Slice coercion is too conservative with generic receiver.

[nagisa]

fn main(){
    let x = "hello world";
    let y = ['h', 'e'];
    println!("{:?}", x.find(&y));
}

will not compile with “error: the trait core::ops::Fn<(char,)> is not implemented for the type [char; 2]”, but there’s impl<'a, 'b> Pattern<'a> for &'b [char], which could’ve been used if coercion happened.

[Mark-Simulacrum]

Closing in favor of #39511.