explicit-outlives-requirements suggestion breaks code

[matthiaskrgr]

I tried this code:

//@ run-pass
// Test that the lifetime of the enclosing `&` is used for the object
// lifetime bound.


#![allow(dead_code)]

use std::fmt::Display;

trait Test {
    fn foo(&self) { }
}

struct Ref<'a,T:'a+?Sized> {
    r: &'a T
}

struct Ref2<'a,'b,T:'a+'b+?Sized> {
    a: &'a T,
    b: &'b T
}

struct SomeStruct<'a> {
    t: Ref<'a, dyn Test>,
    u: Ref<'a, dyn Test+'a>,
}

fn a<'a>(t: Ref<'a, dyn Test>, mut ss: SomeStruct<'a>) {
    ss.t = t;
}

fn b<'a>(t: Ref<'a, dyn Test>, mut ss: SomeStruct<'a>) {
    ss.u = t;
}

fn c<'a>(t: Ref<'a, dyn Test+'a>, mut ss: SomeStruct<'a>) {
    ss.t = t;
}

fn d<'a>(t: Ref<'a, dyn Test+'a>, mut ss: SomeStruct<'a>) {
    ss.u = t;
}

fn e<'a>(_: Ref<'a, dyn Display+'static>) {}
fn g<'a, 'b>(_: Ref2<'a, 'b, dyn Display+'static>) {}


fn main() {
    // Inside a function body, we can just infer all
    // lifetimes, to allow Ref<'tmp, Display+'static>
    // and Ref2<'tmp, 'tmp, Display+'static>.
    let x = &0 as &(dyn Display+'static);
    let r: Ref<dyn Display> = Ref { r: x };
    let r2: Ref2<dyn Display> = Ref2 { a: x, b: x };
    e(r);
    g(r2);
}

rustc --edition=2024 --crate-type lib --force-warn explicit-outlives-requirements object-lifetime-default-from-ref-struct.rs
=>

warning: outlives requirements can be inferred
  --> object-lifetime-default-from-ref-struct.rs:14:17
   |
14 | struct Ref<'a,T:'a+?Sized> {
   |                 ^^^ help: remove this bound
   |
   = note: requested on the command line with `--force-warn explicit-outlives-requirements`

warning: outlives requirements can be inferred
  --> object-lifetime-default-from-ref-struct.rs:18:21
   |
18 | struct Ref2<'a,'b,T:'a+'b+?Sized> {
   |                     ^^^^^^ help: remove these bounds

warning: 2 warnings emitted

applying the suggestion causes to code to no longer build:

error: lifetime may not live long enough
  --> object-lifetime-default-from-ref-struct.rs:37:5
   |
36 | fn c<'a>(t: Ref<'a, dyn Test+'a>, mut ss: SomeStruct<'a>) {
   |      -- lifetime `'a` defined here
37 |     ss.t = t;
   |     ^^^^^^^^ assignment requires that `'a` must outlive `'static`

error: aborting due to 1 previous error

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rustc --version --verbose:

rustc 1.85.0-nightly (8742e0556 2024-12-28)
binary: rustc
commit-hash: 8742e0556dee3c64f7144de2fb2e88936418865a
commit-date: 2024-12-28
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6