Introduce NODE_SYM to manage symbol literal

`:sym` was managed by `NODE_LIT` with `Symbol` object.
This commit introduces `NODE_SYM` so that

1. Symbol literal is detectable from AST Node
2. Reduce dependency on ruby object

1 files changed, 2 insertions, 0 deletions

diff --git a/ast.c b/ast.c
index 1fc0a88963..b61dfbf4cb 100644
--- a/ast.c
+++ b/ast.c
@@ -581,6 +581,8 @@ node_children(rb_ast_t *ast, const NODE *node)
             }
             return rb_ary_new_from_args(3, RNODE_DSTR(node)->nd_lit, head, next);
         }
+      case NODE_SYM:
+        return rb_ary_new_from_args(1, rb_node_sym_string_val(node));
       case NODE_EVSTR:
         return rb_ary_new_from_node_args(ast, 1, RNODE_EVSTR(node)->nd_body);
       case NODE_ARGSCAT: