Incorrect `'static` lifetime bound error with associated type defaults

Code

#![feature(associated_type_defaults)]

struct Bar<A>(A);

trait Foo<A> {
    type Inner<'a> = &'a mut Bar<A> where A: 'a;

    fn expects_inner(&self, inner: Self::Inner<'_>);
}

impl<A> Bar<A> {
    fn something<F>(&mut self, foo: F)
    where
        for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>>,
    {
        foo.expects_inner(self);

        let _ = Box::new(|| {});
    }
}

Current output

error: `A` does not live long enough
  --> src/lib.rs:19:17
   |
19 |         let _ = Box::new(|| {});
   |                 ^^^^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
  --> src/lib.rs:14:20
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>>,
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>> + 'static,
   |                                                       +++++++++

error: `A` does not live long enough
  --> src/lib.rs:19:17
   |
19 |         let _ = Box::new(|| {});
   |                 ^^^^^^^^^^^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
  --> src/lib.rs:14:20
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>>,
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>> + 'static,
   |                                                       +++++++++

error: `A` does not live long enough
  --> src/lib.rs:19:26
   |
19 |         let _ = Box::new(|| {});
   |                          ^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
  --> src/lib.rs:14:20
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>>,
   |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>> + 'static,
   |                                                       +++++++++

Desired output

error: `A` does not live long enough
  --> src/lib.rs:19:17
   |
19 |         let _ = Box::new(|| {});
   |                 ^^^^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         A: 'static,
   |         +++++++++++

error: `A` does not live long enough
  --> src/lib.rs:19:17
   |
19 |         let _ = Box::new(|| {});
   |                 ^^^^^^^^^^^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         A: 'static,
   |         +++++++++++

error: `A` does not live long enough
  --> src/lib.rs:19:26
   |
19 |         let _ = Box::new(|| {});
   |                          ^^^^^
   |
note: due to a current limitation of the type system, this implies a `'static` lifetime
help: consider restricting the type parameter to the `'static` lifetime
   |
14 |         A: 'static,
   |         +++++++++++

(or whatever is the correct error format for requiring a new bound)

Rationale and extra context

If I understand correctly, the limitation of the trait system is referring to the fact that closure will capture all the generics from the outer environment. In the example code, it will capture both A and F, but because of the Box, it requires that A must be 'static. This is stated in the error message:

error: `A` does not live long enough

However, the diagnostic help text incorrectly says to apply the 'static bound to F, which is wrong. Even doing so, it will just continue to ask for 'static to be added to F:

   |
14 |         for<'a> F: Foo<A, Inner<'a> = &'a mut Bar<A>> + 'static + 'static,
   |                                                                 +++++++++

Instead, adding A: 'staticwill fix the error.

Other cases

Rust Version

rustc 1.93.0-nightly (b84478a1c 2025-11-30)
binary: rustc
commit-hash: b84478a1c477756cd3e1974eda867a6bb31e8902
commit-date: 2025-11-30
host: x86_64-pc-windows-msvc
release: 1.93.0-nightly
LLVM version: 21.1.5

Anything else?

No response

Start by compiling the reproducer in src/lib.rs with rustc 1.93.0-nightly and compare the current diagnostics with the desired output. The completed fix should attribute the suggested 'static bound to A rather than F, or produce the correct format for requiring the new bound.