Fix memory leak in prism when syntax error in iseq compilation

If there's a syntax error during iseq compilation then prism would leak
memory because it would not free the pm_parse_result_t.

This commit changes pm_iseq_new_with_opt to have a rb_protect to catch
when an error is raised, and return NULL and set error_state to a value
that can be raised by calling rb_jump_tag after memory has been freed.

For example:

    10.times do
      10_000.times do
        eval("/[/=~s")
      rescue SyntaxError
      end

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

Before:

    39280
    68736
    99232
    128864
    158896
    188208
    217344
    246304
    275376
    304592

After:

    12192
    13200
    14256
    14848
    16000
    16000
    16000
    16064
    17232
    17952

1 files changed, 24 insertions, 0 deletions

diff --git a/test/ruby/test_eval.rb b/test/ruby/test_eval.rb
index cf1c2bb2f6..2129272b00 100644
--- a/test/ruby/test_eval.rb
+++ b/test/ruby/test_eval.rb
@@ -612,4 +612,28 @@ class TestEval < Test::Unit::TestCase
     x = orphan_lambda
     assert_equal(:ok, x.call)
   end
+
+  def test_syntax_error_no_memory_leak
+    assert_no_memory_leak([], "#{<<~'begin;'}", "#{<<~'end;'}", rss: true)
+    begin;
+      100_000.times do
+        eval("/[/=~s")
+      rescue SyntaxError
+      else
+        raise "Expected SyntaxError to be raised"
+      end
+    end;
+
+    assert_no_memory_leak([], "#{<<~'begin;'}", "#{<<~'end;'}", rss: true)
+    begin;
+      a = 1
+
+      100_000.times do
+        eval("if a in [0, 0] | [0, a]; end")
+      rescue SyntaxError
+      else
+        raise "Expected SyntaxError to be raised"
+      end
+    end;
+  end
 end