Using str::contains inside of a filter leads to confusing error message.

I've been trying to learn some Rust by doing CodeWars. I've spent some time being stuck on this diagnostic. One of the easiest exercises there is to count vowels in a string. First I did it with a loop, but then got stuck trying to rewrite is as a filter.

Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=785ded94c58b6d9a3a8acd16145a4970

fn get_vowel_count(string: &str) -> usize {
        string
        .chars()
        .filter(|c| "aeiou".contains(c))
        .count()
}

The current output is:

error[E0277]: expected a `Fn<(char,)>` closure, found `char`
 --> src/lib.rs:4:38
  |
4 |         .filter(|c| "aeiou".contains(c))
  |                                      ^ expected an `Fn<(char,)>` closure, found `char`
  |
  = help: the trait `Fn<(char,)>` is not implemented for `char`
  = note: required because of the requirements on the impl of `FnOnce<(char,)>` for `&char`
  = note: required because of the requirements on the impl of `Pattern<'_>` for `&char`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.
error: could not compile `challenge`

Ideally the output should not lead with "expected an Fn" and also help me to add a missing ampersand.

and also help me to add a missing ampersand.

Do you mean a missing star? Working version:

fn get_vowel_count(string: &str) -> usize {
        string
        .chars()
        .filter(|c| "aeiou".contains(*c))
        .count()
}

I agree that the error message is very misleading.

Smaller repro:

fn test(c: &char) -> bool {
    "aeiou".contains(c)
}

Do you mean a missing star?

Both |c| "aeiou".contains(*c) and |&c| "aeiou".contains(c) are accepted. At the time of writing the ticket I found only the latter way to fix the error, that's why I said ampersand.