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, 8 insertions, 1 deletions

diff --git a/load.c b/load.c
index e4dd1e47ba..19d0849bc7 100644
--- a/load.c
+++ b/load.c
@@ -752,8 +752,15 @@ load_iseq_eval(rb_execution_context_t *ec, VALUE fname)
             VALUE error = pm_load_parse_file(&result, fname, NULL);
 
             if (error == Qnil) {
-                iseq = pm_iseq_new_top(&result.node, rb_fstring_lit("<top (required)>"), fname, realpath_internal_cached(realpath_map, fname), NULL);
+                int error_state;
+                iseq = pm_iseq_new_top(&result.node, rb_fstring_lit("<top (required)>"), fname, realpath_internal_cached(realpath_map, fname), NULL, &error_state);
+
                 pm_parse_result_free(&result);
+
+                if (error_state) {
+                    RUBY_ASSERT(iseq == NULL);
+                    rb_jump_tag(error_state);
+                }
             }
             else {
                 rb_vm_pop_frame(ec);