奇怪的错误:不能使用`?`返回`()`[duplicate]的函数中的运算符

我试图在一个非常小的程序中重现这个问题(你可以在这里找到它) Rust REPL )

#[macro_use]
extern crate quick_error;

quick_error! {
    #[derive(Debug)]
    pub enum Error {
        SomeError{
            description("SomeError")
        }
    }
}


pub struct Version {
    foo: u8,
}

pub struct Bar();

impl Bar {
    pub fn version() -> Result<Version, Error> {
        Ok(Version{foo: 1})
    }
}

fn main() {
    let tmp = Bar::version()?;
}

error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `std::ops::Try`)
  --> src/main.rs:27:15
   |
27 |     let tmp = Bar::version()?;
   |               ^^^^^^^^^^^^^^^ cannot use the `?` operator in a function that returns `()`

然而,这个版本正在回归 Result<Version, Error> . 怎么回事?