Confusing error message for lifetime mismatch

[Kushagra-0801]

Code

use bytes::Bytes;

#[allow(unused)]
struct SimpleString(Bytes);

fn deserialize_simple_string(buf: &[u8]) -> Result<(SimpleString, &[u8]), &'static str> {
    let Some((s, rest)) = split_on_crlf(buf) else {
        return Err("No CRLF found");
    };
    Ok((SimpleString(Bytes::from(s)), rest))
}


fn split_on_crlf(buf: &[u8]) -> Option<(&[u8], &[u8])> {
    let pos = buf.windows(2).position(|win| win == b"\r\n")?;
    let part = &buf[..pos];
    let rest = &buf[pos + 2..];
    Some((part, rest))
}

fn main() {
    let x = Vec::from(b"non-static user data\r\n");
    let _ = deserialize_simple_string(&x).unwrap();
}

Current output

error[E0521]: borrowed data escapes outside of function
 --> src/main.rs:7:27
  |
6 | fn deserialize_simple_string(buf: &[u8]) -> Result<(SimpleString, &[u8]), &'static str> {
  |                              ---  - let's call the lifetime of this reference `'1`
  |                              |
  |                              `buf` is a reference that is only valid in the function body
7 |     let Some((s, rest)) = split_on_crlf(buf) else {
  |                           ^^^^^^^^^^^^^^^^^^
  |                           |
  |                           `buf` escapes the function body here
  |                           argument requires that `'1` must outlive `'static`

Desired output

main.rs:23

In main()

`x` does not live for `'static` but `deserialize_simple_string` expects the argument to outlive `'static`.

Rationale and extra context

The real problem is that the Bytes::from implementation is only for &'static [u8]. Whatever the output is, it shouldn't be pointing to split_on_crlf as the culprit. I also don't see how it could be leaking the reference at all.

Playground link: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=631eaea4377ffad8120532ea9e356233

Other cases

No response

Rust Version

Its the stable channel, debug build, 2021 edition on playground. Version 1.82.0

Anything else?

No response

[dianne]

@rustbot claim