False positive for unnecessary_sort_by lint: Suggestion does not compile

[psychon]

I tried this code:

#[derive(Debug)]
pub struct Test {
    name: String,
}

impl Test {
    fn name(&self) -> &str {
        &self.name
    }
}

fn main() {
    let mut args: Vec<_> = std::env::args().map(|name| Test { name }).collect();
    args.sort_by(|a, b| a.name().cmp(b.name()));
    // Suggested by clippy, but causes a lifetime error:
    // args.sort_by_key(|a| a.name());
    println!("{:?}", args);
}

Clippy says:

    Checking playground v0.0.1 (/playground)
warning: use Vec::sort_by_key here instead
  --> src/main.rs:14:5
   |
14 |     args.sort_by(|a, b| a.name().cmp(b.name()));
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `args.sort_by_key(|&a| a.name())`
   |
   = note: `#[warn(clippy::unnecessary_sort_by)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_sort_by

warning: 1 warning emitted

    Finished dev [unoptimized + debuginfo] target(s) in 0.33s

When applying the suggestion (= uncommenting the marked line in the code), the following happens:

    Checking playground v0.0.1 (/playground)
error: lifetime may not live long enough
  --> src/main.rs:16:26
   |
16 |     args.sort_by_key(|a| a.name());
   |                       -- ^^^^^^^^ returning this value requires that `'1` must outlive `'2`
   |                       ||
   |                       |return type of closure is &'2 str
   |                       has type `&'1 Test`

error: aborting due to previous error

error: could not compile `playground`.

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

Meta

No idea. This happens on the Rust playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=732732b92adbc28314716081acc4e733

The playground says this is clippy 0.0.212 (2020-06-26 7750c3d) and I have no idea were to find the rustc version. Sorry.

I cannot reproduce locally with clippy 0.0.212 (d4092ac 2020-05-11).

[phansch]

Thanks for the report, this is certainly a bug in Clippy.

There's an old open rust issue about fixing the differences between sort_by and sort_by_key: rust-lang/rust#34162 about exactly your case. However, that requires more fundamental work, so we should fix this bug in Clippy first.