save/restore arena index around yield; ref #3359

mrbgems/mruby-string-ext/src/string.c

@@ -315,7 +315,7 @@ mrb_str_lines(mrb_state *mrb, mrb_value self)
   mrb_get_args(mrb, "&", &blk);
 
   result = mrb_ary_new(mrb);
-
+  ai = mrb_gc_arena_save(mrb);
   if (!mrb_nil_p(blk)) {
     while (p < e) {
       t = p;
@@ -324,6 +324,7 @@ mrb_str_lines(mrb_state *mrb, mrb_value self)
       len = (mrb_int) (p - t);
       arg = mrb_str_new(mrb, t, len);
       mrb_yield_argv(mrb, blk, 1, &arg);
+      mrb_gc_arena_restore(mrb, ai);
       if (b != RSTRING_PTR(self)) {
         ptrdiff_t diff = p - b;
         b = RSTRING_PTR(self);
@@ -334,7 +335,6 @@ mrb_str_lines(mrb_state *mrb, mrb_value self)
     return self;
   }
   while (p < e) {
-    ai = mrb_gc_arena_save(mrb);
     t = p;
     while (p < e && *p != '\n') p++;
     if (*p == '\n') p++;