RPIT can't capture LUB of two lifetimes

I'm not sure if this is a bug or not.

fn weird(x: &i32, y: &i32) -> impl Sized {
    [x, y]
}

This code doesn't compile, giving the following error.

error[E0700]: hidden type for `impl Sized` captures lifetime that does not appear in bounds
 --> src/lib.rs:2:5
  |
1 | fn weird(x: &i32, y: &i32) -> impl Sized {
  |                               ---------- opaque type defined here
2 |     [x, y]
  |     ^^^^^^
  |
  = note: hidden type `[&i32; 2]` captures lifetime `'_`

For more information about this error, try `rustc --explain E0700`.

The return type captures the lifetime that outlives both the input lifetimes. There is not an easy way to name this lifetime. At the very least, the error is rather confusing.

Seems related to https://github.com/rust-lang/rust/issues/128752

Meta

Reproducible on the playground in version 1.93.0-nightly (2025-11-01 bd3ac0330018c23b111b)

Start with the Rust Playground reproduction on nightly 1.93.0 and inspect the E0700 diagnostic for the weird function. Compare the behavior and proposed scope with issue 128752; the work is complete when the behavior is classified and, if appropriate, the lifetime-capture error is made less confusing.