Fix memory leak in syntax error in prism

If there is a syntax error, there could be an ast_node in the result.
This could get leaked if there is a syntax error so parsing could not
complete (parsed is not set to true).

For example, the following script leaks memory:

    10.times do
      10_000.times do
        eval("def foo(...) super(...) {}; end")
      rescue SyntaxError
      end

      puts `ps -o rss= -p #{$$}`
    end

Before:

    31328
    42768
    53856
    65120
    76208
    86768
    97856
    109120
    120208
    131296

After:

    20944
    20944
    20944
    20944
    20944
    20944
    20944
    20944
    20944
    20944

1 files changed, 14 insertions, 0 deletions

diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 7a6c66d782..edf5886a53 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -2204,6 +2204,20 @@ eom
     assert_syntax_error('def foo(...) super(1, ...) {}; end', /both block arg and actual block/)
   end
 
+  def test_argument_forwarding_with_super_memory_leak
+    assert_no_memory_leak([], "#{<<-'begin;'}", "#{<<-'end;'}", rss: true)
+      code = proc do
+        eval("def foo(...) super(...) {}; end")
+        raise "unreachable"
+      rescue SyntaxError
+      end
+
+      1_000.times(&code)
+    begin;
+      100_000.times(&code)
+    end;
+  end
+
   def test_class_module_Object_ancestors
     assert_separately([], <<-RUBY)
       m = Module.new