Nested `decl_macro` has incorrect hygiene

I tried this code:

#![feature(decl_macro)]

macro foo() {
    macro bar() {
        fn wut() {}
        wut();
    }
    bar!();
}

fn main() {
    foo!();
}

#![feature(decl_macro)]

macro foo($name:ident) {
    macro $name() {
        fn wut() {}
        wut();
    }
}

fn main() {
    foo!(bar);
    bar!();
}

I expect the above code should compile, since the fn wut item and the wut() call are in the same "macro scope". Instead, I got the following compile error:

error[E0425]: cannot find function `wut` in this scope
  --> src/main.rs:6:9
   |
 6 |         wut();
   |         ^^^ not found in this scope
...
12 |     foo!();
   |     ------ in this macro invocation
   |
   = note: this error originates in the macro `bar` which comes from the expansion of the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0425`.

However, if the fn wut item is defined in the foo macro instead, the wut() call finds that item and uses it. For example, the following code compiles and prints "outer":

#![feature(decl_macro)]

macro foo() {
    fn wut() {
        println!("outer");
    }
    macro bar() {
        fn wut() {
            println!("inner");
        }
        wut();
    }
    bar!();
}

fn main() {
    foo!();
}

This seems incorrect / undesirable.

My (uninformed) guess is that the fix would require each identifier to keep track of the entire "macro stack" that it went through.

Meta

Reproducible on the playground with version 1.95.0-nightly (2026-01-23 d222ddc4d90743dfc1e5)

Start by compiling the reproducer in src/main.rs with a nightly Rust toolchain and confirm the nested decl_macro hygiene failure. Trace how the foo! and bar! expansions resolve wut, then verify the fix by compiling both snippets and confirming the inner function is found without changing the expected macro behavior.