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]

1 files changed, 8 insertions, 0 deletions

diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 2985f75fd6..3be9b9aee0 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -1192,6 +1192,14 @@ $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;