import #[macro_export] from crate root help uses 2015 use syntax

[CAD97]

Given the following code: [playground]

mod m {
    #[macro_export]
    macro_rules! nu {
        {} => {};
    }

    pub use self::nu;
}

The current output is:

error[[E0432]](https://doc.rust-lang.org/nightly/error-index.html#E0432): unresolved import `self::nu`
 --> src/lib.rs:7:13
  |
7 |     pub use self::nu;
  |             ^^^^^^^^ no `nu` in `m`
  |
  = note: this could be because a macro annotated with `#[macro_export]` will be exported at the root of the crate instead of the module where it is defined
help: a macro with this name exists at the root of the crate
  |
7 |     pub use ::nu;
  |             ~~~~

For more information about this error, try `rustc --explain E0432`.

This is using the edition2015 syntax to import from the crate root, rather than the edition2018+ required crate::nu.

Related: #99695

@rustbot label +D-edition +D-invalid-suggestion

[CAD97]

In this case, the ideal solution is actually to write just pub use nu; and get the import from legacy-lexical-macro-scope into the namespace.