The part complaining about missing details in the error message seems weird. You get a pretty detailed error even without using `--explain`:

    error[E0384]: cannot assign twice to immutable variable `x`
     --> src/main.rs:4:5
      |
    3 |     let x = 3;
      |         -
      |         |
      |         first assignment to `x`
      |         help: make this binding mutable: `mut x`
    4 |     x = 5;
      |     ^^^^^ cannot assign twice to immutable variable

    error: aborting due to previous error; 2 warnings emitted

    For more information about this error, try `rustc --explain E0384`.