Proc#ruby2_keywords

static VALUE
proc_ruby2_keywords(VALUE procval)
{
    rb_proc_t *proc;
    GetProcPtr(procval, proc);

    rb_check_frozen(procval);

    if (proc->header.is_from_method) {
            rb_warn("Skipping set of ruby2_keywords flag for proc (proc created from method)");
            return procval;
    }

    switch (proc->block.type) {
      case block_type_iseq:
        if (ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_rest &&
                !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_post &&
                !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_kw &&
                !ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.has_kwrest) {
            if (proc->header.is_refined) {
                /* on a copy of this Proc's own: the block is shared with the
                 * source Proc until the first call, and the copy installed by
                 * it may be memoized and shared with sibling Procs */
                const rb_iseq_t *copy =
                    rb_iseq_dup_with_independent_caches(proc->block.as.captured.code.iseq);
                ISEQ_BODY(copy)->param.flags.ruby2_keywords = 1;
                RB_VM_LOCKING() {
                    RB_OBJ_WRITE(procval, &proc->block.as.captured.code.val, (VALUE)copy);
                }
            }
            else {
                ISEQ_BODY(proc->block.as.captured.code.iseq)->param.flags.ruby2_keywords = 1;
            }
        }
        else {
            rb_warn("Skipping set of ruby2_keywords flag for proc (proc accepts keywords or post arguments or proc does not accept argument splat)");
        }
        break;
      default:
        rb_warn("Skipping set of ruby2_keywords flag for proc (proc not defined in Ruby)");
        break;
    }

    return procval;
}