merge revision(s) 9e0a91d0640600f2dfd7fc1d5fae6667019c9ca5: [Backport #18458]

	Don't segfault if Warning.warn is undefined

	Check that there is a method entry for the method before passing
	it to rb_method_entry_arity.

	Fixes [Bug #18458]
	---
	 error.c                     | 3 ++-
	 test/ruby/test_exception.rb | 8 ++++++++
	 2 files changed, 10 insertions(+), 1 deletion(-)

1 files changed, 8 insertions, 0 deletions

diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 087bcda5ac..0f3e11b566 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -1100,6 +1100,14 @@ $stderr = $stdout; raise "\x82\xa0"') do |outs, errs, status|
     assert_empty warning
   end
 
+  def test_undef_Warning_warn
+    assert_separately([], "#{<<-"begin;"}\n#{<<-"end;"}")
+    begin;
+      Warning.undef_method(:warn)
+      assert_raise(NoMethodError) { warn "" }
+    end;
+  end
+
   def test_undefined_backtrace
     assert_separately([], "#{<<-"begin;"}\n#{<<-"end;"}")
     begin;