warning: nested `impl Trait` is not allowed
  --> $DIR/issue-57979-nested-impl-trait-in-assoc-proj.rs:21:45
   |
LL |     pub fn demo(_: impl Quux<Assoc=impl Foo<impl Bar>>) { }
   |                                    ---------^^^^^^^^-
   |                                    |        |
   |                                    |        nested `impl Trait` here
   |                                    outer `impl Trait`
   |
note: lint level defined here
  --> $DIR/issue-57979-nested-impl-trait-in-assoc-proj.rs:16:13
   |
LL |     #![warn(nested_impl_trait)]
   |             ^^^^^^^^^^^^^^^^^
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #59014 <https://github.com/rust-lang/rust/issues/59014>

error: nested `impl Trait` is not allowed
  --> $DIR/issue-57979-nested-impl-trait-in-assoc-proj.rs:32:45
   |
LL |     pub fn demo(_: impl Quux<Assoc=impl Foo<impl Bar>>) { }
   |                                    ---------^^^^^^^^-
   |                                    |        |
   |                                    |        nested `impl Trait` here
   |                                    outer `impl Trait`
   |
note: lint level defined here
  --> $DIR/issue-57979-nested-impl-trait-in-assoc-proj.rs:27:13
   |
LL |     #![deny(nested_impl_trait)]
   |             ^^^^^^^^^^^^^^^^^
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #59014 <https://github.com/rust-lang/rust/issues/59014>

error: aborting due to previous error