Diagnostic recommends `+ '_` instead of `+ use<'_>` or nothing to express capturing

Code

use std::fmt::Debug;

fn f(x: &i32) -> (Box<dyn Debug>, impl Debug) {
    (Box::new(x), x)
}

Current output

error: lifetime may not live long enough
 --> src/lib.rs:4:5
  |
3 | fn f(x: &i32) -> (Box<dyn Debug>, impl Debug) {
  |         - let's call the lifetime of this reference `'1`
4 |     (Box::new(x), x)
  |     ^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
  |
help: to declare that the trait object captures data from argument `x`, you can add an explicit `'_` lifetime bound
  |
3 | fn f(x: &i32) -> (Box<dyn Debug + '_>, impl Debug) {
  |                                 ++++
help: to declare that `impl Debug` captures data from argument `x`, you can add an explicit `'_` lifetime bound
  |
3 | fn f(x: &i32) -> (Box<dyn Debug>, impl Debug + '_) {
  |                                              ++++

Desired output

Rationale and extra context

Legacy from #72543 when we didn't have precise capturing and a good understanding of outlives vs captures relationships.

We should probably replace the advice for the RPIT with impl Debug + use<'_>. On edition 2024, the RPIT hint should be removed altogether -- there doesn't seem to be any check against recommending implicit captures currently.

I have no idea about the right solution for dyn. We could maybe leave it as-is, but

fn f<'a, 'b>(x: &'a i32, y: &'b i32) -> Box<dyn Debug> {
    if true {
        Box::new(x)
    } else {
        Box::new(y)
    }
}

currently recommends to add both + 'a and + 'b, which obviously doesn't work. Does anyone know if there's ongoing work on adding use to dyn?

Other cases

Rust Version

rustc 1.90.0-nightly (a00149764 2025-07-14)
binary: rustc
commit-hash: a001497644bc229f1abcc5b2528733386591647f
commit-date: 2025-07-14
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.8

Anything else?

No response

Start by reproducing the diagnostic with the issue's Rust code on the noted nightly version, then trace the compiler diagnostic that suggests lifetime bounds for RPIT and dyn trait objects. Done should include appropriate use<'_> advice for RPIT, no inappropriate RPIT hint on edition 2024, and a decided behavior for dyn captures, covered by regression tests.