Lifetime trouble with hidden Self when going to edition 2018

[vorner]

OK, so I'm not sure this is a bug or annoyance, but it still acts a bit weird. And I don't know what to search for if it was already reported.

Anyway, let's have this code that compiles under edition 2015:

struct Parsed<'a> {
    parts: Vec<&'a str>,
}

impl<'a> Parsed<'a> {
    fn parse(s: &'a str) -> Self {
        let parts = s.split_whitespace().collect();
        Parsed {
            parts
        }
    }

    fn len(&self) -> usize {
        self.parts.len()
    }

    fn parsed_len(s: &str) -> usize {
        Self::parse(s).len()
    }
}

fn process<F: Fn(&str) -> usize>(f: F) {
    unimplemented!()
}

fn main() {
    process(Parsed::parsed_len)
}

When I switch to 2018, it starts complaining that the s parameter of parsed_len needs the 'a lifetime. Well, I guess that's because of Self in there (if I use Parsed instead, it is OK with it).

But if I obey, the process no longer wants to accept the associated function, it says: expected bound lifetime parameter, found concrete lifetime. Putting it into a closure (process(|s| Parsed::parsed_len(s))) fixes that. Which is strange, it's still the same function, isn't it?

Should it be doing this? I'd hope the process would still accept the associated function, even though the lifetime is on the struct, not only on the parameter.

Also, cargo fix doesn't help with this transition (though I don't know what it should do about it).

[jackh726]

@estebank this no longer errors on current stable/nightly.

It does give the following warning though, which is the same seen in #62953:

warning[E0621]: explicit lifetime required in the type of `s`
  --> src/lib.rs:16:9
   |
15 |     fn parsed_len(s: &str) -> usize {
   |                      ---- help: add explicit lifetime `'a` to the type of `s`: `&'a str`
16 |         Self::parse(s).len()
   |         ^^^^^^^^^^^^^^ lifetime `'a` required
   |
   = warning: this error has been downgraded to a warning for backwards compatibility with previous releases
   = warning: this represents potential undefined behavior in your code and this warning will become a hard error in the future
   = note: for more information, try `rustc --explain E0729`

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=54dc9c4f9d81a0fa35250e09cebde1a8

[estebank]

Closing as duplicate of #62953.