that method definition, instead of the reference count
    increment.  Although this kind of alias has no actual effect at
    runtime, is used as the hack to suppress the method re-definition
    warning.
    ---
     method.h                |  1 +
     test/ruby/test_alias.rb | 18 ++++++++++++++++++
     vm_method.c             |  9 ++++++++-
     3 files changed, 27 insertions(+), 1 deletion(-)

1 files changed, 29 insertions, 0 deletions

diff --git a/test/ruby/test_alias.rb b/test/ruby/test_alias.rb
index 33fb82e1d7..1acf12f7f3 100644
--- a/test/ruby/test_alias.rb
+++ b/test/ruby/test_alias.rb
@@ -227,4 +227,33 @@ class TestAlias < Test::Unit::TestCase
     assert_equal(:foo, k.instance_method(:bar).original_name)
     assert_equal(:foo, name)
   end
+
+  def test_alias_suppressing_redefinition
+    assert_in_out_err(%w[-w], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      class A
+        def foo; end
+        alias foo foo
+        def foo; end
+      end
+    end;
+  end
+
+  def test_alias_memory_leak
+    assert_no_memory_leak([], "#{<<~"begin;"}", "#{<<~'end;'}", rss: true)
+    begin;
+      class A
+        500.times do
+          1000.times do |i|
+            define_method(:"foo_#{i}") {}
+
+            alias :"foo_#{i}" :"foo_#{i}"
+
+            remove_method :"foo_#{i}"
+          end
+          GC.start
+        end
+      end
+    end;
+  end
 end