match_on_vec_items: false positive on `match vec[..]`

[goffrie]

Sample program:

fn main() {
    let x = vec![1,2,3];
    match x[..] {
        [1, 2, 3] => println!("123"),
        _ => println!("not 123"),
    }
}

Clippy output:

error: indexing into a vector may panic
 --> src/main.rs:3:11
  |
3 |     match x[..] {
  |           ^^^^^ help: try this: `x.get(..)`
  |
  = note: `#[deny(clippy::match_on_vec_items)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#match_on_vec_items

error: aborting due to previous error

However, this use of indexing is infallible.

(note that I'm silencing this lint globally anyway because I don't consider it useful)

[flip1995]

cc @CrazyRoka This lint shouldn't trigger on wild [..] patterns.

@goffrie Why do you think this lint isn't useful? x.get(/*...*/) can never panic, while x[/*...*/] can. IMO using get is a clear improvement, since you get a compile time guarantee.

[goffrie]

When I updated clippy a number of callsites lit up with the lint where it was impossible for the indexing to panic (usually because the length was just checked in some way). Using `get` would have made the the code less clear. Though I feel that this is more of a "teaching" lint for people writing new code.

…

On Fri., May 1, 2020, 05:24 Philipp Krones, ***@***.***> wrote: cc @CrazyRoka <https://github.com/CrazyRoka> This lint shouldn't trigger on wild [..] patterns. @goffrie <https://github.com/goffrie> Why do you think this lint is not useful? x.get(/*...*/) can never panic, while x[/*...*/] can. IMO using get is a clear improvement. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#5551 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAJO2TXUKOP6UEDS6XO6MR3RPK5OXANCNFSM4MW2ODTQ> .

[flip1995]

Alright, that is a fair point. I'll move the lint to pedantic (allow-by-default)