Compiler doesn't explain that unfulfilled lifetime requirement comes from object lifetime default when it's behind an assoc ty in trait impl

Code

use std::ops::Deref;

enum Either {
    Foo(Box<dyn Foo>),
    Bar(Box<dyn Bar>),
}

impl Either {
    fn as_foo(&self) -> &dyn Foo {
        // Compiles
        match self {
            Self::Foo(f) => f.as_ref(),
            Self::Bar(b) => b.as_foo(),
        }
    }
}

impl Deref for Either {
    type Target = dyn Foo;

    fn deref(&self) -> &Self::Target {
        // "lifetime may not live long enough, `&self` must outlive `'static`"
        match self {
            Self::Foo(f) => f.as_ref(),
            Self::Bar(b) => b.as_foo(),
        }
    }
}

trait Bar: Foo {
    fn as_foo(&self) -> &dyn Foo;
}

trait Foo {}

Playground.

Current output

error: lifetime may not live long enough
  --> src/lib.rs:23:9
   |
21 |       fn deref(&self) -> &Self::Target {
   |                - let's call the lifetime of this reference `'1`
22 |           // "lifetime may not live long enough, `&self` must outlive `'static`"
23 | /         match self {
24 | |             Self::Foo(f) => f.as_ref(),
25 | |             Self::Bar(b) => b.as_foo(),
26 | |         }
   | |_________^ returning this value requires that `'1` must outlive `'static`

Desired output

It's very unclear where the `'static` requirement is coming from in this case.

Rationale and extra context

No response

Other cases

Note that the same code works in an inherent impl method, which makes the error unintuitive.

Rust Version

rustc 1.90.0 (1159e78c4 2025-09-14)
binary: rustc
commit-hash: 1159e78c4747b02ef996e55082b704c09b970588
commit-date: 2025-09-14
host: aarch64-apple-darwin
release: 1.90.0
LLVM version: 20.1.8

Anything else?

No response

Reproduce the Rust snippet with rustc 1.90.0 and compare the inherent impl with the Deref impl. Trace the compiler's lifetime diagnostics for the associated Target type and object lifetime default; done means the diagnostic identifies why the 'static requirement arises and includes a focused regression test.