compiler suggests invalid code with ref pattern

[ehuss]

The following example:

struct S {
    f1: i32,
}

fn main() {
    let s = S { f1: 123 };
    let S { ref f1 } = s;
}

Gives the following suggestion:

warning: unused variable: `f1`
 --> src/main.rs:9:15
  |
9 |     let S{ref f1} = s;
  |               ^^ help: try ignoring the field: `f1: _`
  |
  = note: #[warn(unused_variables)] on by default

When the suggestion is applied, the code does not compile:

error: expected `,`
 --> src/main.rs:9:17
  |
9 |     let S { ref f1: _ } = s;
  |                 ^^

error[E0027]: pattern does not mention field `f1`
 --> src/main.rs:9:9
  |
9 |     let S { ref f1: _ } = s;
  |         ^^^^^^^^^^^^^^^ missing field `f1`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0027`.

I'm not sure what the best suggestion would be. Removing the ref might be an option (I'm not sure if using a wildcard is equivalent in this case?). Suggesting .. is another option.

This suggestion was changed in 1.28 (previous versions gave a different, wrong suggestion). Tested up to rustc 1.30.0-nightly (2d4e34c 2018-09-09).

[csmoe]

warning: unused variable: `f1`
 --> src/main.rs:9:15
  |
9 |     let S{ref f1} = s;
- |               ^^ help: tryignoring the field: `f1: _`
+ |           ^^^^^^ help: try ignoring the field: `f1: _`
  |
  = note: #[warn(unused_variables)] on by default

the ambiguity in the lint caused by the wrong span.
(btw, this won't be an issue in edtion-2018 since ref isn't "recommended" there https://rust-lang-nursery.github.io/edition-guide/rust-2018/ownership-and-lifetimes/default-match-bindings.html)

[ambaxter]

There is an issue regarding this with the 2018 edition.

[ehuss]

Just to be clear, AFAIK there are no lints for transitioning to default binding mode (edition idiom or otherwise), so the comment that it won't be an issue in 2018 isn't correct, this issue still applies to all editions.