Suggest adding & for "mismatched types: expected reference &&[&str], found reference &[&str]"

This code can be easily fixed by adding an & in the call to contains.

fn main() {
    let haystack = [&["A1", "A2"][..], &["B1", "B2"], &["C1", "C2"]];
    let needle: &[&str] = &["D1", "D2"];
    println!("{}", haystack.contains(needle));
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
error[E0308]: mismatched types
 --> src/main.rs:4:38
  |
4 |     println!("{}", haystack.contains(needle));
  |                                      ^^^^^^ expected `&[&str]`, found slice `[&str]`
  |
  = note: expected reference `&&[&str]`
             found reference `&[&str]`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
error: could not compile `playground`.

To learn more, run the command again with --verbose.

Also, I don't think autoref is documented anywhere.

Autoref doesn't happen for arguments, only for the receiver

Maybe we could suggest adding an & then?

Current output, little change, still no suggestion:

error[E0308]: mismatched types
    --> src/main.rs:4:38
     |
   4 |     println!("{}", haystack.contains(needle));
     |                             -------- ^^^^^^ expected `&&[&str]`, found `&[&str]`
     |                             |
     |                             arguments to this method are incorrect
     |
     = note: expected reference `&&[&str]`
                found reference `&[&str]`
note: method defined here
    --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/slice/mod.rs:2583:12
     |
2583 |     pub fn contains(&self, x: &T) -> bool
     |            ^^^^^^^^

Rollup merge of rust-lang#162329 - chenyukang:yukang-fix-78613-sugges…

Unrolled build for #162329 in rollup 162353

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Suggest adding `&` for "mismatched types: expected reference `&&[&str]`, found reference `&[&str]`" #78613

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Suggest adding & for "mismatched types: expected reference &&[&str], found reference &[&str]" #78613

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camelid commented on Oct 31, 2020

jonas-schievink commented on Oct 31, 2020

camelid commented on Oct 31, 2020

estebank commented on Aug 12, 2025

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Suggest adding `&` for "mismatched types: expected reference `&&[&str]`, found reference `&[&str]`" #78613