Tracking Issue for future-incompatibility lint `out_of_scope_macro_calls`

The out_of_scope_macro_calls lint detects macro_rules called when they are not in scope,
above their definition, which may happen in key-value attributes.

Example

#![doc = in_root!()]

macro_rules! in_root { () => { "" } }

fn main() {}

Explanation

The scope in which a macro_rules item is visible starts at that item and continues
below it. This is more similar to let than to other items, which are in scope both above
and below their definition.
Due to a bug macro_rules were accidentally in scope inside some key-value attributes
above their definition. The lint catches such cases.
To address the issue turn the macro_rules into a regularly scoped item by importing it
with use.

Implementation history

• https://github.com/rust-lang/rust/pull/125741 introduced the lint
• https://github.com/rust-lang/rust/pull/126987 fixed some positives
• https://github.com/rust-lang/rust/pull/127191 integrated it into the allow/warn/deny infrastructure
• https://github.com/rust-lang/rust/pull/143929 made the lint deny-by-default and report-in-deps
• https://github.com/rust-lang/rust/pull/147914 avoided an undesirable unused_imports warning
• XXX turned the lint into a hard error

Review the lint behavior and implementation history through the linked pull requests, starting with the introduction of out_of_scope_macro_calls and its allow/warn/deny integration. The work is complete when the lint is turned into a hard error without reintroducing the documented false positives or the undesirable unused_imports warning.