Code `&impl A + B`, which cannot compile, may be suggested by the lint `refining_impl_trait`

Code

pub trait Foo {
    fn bar(&self) -> &(impl BarA + BarB);
}

pub trait BarA {}
impl<T> BarA for T {}

pub trait BarB {}
impl<T> BarB for T {}

pub struct Fool;

impl Foo for Fool {
    fn bar(&self) -> &Fool {
        &Fool
    }
}

Current output

warning: impl trait in impl method signature does not match trait method signature
  --> src\lib.rs:14:22
   |
2  |     fn bar(&self) -> &(impl BarA + BarB);
   |                      ------------------- return type from trait method defined here
...
14 |     fn bar(&self) -> &Fool {
   |                      ^^^^^
   |
   = note: add `#[allow(refining_impl_trait)]` if it is intended for this to be part of the public API of this crate
   = note: we are soliciting feedback, see issue #121718 <https://github.com/rust-lang/rust/issues/121718> for more information
   = note: `#[warn(refining_impl_trait_reachable)]` on by default
help: replace the return type so that it matches the trait
   |
14 -     fn bar(&self) -> &Fool {
14 +     fn bar(&self) -> &impl BarA + BarB {
   |

Desired output

warning: impl trait in impl method signature does not match trait method signature
  --> src\lib.rs:14:22
   |
2  |     fn bar(&self) -> &(impl BarA + BarB);
   |                      ------------------- return type from trait method defined here
...
14 |     fn bar(&self) -> &Fool {
   |                      ^^^^^
   |
   = note: add `#[allow(refining_impl_trait)]` if it is intended for this to be part of the public API of this crate
   = note: we are soliciting feedback, see issue #121718 <https://github.com/rust-lang/rust/issues/121718> for more information
   = note: `#[warn(refining_impl_trait_reachable)]` on by default
help: replace the return type so that it matches the trait
   |
14 -     fn bar(&self) -> &Fool {
14 +     fn bar(&self) -> &(impl BarA + BarB) {
   |

Rationale and extra context

After applying the fix suggested in the current output, a compilation will give an error:

error: ambiguous `+` in a type
  --> src\lib.rs:14:23
   |
14 |     fn bar(&self) -> &impl BarA + BarB {
   |                       ^^^^^^^^^^^^^^^^
   |
help: try adding parentheses
   |
14 |     fn bar(&self) -> &(impl BarA + BarB) {
   |                       +                +

Users can follow the hint to add missing parentheses. It is still an improvement to avoid the invalid suggestion though.

Other cases

Rust Version

rustc 1.88.0 (6b00bc388 2025-06-23)
binary: rustc
commit-hash: 6b00bc3880198600130e1cf62b8f8a93494488cc
commit-date: 2025-06-23
host: x86_64-pc-windows-gnu
release: 1.88.0
LLVM version: 20.1.5

Anything else?

No response

Reproduce the refining_impl_trait lint with the Rust code and compiler version shown in the issue. Trace the lint's help suggestion generation, update it to preserve parentheses around impl BarA + BarB, and verify that the suggested code compiles without the ambiguous-+ error.