Module#refine

static VALUE
rb_mod_refine(VALUE module, VALUE klass)
{
    /* module is the receiver of #refine, klass is a module to be refined (`mod` in the doc) */
    rb_thread_t *th = GET_THREAD();
    VALUE block_handler = rb_vm_frame_block_handler(th->ec->cfp);
    struct rb_refinements_data data;

    if (block_handler == VM_BLOCK_HANDLER_NONE) {
        rb_raise(rb_eArgError, "no block given");
    }
    if (vm_block_handler_type(block_handler) != block_handler_type_iseq) {
        rb_raise(rb_eArgError, "can't pass a Proc as a block to Module#refine");
    }

    ensure_class_or_module(klass);

    rb_refinement_setup(&data, module, klass);

    rb_yield_refine_block(data.refinement, data.refinements);
    return data.refinement;
}