False Positive for rust-lang/rust#83583

The deprecation lint proc_macro_derive_resolution_fallback is intended to catch proc macro generated code that refers to items from parent modules that should not be in scope:

struct Outer {}

mod generated {
    struct Dummy {
        inner: Outer,
    }
}

The lint works for this case, and a proc macro can add a use super::*; line to make this code valid:

struct Outer {}

mod generated {
    use super::*;

    struct Dummy {
        inner: Outer,
    }
}

However, if the same corrected proc macro runs inside a fn body the lint will still be triggered, incorrectly:

fn item() {
    struct Inner {}

    mod generated {
        use super::*;

        struct Dummy {
            inner: Inner,
        }
    }
}

warning: cannot find type `Inner` in this scope
  --> src\lib.rs:12:12
   |
12 |     struct Inner {}
   |            ^^^^^ names from parent modules are not accessible without an explicit import
   |
   = note: `#[warn(proc_macro_derive_resolution_fallback)]` on by default
   = 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 #83583 <https://github.com/rust-lang/rust/issues/83583>

See foo-derive/src/lib.rs for the proc macro implementation and src/lib.rs for usage. This warning can be reproduced with

cargo check