Implementing `Reborrow` prevents normally moving a value of that type.

I tried this code:

#![feature(reborrow)]

use std::marker::Reborrow;

struct Thing<'a>(&'a ());

impl<'a> Reborrow for Thing<'a> {}

fn foo<'a>(x: Thing<'a>) -> Thing<'a> {
    x
}

I expected this code to compile, since it's just an identity function. Instead, I got the following error:

    Checking foo v0.1.0 (/Users/timch/foo)
error[E0515]: cannot return reference to temporary value
  --> src/lib.rs:9:39
   |
 9 |   fn foo<'a>(x: Thing<'a>) -> Thing<'a> {
   |  _______________________________________^
10 | |     x
11 | | }
   | |_^ returns a reference to data owned by the current function

error[E0515]: cannot return value referencing function parameter `x`
  --> src/lib.rs:9:39
   |
 9 |   fn foo<'a>(x: Thing<'a>) -> Thing<'a> {
   |  _______________________________________^
10 | |     x
   | |     - `x` is borrowed here
11 | | }
   | |_^ returns a value referencing data owned by the current function

For more information about this error, try `rustc --explain E0515`.
error: could not compile `foo` (lib) due to 2 previous errors

cc @aapoalas

Meta

rustc --version --verbose:

rustc 1.97.0-dev
binary: rustc
commit-hash: unknown
commit-date: unknown
host: aarch64-apple-darwin
release: 1.97.0-dev
LLVM version: 22.1.4

Compiled from the main branch at commit 63b1dfc0e00fd6f8ad7cd8817fc712e7d9b7be59.

Reproduce the issue using the example in src/lib.rs with the reborrow feature enabled, then trace how the compiler handles Reborrow implementations during borrow checking. Compare the result with the expected identity-function behavior. Done means the example compiles without the E0515 diagnostics.