This moves `ast->node_buffer->config` to `ast->config` aiming to improve readability and maintainability of the source. ## Background We could not add the `config` field to the `rb_ast_t *` due to the five-word restriction of the IMEMO object. But it is now doable by merging https://.com/ruby/ruby/pull/10618 ## About assigning `&rb_global_parser_config` to `ast->config` in `ast_alloc()` The approach of not setting `ast->config` in `ast_alloc()` means that the client, CRuby in this scenario, that directly calls `ast_alloc()` will be responsible for releasing it if a resource that is passed to AST needs to be released. However, we have put on hold whether we can guarantee the above so far, thus, this looks like that. ``` // ruby_parser.c static VALUE ast_alloc(void) { rb_ast_t *ast; VALUE vast = TypedData_Make_Struct(0, rb_ast_t, &ast_data_type, ast); #ifdef UNIVERSAL_PARSER ast = (rb_ast_t *)DATA_PTR(vast); ast->config = &rb_global_parser_config; #endif return vast; } ```