Macro iprs::err_at

macro_rules! err_at {
    ($v:ident, msg:$m:expr) => { ... };
    ($v:ident, $e:expr) => { ... };
    ($v:ident, $e:expr, $m:expr) => { ... };
}

Short form to compose Error values.

Here are few possible ways:

use crate::Error;
err_at!(Error::Invalid(String::default(), "bad argument"));

use crate::Error;
err_at!(Invalid, msg: format!("bad argument"));

use crate::Error;
err_at!(Invalid, std::io::read(buf));

use crate::Error;
err_at!(Invalid, std::fs::read(file_path), format!("read failed"));