Rust: Provide suggestion for use after move caused by match expression

[estebank]

Provide suggestion for use after move in match arm, either using ref in the pattern or borrowing the moved variable:

enum Message {
    Quit,
    Move {x: String, y: String},
    Write(String),
}

fn main() {
    let msg = Message::Move { x: String::new(), y: String::new()};
    match msg {
        Message::Quit => println!("q"),
        Message::Move {x, y} => println!("m {} {}", x, y),
        Message::Write(s) => println!("w: {}", s),
    }
    if let Message::Move { x, y } = msg {
        println!("{} {}", x, y);
    }
}

Has the following output:

error[E0382]: use of moved value
  --> src/main.rs:14:28
   |
11 |         Message::Move {x, y} => println!("m {} {}", x, y),
   |                        - value moved here
...
14 |     if let Message::Move { x, y } = msg {
   |                            ^ value used here after move
   |
   = note: move occurs because value has type `std::string::String`, which does not implement the `Copy` trait

error[E0382]: use of moved value
  --> src/main.rs:14:31
   |
11 |         Message::Move {x, y} => println!("m {} {}", x, y),
   |                           - value moved here
...
14 |     if let Message::Move { x, y } = msg {
   |                               ^ value used here after move
   |
   = note: move occurs because value has type `std::string::String`, which does not implement the `Copy` trait

_Reported at https://mobile.twitter.com/mountain_ghosts/status/1105168489160032257_

---

A possible output:

error[E0382]: use of moved value
  --> src/main.rs:14:28
   |
 9 |    match msg {
   |          --- help: consider borrowing instead of consuming here: `&msg`
...
11 |         Message::Move {x, y} => println!("m {} {}", x, y),
   |                        -
   |                        |
   |                        value moved here
   |                        help: borrow the binding to avoid consuming `msg`: `ref x`
...
14 |     if let Message::Move { x, y } = msg {
   |                            ^ value used here after move
   |
   = note: move occurs because value has type `std::string::String`, which does not implement the `Copy` trait

[janriemer]

I am new to Rust and just came here after searching for 'rust value moved after match' on the internet.
The suggestion --- help: consider borrowing instead of consuming here: &msg has worked perfectly for me. I didn't know/wasn't aware that values are also moved in match expressions.

Thank you very much for the suggestion. I'd really like to see this in the compiler.

[estebank]

We now suggest using ref in the pattern, which will always work, if not be completely stylistic.