Tracking Issue for `private_macro_use` lint

[bvanjoi]

This is a tracking issue for the private_macro_use, a lint that follows the breaking change policy.

Description

The root of this issue was originally posted in #119301. A macro that should not have been exported was indeed exported. A minimal example to illustrate this issue is shown below:

// extern_macro.rs
macro_rules! foo_ { () => {} };
use foo_ as foo;

// code.rs
#[macro_use]
extern crate extern_macro;

fn main() {
    foo!(); // this should trigger a compile error, but it doesn't
}

The problem was triggered by an oversight where a visibility check for the macro, defined in an external crate, was omitted. Now, we have reintroduced this check to prevent such issues from occurring.

Steps

• Implement: exclude unexported macro bindings from extern crate #119369
• Make it as an error