E0384 needs to be updated to new format

[sophiajt]

E0384 still uses the old format and can be updated to the new format. Ideally, we would move from span_note to span_label, as well as add a few labels.

Given the example:

fn main() {
    let x = 5;
    println!("The value of x is: {}", x);
    x = 6;
    println!("The value of x is: {}", x);
}

This would change the error from this:

error[E0384]: re-assignment of immutable variable `x`
 --> jont/varbinder.rs:4:5
  |
4 |     x = 6;
  |     ^^^^^
  |
note: prior assignment occurs here
 --> jont/varbinder.rs:2:9
  |
2 |     let x = 5;
  |         ^

to:

error[E0384]: re-assignment of immutable variable `x`
 --> jont/varbinder.rs:4:5
2 |     let x = 5;
  |         - first assignment to `x`
3 |     println!("The value of x is: {}", x);
4 |     x = 6;
  |     ^^^^^ re-assignment of immutable `x`

[nagisa]

@jonathandturner usually E-easy issues benefit a lot from a short summary on what should be done.

It would likely involve changing this code to use span_label rather than span_note.

Why is there a distinction between these two?

[sophiajt]

@nagisa - I'm actually hoping up to queue a lot of these to go along with a call-for-volunteers blog post. You're right though it could use some additional guidance.

To your other point, for small messages it makes sense to use labels. For larger, more involved messages, sometimes span_note works a little better. In time, hopefully we'll strike a good balance.

[sophiajt]

@nagisa - updated

[theypsilon]

I would take this one.

[theypsilon]

@jonathandturner there is maybe an issue with this pull request, because I'm using the spec of your blog post instead of the one said here. They are almost identical, but there is a minor difference.

Here says: ^^^^^ re-assignment of immutable x
In blog post: ^^^^^ re-assignment of immutable variable

And the implemented is the later, should I do the former instead? I noticed a bit late, sorry for asking after sending the request.

[sophiajt]

@theypsilon - what you implemented looks good to me. We'll no doubt improve the wording over time, but this looks good for a first pass.

[theypsilon]

Understood, thanks.